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FBH - all you need to know

Discussion in 'Common Faults and Questions' started by The Mad Hat Man, Dec 2, 2012.

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  1. The Mad Hat Man

    The Mad Hat Man Well-Known Member LZIR Despatch Agent

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    What the Fuel Burning Heater (FBH) does (Courtesy of Rhodie)
    The M47 diesel engine is so efficient, that it produces very little waste heat to warm the coolant up to a reasonable temperature within a reasonable distance. The issue is often made worse by a coolant thermostat, which as it ages opens too early, so winter or summer, the engine never achieves its designed working temperature. There is no point installing an FBH unless your stat is working properly at is design opening temperature of 88C.

    The FBH is configured to shut off at 77C and if your stat opens at below this temperature, then it will continue to run indefinitely in cold weather, wasting its warmth to atmosphere via the radiator.

    Check your car's normal running temperature via the OBD dash diagnostics for an accurate temperature and if once warmed up it is much below 88C, either install a replacement OEM stat (expensive) or the cheap option of a second stat in the top hose (cheap fix). A problem with the stat, needs to be addressed early, rather than waste fuel running the FBH unnecessarily.
    Then undo more of the 5x Torx bolts visible behind where you have removed the pump from, to separate the first section of casing, be careful not to bend the metal fuel pipe as you pull that first section away - ease it through the rubber bung.

    Water pump removed and you can just see the exhaust flue pipe stub sticking out on the left. Black plastic cover on the right hides the combustion air fan.
    That should then reveal 4x more Torx bolts holding the burner unit into the heat exchanger. Undo those, but be aware there is a soft thick paper gasket between the two, which is bound to have split in one place - take care not to make it any worse.

    Brass coloured object, with the dog-legged pipe emerging from it is the burner unit. Dog-legged pipe is the fuel pipe.
    Inside the heat exchanger, from where the burner has just been removed. Surrounding the hole you can see the pale green paper gasket, small spilt is just visible at 1 o'clock. It only needs to contain low pressure combustion air, so if this is the only damage, it can be reused. The heat exchanger has not been cleaned, it was clean enough as is. Pipe stubs in top left and bottom right hand corners are the coolant inlets and outlet. Webasto do not recommend stripping the heat exchanger.
    That gets you access to remove the burner unit and see inside the heat exchanger. Follow the two thick wires (mentioned earlier), to the glowpin, unclip the wires, unclip the glowpin - held by a spring P clip and very carefully remove it from the burner chamber. Test it by connecting its two terminals across 12v, where upon its square section end should in a few seconds become close to white hot. It is not designed to run continuously on 12v, so limit this test to a few seconds - just long enough to satisfy yourself that it glows. If it doesn't glow, then it has failed and no one has yet been able find a source for a replacement, but they are very expensive - maybe £60, even if you can manage to source one. Webasto only seem to sell them complete with the combustion chamber.

    For anyone in any doubt, this i the type of glowpin this FBH needs. The end of the pin is about 1/8" square section, it comes with the two wires attached and fitted with a two pin plug.
    If you now look deep into the bottom of the burner, you will most likely see lots of hard carbon build up, which has formed over the gauze at the bottom and particularly around the perimeter. All of that needs to be cleaned off, using the blunt screwdriver. Break it up by pushing the screwdriver hard against the carbon. You will need the chamber to be well supported, without damaging the fuel pipe so you have something to push against. Don't try to tease it out or you might damage the gauze, just break it up by pressing. The gauze is held by a metal frame, which should come into view as the carbon is removed around the edges. Finally check all of the air inlet holes around the perimeter of the combustion chamber are completely clear, then blow down the fuel pipe to make sure that is also clear. It should seem as if there is some restriction in the pipe - I'm guessing quite a large bore jet, to get it to squirt fuel through the gauze.

    Removed combustion chamber, sat upside down on top of the heat exchanger - this example has already been cleaned out. No need for it to be spotless, providing all of the hard carbon is removed. Blue and white wires emerging from the right, are the wires from the glowpin - with its 2 pin plug just visible.
    Reassemble reusing the paper gasket by pushing the split back together. That joint only seals the combustion air section from the combustion chamber.

    Servicing the Water Pump

    This can be tackled with the FBH on or off the car. Symptoms of it needing to be checked and serviced are that with the FBH running, the heated coolant from the FBH is not pushed around the system unless the engine is running and the FBH may also run in short bursts, rather than the 10 to 20 minutes of continuous running it should normally take to pre-heat the engine. (Photos provided by Tam (Rotrex)).

    If the pump is not already removed from the FBH, remove one torx bolt to unclamp it and unclip the coolant hoses to get it onto the bench.

    Remove 4x top cover Torx bolts, top cover should then lift off.
    Remove circlip which holds impeller on the shaft and remove impeller.
    Check motor shaft is now free to turn and turns smoothly.
    Clean out all of the accumulated deposits, then apply 12v across the motor terminals to ensure it runs before finally reassembling and refitting.
    Terminals

    This is for the later Model 98570B FBH
    Looking at the FBH as it is mounted in the car, from the top down, the terminals and plugs are as follows..

    1 A blank unused socket.
    2 Water circulation pump
    3 Combustion air fan
    4 Glowpin
    5 Power plug +12v at top, ground at the bottom

    The 6 pin plug as follows-
    Top left down...
    1 signal from +5C stat
    2 K-bus connection (this is recommended to be disconnected)
    3 ground this, to force it to run

    Top right down
    4 Not used
    5 Not used
    6 Pulsed output to the fuel pump.

    PCB Removal

    This can be removed and replaced with the FBH still mounted in the car.
    1. Unplug the power, 6 pin plug and move the rubber air intake pipe out of the way.
    2. Unhook the catch for the middle section of the three plastic covers, by squeezing a flat bladed screwdriver up from below, between the edge of the cover and the alloy casing. It should then ease off the rear catch, giving access to the FBH's internal plugs.
    3. Remove the plug for water pump, air fan and glowpin
    4. Remove the 4x screws for the right hand plastic cover and lift it off
    5. Undo the small torq screw in the centre of the SS clamp plate on the right of the PCB, which then releases the PCB. Before trying to lift the PCB, make sure that the small white two pin component, which was clamped onto the alloy, has not stuck to the body - then lift the PCB complete with its plastic frame away from the FBH. DO NOT attempt to part the PCB, from the plastic frame.

    Faults and Issues
    If the FBH is triggered into life when a door is opened, or at other times when you would not expect the FBH to run, or your battery goes flat, or other things on the car misbehave - cut and insulate each end of the K-bus wire at the FBH 6 pin plug, this is the white/ red/ yellow wire. It serves no useful purpose and can cause issues, so worth disconnecting whether there are problems or not. Make sure the cut wire can easily be reconnected if needed, because it can cause issues when a T4 is used and the T4 cannot see the FBH on the K-bus.

    FBH is still running at the end of a long reasonable speed journey, outdoor temperature below about +5C. Check the coolant stat opening temperature using the OBD dash diagnostics, it may be opening too early.

    Testing by shorting pin 3 to ground and the FBH just runs without actually firing - Usually an indication that the PCB has failed - talk to FrenchMike.
    FBH acts as above, but with the silent pause, but still fails to fire. Possible glowpin failure. You can check the glowpin with a meter, it should measure 0.3 Ohms - which is below the usable range of most meters, so expect it to show a short. The unit measures the resistance of the glowpin to determine whether it is burning, if the resistance it measures proves to be too high, then it might apear to fire initially, but then shut down. FrenchMike suggests this theory can be tested by connencting a 12v 21w (stop lamp) in parallel with the glowpin. Basically connect the bulb across a pair of sewing needles so you can spear through the insulation to connect to the glowpin wires or connect between the output of the FET driver and ground. Then see if it will run normally.

    An alternative way to check the glowpins operation, would be to measure the total current the entire FBH consumes. There should be a large sudden draw of current, when the glowpin is powered up which should be around 15 to 20amps and the easy way to measure it is by replacing the fuse #8 with a meter, but that will not confirm its resistance is within spec.

    Any smoke, or lots of smoke, or unit shutting down early, maybe trying to restart. It needs a service, see above.

    If the unit fails to fire properly three times in a row, it will go into lock out. Reset by removing and reinserting fuse #8 in the under bonnet fuse panel.

    The heated coolant from the FBH is not pushed around the system unless the engine is running and the FBH may also running in short bursts, rather than the 10 to 20 minutes of continuous running it should normally take to pre-heat the engine. See above under servicing the FBH and particularly the section on servicing the water pump.

    To avoid the rubber pipe from Intercooler to EGR contacting the extremely hot FBH exhaust


    Assuming the FBH is installed and working, a temperature switch on the left hand side of the lower grill should (with the engine running) close at below approximately +5C. The FBH will then fire itself up and run, gradually ramping up its output to maximum burn. The FBH will then continue to run until the coolant gets to 74C then drops its output to half power. The process then continues until 77C is achieved and it then shuts down completely. If the outdoor temperature remains below +5C and your coolant temperature falls, the FBH may fire again to bring the coolant back up to temperature. Maximum output is around 5Kw worth of heat transferred into the coolant.

    So the basic operation is completely automatic, starting to produce extra heat only when you start to drive the car. An optional extra was a timer, which would run the FBH to warm the car up prior to your starting it, at a set time. Another optional extra was a remote control to trigger it into operation manually from a short distance.

    FrenchMike has added a third way to that, of using a mobile phone to trigger the FBH into starting up by ringing a mobile phone interfaced to the FBH to start it. None of these methods suited me, so I simply wired up a switch and LED in the cabin, so I can decide myself whether I want to bypass the +5C automatic start and manually start it, irrespective of whether the engine is running or not.

    With the engine not running, cold and an ambient of around +2C, the FBH can pre-heat the engine to the FBH's cut off of 77C in about 20 minutes. With engine and FBH running, this drops to around 5 or 10 minutes, depending upon the load /speed on the engine. So well worth having an FBH.

    The shut down process is one of the fuel flow being stopped first, then the unit should continue to run the combustion air fan and water pump for several seconds to burn off the residual fuel in the burner and cool it down with water flow.

    What is inside the FBH

    Not very much really, it is just a miniaturised oil burning central heating boiler. It has a pump bolted externally on the left hand side to circulate coolant through the 'boiler' - making it possible to run it without the engine running; a combustion air fan, drawing air through the filter on top, down into the combustion chamber; a glowpin to ignite the fuel and provide proof that the unit has ignited to the ECU; and finally a gauze at one end of the combustion chamber, next to the glowpin, which is soaked by the diesel which is pumped up from the tank.

    If pulled apart it splits into three overlapping sections. The air fan chamber, the combustion chamber and the coolant/ heat exchanger section.

    On top of the unit is the ECU PCB, with a (white) temperature sensor clamped onto the alloy casing of the heat exchanger, so the ECU knows the coolant water flow temperature and can turn itself off.

    To fire the unit, it goes through an initial purge sequence, goes quiet, then starts an ignition sequence of pumping fuel into the gauze, runs the glowpin, then checks with the glowpin that there is combustion. It then gradually ramps up the fuel rate by triggering the pump more frequently and increasing the combustion air fan speed until they reach maximum output. At 74C, it begins to reduce the output to 50%, then at 77C it shuts down, by cutting the fuel and keeping the fan running for a while to burn off the existing fuel. While ever the FBH is in operation the coolant pump runs, to take the heat away.

    Installation (consider servicing the FBH before installing)

    FBH
    Installation is fairly straight forward process, the cars are already plumbed and wired for the FBH. It was an optional fitting, so many cars will not have had one. Most will be installing a second hand unit and the biggest problem is that of knowing if a potential buy is working before you splash out on it, as the chances are that the PCB will be almost certainly faulty, but FrenchMike can repair many of the PCB's and I have included his repair for the most common faults below. Plugging it in and the unit seeming to run and make a noise is NOT proof that the unit is working, the only way to be sure it is working is to see it run, fire and produce heat (or at least produce some white smoke from its exhaust, should it need a service). The unit should never be tested without any water to dispose of the produced heat - it will self destruct.

    For an after market installation what will be needed is - the Webasto FBH, the flue or exhaust pipe, the rubber inlet silencer / filter and a pump. The pump is mounted just forward of the rear OS wheel and due to the exposed location, the outer casing tends to rust through very quickly. So a second hand one should be checked very carefully and if worth using maybe given a coat of Hammerite after removing the worst of the rust. A new replacement can be had for about £35 - look up 'sarkblue' on Ebay.

    Installation is a simple matter of partially draining the coolant, enough to be able to slot the FBH in place in the small coolant pipes ahead of the battery. I found it easier to slot the FBH in place with the flue just loosely attached, to enable it to be turned, to get it onto its support bracket on the wing. One hose joint needs to be parted and one hose needs to be cut, the place to cut the hose is marked on the hose. The hose to be cut is below the FBH mounting bracket. Part the hose at the joint piece first, as this makes the release of the coolant a bit more controlled, so you should be able to easily catch what comes out in a dish so it can be returned once the job is done. The entire area will look much tidier pipe work wise, once the FBH is in place. Once the plumbing is reconnected, the saved coolant can be put back in the header tank and the bleed screw opened to release any air lock. Some small amount of topping up may be needed to take account of the water in the FBH.

    All that is then left to do, is to find the end of the fuel pipe and the 2 pin + 6 pin plugs. The fuel pipe is clipped to another pipe down and to the left of the FBH - a short bit of rubberised pipe, on the end of a more rigid plastic pipe, with a bung in the end. The two plugs should be tucked in somewhere below the fusebox area and will need to be routed around to the FBH. A 20amp fuse will also be need to be fitted in position #5 of the under bonnet fuse panel.

    Pump
    If you are fitting a second hand original pump, then some sort of metal bracket will need to be fabricated. The original from a second hand pump will have long since corroded away. A later type pump comes with a rubber clamp which bolts straight on to the pump bracket. The power plug for the pump will be coiled up on top of the fuel tank, so the rear seat will need to be lifted, the OS tank access panel removed, then the lead released and threaded down the front of the tank to the outside.

    The plug connection for the pump, the mounting bracket and the two pipes linked by another bung can be found under the car just ahead of the rear OS wheel - you can find the position of these by just reaching under the car with your arm, with no need to jack it up. One pipe goes up then down into the tank, the other goes all the way forward to the FBH. Remove the bung from both pipes and fit the pump to the two pipes. No diesel should escape, both pipes should be dry and will need to be primed.

    Find a way to connect 12v from a battery, directly to the pump - polarity does not matter. I used a spare battery and some short leads. You will also need someone at the front to either suck on the end of the pipe under the bonnet or use a syringe to create some vacuum in the pipe to fill the pump with fuel - what ever method used, the pump needs to be caused to run, at the same time as vacuum is applied, or they will be fighting the pumps valves. The pump is a one shot solenoid pump, rather than a rotary pump - so each time it is powered, it produces one pump stroke of fuel.

    The pump needs to be briefly connected to the 12v (rapid on and off), while the vacuum is created at the far end of the pipe until the fuel is drawn into the pump. Once the fuel gets to the pump, air will start to be blown out at the under bonnet end of the pipe, so no need to suck anymore.
    Repeat the rapid on /off connection of the pump power, until diesel fuel emerges from the pipe by the FBH with no air emerging, then connect the plug.

    Connect the pipe to the FBH along with the two plugs.

    Ready to test
    If the temperature of the +5C sensor is less than around its set temperature and you start the engine, the FBH should start up and fire. Alternatively, if it is warmer, you can spray the sensor with freezer spray to force it to operate. It is located to the left, between two oil cooler pipes and visible through the lower front grill - look for a mushroom shaped object.

    The alternative method is to remove the blue bung from pin 3 of the 6 pin plug (left hand hole nearest to you) and using some small diameter wire, connect that to one of the three FBH fixing bolts firmly.

    Note - Model 66232C (early) requires +12 volt to pin 1
    Whereas Model 98570B (later) requires earth to pin 3

    The FBH should start up, run for several seconds, go quiet, start up again
    followed by a regular clicking noise from the pump at the rear. Shortly after which you should hear a low rumble from the exhaust as it starts to burn fuel. The FBH's noise should then gradually increase as it gently ramps itself up to full heat output power.

    Any white smoke at all from the exhaust, would suggest the FBH needs a service. Clouds of smoke indicate a misfire and that it desperately needs a service.

    A very short run of 3 seconds, followed by a quiet pause of 4 seconds, then a run which terminates at 127 seconds - indicates a fault.
    Servicing the FBH
    It is possible for the build up of hard carbon, to completely shield the glow pin and assuming everything else is right, prevent it from actually firing.

    The unit is in three casing sections, plus the water pump all bolted together with small Torx bolts (T20). You will just need one Torx bit size (T20), a large blunt flat bladed screwdriver and a pair of pliers. Remove the waterpump by undoing its short pipe, then the clamp which holds it to the FBH body.

    FBH clamped in the vice, ready to start to strip it down. Black unit uppermost, is the the water circulation pump. Pipe stub in top right corner is the combustion air inlet to the air fan, when installed in the car it would normally have the rubber inlet filter fitted. Small metal pipe emerging from the grommet is the diesel fuel inlet.
    Then undo more of the 5x Torx bolts visible behind where you have removed the pump from, to separate the first section of casing, be careful not to bend the metal fuel pipe as you pull that first section away - ease it through the rubber bung.

    Water pump removed and you can just see the exhaust flue pipe stub sticking out on the left. Black plastic cover on the right hides the combustion air fan
    That should then reveal 4x more Torx bolts holding the burner unit into the heat exchanger. Undo those, but be aware there is a soft thick paper gasket between the two, which is bound to have split in one place - take care not to make it any worse.

    Brass coloured object, with the dog-legged pipe emerging from it is the burner unit. Dog-legged pipe is the fuel pipe.


    Default FBH - How to install, test and service
    Everyone else - please feel free to report any errors or amendments it might need......

    As I have accumulated a bit of experience on the Webasto FBH and lots of questions are being asked about it, I thought it worth documenting. I only have experience of the later unit (98570B), though most of this is applicable to both units.

    What the Fuel Burning Heater (FBH) does
    The M47 diesel engine is so efficient, that it produces very little waste heat to warm the coolant up to a reasonable temperature within a reasonable distance. The issue is often made worse by a coolant thermostat, which as it ages opens too early, so winter or summer, the engine never achieves its designed working temperature. There is no point installing an FBH unless your stat is working properly at is design opening temperature of 88C.

    The FBH is configured to shut off at 77C and if your stat opens at below this temperature, then it will continue to run indefinitely in cold weather, wasting its warmth to atmosphere via the radiator.

    Check your car's normal running temperature via the OBD dash diagnostics for an accurate temperature and if once warmed up it is much below 88C, either install a replacement OEM stat (expensive) or the cheap option of a second stat in the top hose (cheap fix). A problem with the stat, needs to be addressed early, rather than waste fuel running the FBH unnecessarily.

    Assuming the FBH is installed and working, a temperature switch on the left hand side of the lower grill should (with the engine running) close at below approximately +5C. The FBH will then fire itself up and run, gradually ramping up its output to maximum burn. The FBH will then continue to run until the coolant gets to 74C then drops its output to half power. The process then continues until 77C is achieved and it then shuts down completely. If the outdoor temperature remains below +5C and your coolant temperature falls, the FBH may fire again to bring the coolant back up to temperature. Maximum output is around 5Kw worth of heat transferred into the coolant.

    So the basic operation is completely automatic, starting to produce extra heat only when you start to drive the car. An optional extra was a timer, which would run the FBH to warm the car up prior to your starting it, at a set time. Another optional extra was a remote control to trigger it into operation manually from a short distance.

    FrenchMike has added a third way to that, of using a mobile phone to trigger the FBH into starting up by ringing a mobile phone interfaced to the FBH to start it. None of these methods suited me, so I simply wired up a switch and LED in the cabin, so I can decide myself whether I want to bypass the +5C automatic start and manually start it, irrespective of whether the engine is running or not.

    With the engine not running, cold and an ambient of around +2C, the FBH can pre-heat the engine to the FBH's cut off of 77C in about 20 minutes. With engine and FBH running, this drops to around 5 or 10 minutes, depending upon the load /speed on the engine. So well worth having an FBH.

    The shut down process is one of the fuel flow being stopped first, then the unit should continue to run the combustion air fan and water pump for several seconds to burn off the residual fuel in the burner and cool it down with water flow.

    What is inside the FBH

    Not very much really, it is just a miniaturised oil burning central heating boiler. It has a pump bolted externally on the left hand side to circulate coolant through the 'boiler' - making it possible to run it without the engine running; a combustion air fan, drawing air through the filter on top, down into the combustion chamber; a glowpin to ignite the fuel and provide proof that the unit has ignited to the ECU; and finally a gauze at one end of the combustion chamber, next to the glowpin, which is soaked by the diesel which is pumped up from the tank.

    If pulled apart it splits into three overlapping sections. The air fan chamber, the combustion chamber and the coolant/ heat exchanger section.

    On top of the unit is the ECU PCB, with a (white) temperature sensor clamped onto the alloy casing of the heat exchanger, so the ECU knows the coolant water flow temperature and can turn itself off.

    To fire the unit, it goes through an initial purge sequence, goes quiet, then starts an ignition sequence of pumping fuel into the gauze, runs the glowpin, then checks with the glowpin that there is combustion. It then gradually ramps up the fuel rate by triggering the pump more frequently and increasing the combustion air fan speed until they reach maximum output. At 74C, it begins to reduce the output to 50%, then at 77C it shuts down, by cutting the fuel and keeping the fan running for a while to burn off the existing fuel. While ever the FBH is in operation the coolant pump runs, to take the heat away.

    Installation (consider servicing the FBH before installing)

    FBH
    Installation is fairly straight forward process, the cars are already plumbed and wired for the FBH. It was an optional fitting, so many cars will not have had one. Most will be installing a second hand unit and the biggest problem is that of knowing if a potential buy is working before you splash out on it, as the chances are that the PCB will be almost certainly faulty, but FrenchMike can repair many of the PCB's and I have included his repair for the most common faults below. Plugging it in and the unit seeming to run and make a noise is NOT proof that the unit is working, the only way to be sure it is working is to see it run, fire and produce heat (or at least produce some white smoke from its exhaust, should it need a service). The unit should never be tested without any water to dispose of the produced heat - it will self destruct.

    For an after market installation what will be needed is - the Webasto FBH, the flue or exhaust pipe, the rubber inlet silencer / filter and a pump. The pump is mounted just forward of the rear OS wheel and due to the exposed location, the outer casing tends to rust through very quickly. So a second hand one should be checked very carefully and if worth using maybe given a coat of Hammerite after removing the worst of the rust. A new replacement can be had for about £35 - look up 'sarkblue' on Ebay.

    Installation is a simple matter of partially draining the coolant, enough to be able to slot the FBH in place in the small coolant pipes ahead of the battery. I found it easier to slot the FBH in place with the flue just loosely attached, to enable it to be turned, to get it onto its support bracket on the wing. One hose joint needs to be parted and one hose needs to be cut, the place to cut the hose is marked on the hose. The hose to be cut is below the FBH mounting bracket. Part the hose at the joint piece first, as this makes the release of the coolant a bit more controlled, so you should be able to easily catch what comes out in a dish so it can be returned once the job is done. The entire area will look much tidier pipe work wise, once the FBH is in place. Once the plumbing is reconnected, the saved coolant can be put back in the header tank and the bleed screw opened to release any air lock. Some small amount of topping up may be needed to take account of the water in the FBH.

    All that is then left to do, is to find the end of the fuel pipe and the 2 pin + 6 pin plugs. The fuel pipe is clipped to another pipe down and to the left of the FBH - a short bit of rubberised pipe, on the end of a more rigid plastic pipe, with a bung in the end. The two plugs should be tucked in somewhere below the fusebox area and will need to be routed around to the FBH. A 20amp fuse will also be need to be fitted in position #8 of the under bonnet fuse panel.

    Pump
    If you are fitting a second hand original pump, then some sort of metal bracket will need to be fabricated. The original from a second hand pump will have long since corroded away. A later type pump comes with a rubber clamp which bolts straight on to the pump bracket. The power plug for the pump will be coiled up on top of the fuel tank, so the rear seat will need to be lifted, the OS tank access panel removed, then the lead released and threaded down the front of the tank to the outside.

    The plug connection for the pump, the mounting bracket and the two pipes linked by another bung can be found under the car just ahead of the rear OS wheel - you can find the position of these by just reaching under the car with your arm, with no need to jack it up. One pipe goes up then down into the tank, the other goes all the way forward to the FBH. Remove the bung from both pipes and fit the pump to the two pipes. No diesel should escape, both pipes should be dry and will need to be primed.

    Find a way to connect 12v from a battery, directly to the pump - polarity does not matter. I used a spare battery and some short leads. You will also need someone at the front to either suck on the end of the pipe under the bonnet or use a syringe to create some vacuum in the pipe to fill the pump with fuel - what ever method used, the pump needs to be caused to run, at the same time as vacuum is applied, or they will be fighting the pumps valves. The pump is a one shot solenoid pump, rather than a rotary pump - so each time it is powered, it produces one pump stroke of fuel.

    The pump needs to be briefly connected to the 12v (rapid on and off), while the vacuum is created at the far end of the pipe until the fuel is drawn into the pump. Once the fuel gets to the pump, air will start to be blown out at the under bonnet end of the pipe, so no need to suck anymore.
    Repeat the rapid on /off connection of the pump power, until diesel fuel emerges from the pipe by the FBH with no air emerging, then connect the plug.

    Connect the pipe to the FBH along with the two plugs.

    Ready to test
    If the temperature of the +5C sensor is less than around its set temperature and you start the engine, the FBH should start up and fire. Alternatively, if it is warmer, you can spray the sensor with freezer spray to force it to operate. It is located to the left, between two oil cooler pipes and visible through the lower front grill - look for a mushroom shaped object.

    The alternative method is to remove the blue bung from pin 3 of the 6 pin plug (left hand hole nearest to you) and using some small diameter wire, connect that to one of the three FBH fixing bolts firmly.

    Note - Model 66232C (early) requires +12 volt to pin 1
    Whereas Model 98570B (later) requires earth to pin 3

    The FBH should start up, run for several seconds, go quiet, start up again
    followed by a regular clicking noise from the pump at the rear. Shortly after which you should hear a low rumble from the exhaust as it starts to burn fuel. The FBH's noise should then gradually increase as it gently ramps itself up to full heat output power.

    Any white smoke at all from the exhaust, would suggest the FBH needs a service. Clouds of smoke indicate a misfire and that it desperately needs a service.

    A very short run of 3 seconds, followed by a quiet pause of 4 seconds, then a run which terminates at 127 seconds - indicates a fault.

    Servicing the FBH
    It is possible for the build up of hard carbon, to completely shield the glow pin and assuming everything else is right, prevent it from actually firing.

    The unit is in three casing sections, plus the water pump all bolted together with small Torx bolts (T20). You will just need one Torx bit size (T20), a large blunt flat bladed screwdriver and a pair of pliers. Remove the waterpump by undoing its short pipe, then the clamp which holds it to the FBH body.

    FBH clamped in the vice, ready to start to strip it down. Black unit uppermost, is the the water circulation pump. Pipe stub in top right corner is the combustion air inlet to the air fan, when installed in the car it would normally have the rubber inlet filter fitted. Small metal pipe emerging from the grommet is the diesel fuel inlet.


    Then undo more of the 5x Torx bolts visible behind where you have removed the pump from, to separate the first section of casing, be careful not to bend the metal fuel pipe as you pull that first section away - ease it through the rubber bung.

    Water pump removed and you can just see the exhaust flue pipe stub sticking out on the left. Black plastic cover on the right hides the combustion air fan.


    That should then reveal 4x more Torx bolts holding the burner unit into the heat exchanger. Undo those, but be aware there is a soft thick paper gasket between the two, which is bound to have split in one place - take care not to make it any worse.

    Brass coloured object, with the dog-legged pipe emerging from it is the burner unit. Dog-legged pipe is the fuel pipe.


    Inside the heat exchanger, from where the burner has just been removed. Surrounding the hole you can see the pale green paper gasket, small spilt is just visible at 1 o'clock. It only needs to contain low pressure combustion air, so if this is the only damage, it can be reused. The heat exchanger has not been cleaned, it was clean enough as is. Pipe stubs in top left and bottom right hand corners are the coolant inlets and outlet
    That gets you access to remove the burner unit and see inside the heat exchanger. Follow the two thick wires (mentioned earlier), to the glowpin, unclip the wires, unclip the glowpin - held by a spring P clip and very carefully remove it from the burner chamber. Test it by connecting its two terminals across 12v, where upon its square section end should in a few seconds become close to white hot. It is not designed to run continuously on 12v, so limit this test to a few seconds - just long enough to satisfy yourself that it glows. If it doesn't glow, then it has failed and no one has yet been able find a source for a replacement, but they are very expensive - maybe £60, even if you can manage to source one. Webasto only seem to sell them complete with the combustion chamber.

    For anyone in any doubt, this i the type of glowpin this FBH needs. The end of the pin is about 1/8" square section, it comes with the two wires attached and fitted with a two pin plug.
    If you now look deep into the bottom of the burner, you will most likely see lots of hard carbon build up, which has formed over the gauze at the bottom and particularly around the perimeter. All of that needs to be cleaned off, using the blunt screwdriver. Break it up by pushing the screwdriver hard against the carbon. You will need the chamber to be well supported, without damaging the fuel pipe so you have something to push against. Don't try to tease it out or you might damage the gauze, just break it up by pressing. The gauze is held by a metal frame, which should come into view as the carbon is removed around the edges. Finally check all of the air inlet holes around the perimeter of the combustion chamber are completely clear, then blow down the fuel pipe to make sure that is also clear. It should seem as if there is some restriction in the pipe - I'm guessing quite a large bore jet, to get it to squirt fuel through the gauze.

    Removed combustion chamber, sat upside down on top of the heat exchanger - this example has already been cleaned out. No need for it to be spotless, providing all of the hard carbon is removed. Blue and white wires emerging from the right, are the wires from the glowpin - with its 2 pin plug just visible.
    Reassemble reusing the paper gasket by pushing the split back together. That joint only seals the combustion air section from the combustion chamber.

    Servicing the Water Pump

    This can be tackled with the FBH on or off the car. Symptoms of it needing to be checked and serviced are that with the FBH running, the heated coolant from the FBH is not pushed around the system unless the engine is running and the FBH may also run in short bursts, rather than the 10 to 20 minutes of continuous running it should normally take to pre-heat the engine. (Photos provided by Tam (Rotrex)).

    If the pump is not already removed from the FBH, remove one torx bolt to unclamp it and unclip the coolant hoses to get it onto the bench.

    Remove 4x top cover Torx bolts, top cover should then lift off.
    Reassemble reusing the paper gasket by pushing the split back together. That joint only seals the combustion air section from the combustion chamber.

    Servicing the Water Pump

    This can be tackled with the FBH on or off the car. Symptoms of it needing to be checked and serviced are that with the FBH running, the heated coolant from the FBH is not pushed around the system unless the engine is running and the FBH may also run in short bursts, rather than the 10 to 20 minutes of continuous running it should normally take to pre-heat the engine. (Photos provided by Tam (Rotrex)).

    If the pump is not already removed from the FBH, remove one torx bolt to unclamp it and unclip the coolant hoses to get it onto the bench.

    Remove 4x top cover Torx bolts, top cover should then lift off.
    Check motor shaft is now free to turn and turns smoothly.
    Clean out all of the accumulated deposits, then apply 12v across the motor terminals to ensure it runs before finally reassembling and refitting.



    See also http://www.landyzone.co.uk/lz/f9/how-i-repaired-modified-my-fbh-system-203702.html
     
  2. fredi250

    fredi250 Well-Known Member

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    f...ing brilliant post
     
  3. Echohowl

    Echohowl New Member

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    Very helpful post thank you, just what i was looking for. :D
     
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