Fluctuating Idle

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pos

pos

Well-Known Member
Posts
3,685
Location
West Yorkshire
Good evening,

I have noticed over the course of the last four weeks that my 200TDi has developed a strange, fluctuating idle, and it seems to reproduce its self in a few different ways. In one circumstance, when I dip the clutch whilst the vehicle is rolling, the engine will drop down to a steady idle speed which is higher than the usual idle speed, until the vehicle has come to a total stand still where it may then either drop back down to the normal idle speed or in some cases, it may rev up slightly higher. The second circumstance is when the vehicle is stationary. The engine idle will sometimes increase and then hold its self at a higher idle for anything between ten seconds to a couple of minutes (it varies from time to time) and then it will then drop back down to the normal idle speed.

I've been trying to find the cause of the problem, and so far I haven;t had any luck. The lift pump is in good shape, there are no leaks or blockages along the fuel lines, injector pipes or spill rail and it doesn't effect performance when the engine is working hard. I do have one theory based on the fact that I installed new nozzles into my injectors a couple of months ago. The problem didn't exist immediately following the new nozzles however. I suppose it is possible that one or two of the injectors are passing more fuel than the other one / two (although wear was even in the first place and parts have been re-assembled exactly as they were taken out albeit the new nozzles).

I have also installed a new timing belt within the last month (time frame is about right) but everything lines up and it aint white smoking.

Does any one have any ideas? It's beginning to bug me a bit and it makes gear changing a little crunchy!

Thanks,
-Pos
 
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Don't quote me on this because I'm just suggesting here (more like guessing). If the engine revs until stationary, could the clutch be not disengaging properly? It could be touching just enough to speed the engine up?
 
Is it because for instance you may have the brake pedal depressed and then release it. the brake lights take quite a bit of power and load the alternator slowing the idle slightly.

Mine does the same as yours but I haven't checked the brake light scenario as I only just thought of it.:rolleyes:

My idle will drop slightly for no reason or pick up slightly for no reason. Be interested to know the answer.:)
 
khaos said:
Don't quote me on this because I'm just suggesting here (more like guessing). If the engine revs until stationary, could the clutch be not disengaging properly? It could be touching just enough to speed the engine up?
Click to expand...

I had thought that the clutch might be binding slightly and I do think that this is a possibility. If I sit stationary with the engine idling and my foot fully down on the clutch, the prop shaft will knock at the back when I move the gear level towards first gear, something that it should only do when the clutch pedal is fully released. Not sure really.
 
landowner said:
Is it because for instance you may have the brake pedal depressed and then release it. the brake lights take quite a bit of power and load the alternator slowing the idle slightly.

Mine does the same as yours but I haven't checked the brake light scenario as I only just thought of it.:rolleyes:

My idle will drop slightly for no reason or pick up slightly for no reason. Be interested to know the answer.:)
Click to expand...

I like your theory here and this is also interesting. I currently have a bad earth at the back (in the process of fixing) which means that when I press the brake pedal, both my rear stop lights, and both my front side lights illuminate. I cant imagine this would have much drag on the alternator however, it doesn't effect the idle if I put full beam on and that's with two spots too.
 
more likely the loom has eaten through either on seam behind rubber flap or chassis entry front or rear
 
A few valid points, but on thinking them through I think they are all pretty unlikely and the cause is almost certainly IP related.

Regarding electrical load, it takes about 0.056hp to operate brake lights via a properly functioning alternator, so, assuming the lights are not creating a HUGE draw due to an electrical problem which I would expect would blow the fuse, I really don't think it has anything to do with electrical loading. Also, remember that a loaded alternator will simply offer some more resistance to the engine, so the injection pump will only throw in more fuel to keep the engine turning at the governed speed for idle, not increase the revs; unlike an ECU controlled engine that will increase the revs of the engine if the electrical system demand is high at idle speed.

If one or two of the injectors were passing more fuel than the other one - which would be quite evident if you were to look at the spill off pipes from each and see if one was leaking much more than the rest, known as a leak off test - the engine would almost certainly be running lumpy and it would not account for the engine gaining speed.

It sounds to me like the control sleeve (the bit that meters the diesel injected) is sticking, either because it's dirty or the idle spring and or governor which controls the sleeve on idle is gummed up.

Do you ever run this engine on bio diesel or used veg oil?

It could also be air related, however that would be a bad air fault at the Bosch injection pump fitted to your engine is very good at ridding the IP of any air in the fuel, but enough of it and the pump would struggle, the pump could then struggle to work properly because it doesn't have enough diesel to work with.

My advice would be to clean the pump, get a new fuel filter, fill it with petrol, screw it back onto the filter body and start the engine, let it tick over on pure petrol, the pump will take it all through in about 30 seconds as the Bosch system ALWAYS circulates diesel as a coolant. That may work like a solvent and clear any gum, if it is dirt then you may be looking at a top off job. Don't by injector cleaner stuff, it's just kero, petrol and any other light oils they have spare.
 
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discomania said:
A few valid points, but on thinking them through I think they are all pretty unlikely and the cause is almost certainly IP related.

Regarding electrical load, it takes about 0.056hp to operate brake lights via a properly functioning alternator, so, assuming the lights are not creating a HUGE draw due to an electrical problem which I would expect would blow the fuse, I really don't think it has anything to do with electrical loading. Also, remember that a loaded alternator will simply offer some more resistance to the engine, so the injection pump will only throw in more fuel to keep the engine turning at the governed speed for idle, not increase the revs; unlike an ECU controlled engine that will increase the revs of the engine if the electrical system demand is high at idle speed.

If one or two of the injectors were passing more fuel than the other one - which would be quite evident if you were to look at the spill off pipes from each and see if one was leaking much more than the rest, known as a leak off test - the engine would almost certainly be running lumpy and it would not account for the engine gaining speed.

It sounds to me like the control sleeve (the bit that meters the diesel injected) is sticking, either because it's dirty or the idle spring and or governor which controls the sleeve on idle is gummed up.

Do you ever run this engine on bio diesel or used veg oil?

It could also be air related, however that would be a bad air fault at the Bosch injection pump fitted to your engine is very good at ridding the IP of any air in the fuel, but enough of it and the pump would struggle, the pump could then struggle to work properly because it doesn't have enough diesel to work with.

My advice would be to clean the pump, get a new fuel filter, fill it with petrol, screw it back onto the filter body and start the engine, let it tick over on pure petrol, the pump will take it all through in about 30 seconds as the Bosch system ALWAYS circulates diesel as a coolant. That may work like a solvent and clear any gum, if it is dirt then you may be looking at a top off job. Don't by injector cleaner stuff, it's just kero, petrol and any other light oils they have spare.
Click to expand...

Thanks for the reply Disco. I am certain that the problem is not air related as I installed all new components into the fuel line (before the injection pump) just after the engine conversion and these were the first things I checked again. I will buy a new fuel filter tomorrow and fit it filled with petrol. I will then chuck a little petrol in the fuel tank as well to help it all along after the initial dose. It hasn't had any veg oil or bio diesel running through it with this engine. If this doesn't fix it then how complex a job is it to whip the top of the pump off?

Cheers
-Pos
 
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Right, i've installed a new fuel filter (mann-hummell) filled it with petrol and fired her up. She started up alright obviously with the diesel remains in the injection pump and then I let the petrol run through the system (evident with rougher idle and blue smoke when revved). The old fuel filter I removed (which is about 2 months old) was only half full in the central channel. It's supposed to be full to the brim in the central channel isn't it? This could be demonstrating a weak lift pump?

I've left the engine sat with the petrol in the injection pump, hoping that it will dissolve any crap away and all being well this should fix the problem. I' not happy about the fuel filter not being full mind, any suggestions - lift pump?

Thanks
-Pos
 
With the engine running, see how much diesel is being returned via the return pipe from the injection pump. You can either do this by undoing it at the injection pump, or at the tank (whichever looks least corroded and most likely to go back together without too much hassle).

You should see a steady flow of diesel returning from the pump when the engine is running.

Now consider this, even when doing motorway speeds, there is no way the engine will use as much fuel as the lift pump can deliver even at idle, so if you have good flow at idle you are OK, and the lift pump is doing just fine.

Have a reread at my original post; I think it is more likely to be the injection pump.
 
discomania said:
With the engine running, see how much diesel is being returned via the return pipe from the injection pump. You can either do this by undoing it at the injection pump, or at the tank (whichever looks least corroded and most likely to go back together without too much hassle).

You should see a steady flow of diesel returning from the pump when the engine is running.

Now consider this, even when doing motorway speeds, there is no way the engine will use as much fuel as the lift pump can deliver even at idle, so if you have good flow at idle you are OK, and the lift pump is doing just fine.

Have a reread at my original post; I think it is more likely to be the injection pump.
Click to expand...

Hi Disco,

Thanks for the info. I removed the fuel return line at the injection pump end and with the engine idling, there was a good flow of diesel flowing from the pump (back towards the tank).

Following a few days of researching the problem on the Internet, I stumbled across the following post:

At this point it should be running. Try 'burping' the throttle a few times. Make sure that the engine returns to idle promptly as it did before the spring change. If it lingers at higher RPM and slowly drops down, take that as a sign of being close to runaway condition. Back out the full fuel screw 1/4 ~ 1/2 turn, restart and try again. I also recommend running your high idle screw in a fair bit to make sure you can "work up to" you intended high idle setting and avoid RPM flare. You should be able to reset your low idle, full fuel, etc without too much trouble.

(source VE Pump Governor Spring Install - A - Dodge Cummins Diesel Forum)

Now considering that I installed new injector nozzles about 2 months ago, do you think that it is possible that this will have had any effect onthe way that the pump meters fuel? And would turning the overall fuelling down slightly be of benefit? What is this high idle adjustment that is mentioned?

I must also ask what the significance of indexing the throttle lever on the throttle spindle is? I have had to remove the lever from the throttle shaft (which attaches to the govenor) in the past to get access to the boost diaphragm pin and I did not mark the way that it came off. In fact, I rotated the spindle manually to increase my engine idle speed up ever so slightly before refitting the throttle lever. Could this have been the cause of my problem?

If this is not the solution, I will crack on with removing the top cover in order to give the governor a good clean out.

Thanks again for your help! :)
-Pos
 
Well I've had a go at re-indexing / correctly aligning the throttle lever on the splined throttle shaft and so far the results have been very good. Just exactly how I align everything just as it is supposed to be, I do not know, but the kind gentleman at DC Woodhead & Partners in Pudsey explained everything to me in detail over the phone :) Generally speaking, to set it up correctly, I would have to take the pump into the workshop and have it calibrated and tested. I also came across a small leak between the throttle shaft and the injection pump body - a leak which he confirmed would not draw air into the system (it is only on the lubrication side of the pump). You can see the diesel weeping in the photo below.

pump.jpg


Whether or not I can whip the top off and actually do these jobs myself, I do not know. I'd certainly like to have a go at it, but I have been warned that I may do more harm than good, calibration wise anyway.

-Pos
 
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