Disco 2( 2000) V8 LPG poor start up on Petrol

Have been recently experiencing poor, erratic initial starting on Petrol, does not want to rev and the brake servo appears to be non operational- hard pedal and no braking effect.
Initially thought that there was a vacuum leak problem, but nothing untoward discovered. Within a few seconds the power/revs increase and return to normal with full braking capability. Could this be an ECU problem also with the ABS?
Has anyone else experienced this problem?

I'd have a sniff around the plenum chamber and the plastic pipe that feeds the servo and the connections of said pipe.

There is also the idler air bleed valve motor on the other side of the throttle, but that shouldn't affect start up, only tickover.

On the Plenum you have:

Servo connection.
Breather to the driver's side rocker cover (which should have a restrictor in the spout)
Vacuum connection for the cruise control if fitted.
Bleed air hose from the stepper motor.

Any loss of vacuum on the engine side will cause starting problems, it sounds to me like a cracked connection or broken pipe, as once the engine gets going the vacuum will build up to normal.

The plenum also has two gaskets where it joins the 'bunch of bananas' manifold.

Peter

Many thanks for your reply, will investigate each section in turn, but having already checked pretty thoroughly all above, can't see anthing obvious.

Having checked all Peter's suggested areas, nothing found to be causing the initial staring and running problem. The only common factor between no servo effect( lack of vacuum) and the uneven running could be the Idle Speed Controller(ERR6078). If this is not controlling or open too far this will create a vacuum loss - giving poor mixture and also affecting the brakes. I am going to exchange this unit with another known good Idle speed controller to prove one way or the other.
Has anyone any other thoughts on the matter - all greatly appreciated. What about the MAF unit?

The MAF (Just changed my own one) only senses the volume of air and air temperature. It has no connection or control over the vacuum build-up in the manifold.

The air bleed motor is a good possibility, it was one of the things to check on my original list. It would need to be non-functional and stuck open. It normally buzzes when the ignition is on and the engine stopped. It uses two opposing magnetic fields to change the orifice size by way of a rotating armature arrangement.

Peter

is this the same engine as the disco 1 3.9v8i as I have idle speed issues and wonder where that idle speed controller is..

It is similar, but many differences, especially the injection system, which is Bosch on the later one and Lucas-Sagem on the earlier one.

Mechanically very similar once all the bolted-on bits are removed



Peter

Re the MAF - on the Disco 2 the MAF senses the Vacuum and the Gas Manifold pressures which in turn must control mixture via the ECU even at idle speed which will obviously vary the Idle speed controller.
Have exchanged Idle speed controllers with my mate's V8 LPG unit and it makes no difference. Swapped units both ways and his unit runs normally with my idle speed controller - therefore will have to go back to the drawing board and re-think the problem.

Not quite.

The MAF (Mass Air Flow) sensor detects the volume of air flowing through the housing, the housing also incorporates the ambient air temperature sensor.

There is no vacuum on the sensor side of the throttle, or at least, not until your air filter clogs up!

The MAP (Manifold Absolute Pressure) sensor is on the engine side of the throttle and senses the depression in the manifold, which is often matches by the owner's depression when he gets his bills!

All joking aside, if you have eliminated the idle air valve successfully, then there has to be further investigation, so first thing on my list would be the servo diaphragm, can you setup a vacuum in the line to the servo and does it hold it OK?

Next is the breather restrictor in the driver's side rocker cover breather, that is not a simple tube, it has a restrictor in there that takes crankcase fumes out of the engine. They call it an oil separator, but it's another area where a missing or damaged part could cuase problems.

Peter

Peter, many thanks for your input, much appreciated.
Will check out the breather pipes, but it does not ring true when the "defect" clears, I would expect this to be a constant problem and not at each start up, and this is regardless of the engine temperature.
The Servo system is "tight" and fully operational.
The latest update on the poor initial starting and running will eventually clear if the engine is revved prior to attempting to drive off, the power and engine RPM returns to normal, but initially it runs very rough(as if on 4 cylinders). If you start the engine and move off immediately, the engine runs rough and their is no power and will then suddenly "clear" and can be dangerous to say the least.

The engine has had a history of hunting at certain RPM's when on full gas and I have replaced plugs, leads inline gas filters etc to no avail. On the diagnostic unit all that could be found wrong was the air flow meter, which was subsequently renewed, but problem still persists even today.

Could you just outline the engine, fuel supply and other pertinent details?

If it has lpg, whose system is it? Presume it is Bosch Motronic (Thor) petrol system?

Year and engine type etc.

I'm just looking between model years to see if there is anything significant in there.

Peter

try starting it on gas, if its possible with your system, should be somehow. if it starts fine on gas then i would be looking at the parts the gas system doesnt use. i.e maf, temp sender etc.

if its the same on gas then it'll be the common items plugs, leads coilpack!

gavbriggs said:

try starting it on gas, if its possible with your system, should be somehow. if it starts fine on gas then i would be looking at the parts the gas system doesnt use. i.e maf, temp sender etc.

if its the same on gas then it'll be the common items plugs, leads coilpack!

Click to expand...

It won't start on gas if the vapouriser isn't up to temperature.

I think that the multipoint systems use some of the engine sensors to control gas volume etc.

Peter

listerdiesel said:

Could you just outline the engine, fuel supply and other pertinent details?

If it has lpg, whose system is it? Presume it is Bosch Motronic (Thor) petrol system?
Year and engine type etc.

I'm just looking between model years to see if there is anything significant in there.

Peter

Click to expand...

It's a BIGAS multi point injection system, Bosch Petrol system.

Reg DEC 2000 ,V8i 4.0 , 7-seat, ES trim.
81,000 miles

Something that might be of interest, and also some help with this problem.

I have been playing with an OBDII Code Reader Interface which I bought on ebay.

After a bit of setting up and finger 'trouble' I was able to read fault codes and engine sensor information in real time with the engine running.

Have a look at this thread, you'll need to register to see the pictures, but there are shots of my V8 sensors in real time on there.

OBDII Interfacing Equipment - Land Rover UK Forums

Peter

Peter,
Very interesting your purchase of the OBDII Code Reader, did it come complete with leads etc? What site did you purchase from?

Re My starting problem on Petrol - have now rectified the problem by re-fitting my old Air Flow Meter - this unit was replaced some 3 months ago and I have only covered about 1000 miles in that period. Will be sending the defective unit back as I do not reckon that is at all satisfactory.
The initial starting tick-over has increased to about 1300RPM and the engine revs freely and no further problems with vacuum/servo pedal effect.
Hopefully this should be the end of my investigations - well at least into the fuel side of things - being a Disco, there is never a dull moment with numerous other faults to rectify.
Again Peter, many thanks for your assistance over this matter.
John

Glad to hear that it's sorted at last, but that tickover is too high, it should be 680-690 rpm.

On start-up, the ECU holds the revs at 1200 rpm for 20 seconds and then drops down, is that what you are experiencing?

Sorry we didn't catch the MAF, did you mention it had been replaced earlier?

I ran the diagnostic reader today and changed the camshaft sensor, which cured our low speed misfire, and it goes like a rocket now!

The reader is available from many sellers, I don't think they differ much. If you get one, drop me a PM if you get problems, I'll talk you through it. Clue: The supplied CD doesn't autorun.

Ebay 270428924348

Peter

I ran the diagnostic reader today and changed the camshaft sensor, which cured our low speed misfire, and it goes like a rocket now!

Hi Peter,
I have been reading this thread with interest and I picked up on your comment above about low speed misfire. I have an intermittent misfire at 35-40mph in top gear (autobox) if i try to accelerate without the box changing down or try to maintain this speed up an incline It will misfire and judder , not badly but enough to be annoying.
it has had new leads and coil packs and new lambda sensors as well as a new maf.
It only happens in top gear , I can cruise at 1250/1500 rpm in the other gears no problem so i assumed it was a fuelling problem and changed the lambdas as they had shown a fault at the last lpg service. sorry to hijack the thread but any thoughts????

thanks
Andy

Andy:

Does it do it on gas as well as petrol?

If it does, then you'll need to check the timing on one of these readers to see if the advance is changing with speed or not.

If the camshaft sensor fails, there is a fall-back setting in the ECU, but it goes for fixed timing as far as I can see.

If the flywheel sensor fails, there is no fall-back and the engine stops.

Peter

thanks for reply
Thinking about it I dont recall it happening on petrol , (i dont use petrol apart from start up) I think it is a gas problem only.
ag multipoint system