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Discussion Starter #1
Hi there,

4.6 HSE 1999 with bosch motronic with engine problem.
Faultmate ODB P0172 and P0175 say both cilinder banks lean mixture.
Also misfire at specially at nr 7, have change HT lead and plugs, no result.
Engine hesitates during acceleration.
I guess the misfire is a result of the lean mixture.
On petrol less misfire then at LPG.
It's not every day very bad, cold weather and cold engine is worse.
Something to do with an airleak after MAF sensor? , broken inlet manifold ?

Allyv8?

Regards,

Klaas
 

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1995-2002 Range Rover P38A
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164 Posts
Try cleaning your O2 sensors and MAF with no-residue cleaner.
 

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1995-2002 Range Rover P38A
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1,851 Posts
Hi

You do not state if your LPG system is single point or multi point injection nor if you have any controller open or closed loop installed. A closed loop system should correct the lean mixture. Check your pressure settings of the LPG at the evaporator. With cold engine the evaporator doesn´t work so well either which can explain the increased problems.

From what I have read on this forum I believe that running on LPG will upset the petrol ecu adaptive settings as the ecu signals are bypassed during LPG usage and the engine doesn´t repond to petrol ecu outputs. Try resetting the adaptive values as this might cure the lean problem during petrol operation.

You might want to PM Alley V8 as he is the expert in this field.

Regards

Jos
 

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2010-2012 Range Rover MkIII / L322
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4,635 Posts
Both those DTC's point towards bad HO2 sensors. Change both of them and then reset the adaptions.

A pair of genuine part sensors are around £100. Don't be tempted to take short cuts with lesser brands here either, especially anything cheap from EuroCarParts...!
 

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From your post it suggests you have a faultmate. It would be wise to use this to diagnose the problem, rather than guess and throw parts at it.
You can use Faultmate to test MAF to probably eliminate this as the fault.
You can also use it to read the live values from your O2 sensors to see how these are performing, together with the fuel trims.

As to the lpg on a Bosch you should really only be running a full sequential system, calibrated to ensure it doesn't throw out the petrol fuel trims.
One thing to be wary about is if your MAF is at fault and you reset the adaptive values you could make it run worse.
 

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2010-2012 Range Rover MkIII / L322
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Does faultmate offer some sort of fixed/expected data to show if the sensor is working? When you bring up live data on T4, the software tends to highlight any data it feels to be out of range in some way. Does faultmate do the same?
 

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I think this is probably all a result of a low Maf reading,if it was just inactive Oxy sensors the engine would end up running very rich,but if the Maf reads low the ecu wont allow a wide enough injector pulse width to get the sensors to switch rich.So have a look at airflow readings,22-25Kg at idle and approx 90-100kg at 3000rpm engine hot all loads off.So if the readings are low its either leaks or a failing Maf.After a short period of Oxy sensor inactivity the ecu will get fed up and go open loop making the situation worse.What you can try with the failing Maf - just at idle is to carefully tape off part of the Maf to increase the speed of the air going through the remaining open part. If you then watch live data you should be able to get the Maf to read right - then watch to see if it will trim the fuelling and make the Oxy sensors switch.Apart from being an interesting thing to play with it can also prove the state of the Oxy sensors.
 

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Discussion Starter #10
Hi all,

The MAF readings looks OK.
The engine runs very smooth at idle if hot, cold it will run unstable.
22-23 at idle and approx 65 -68 @ 2500 rpm, I don't have checked at 3000 rpm.
The problem starts during acceleration between 1500 up to 2200 rpm, if I shift back to 3th or even 2th gear and the engine runs at 2500/2800 rpm it runs OK.
At the highway with 120 kmh and 2800 rpm it also runs OK.
The problem is (with sequential and multipoint LPG) also there at petrol, but less worse then on LPG.
I have drive the car several times with the faultmate with laptop aside but I can't find any mutation in the faultmate readings.

I have ordered new HT leads from Magnecor (the red one's) but I think this is not the solution.
Ally V8, I will try your magnificent solution with duct tape! see what happens.
Thanks guys for your time and help.

Regards,
 
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