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hi guys,

i recently purchased a thor 4.6, which had suffered a head gasket failure (loose bolts, compression leakage under the exhaust manifold). the car came to me with the right head off.

i rebuilt both heads and replaced the cam/lifters.

during cam break in, it was clear it wasn't running happily - missfires, flat spots which come and go, etc.

i put it on a code reader which returned -

* catalyst damaging missfire multiple cylinders
* catalyst damaging missfire cyl 7
* missfire with low/empty fuel
* lambda sensor upstream bank 1
* lambda sensor upstream bank 2
* emission relevant missfire multiple cylinders
* emission relevant missfire cyl 5

i cleared the codes and reset the adaptations. for about 20km the thing drove amazingly, then deteriorated again.

as an experiment i fitted a MAF from a similar vintage mercedes, which gave a good idle but flat performance. figured the latter was down to calibration and that a new MAF would sort it.

ordered a bosch 4.0 MAF from ebay, thinking 4.0 and 4.6 was the same. the inserts had the same part number so i swapped over the housings.

with the new MAF the car runs as it did from the beginning. sometimes it will clear its lungs and start to pull, but a far cry compared to how it was after i reset the adaptations. seems unlikely both MAFs are faulty, but then again, it ran quite consistently with the mercedes sensor.

temp gauge reads at the end of the blue, but diagnostic had it idling at approx 90C. does a code reader base that on the gauge side of the sensor, or EFI? which is to say, could it be a faulty temp sensor?

i feel it runs slightly better on LPG, which to my mind rules out ignition.

any thoughts appreciated!
 

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1995-2002 Range Rover P38A
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Have you reset the Adaptives since fitting the correct MAF?
2 temp sensors in 1 housing on the Thor. One side feeds the BECM (gauge) and the other the ECM. Diagnostics reads the ECM side, so it appears that as far as engine management goes your ECM is seeing the correct temperature.
How are your lambda sensors? If they were bathed in coolant and nastiness, they could be contaminated or damaged.
 

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1995-2002 Range Rover P38A
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As you have had it running properly (if only briefly) then this would seem to rule mechanical issues on a particular cylinder. If the EMC can identify a particular cylinder misfiring then that cylinder isn't going bang but the others are. Nine times out of ten this is ignition related but it could be that the mixture is so lean that it doesn't ignite reliably in some cylinders.

Fuel pressure is worth a check. Have you looked at the plugs to see if one or more cylinders are different? This might help differentiate between a particular cylinder problem and a general problem. If your code reader does realtime data, have a look at the upstream lambda sensors and see if it is running closed loop (traces should oscillate at about 1 HZ). Leads 5 & 7 are next to each other - you haven't have you? As 7 seems to be the worst and 5 the next it might be the rearmost injector on bank 1 but you also have a bank 2 lambda sensor fault so this seems unlikely.
 
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