Bad missfire

[Disco99]

Hey guys, my d2 v8 auto has developed a misfire that only seems to happen above 3200rpm, it just feels like the motor losses all its power and really struggles to keep going, but when it changes into a higher gear and drops below that rpm its fine again... i just just done plugs and leads but hasnt changed a thing, car was fine up till the saturday when i noticed it getting worse and worse. Any help would be much appreciated.

[PhilipA]

I would be looking at a dying fuel pump or the fuel pump screen blocked, as they do not have a filter.
What about the amount of accelerator? Does the miss depend on how hard you push?

Next I would look at crank angle sensor or cam angle sensor. I presume you have visually inspected the coils when you changed the leads. Any drooling from a coil is bad.
Third I gues the MAF would be a contender. Clean it with MAF spray or electronic contact spray.
Regard sPhilip A

[Disco99]

Yeah coil packs looked fine. Pushing the accelerator down further does make it stutter more. Will probably book it into British off road and let them look at it.Will try and clean the MAF and see how that goes too, thanks!


I would be looking at a dying fuel pump or the fuel pump screen blocked, as they do not have a filter.
What about the amount of accelerator? Does the miss depend on how hard you push?

Next I would look at crank angle sensor or cam angle sensor. I presume you have visually inspected the coils when you changed the leads. Any drooling from a coil is bad.
Third I gues the MAF would be a contender. Clean it with MAF spray or electronic contact spray.
Regard sPhilip A

[justinc]

Very likely a failed MAF.

JC

[garywinter]

The easiest way to find out is to get it to a place that can read the fault codes. I had it done some time back.

[justinc]

Fault codes may not appear with a faulty MAF, save for 'catalyst damaging missfire' and individual cylinder missfires, all due to excessively lean mixtures due to MAF signals out of range. Seldom does a MAF actually throw up a fault code of its own with the Motronic D2 system. You actually need to watch the real time figures for incoming air flow, in Kg/Hr, to work out whether the MAF is working properly or not. IIRC 25 to 30 KG/Hr at idle is an acceptable figure, but I could be a bit out there.

JC

[Disco99]

Thanks guys, went and spoke to british off road today and we are pretty sure its the maf, he said maybe o2 sensor but more likely to be maf. Now just have to save up for a maf sensor, quoted me just over 300 for one does that sound right?

[biggin]

Thanks guys, went and spoke to british off road today and we are pretty sure its the maf, he said maybe o2 sensor but more likely to be maf. Now just have to save up for a maf sensor, quoted me just over 300 for one does that sound right?
If it's a genuine LR part, then yes.

[Cannon]

Fault codes may not appear with a faulty MAF, save for 'catalyst damaging missfire' and individual cylinder missfires, all due to excessively lean mixtures due to MAF signals out of range. Seldom does a MAF actually throw up a fault code of its own with the Motronic D2 system. You actually need to watch the real time figures for incoming air flow, in Kg/Hr, to work out whether the MAF is working properly or not. IIRC 25 to 30 KG/Hr at idle is an acceptable figure, but I could be a bit out there.

JC

it would be handy to know the readings for a good MAF if anyone has them.

I spent a while trawling through the RAVE CD today but couldn't find it:)