My 98 Polo (8 Valve AEX engine) is not firing at tickover on cylinders 1 and 3. Pulling the plug caps off makes no difference to the tickover speed (its very lumpy of course). Its also overfuelling and very high Hydrocarbons reading coming from it. So far the garage and I have:
Changed plugs, leads and coil. (it always has a good spark).
swapped injectors with 2 and 4.
Cleaned out the throttle body twice.
Sent the ECU away and had it lab tested, no problems at all they say.
Its now out of MOT and won't pass because of the high emissions, its practically undrivable anyway. My independant garage doesnt know what to try next, I've also heard horror stories of people going to the dealer and spending £1500 on similar problems and it's still not completely fixed.
It's always the same 2 cyclinders that are not properly firing. If it was a temp sensor i'd expect the fault not to be cylinder specific.
All suggestions very welcome!!!
Will.
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Will
I'd have hoped that they would have done a compression test too...?
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Hi,
Yes they did, all cylinders about the same and within spec. I forgot to mention that, sorry.
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Will
In that case; your garage [like most] are out of their depth. Parts swapping is no way to find this.
They should be testing and proving every required function - not guessing.
Have they checked the feed and scoped the signal to the 2 non-functional injectors? That should have followed checking the plugs and the compressions at the outset, before anything else was done.
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It has good compression. a good spark, fuel and it is timed ok because it runs.
Either 1 or more of those is incorrect, or electrical info is going wrong (to the injectors?)
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Its also overfuelling and very high Hydrocarbons reading coming from it. So far the garage and I have:
Its now out of MOT and won't pass because of the high emissions its practically undrivable anyway.
Just on that point, the high hydrocarbon reading is a symptom of the misfire rather than a fault in itself. High HC readings mean unburnt fuel.Of which there will be a lot if it's only running on 2.
Cheers
DP
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DP is right - and, paradoxically, it will still run rich even if those two non-running cylinders aren't getting any fuel at all.
The amount of unused oxygen in the exhaust will send the oxygen sensor scatty and it will scream "more fuel" at the ECU as it thinks that the engine is too lean. [Putting the short-term fuel trims off the scale and setting P0171 in the process - to further baffle the garage.]
Incidentally; what codes do they get and what looks odd in the measuring value blocks?
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Thanks, can I ask what the P0171 is? I'll ask the garage what the codes were and report back.
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