Negative Fuel Trim
Joined: Jan 2006
Posts: 20,788
Likes: 8
From: location, location
Yeah i have a problem with my airpump its just for emissions really/cold start up really, i know what it is but havent been arsed to properly fix it, besides i dont run a CAT - get the CAT hot enough (easily done) for an MOT beforehand and you dont need the pump.
Yup, its the only way you learn via fault finding in anything really, i've had problems with my car in the past i had an annoying problem with misfiring a few years back and a few others which i evenutally solved - stick in I'm sure you will solve it someday
.
Aj
Yup, its the only way you learn via fault finding in anything really, i've had problems with my car in the past i had an annoying problem with misfiring a few years back and a few others which i evenutally solved - stick in I'm sure you will solve it someday
.Aj
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Joined: Mar 2005
Posts: 294
Likes: 0
From: Malvern, Worcestershire
Ok,
well this is an interesting development. This morning, when the problem happened, i had my vac gauge already rigged up and my fuel pressure gauge.
The vac gauge fluctuated violently between 5 and 10 ins/hg. It did this as the revs fluctuated violently and at the same time, the fuel pressure fluctuated violently between 40psi and 50psi.
It makes sense that the vac pressure is fluctuating, causing the FPR to cut off and on repeatedly, causing the engine to fluctuate from rich to normal fuelling constantly.
The totally confusing bit is " how could a vacuum leak disappear as the engine heats up.
The only conclusions i can come to are:
1. A crack in the inlet manifold which expands as it warms (this seems unlikely because surely the problem would always occur when the metal was cool.
2. A join which again seals as the materials swell.
3. Some part of the evap system (maybe the purge solenoid) stealing vacuum pressure when the engine is cold. ( i have not idea about how the evap system works, or if this is possible).
5. The IAC valve is to blame.
It is worth noting that:
When the throttle is blipped hard and the engine is in this state, the vac pressure & fuel pressure stabilise and the engine returns to smooth running. This is accompanied by the strong smell of unburnt fuel.
well this is an interesting development. This morning, when the problem happened, i had my vac gauge already rigged up and my fuel pressure gauge.
The vac gauge fluctuated violently between 5 and 10 ins/hg. It did this as the revs fluctuated violently and at the same time, the fuel pressure fluctuated violently between 40psi and 50psi.
It makes sense that the vac pressure is fluctuating, causing the FPR to cut off and on repeatedly, causing the engine to fluctuate from rich to normal fuelling constantly.
The totally confusing bit is " how could a vacuum leak disappear as the engine heats up.
The only conclusions i can come to are:
1. A crack in the inlet manifold which expands as it warms (this seems unlikely because surely the problem would always occur when the metal was cool.
2. A join which again seals as the materials swell.
3. Some part of the evap system (maybe the purge solenoid) stealing vacuum pressure when the engine is cold. ( i have not idea about how the evap system works, or if this is possible).
5. The IAC valve is to blame.
It is worth noting that:
When the throttle is blipped hard and the engine is in this state, the vac pressure & fuel pressure stabilise and the engine returns to smooth running. This is accompanied by the strong smell of unburnt fuel.
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