Thread: Misfire driving me spare

You may be on to something with the petrol cap/ fluttering noise. The American EPA makes manufacturers incorporate complicated petrol vapour controls on all vehicles as part of their emission regulations. When your motor was changed, a couple of the pipes may have been connected the wrong way around, perhaps giving the motor a lean mixture, ( because the system works by vacuum). You could check the fuel trims for lean mix. A member with a similar car might allow you to compare the arrangement of vacuum pipes on the motor.

good luck
Pete

Not that familiar with the petrol engines in these either. Just an idea, have all the injectors been correctly coded to the ECU when replaced? Might be an idea to check, but this needs you to check/ verify the injector serial numbers against whats in the ECU.

Pretty sure they run a closed loop fuel pump system to dump fuel back to the tank after the rail reaches pressure. Seeing as youve said injector and rail pressure is all good, i dont see (yet) how the in tank pump would affect cylinder firing/misfiring if fuel pressure behind the injector is fine.

If not correctly coded, the injector is not firing at the correct time or rate, causing misfiring (just thinking out loud here)

Perhaps you need to log rail pressures from cold, could be a pressure control valve in the system sticking that starves one of the injectors (first one on the rail?)

Hope this helps ?

Originally Posted by fredd63

You may be on to something with the petrol cap/ fluttering noise. The American EPA makes manufacturers incorporate complicated petrol vapour controls on all vehicles as part of their emission regulations. When your motor was changed, a couple of the pipes may have been connected the wrong way around, perhaps giving the motor a lean mixture, ( because the system works by vacuum). You could check the fuel trims for lean mix. A member with a similar car might allow you to compare the arrangement of vacuum pipes on the motor.

good luck
Pete

Thanks Peter. Luck is needed.
The car has been running brilliantly for the past 10,000km since engine change, so hard to think it would be only beginning to be problematic now.

Originally Posted by Eric SDV6SE

Not that familiar with the petrol engines in these either. Just an idea, have all the injectors been correctly coded to the ECU when replaced? Might be an idea to check, but this needs you to check/ verify the injector serial numbers against whats in the ECU.

Pretty sure they run a closed loop fuel pump system to dump fuel back to the tank after the rail reaches pressure. Seeing as youve said injector and rail pressure is all good, i dont see (yet) how the in tank pump would affect cylinder firing/misfiring if fuel pressure behind the injector is fine.

If not correctly coded, the injector is not firing at the correct time or rate, causing misfiring (just thinking out loud here)

Perhaps you need to log rail pressures from cold, could be a pressure control valve in the system sticking that starves one of the injectors (first one on the rail?)

Hope this helps ?

Hi Eric.

The injectors on this petrol motor are just a resistor as far as engine management is concerned, opening for a pulse that varies in timing/width according to how long they receive voltage.

I have not yet excluded a fuel pressure regulator problem which might be allowing fuel back to the tank.

I have not yet tested fuel pressure at the rail, my mistake if that was something I mentioned.



I'm poring over the workshop manual to see if there is a vapour relief or purge system that might be leading to tank/pump vaccuum on the inlet side leading to suboptimal fuelling.

So the pulsing noise is the purge valve opening and closing against manifold vacuum- drawing air presumably through the charcoal canister from the filler neck and into the motor. Blocking off the port at the manifold makes zero difference to running condition so this seems unlikely.

Taking close notice to the stuttering/misfire it is present at idle, and when driving in high engine loads, but not when revving in neutral. This to me feels very much like unmetered air leak.
There is no stalling or bogging down under load which to me points away from a fuel deficit.

Blanking off the EGR makes no difference to the condition when driving or idling, so seems not likely to be a fault, and the purpose of the EGR is to allow essentially inert exhaust gas to flow to the motor to reduce NOx emissions (as I understand it).

Replace faulty coilpack

Number 5 cyl is middle of left hand bank ( passengers side ) iirc

Originally Posted by discorevy

Number 5 cyl is middle of left hand bank ( passengers side ) iirc

Cylinder layout from a manual I read stated driver's side closest to firewall was cylinder 5.

If you are correct I owe you a beer.

Mate the layout you quoted is correct, but changing the coil on this cylinder lead to no improvement on misfiring condition.