Misfire- possible causes?

[Christophski]

Hi guys

Just got the car back on the road after doing head gasket and cambelt etc. Been using it gently for a few days and have noticed on e or twice a misfire when gone over bumps. It always then goes back to normal running. Twice I have floored it and it boosts fine.

Yesterday night I went over some speed bumps and it started misfiring badly for a few minutes but then when I went back to drive home a few hours later it was fine. Today it's also fine.

So my question is what are the possible causes? I know I need to check codes but don't have a code reader but will get a mate to next week. It's an ABY engine.

Coil packs
Pos...
???

Cheers
Chris

[prj]

Fuel pump on it's way out or bad ground.

[Christophski]

Bad ground for what bud? Anything else?

[prj]

Check the grounds on the intake manifold.

But better to pull the codes. If it's the grounds likely you will have faults too...
If you don't have codes then my bet is it is the fuel pump, especially if it happens when you go over bumps.

In that case hook up a fuel pressure gauge and see what happens to the fuel pressure when this problem occurs.

[Christophski]

Ok cool cheers bud. From using the car today I think I have noticed it happen when heading with the front of the car on a downward slope. Almost like going downhill

[Monkeymagic]

possible that one of the wires to coil pack rubbing on something and short. that said a fuel pressure check might answer all problems

[Christophski]

Will it leave a code in the ecu?

[rynaqui]

Think it leaves a code if it's fuel pump or injector related.

[UrS4boy]

Think it leaves a code if it's fuel pump or injector related.

You can get injector issue codes but there is no fuel pump failure code. It just gets weak and dies on you (if you let it - I advocate pre-emptive fuel pump replacement every 100,000 miles)

http://www.sjmautotechnik.com/trouble_shooting/20vcodes.htm

Some fuel pump info (follow the internal hyperlinks as needed):

http://forums.quattroworld.com/s4s6/msgs/22623.phtml

[A1QSHIP]

Check your battery connections for being loose.

[Christophski]

So the misfire is still there. I havent pulled codes yet as not had access to a reader. It has got progressively worse but only happens reallyw hen the car reaches running temp really. It also goes away (after a short while) when the temp drops abit if I have been in traffic. it also misfires when I start the engine and it has been used previously so still has some heat left in it from the previous journey, even if the engine is not up to running temp. This to me does not seem like it is fuel pump related but more heat soak on a coil that is on its way out... is this plausible? Anything else I should consider here? (I am in the process of getting the loom sorted for the Coil conversion)

[rynaqui]

Does it misfire on light throttle? Mine had coil issues till I replaced the lot with 1.8T conversion, would only misfire if I used half or more throttle (thereabouts).

Other thoughts
Dodgy wiring
Bad Spark Plugs
Did you also carry out a compression test?

Hope this helps somewhat

[Christophski]

It doesnt make any difference as to how much I throttle it. It will do it on idle too if its at running temp. (thats when it starts to misfire, hence me thinking heat soak from a warm engine) This weekend im hoping to get a few tests done on it to at least narrow it down to which cylinder is misfiring. The plugs are all new and the headgasket is new.... Am also going to check the earth for it.

[jade]

So the misfire is still there. I havent pulled codes yet as not had access to a reader)

Just blink them off, check S2centrals site for info

[Christophski]

Sorry Jade, was is meant by Blink them off?