strange misfire on my gti

the car is a standard 1.6 gti with no moddifications that i know of and basically what happened, on my way home from swansea to worcester the other day i was pretty much home car was running fine, called in for petrol and when i restarted it, it had developed a bad misfire on 1 cylinder.  the strange thing is that when on the move and flooring it, it clears out after about a second or two and runs fine again.  however when you ease back of the throtle the misfire comes back again.

checked for a spark and that was fine, replaced the plugs, leads, rotor arm and dissy cap to be sure and the spark is a bit better now but the problem was still there.  checked at the injectors that fuel was getting through and they were also fine, put them back in with new seals and still there is a misfire.  

im now thinking it must be electrical, maybe ecu but i was wondering if there is anythink else that i could test first as i hate electrics  :roll:
the engine is using a bit of oil through the stem seals (i think, the tappets keep getting loud then going quiet again) but i wouldn't have thought this would make a difference, it may be somethink else though?

has anyone else experienced something like this or have any thoughts/ideas on a solution.  help would be very much apreceated.

also if all else fails how hard would it be to swap the engine for the 1.8 8v gti engine?

thanks

try disconnecting the cold start injector, failing that have you done a compression test on it?

Swop a metering head injector pipe around and see if the problem moves ? move no1 to next door on the metering head , if it moves the missfire its the metering head if it don't its ignition .

Cheers…………..

did you stop at a tesco petrol station by anychance and put their super in?? I ask as this has happened to mine the other night and think its cheap nasty fuel related

cheers for the help guys, will be getting a compression tester tomorow so wil check that first and if all cylinders seem to be ok ill have a look at the metering head. dont think that its the fuel as i have filled up once or twice since and the problem carries on.  will let you no if i find the problem.

cheers

I had very similar symptoms, including the leaking stem seals. Turned out to be a blown valve seat. It came on suprisingly quickly. When I replaced the pitted valve I re-bedded all the rest and fitted new stem seals and the blown valve looked like it had the worst leak so it got the blame. Hopefully yours will turn out to be something else but might be a clue if your compression test shows the lowest compression in the bore with the oiliest plug.

thanks for that buddy, i still need to get hold of a compression tester but i will get round to it before the end of the week.
also got a new ignition module earlier as i have heard similar symptoms from these failing.
if none of these things work, i have acess to a bosch gas analyser / dyagnostics computer at uni so ill get it on that and see whats what.
thanks for the help.

Be interested to find the outcome of this one  

replaced the ignition module yesterday, no joy    but i now have a compression tester and am about to got try that and see what it shows up.  does anyone know what cylinder presure should be for the 1.6 GTI engine?  dont think it matters too much as if one is way off the others it is pretty obvious that sommethings wrong.  anywho i will report my findings later.

right, just done the compression test, cylinders 1,3 and 4 were all at 120psi cylinder 2 was at 115psi.  i've never done a compression test before so dont really know if this would make much of a difference or not.  

also the plugs wern't looking too clever. no. 1 looks as it should, sort of grey and dry, however the other three are all black, kind of sooty and a bit damp.  im guessing the fuel must not be burning properly in these three cylinders but i dont know why.

any ideas people?

When you had the plugs out did the damp residue dry out or did it stay. If it didn't dry fairly quickly is it an oily residue? You say you changed the plugs recently so the damp sooty residue has built up fairly quickly.

Following your compression test you could try putting a drop of oil down the plug hole of no.2 cylinder and testing again. The oil down the bore can create a temporary seal around the piston until it gets spread around. If the pressure comes up a bit then dips away it might indicate worn rings/bore. If the pressure doesn't come up it might point to the valves or head gasket. Doesn't tie in with the no.1 missfire though.

that is a good plan, will try that tomorow however i just remembered that i didn't have the throtle open to do the compression test.  (throtle should be fully open to allow air into the cylinders) so i'll check that first, then the oil trick.

try swapping injectors around, maybe the one that is dry could not be working properly

i have tried all of the injectors to make sure they were not blocked up of anything and they all seem to be spraying ok so i dont think it is those.
did another compression test yesterday with the throtle fully open, cyl 1 showed 130psi, cly 2 130 psi, cyl 3 125 psi and cyl 4 135 psi??  as you can see these bear no relation to the first set of results that i got so i still dont know what to make of it.  hopefuly i'll be gas testing it later so that may show something (fingers crossed).