Missfire

[markd77]

Wonder if anyone has any idea about this one.

I was suffering a slight intermittent missfire on my Evo 8 FQ340 so changed coil packs, plugs and leads.

Car still ran like a dog.

Gradually got worse to the point where when I started it revs would dive up to about 2000 then drop to less than 500 and car would stall.

If I unplug one of the ignition leads, run the car for a few seconds on 3 cylinders, then plug the lead back in, the car runs perfect.

I'm getting no fault codes when I try to pull them.

Totally confused with this one.

Any ideas?

 

[stevolution2010]

are the leads brandnew?

maybe idle control valve?

 

[markd77]

Yep, I've put 2 new sets of leads on it.

Would the idle control valve cause a miss while it was running, not just on idle?

 

[stevolution2010]

Yep, I've put 2 new sets of leads on it.

Would the idle control valve cause a miss while it was running, not just on idle?

not sure have you tried re-setting ecu i think u have to leave the battery off for 24hours then it re-sets everything

may be crank sensor?

wheres lee he mite have a better idea:blush:

 

[B6lee]

I would have said plugs, leads or coil pack but if you have changed it already then I'm unsure.

Did you gap the plugs before you fitted them ??

 

[markd77]

I had them fitted at a garage so I've no idea

If the plugs weren't gapped correctly wouldn't it run like a dog all the time? This fault is intermittent.

Cheers.

 

[stevolution2010]

I had them fitted at a garage so I've no idea

If the plugs weren't gapped correctly wouldn't it run like a dog all the time? This fault is intermittent.

Cheers.

yes mate my plugs were gapped incorrectly and mine was missfiring on the rollers id check what plugs were put in it aswell

 

[markd77]

Okay thanks will give it a go. What should they be gapped to?

Also, I've heard they need to be torqued when refitted, is this right?

 

[stevolution2010]

Okay thanks will give it a go. What should they be gapped to?

Also, I've heard they need to be torqued when refitted, is this right?

no dont need to be torqued just a slight nip once they start getting tight say quarter of a turn gap size not to sure,what bhp u running?

try gapping plugs to 0.55

 

[markd77]

Cheers, really appreciate all the help.

Again, no idea on the bhp. Bought it decatted and it's an FQ340 so it will be somewhere around 350/360?

I'll have a got at 0.55 and take it from there.

 

[stevolution2010]

Cheers, really appreciate all the help.

Again, no idea on the bhp. Bought it decatted and it's an FQ340 so it will be somewhere around 350/360?

I'll have a got at 0.55 and take it from there.

if that doesnt work try 0.7 as u have more bhp than standard

 

[ElDopesta]

Hi Mark and welcome along buddy!

Have you compression tested the engine???

Please update your User Profile to include your Location.


El

 

[markd77]

Nope, not done a compression test. Is it worth getting one done?

 

[ElDopesta]

If the plugs are out then it will only take around 10 minutes at the most buddy.

It is well worth doing as you might just end up spending days trying to fault find because you were looking in the wrong place.


El

 

[markd77]

Okay, will give this a go as well. Cheers.

 

[ElDopesta]

Just out of interest, how long have you had the VIII???

Have you inspected the ECU at all???


El

 

[markd77]

I've had it since April of last year.

The one other thing I have done recently that I forgot about was switch back to the CAT for the MOT. I ran it like this for a few weeks then got it switched back over. Could I have confused the ECU?

 

[zemaxs]

check injectors are working and check bore pressure

 

[markd77]

Right, I've gapped all the spark plugs to 0.7. I've also run a compression test on each cylinder. They came out at 11bar which I think is good.

One thing I did notice is that the bottom of the spark plus (around the screw thread) were pretty coked up and they've only been on a week. Could this be telling me something?

I've got my usual trek up to the north east tomorrow so that should tell me if gapping the plugs to 0.7 has worked.

Thanks for all the help so far.

 

[markd77]

check injectors are working and check bore pressure

Sorry mate, I have no idea how to do this. Today was the first time I've ever removed a spark plug :blush: