Misfire... Thoughts?

[SturdyHSV]

Old Bruce has developed a misfire of late.

The ECU hasn't picked up anything, checked via OBD2 reader and also with EFI Live (I guess that assumes I'm logging the right PID, but Misfire Count Cylinder 1 (Current) seemed sensible...?)

Before I go wild with the scatter gun, I thought I'd ask for some opinions...

Misfire occurs at idle (more so once warm, but possibly just because of lower idle speed once warmed up?) and at load between 1,250 and 1,750 rpm. Higher up the rev range it is absolutely fine.

It has slowly become more frequent, it was initially just an occasional shudder at idle, then it started doing it at low rpm as described after a day at Santa Pod (coincidence? )

I have also swapped the fuel rails over, although it had completed a lot of miles with them on before it got worse, and was occasionally doing it at idle before they were ever fitted.

My thoughts are:

Coilpack failing?
Possible obstruction of an injector in the fuel rail as these have been played about with?
Injector failing?
Spark plug?
HT Lead?

Car is just about to get to 60,000 miles, serviced at the fish every year so presumably plugs were changed fairly recently as part of a 50k service? I can't remember though to be honest

I was thinking of getting hold of another coil pack and then swap it between the 8 cylinders and see if it clears it up in any position, as this seems the quickest / cleanest / cheapest thing to try as I could just borrow a coilpack for 10 minutes and rule that off the list...

Any thoughts? Anybody with an LS2 near Aylesbury? Topcats up the road have LS3 and LS7 coils to hand and are happy to let me tinker with it in their car park, the internet is trying to tell me that LS7 coils are compatible with the LS2, is this just typical Yank nonsense...?

Any help appreciated

[SturdyHSV]

OK, sounds like concensus is plugs/leads then

I'm relocating the coilpacks so will be making up some MSD leads, so hopefully that'll fix the problem...

Plugs probably worth doing though, any particular plugs to go for with a bolt on NA motor?

Thanks all

[SturdyHSV]

As much as £2k is tempting... I think I'll try an HT lead or 2 before I chuck it all in! Thanks though chaps

[SturdyHSV]

Tattooboy said:

Have a few LS3 OEM leads spare if you want to swap a few out to try ??

Presumably they fit, so if that's not a hassle that'd be great! Will get you a bottle of rum or something

[SturdyHSV]

Right, an update, and bear with me as it's a pretty poor show...!

So, got Ian's leads that he very kindly sent to me. As I have AAS headers, the leads for 5, 6 and 7 are MSD leads, as the stock ones foul the headers.

So I replaced the other 5. When I removed 3, the lead had come apart on the inside, so I assumed this was my culprit!

No such luck though, so next up, spark plugs.

Just did those, and the spark plug socket won't fit onto plug 7 because the header is in the way... Great. So I've now changed 7 of the plugs, so still nothing conclusive, and it's still there, and in fact is still getting worse.

I didn't have a feeler gauge to check the gap on the new plugs, so all in all not a very successful venture!

Is the best bet just to loosen the header to get to 7, or get a different socket that'll fit?

All the plugs looked absolutely fine that came out of the car, all the same colour and so on, here's a pic of some (the clean girly hands are my friend's not mine )

[SturdyHSV]

Yep I know, it's been so frustrating not being able to do a complete job each time!

I am planning to relocate my coilpacks, so I have the MSD kit for making up new leads, but as they'll be longer etc I don't want to make them up now, hence trying some borrowed leads just in case!

Changed out plug 7 today, slackened the header, also took them all out to check the gap and it was as expected. Hilariously, whilst putting them all back in, the ceramic broke on plug 6 somehow, so I've had to put the old bloody plug back in so still haven't got my complete new set!

So frustrating. Will get another new plug for 6 do at least that is ruled out, then will get the leads sorted. Saving money on fuel at least!

[SturdyHSV]

As it's always nice to get an update on these things, it was HT leads as suggested.

One of the MSD ones had been spoiled by a header, bit of a white mark etc. Anyway, chopped the end off it and it was a real mess in there.

Car is back running like it should do

[SturdyHSV]

It's a long story, I'm planning on relocating the coilpacks, so I'd already bought a set of MSD 'make your own' jobbies to make up to length once I'd decided where the coilpacks were going to go.

So I didn't want to buy another set of leads when I had a set ready to be made up

In the end I gave up, decided roughly where they're going to go and just made the leads

[SturdyHSV]

I think the shelf life of my parts is still on average over a year, stuff does have a tendency to sit around for a while before it goes on