Misfiring on 3sge engine

[Klawrence]

Noticed a rough idle when I fired up my mk2 last night. Felt like it was missing a cylinder so pulled each of the leads in turn and tracked it down to no2.

Pulled the lead and swapped out the spark plug with a known good one, no difference. Pulled the lead again and put the original plug into end of the lead and grounded it to the engine while it was running - good strong spark so it doesn’t look like a lead/coil problem.

I guess the next step is pulling the fuel rail and swapping injectors round to see if the misfire follows? Anything else to check before that step? I assume I have to pull out the intake manifold to get access to the fuel rail on that engine?

[Klawrence]

5C54E227-62F0-47CC-A703-7245D487C44C.jpeg (95.33 KiB) Viewed 680 times

Took it out for a spin and the misfiring seemed to improve so I stopped and pulled leads again to see what was happening. This time cylinder 2 seemed to behaving normally but when I pulled the lead out of cylinder 4, the metal clip stayed on the plug. The wiring was completely disintegrated on the end of the lead and more or less turned to dust. It must have been getting very poor spark on that plug.

So first stop is a new set of leads!

[jeff]

glad you have traced the issue, but just out of interest, why did you initially think it was cylinder 2 ?

[Klawrence]

glad you have traced the issue, but just out of interest, why did you initially think it was cylinder 2 ?

I pulled each lead in turn and listened to the engine note. Cylinder 2 was the only one where there was no change in note/vibration when unplugged so that’s usually a sign it’s not firing.

However after the short drive, I did the same test and found that the note did change when I pulled the lead on cylinder 2, so it appeared to have recovered. Wierd one. Cylinder 4 lead was a mess though.

Will replace all the leads to rule out any HT lead issues and test again. There may still be some injector issues.

[_Al_]

Compression test?

If you’re going to pull the injectors be sure to install new OEM seals. I know of a man who decided to re use his. Engine bay fire 300 miles later.

[Klawrence]

Compression test?

If you’re going to pull the injectors be sure to install new OEM seals. I know of a man who decided to re use his. Engine bay fire 300 miles later.

Cheers for the advice. Haven’t tested compression yet but will do it when fitting the new leads.

[_Al_]

I’m no guru but I think that’s the cylinder paired with your failed ignition lead. As such I wonder if it’s been taking progressively more load as the paired cylinder’s HT lead broke down. Could literally have blown a gasket.

[jimi]

No point in guessing/speculating it could be 101 things. Change all the HT leads and see how it runs wouldn't bother with anything else until that's done

[Klawrence]

Well, I replaced all the leads with new ones and took the car out for a few spins. All seems good but it did take a handful of miles before it started feeling properly good again.

I’m thinking maybe it’s just not getting out enough at the moment and sitting for too long between drives, maybe gumming up the injectors somewhat?

Noticed a ticking noise under acceleration also which I think sounds like a small exhaust manifold leak, so will probably get a new gasket for that soon also.

[_Al_]

If one cylinder hasn’t been firing then the plug would have been wet with petrol and likely not working well.

Clicking sounds odd. Can you get a video?