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'95 C4 with LT1 missfire



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Lankybloke

Club Member

Thu 20 Sep 18 18:08

'95 C4 with LT1 missfire


Hi all, Help!
I have a 1995 C4 auto with an LT1 and 75k miles. It has developed a missfire at idle. It started when it was at normal temp at idle in drive, and over a few hundred miles has worsened so it now drops no.2 cylinder every couple of seconds starting about 10 seconds after cold start, whether in drive or not. If I increase the rpm gently to say 900 it missfires worse, but as soon as it hits 1000 rpm it's perfect. It may drop a cylinder when cruising at very light throttle, but it's hard to be sure. In all other respects it runs very well, at any load. A Tech 2 shows Right Front Oxy sensor moving very slightly slower than the others. But It makes no difference if I disconnect the oxygen sensors so it runs on the map. It makes no difference if I swap no.2 plug & lead for the adjacent cylinder. It starts instantly. The injectors are all clean with new O rings and filters. Logic suggests the optispark as the only remaining possible culprit, unless I'm missing something! Has anyone experience this? If so, what was the cause? I'd like to be sure before I shell out for the Optispark......
Appreciate anyone's help, cheers

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corvetteville

Club Member

Thu 20 Sep 18 19:00

Re: '95 C4 with LT1 missfire


I had a 94, which I think is virtually the same as your 95. I had various running, stalling issues. I read the numerous & changing codes ( all spurious as it turned out) & set about testing every sensor. Nothing. So got a new Optispark, & wow! Totally fixed & much more performance than even before the faults. From your post I figure you have much more knowledge than me so please don't think I know what I'm doing, but it was the Optispark all along. Hope this helps. Steve

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corvetteville

Club Member

Lankybloke

Club Member

Fri 21 Sep 18 13:53

Re: '95 C4 with LT1 missfire


Hi Steve
Much appreciated, thanks. Strange thing is there's no fault codes, nor any warning light comes on. Also my technician mates tell me that typically idle problems = fuel (air leak, dirty injector etc) and electrical shows as misfires under load. But I borrowed some of those spark testers that fit between the plug and the HT lead, and it's clearly no.2 cylinder that's misfiring, so it's gotta be electrical.

What make of Opti did you get? Any issues since? Would you buy it again? Any fitting tips (apart from endless patience and an understanding wife....)?

Thanks for yr help

Mark

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corvetteville

Club Member

Fri 21 Sep 18 14:12

Re: '95 C4 with LT1 missfire


Hi Mark, Think I got the Cardone? It was 10+ years ago now. Only had the car for less than 2 yrs after that. I believe my issue was corrosion inside. There's a disc with slots that the sensor light uses to time the ignition, I think. Your problem sounds different. Maybe Duff lead or bad connection at the opti end, or lead touching something & arching? Try running hood up, in the dark! Firing order, leads on correct plug?
Hard to reach the opti end of the leads, but could be burnt, loose, dirty.
A friend found a bad lead on a new set. and was misfiring and ended up putting the old one back on. Steve

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Lankybloke

Club Member

Fri 21 Sep 18 15:29

Re: '95 C4 with LT1 missfire


Keith at Eurovettes said the Cardone one was OK, too. It's deffo not leads because I swapped them around and made no difference.

Better get my wallet out...........

Cheers mate

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corvetteville

Club Member

Fri 21 Sep 18 17:42

Re: '95 C4 with LT1 missfire


The prices seem more reasonable now than I remember. I believe they fitted a drain pipe on later years , maybe yours, to fix any condensation problem. So check the year etc I installed it myself, not to bad. I suspected the water pump so fitted a reconditioned one. Especially as it's a lot easier to get to the opti with it removed. There's quite a good video on YouTube to give an idea. I can give a bit more of my experience if required. Good luck let us know how it goes. Steve

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Lankybloke

Club Member

Tue 25 Sep 18 09:17

Re: '95 C4 with LT1 missfire


Well I've got down to the crank damper now, bad oil leak from the front somewhere, drivers side waterpump bolts not tight, tensioner pulley noisy. Have ordered waterpump, timing cover seal kit, damper repair sleeve just in case snout is worn, tensioner, optispark and a new drive belt. Already got new leads ready. Have realised I'll have to put the drive belt back on to stop the crank turning when I undo the damper pulley bolts as it's an auto.........d'oh...........Tons of info on Youtube, am beginning to think that the interweb was invented specifically for info about Optispark, and all other subjects are getting a free ride! You're right about the late optisparks, they have a vent tube to the intake manifold to suck guck & dampness out. I cant understand why GM left the weep hole under the waterpunp as is, why not tap it for a nipple and put a hose on it to avoid the opti?

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corvetteville

Club Member

Tue 25 Sep 18 16:31

Re: '95 C4 with LT1 missfire


Sounds like you've got it all covered! I only did pump & opti so don't really know about the damper etc. Does the opti come with the lead & plug, as it's preferable to put a new one on to be sure.

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