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L98 Misfire problem


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Sid.123

Club Member

Mon 09 Oct 17 18:22


I was going to suggest a vacuem leak as did roppa as mine had an initial flat spot on acceleration which I found to be caused by perished 30yr old vacuem pipes....
But if you say number 7 plug was black/rich it could be that athough the injector may be clicking it may be stuck open.I would try cleaning the plug and running with the injector unplugged to see if the plug still gets wet etc or run it with the plug out while unplugged to see if fuel is ejected from the hole.


--------------------
59/69 silver beige/medium brown. 1 of 1,014 in 1986. C4 glasstop

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Manj82

New Comer

Sat 14 Oct 17 22:21

Re: L98 Misfire problem


I'm chasing a miss on a LB9 Trans Am so will watch this with interest Smile

Noticed you mentioned you replaced your injectors with Bosch D3's. Have you checked your fuelling after this and what's your crank times like

I query as I changed the injectors in my trans am to D3's (that according to a vendor were supposedly a like for like replacement) and the car was running pretty lean according to a scan of the fuel trims; BLM high 140's, low 150's on idle and max out at 160 in some cases when driving. Had I not had a scan tool, I would've been clueless about this other than an occasional lean surge

I had to burn a chip with adjustments to the injector constant and some other tables to get the fuelling close to the desired 128.

A google search whilst diagnosing found that quite a few people experienced similar lean conditions with their TPI cars (L98, LB9) and had to pull out the laptop...

just thought to mention

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FelixP

Regular

Wed 08 Nov 17 09:55

Re: L98 Misfire problem


I finally got to the bottom of this and it was a cheap and easy fix!

When I changed the leads a few had got a little too hot near the headers despite having those socks on the boots. When I put new leads on, I didn't take the boots off to slide on the heatshields. Anyway, I started it up and now we have darker evenings, I saw one of the leads shorting against the header!

I'll have to run them very neatly. I was using Summit racing leads but had put new AC Delco ones on, I guess the insulation isn't as good, as they were further away from everything previous but still the spark jumped across. Thank you daylight savings! And a good lesson in checking & double checking the simple things silly


--------------------
1989 Corvette C4 L98 6 speed ZF with Z51 & FX3

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chevrolet

Club Member

Wed 08 Nov 17 11:41

Re: L98 Misfire problem


Well Done/Top Marks Thumbs up So can we call that a "Leaking Spark Plugs Wire" job/fault, as in the Haynes manual Trouble Shooting section above?



Last edited by chevrolet on Wed 08 Nov 17 11:45; edited 1 time in total. [66 %]
--------------------
AKA "Silver C6" on Pistonheads

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