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89 Rough Running



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Bowler

Committee Member

Wed 29 Nov 17 16:16

89 Rough Running


One of my regional members who ďdoesnít do the internetĒ has been on the phone to me seeking advice over a rough running issue he has got, with his 1989 C4

He is seeking advice, but being as he canít access this site, Iíve agreed to post the problem here, on his behalf. The following is my understanding of what has been explained to me. Iím not particularly knowledgeable on the specific issue, so forgive me if this all sounds a little vague

The car has been running rough, so he has taken it to a couple of general American specialists, who have changed the MAF, the plugs and a sensor. Although running better (particularly under throttle) it is still running rough at idle (rich/hunting). So much so, that it canít pass the emissions test at Idle

The latest garage to look at it has said that the root cause of the fault is the E-PROM, which costs about £45. Theyíve also claim that theyíve been onto GM who advise that the part required is unique for a 1989 and no longer in manufacture. Both the garage and our fellow member have been unable to source this item and with no MOT and no solution, the Member has removed the car from the garage.

My Member is seeking advice both about this problem and the sourcing of the E-PROM, because with no MOT, the car is virtually junk without a fix.

He (says that he) is happy to take the car to another specialist, but whilst the costs is not a particular issue, heís unwilling to continue to throw money at people who cannot fix the fault

Has anyone any idea about this? Based on the description is this likely to be the E-PROM or something else? Is this a common fault? Can the part be sourced? If not, is there a work around? Etc Etc.

If anyone can take him through the fault and the potential fix over the phone, then heís quite happy to call whoever he needs to.

Thanks on his behalf

Or should I make him read this thread? - http://www.corvetteclub.org.uk/viewtopic.php?t=18638


--------------------
Guy Waltham

2003 Euro Spec Coupe.
1966 Convertible

I suffer from an addiction called CH≥ No≤ - a disease with no known cure....

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stevel98

Club Member

Wed 29 Nov 17 21:27

Re: 89 Rough Running


I'm assuming its an L98 motor, and all ignition components are good, plugs, leads, coil, rotor arm, condensor, HEI chip, distributor gear drive.

Did anyone check the fuel pressure on the rail? It should be rock steady at around 43psi. If not, it could be the pump or the fpr. Also, the air idle valve could be u/s or even just really dirty inside the throttle body.

Also, the tps could be checked and maybe the single O2 sensor on the n/s down pipe.

If it is the chip, and I really doubt it, you can get them in the US from various sources. Not having internet and trying to run a C4 could be a totally frustrating trip.. I couldn't do that.

Any codes?



Last edited by stevel98 on Wed 29 Nov 17 21:38; edited 1 time in total. [17 %]
--------------------
RIP Gunny.. Hoo Ra, Semper Fi, Carry on..

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FranV8

Club Member

Wed 29 Nov 17 23:34


Internet diagnosis cimes with the usual caveats, but I spent ages trying to sort out my Mum's old '87 vert, redoing all the settings, checking trouble codes but it wouldn't quite run right and ran so rich 11mpg was normal. No trouble codes, in the end Keith Beschi changed the ECM (pretty cheap) and it was great after that.

Keith of course would be a great person to look at it.


--------------------
1995 Corvette LT1 6-Speed Coupe
2007 Honda UFO

Previous
1986 Corvette Z51 Coupe

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Bowler

Committee Member

Thu 30 Nov 17 08:04


Thanks both. I will print this off and hand it to him

Like you say a modern(ish) car without any access to the internet isn't a particularly good situation....


--------------------
Guy Waltham

2003 Euro Spec Coupe.
1966 Convertible

I suffer from an addiction called CH≥ No≤ - a disease with no known cure....

Reply with quote

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