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1988 Mj Random Misfire On #s 1, 2, & 6


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This is not my truck, but I'd like to make a remote diagnosis from 300 miles away having never seen it. Here is as much as I know:

 

"a misfire that I can't track down. The misfire jumps between cylinders 1, 2, and 6. I think it's due to a manifold leak I am going to replace the gasket tomorrow to be sure but I'm not positive in that. If thats not it then I think it will be a valve spring or the maf sensor. Other than that everything else the truck needed has been replaced... take the head off and have it worked (?)... and for the record the head gasket is not blown the compression is good on all cylinders and it does not mix anything or overheat."

 

I think the fella is on the wrong track about "a bad valve spring or MAF sensor (sic)". I am unfamiliar with the Renix engine management system, but doesn't it use manifold air pressure (MAP) sensor and not mass air flow (MAF)? If the truck has sat up for a long time (or if it was seriously over-revved in the past) there could be valve spring problems, but those would show up predominantly at high RPM, right?

 

He doesn't mention if it is a fuel or a spark problem - perhaps he never got that far in his thinking. From this forum I have seen a great deal about insufficient grounding of circuits and crank position sensor (CPS) failure, diagnostics, and replacement; I am guessing that would be a good place to start checking. Is the CPS signal the master input for both fuel and spark on a Renix system?

 

Looking forward to reading your thoughts on the matter - practical advice of this kind is in large part what makes this sort of forum invaluable. Thanks in advance.

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I ck out the easiest things 1st - Things mechanical or the ladies - - This one I'd start with the dist cap & wires

:wrench:

Y'know, I just sort of took it for granted that he would have done that already... but in fact he never mentioned if he ever even checked for spark.

 

You were smart to mention it, and you're dead right about that being the first thing to check for, alright.

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