98 S-10 Random misfire

[BigRandy]

4.3 V6
170,000 miles. No ticking or noise at any time and it doesn't burn a drop of oil.

It's my nephew's truck and I'm going to see if I can help correct a misfire problem.

What he's done or replaced so far: New MAP sensor, cap, rotor, plugs, wires..... and then injectors.

The truck was running great and this this came on sudden. With a cold start it has a slight miss but gets worse once it reaches operating temp.

When this all started the codes initially indicated a MAP-MAF sensor and random misfire. He replaced the MAP, cleaned the MAF, completed the tune up and the MAP-MAF codes did not return, but it started reporting a misfire on cyl 5. Next he replaced the injectors with a remanufactured set and the misfire moved to cyl 4.

The code almost always reports a miss on cyl 4 but will occasionally report a random misfire instead.

It idles fine except for the misfire.

He's done a feel and visual check of all vacuum lines and did not find any leaks. To me, it just doesn't feel or sound like a vacuum leak but a check with a gauge wouldn't hurt. I also recommended a compression test but that wouldn't explain the misfire moving from 4 to 5.

Oil and water are clean.

Today I suggested he swap out the #4 plug wire even though the wires are new. He hasn't had a chance to do that yet.

While I'm waiting on him to swap the plug wire can anyone suggest what else to look for? I suppose it's possible that one of the reeman injectors is bad. Whatever it is it gets worse once the engine reaches temp.

[krue]

Did he swap to the newer style "spider" injectors?

[68bbcst]

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[68bbcst]

Originally Posted by 68bbcst

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Have you ever changed your distributor? check the gear on the bottom that gets turned with the cam the gear wears out and Creates a misfire.
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[68bbcst]

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