98 S-10 Random misfire
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.
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Repairing and driving old trucks is an analog experience. No computers or sensors and they can be fixed with basic hand tools
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