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1997 Chevy: misfires..distributor cap..corroded..rotor cap and it

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I have a 1997 Chevy Silverado with a 5.0L engine. I been getting P0300, multiple/random misfires. The distributor cap posts are severely corroded so I replace the distributor and rotor cap and it works for a short time. I've had it in 2 shops and all they did was replace the same parts as I did with the same results. They said it was because I used aftermarket parts and if they replaced it with OEM parts it would be OK.

I did have an anti-freeze leak several years ago at the back of the head (close to the distributor) but I fixed it and can not find any evidence of anti-freeze in the area now.

My question is what is the source of the problem and how could I repair it permanently? If there isn't a definate answer what should I test?


Usually if there is a misfire it is either caused by spark problem (old or bad, cap, rotor, wires or coil) or by a fuse issue (injectors, vacuum leak, low or high fuel pressure) it seems that the spark issue has been covered so I would start by looking at the fuel issue, since there seems not to be any other codes I would start by getting the fuel injectors professionally cleaned to see if it helps, looking for vacuum leaks should also be done.
Customer: replied 6 years ago.
Relist: Answer quality.
If the problem is with fuel injectors or a vacuum leak why would changing the distributor cap and rotor fix the problem temporarily until the distributor cap posts corroded again.

Another piece of information that I should have included in the first question is that the truck runs good when accelerating but misfires when I let off the gas pedal.

This is very common problem , the root cause is the spark is jumping too large a gap as an rotor comes around to meet the post inside the distributor . This happens due to a variety of problems most commonly someone has installed the distributor incorrectly and even though it's a two phase or two off the spark will jump a very large gap and that's what builds up the corrosion and eats away at the cap . If the distributor has not been removed or installed then this is a very good sign of a Worn distributor gear , Faulty distributor , Wrong cam sensor , Or just a miss adjusted distributor


Install a scanner and look at the cam retard value with the engine at 1200 RPM in park. The factory specification is 0 degrees plus or minus 2 degrees.

If not in specification, turn the distributor slightly, then bring the engine over 1,200 RPM again and the value should update. Repeat this process until 0, plus or minus 2, is achieved.

If the distributor has been replaced, verify the correct distributor has been installed. Remove the rotor and check for an "8" stamped on the cam position sensor shutter blade/rotor plate if equipped with 8 cylinder engine and "6" if equipped with a 6 cylinder engine.

Chevy expert, ASE Certified Technician
Category: Chevy
Satisfied Customers: 10370
Experience: 30 yrs experience ase cetified tech shop owner
Chevy expert and 7 other Chevy Specialists are ready to help you
Sean is most likely right please accept his answer, I misread your question and was thinking you were just having a misfire problem.

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