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Old 09-19-2010, 01:12 AM
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355 Misfire when accelerated

Hey guys I got a 355 with 400hp a slight misfire when I accelerate it. I accelerate it and it misfires, then it continues to rev up just fine. Idles fine

Could this be fuel pressure? Fuel pump or any other ideas? Carb?

Thanks,
JD

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Old 09-19-2010, 06:46 AM
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First, I would check the ignition system from the rotor button to the plugs
(rotor button, inside of the dist. cap, and plug wires) being it only happens under a load. Pay special attn. to the cables for worn boots and arcing between the cables (#5 and #7 especially). How old are your plugs?
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Old 09-19-2010, 07:45 AM
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Agree with checking that^^.

Is it a in-cylinder misfire, or a "cough" into the intake when floored??

What is you initial and total timing?? What carb??

More info you give, easier it is to narrow down what to look for.
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Old 09-19-2010, 07:45 AM
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To add to what the above poster mentioned, if they are carbon core wires, they are probably junk, get some spiral cores, and take a good look at the coil and rotor. A bad wire can over work the coil and burn a hole through the rotor.
Pretty much all the later model tuneups I do include a new coil unless they are COP, and an upgrade there is not a bad idea.
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Old 09-20-2010, 07:18 PM
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I don't know how old they are but I'll change them out and see how she responds.

I'll post back as soon as I replace those cables.

Thanks,
JD
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Old 09-21-2010, 03:34 AM
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I put a new set of Procomp 10.2's on my 350 a week ago, and I swear it runs better. Even the exhaust sounds different. There's no telling how old the stock 8.5's were, they came with the engine I pulled from a 79 chevy.
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Old 09-22-2010, 01:11 AM
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I just went through this on my 350. I had replaced..rockers..push rods..lifters..a new Air Gap. Buttoned it back together and now had that miss.

Thinking I set my valves too tight I reset them..still same..re-did them still same. Idle fine..the under load miss until 2500..then run/rev excellent.

A good friend..75 years old..asked me..

"If I brought my car to you with the same miss-fire..and you knew nothing about my motor history..what would you think it was..?"

I would think electrics..and so it was. Taylor wires..were carbonized under heat shield. Not shorting to header but not getting adequate spark.
Bought some good wire..made my plug wires..runs perfect.

I'd look at those wires..or even a cracked ceramic on a plug..
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