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Old 07-30-2004, 06:50 PM   #1
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Default Hesitation & some knocking when under load

Hi All, newbie here, great site. OK enough of the sucking up

My 2001 non-blown 3.8 (42K) started to miss and knock on gentle acceleration up a hill. Initially, it would then recover and occasionally repeat. Hard acceleration was not a problem. It has gradually got worse and now any acceleration causes major missing and knocking. Also misses and knocks when revved in Park. Idle and all speeds seem to be smooth. I checked an old thread here where corroded coil terminals were a problem. I found the #6 bad and all the rest clean. Air & Fuel filters were replaced about 2 months ago at a GM dealer. I looked at all 3 front plugs; gaps good, but all were looking a bit white coated suggesting weak mixture. Put a pressure gauge on the fuel rail and got 52PSI from the 2 second burst after turning on ignition. Started engine and it dropped to about 46PSI. I am running it on the same 87 octane source that I've used for 3 years with no previous problem on this or the wife'* car. Any suggestions would be appreciated. Thanks
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Old 07-30-2004, 07:19 PM   #2
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While sounds like you might of found your problem, sounds like it'* missing to me. Is it throwing any SES lights? Maybe goto Auto zone and get the codes read to confirm their misses

but a bad coil pack is bad, didn't check the rear plugs, but new plugs and wires might not be a bad idea along with that bad coil pack.
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Old 07-30-2004, 07:42 PM   #3
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Thanks for the comments.

Forgot to mention - no SES lights, but put my scanner on it anyway, no codes or pending codes.

Would a corroded terminal cause/or be caused by a bad coil pack?

I was thinking more that it might be fuel related due to all 3 front plugs having some white coating on them. I'll check the back ones tomorrow. If I am right, what sensors have an effect on the amount of fuel flow?
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Old 07-31-2004, 01:53 AM   #4
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Check for bad plug wires, corrosion on the coil terminals, or bad plugs. and you wouldnt belive how many new' plug wires are bad out of the box. Always check for continuity even if there new.
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Old 07-31-2004, 02:47 AM   #5
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I've had bad wires twice in 2 years. Use an ohmmeter, and look for a progressively higher resistance as the wires get longer. (#1 being the lowest, #6 being the longest). Also start the car at night in the dark, and rev the engine while watching for arcs.

I had a bad miss last year. Turned out to be a nearly new performance wire shorting out to the dipstick tube.

A bad charging system can cause a weak spark. How'* the voltmeter?
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Old 07-31-2004, 12:40 PM   #6
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Thanks to all for the good advice. It was both #6 coil post corrosion and the #6 lead breaking down. The whitish coating on the plugs threw me into thinking that it was a weak mixture problem. However, I'm concerned that there might also be something developing there, so I'll check them again in a couple of weeks to see what they look like then.
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