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Old 03-07-2013, 08:12 AM   #1
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1996 5.7L GMC Spark Knock

I have a 1996 GMC Sierra with a 5.7 L Vortec. I have spark knock even with NO towing. I have spent a huge amount of money repairing and maintaincing this thing. All new parts either NAPA or factory: tune up, O2 sensors, alternator, battery, power steering pump, oil cooler hoses, replaced all oil seals every where, water pump, radiator, Amsoil engine oil, Amsoil transmission oil, brakes complete engine fuel system flush, K&N air filter, fuel filter, etc, etc... I have not replaced the mass air flow sensor. They said it was fine. I run regular gas, either Shell or Chevron. I've tried a higher octane and it doesn't help. I religiously run Sea Foam in it. I have asked about Dyno-tuning and was told either - don't waste your money or we won't do it on a vehicle this old.
Ok Guys, what's next? I can't afford payments on a new TV.
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Old 03-07-2013, 08:40 AM   #2
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1981 31' Excella II
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It should get better when running high octane gas. Are you absolutely sure it is spark knock and not something else? The first thing I would do is check for a bad knock sensor. These go bad a lot and they will ping if this sensor is bad. The computer will lean the mixture and advance the timing till it sees a knock then it will back off a little based on that. This keeps emmisions low and gas miliage high. Have you scanned the codes to see if you have a bad sensor? Sometimes the knock sensor shows up as bad and sometimes not. Also you can try to unplug the O2 sensor and see if the problem goes away. This will put the engine into a full rich condition and you probably don't want to run this way long but it might be a good diagnostic test. If you unplug the sensor and the problem goes way then you know it is mixture related. I still think you have a bad knock sensor.

Perry
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Old 03-07-2013, 08:59 AM   #3
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I'll try it. Looks like something I can do myself.
Thanks
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Old 03-07-2013, 10:40 AM   #4
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O2 sensors indicate you have had problems with the ck engine/SES light.
P0332, (P0325, P0326, P0327, P0328, P0329) are all knock sensor codes.

POI...tapping on the block with the engine idling is an "old school" diag method. If the light comes on sensor is good. The light should go off after several drive cycles. Round end of a ball peen is best.






Bob
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Old 03-07-2013, 11:33 AM   #5
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When somone starts talking about "spark knock", they're generally talking about either pre-ignition or detonation. Detonation typically makes me think of bad fuel or excessively lean mixtures. It sounds like you've gone down this road, so probably not the problem. You've probably checked the timing, and with today's computer controls, adjusting timing isn't as easy as it once was. But one thing the computer won't pick up on is a sloppy timing chain or one that is installed one tooth off. I've seen that cause similar problems several times.
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