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fix that car, GMC Mechanic
Category: GM
Satisfied Customers: 493
Experience:  working on all makes of GMC cars and trucks for over 15 years
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1990 5.7 liter gmc truck. Just tuned up. Engine is running rough.

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1990 5.7 liter gmc truck. Just tuned up. Engine is running rough. Sooty deposits on plugs.
Customer: replied 7 years ago.
Did not have the problem until after the tune up. Never got it to run right. No check engine light. Pulled plug and arced to block. Arc was yellow and not blue.

ok it sounds like the plug wires are not on correctly, here is a diagram showing how they should be. hope this helps.


Customer: replied 7 years ago.
Wish that that was it.
ok well if the problem was not there untill after the tune up then one of the componets must be faulty. does it feel like the engine is missing? if you remove one plug wire at a time is there a cylinder that with the plug wire disconnected the engine runs the same?
Customer: replied 7 years ago.
All of the cylinders are sooty. I can move the distributor almosr 90 degrees with no change in performance. Already changed cap again as it was causing intermittent misfires.
ok this makes no sense. no problem before tune up, after tune up you can move the distributer 90 degrees? with no change? did you remove the dist. during the tune up?
Customer: replied 7 years ago.
Distributor was pulled. Bottom end on engine redone. Heads were not pulled. New timing chain.
ah ha the plot thickins:) ok the timing is definetly off we need to bring the engine to top dead center (TDC) and make sure the distributer is set so the rotor is pointing towards #1 on the cap. if you want to play with it you can move all the wires over one spot on the cap and retest it should get better. maybe two spots depending on how retarded the timing is. did you set the timing chain? if so are you sure the marks were lined up. sorry I mean no offense to your skills just trying to cover the bases.
Customer: replied 7 years ago.
Triple checked tdc. Timing marks lined up just fine. I know why you are asking these things. I've torn into quite a few sbc engines and never had problems like this.
have you checked for a plugged exaust sys.?
Customer: replied 7 years ago.
i'm still here. I have some info for you to check for the sooty plug conditon. hope this helps. I am turning in for the night its almost midnight here I have to be up at 4 am. if you would like I will repost this for you or we can pick it up in the morn. your choice.:)graphic
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hey bud, any news?