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Jay, ASE Certified Technician
Category: Chevy
Satisfied Customers: 13
Experience:  ASE Master Tech for over 10 years - in the automotive repair field over 20 years.
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4.3 engine spark knocks bad after it gets dist

Customer Question

4.3 engine spark knocks bad after it gets warm. its not overheating. new dist. cap, plugs, wires, rotor. new o2 sensor new egr valve and solenoid. timing is right on, only knocks under a load and when you accelerate under this load. new knock sensor although it doesnt seem to respond. i had the wire unhooked and drove it and i did not get any codes like i thought i would . there are no codes in the truck.
Submitted: 7 years ago.
Category: Chevy
Expert:  Jay replied 7 years ago.

How many miles on the truck?

How did you check the timing?

Customer: replied 7 years ago.

truck has 104000 miles to check timing i unplugged the wire under the relay cover and set it to 0 degrees


Expert:  Jay replied 7 years ago.
Sounds good so far. The 4.3l have dual timing marks on the harmonic balancers.They line up with the timing indicators at one o'clock and four o'clock positions. Did you use the mark at the one o'clock position?
Customer: replied 7 years ago.
i will have to check that i am not sure on.
Expert:  Jay replied 7 years ago.
Let me know and we can continue from there.
Customer: replied 7 years ago.
yes the timing mark at one oclock
Expert:  Jay replied 7 years ago.
Well without having the truck in front of me, all I can suggest at this point is to try changing your electronic spark module. It is the component that gets information from the knock sensor and then changes the ignition timimg accordingly. The GM part number for your truck is: 16131231. Thats probably the least expensive thing that it could be at this point. You could also have internal engine items such as a worn out timing chain as well. You may also want to make sure that the ignition rotor is screwed down tight and is of high quality. I've seen where they will move around on the shaft and cause the timing to be very erratic.
Customer: replied 7 years ago.
thanks i have a 91 with a 4.3 that i will try this part off of it as long as there isn't a problem with that
Expert:  Jay replied 7 years ago.
That should be fine.
Customer: replied 7 years ago.
replaced the esc and checked timing ran until it warmed up and still had the severe spark knock
Expert:  Jay replied 7 years ago.
Okay. There are a couple more things to check. Do you have a fuel pressure gauge? If you do, check the pressure. It should be 9-13 psi. Anything less than that will cause a lean condition. If that is correct, the only other thing that I can think for you to try is to go to your local GM dealer and buy a can of Top End Cleaner. This will de-carbonize the combustion chamber. If carbon build up is causing your problem - this will take care of it. Just follow the directions on the can. If that doesn't cure the problem, I'm afraid that you probably have internal engine mechanical issues such as worn vguides or seals, or worn out timing components.

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