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Discussion Starter · #1 ·
I have finally got the timing set to 0 and it idles great. But I still have a knocking noise when I go uphill and at highway speeds (60-65). I have installed a new cap, rotor, and wires. Does anyone else have any ideas?
 

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Year and engine?
 

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Discussion Starter · #4 ·
I still need ideas on why my truck is knocking. I did how ever put in some 93 gas and it ran great, not knocking. But who can afford $3.89 a gallon for gas. Please any ideas would help, again this is a 1991 Chevy v1500 with a K 350 motor with 90,000 (roughly) on the motor.
 

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A knock that goes away with 93 octane gas suggests to me that you are dealing with spark knock or engine ping.

I'm not familiar with the details on the early '90's throttle body injection system, but I know you have to disconnect something (to disable the computer's timing advance) before setting the timing. Double check the procedure to make sure you've got the timing set correctly.

Another possible cause that I've run into on other engines is exscessive carbon buildup in the cylinders. You might run it through a thorough decarbonizing.
 

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Discussion Starter · #6 ·
I did fine the connection for the ECM wire and set the timing correctly. I have heard from a mechanic friend that decarbonizing (Seafoam) could ruin the engine. The parts of carbon could get stuck in small places. If you have another idea of decarboninization, please share.
 

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I've heard similar horror stories. I've also heard a lot of success stories, too.

A few that I've run in to are of the opinion that the only proper and safe way to decarbon an engine is to disassemble the engine and scrape the carbon off the cylinder walls with a suitable scraper. Maybe your mechanic friend is in that group.

Another non-chemical suggestion I've seen made is to take it for a hard drive in 2nd gear. A good run at 3500-4000 RPM will supposedly burn the carbon off the walls. Ford even suggested for the Explorer/Ranger engines a daily burst above 3k RPM to keep carbon from building up.

Of course, if it is pinging, you run the risk of burning a hole in a piston or similar if you don't get it fixed. So you almost have to do something

Did your mechanic friend offer a suggestion? I assume he knows the potential damage pinging can cause an engine, and therefore would have a preferred method for decarbonizing when that becomes a problem.
 

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You can decarbonize it but you do run the risk of a piece of it getting stuck between the exhaust valve and the seat and then you would get burn thru, resulting in you pulling the head and replacing the valve. But, on the other hand, if you don't, a piece of carbon can dislodge itself, resulting in the previous statement.

It looks as though you tried to retard the timing to alleviate the spark knock. Try swapping to a "cooler" spark plug, AC Delco or Champion. No NGK's or Bosch. Also, check your fuel pressure. If you run lean you will cause spark knock under load too. What temp is the truck runinng at after it's warmed up? What total advanced timing is it running under load? There are a few more tests you need to run to figure this one out.
 

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Discussion Starter · #10 ·
You can decarbonize it but you do run the risk of a piece of it getting stuck between the exhaust valve and the seat and then you would get burn thru, resulting in you pulling the head and replacing the valve. But, on the other hand, if you don't, a piece of carbon can dislodge itself, resulting in the previous statement.

It looks as though you tried to retard the timing to alleviate the spark knock. Try swapping to a "cooler" spark plug, AC Delco or Champion. No NGK's or Bosch. Also, check your fuel pressure. If you run lean you will cause spark knock under load too. What temp is the truck runinng at after it's warmed up? What total advanced timing is it running under load? There are a few more tests you need to run to figure this one out.
I have installed AC Delco's. I have a weird fuel pressure thing that I need to get more information on. Right now every time I open the gas cap it sucks a lot of air. I do not know where to start on that one, I did how ever loosen the cap and ran that for a couple of days. With that I am get a back fire when she is under a load like going uphill or towing my camper. I have the timing advanced about 4 degree via the timing light I do not know how to get the advanced timing while it is running under load. Please explain.
 
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