1988 K1500 4.3 V-6 engine knock

[wolfden6]

I have a 1988 K1500 with a 4.3 V-6.
It has developed a knock in the engine, it does not knock when cold, only after the engine has reached full operating temperature.
It does not knock when under acceleration and only when at highway speed when you just barely give it throttleis it present. When you decelerate or under moderate acceleration it does not knock.
It is very faint when at a idle.
Thanks for any help in diagnosing this knocking noise.

[Blue Bowtie]

Since you have an '88, it should be a TBI. There is a timing advance bypass connector under the hood. After the engine is at normal temperature, disconnect this connector and drive it under the same conditions to see if the noise repeats. Running the engine in this mode will set a 42 error code, but you can clear that after the diagnosis.

If the noise does not occur with the connector removed, you may need to check the EST system, including the detonation sensor. You may also need to decarbon the chambers, and check EGR system operation.

If the noise still occurs with no timing advance, there may be mechanical problems.

[wolfden6]

I unplugged the advance bypass connector and drove it and the noise has disappeared.
Does this mean that the ignition has to much advance?? or does it mean that the knock sensor is bad??
I checked the timing and it is dead on .
Any other help would be appreciated.

Thanks

[mbumgua]

check knock sensor-probably needs replacing.

[wolfden6]

what parts exactly does the EST system consist of??

Also what is the best way to de-carbon the combustion chambers (short of removal of cylinder heads)

Thanks for everyones help

[wolfden6]

Also where is the knock sensor located on the block(which side) and does it just screw into the block and are there any other sensors that comprise the EST system??
Also what is a good fuel additive that will help reduce carbon in the combustion chambers

Thanks

[mbumgua]

Look right above the oil pan on lower passenger side of block. It is screwed into the block right above the oil pan. You have to sqeeze the ears of the connector to remove it. Possibly you could have a loose wire. A quart of Mavel Mystery oil or a can of Seafoam poured into the tbi or injected via a vacuum line will clean up the carbon. Also you can add a quart or can to a full gas tank.Also I have used a gallon of diesel to a full tank of gas for cleanup and lubrication.Water injection into the tbi thru a vacuum line with engine running will also clean up carbon. Chevron and GM also make a top end cleaner that you spray into the tbi with engine running. This spray cleaner is the same stuff sold by Gunk as engine degreaser(the non-foaming kind).

[wolfden6]

Where exactly on the block is the knock sensor on a 1988 4.3 V-6??
I looked on the passenger side of the block just above the oil pan and did not see one.
Would you have to remove the starter to get to it??
I retarded the timing back and the knock stopped, but it seems that it has lost some power due to this adjustment.
If the knock went away after I retarded the timing would that point to the knock sensor being bad or should I look elsewhere for the problem??

Any help would be appreciated

Thank you

[wolfden6]

Ttt

[mbumgua]

carbon in cylinder=hot spots = preignition =knock. Try decarbonizing as your next step. Sounds like knock sensor is ok.

[wolfden6]

I already de-carboned the cylinder with GM top engine cleaner and it still knocked.
The only way to get the knock to stop was to retard the timing (WITH the ESC connector CONNECTED) back to TDC and now the knock is gone. Would that point out that the knock sensor is good and that I should try to de-carbon again. The pickup just turned 200,000 miles and could it need another round of top engine cleaner.
Also when I used the GM cleaner it did not smoke as bad as when I have used Seafoam in the past, does Seafoam work better or just produce more smoke in the process.
I am going to readjust the timing as there is a noticable drop in power with the timing set at TDC with the ESC connector connected.
Anyone have any other ideas and also where on a 1988 V-6 is the knock sensor located because I look on the block on the passenger side and all I saw was the starter, is it above the starter and accessanle without removing the starter??

Thanks for all the help!!

[mbumgua]

On most chevy engines there are plugs (block drains) in the block just above the oil pan. Chevy replaced one of these with a knock sensor, usually on passenger side of block. Because of starter on v6, these were placed on driver side of block and sometimes in later models they have one by the distributer about 2 inches from oil pressure switch. Have you checked egr passages for carbon buildup?

[wolfden6]

No I have not checked the EGR passages.
Do you just remove the EGR valve and clean the passages behind the valve??
Any particular cleaner to help clean the carbon off??

Thanks

[mrbee]

Just drive it till it blows up.... lol

[wolfden6]

HA HA You are sooooo funny