I have a situation with knock / detonation, but ONLY when the car has been driven several miles or at highway speeds (bascially only when the engine reaches a full or hot temperature). When the motor is cold or driven for only about 10 minutes, there is no knock. And it ONLY does it when accelerating from a slower speed or when pulling away from a stop. If I hear the knock begin, I drop the pedal a little quicker and further and the knock temoparily stops. I can basically predict when the knock is going to occur.

The car:
'82 Olds Cutlass Supreme.
3.8 Liter / 231 cubic inch Buick V6 (VIN code "A")
Automatic transmission.
61,000 original miles.

I changed the plugs and wires as per factory specifications. Ran a can of BG44K in the fuel one time. The timing was advanced AND retarded and the knock was still evident, so it was returned to the specs on the label under the hood. I run the highest octane gas (91 to 93). All vacuum lines look fine.

After some research, I'm considering a new EGR. Also, I thought since it only knocks after reaching full temperature, perhaps I should put a colder thermostat in it (like a 180). The factory specs are for a 195, I have no idea what is in, but I assume it's a 195.

Any suggestions would be appreciated.

Thanks,
Chad

Are you sure your "knock" is due to "detonation"?


"Quicker" has nothing to do with anything.

More engine load makes your "knock" go away? Does it return at WOT (wide open throttle)? Does it return, only when the engine is unloaded (cruising at a steady speed)? Does it appear, at a constant 1500 RPM, in neutral or in first gear?


More, or less, evident?


"Research" would involve leaning how an EGR system functions, and how it might (or might not) cause the symptoms you described.


Obviously, that would lower the operating temp. What will you do when your "knock" starts at 180°?


If so, it should hold the coolant temp at about 195°, and there is no need to change it. If you do not have a gauge, you can use an infrared thermometer to find out.

Norm

That is my guess since it only occurs when the motor is hot... like after being driven for 20 minutes or on the highway. I'm thinking temps in the combustion chamber are getting that high and causing it.

It does in this situation. When I here the knock, if I drop the pedal quicker/further it knocking stops.

Seems like more engine load does make it go away. Doesn't return at WOT. Doesn't return when cruising at a steady speed. Never heared the knock when in neutral, the car has no tachometer, and I never hooked anything up to read rpms as of yet.

My buddy from whom I bought the car did the timing checks when he still owned the car, and all he said was it did the same thing when advanced or retarded. I bought the car knowing it had a knock, but I needed a means of transportation in a hurry.

Does the phrase "Power of Suggestion" mean anything to you?


How hot?

Norm

I've done the research honestly beleive I know the EGR system fucntions for the most part. I purchased several feet of vacuum line since I saw some on the car that looked a bit questionable. I'm going to replace that first. If that doesn't help, I'm going to pull the EGR and check for carbon deposits and clean it if needed or just replace it since I already have one on the way. The diaphram moves up and down and doesn't seem to bind, so maybe it's clogged.

Don't know if it would or wouldn't.

In this situation, time and distance are not related in any way, shape, or form.

Are you here to play games, or are you here to solve your problem?

Norm

Since the car has no gauge, I may check out the Harbor Freight link.

Precisely what are you trying to suggest?

I don't know how hot... the car has a temp light only on the dash... no gauge, and I currently own no other device to indicate the temp.

Look 88... ALL I'm saying is that when I HEAR the knock, if I accelerate quicker the knock stops!

No. I am absolutely NOT here to play games! I am here because I acquired an Olds that I like very much. It is in good condition inside and out and the ONLY issue with it is the knock.

I'm beginning to think that you are here only to be rude to folks.

Not everyone has tons of money, diagnostic equipment, and your apparent knowledge ( and possible sarcastic personality ).

If you can't try to help someone without making an arse out of them, then why do you bother?

It appears that you do not need any help. Good luck.

Norm

Norm,
It was suggested by another individual that I acquire or purchase an infrared thremometer and shoot the beam on the intake where the coolant temperature is located. I purchased one today for a bit over $50 (figured if it doesn't aid me in diagnosing temps on the car, it's still a neat and handy tool to own... so what the heck, I bought one). Just asking your suggestion here... if the IRT reads a temp that seems to high, would you suggest changing the sensor, the thermostat, or other?

Thanks,
Chad