87 caprice with a few problems

I have a 87 caprice with weird problem. Currently when i start up the car, let it warm up and drive it i have bad octane knock, it goes away after the car gets really warm. IN warm weather this doesnt happen I replaces the plug wires, rebuild the carb, new egr valve, it ran with out a problem for a few days after the egr valve was replaced. What can i do to fix this problem. ?

Fouled plugs? How many miles on the engine?

its got 187000 miles, i have been trying to figuer out where the noise is comming from and partially the manifolds have holes causing some of the noise but still i get some octane knock, I can replace the plugs and see if that helps


thanks

You've got severe carbon build up. Get some SeaFoam from NAPA. Fixed mine to the point I could switch from premium and run regular.

GM makes some stuff called Top Engine Cleaner that works great too. Get the aerosol version for best results I think.

GM makes some stuff called Top Engine Cleaner that works great too. Get the aerosol version for best results I think.
How do you use it? Is it something you add to your gas, oil, or do you apply it directly after disassembling manifolds?

I agree perfectly with TommySS, thats also why I assumes the plugs too. Also... I know this sounds wreckless and kinda dumb, but yesterday I tried toppin' out my '84 Caprice on the highway with my buddy following (my speedometer only goes to 85mph, so he measured my speed w/ his car) I got up to a little over 110 mph, then I had ta slow down because of traffic. ANYWAY, while I had the car floored, my buddy said that there were a lot of black puffs of smoke and dark dust-type crap comin out of my exhaust. Since then I've only driven the car about 3 times, but now my rough idle and slight heasitation is completely gone. The car's never run this good. I've even noticed a little better accelleration. I'm assuming opening up the engine like that cleaned it out. Give it a try if you can find a safe place to do it.

Old people owned the car before, and it only has 60000 on it. Does anybody think that because of it being soft pedaled all its life, and having mostly city driving caused the engine ta buid up dirt and carbon?

How do you use it? Is it something you add to your gas, oil, or do you apply it directly after disassembling manifolds?

Get the car warm and let it idle. Removed the air cleaner assembly. Spray into the carb while using your spare hand to keep the car running, just barely over idle. This stuff will try to make the engine stall. Just keep spraying until the can is empty. Then shut the car off and let it sit for 15-30 minutes. Then start it up and watch the smoke come out of the tailpipe. Best to keep the car at a high idle speed until the smoke stops.

That's it roughly. Read and follow the instructions on the can just to make sure.

How can you tell if you have severe carbon bill-up? What are the symtoms?

How can you tell if you have severe carbon bill-up? What are the symtoms?


The car pings like crazy (even on premium), sluggish, poor mileage, etc.

Another thing, is this carbon build-up we're talking about found in the air cleaner or in the exhaust manifolds?

It's typically found in the heads (around the valves). The carbon absorbs gasoline, and heat, which keeps the cylinder hot (hence the ping and the eventual need for premium - except at some point even that won't help).

When I did my Seafoam treatment, I let the car sit overnight and THEN started it. WOW, it's great stuff.

PeteA216 presented a typical case (old people drove it easy), and the problem solved itself with a couple of high speed runs to blow the carbon out.