Driving my 1999 Tahoe (5.7 liter 105,000 miles) on freeway overheated the temp. gauge was pegged. I couldn't get off the freeway right away drove about 8 miles. When I got towed home I replaced the thermostat filled the radiotor with water and drove around the block all seemed o.k no leaks no water in oil. Next I drove to work on freeway and the motor started to run rough. I pulled the radiator had it rodded, replaced the water pump,coolant, hoses, new spark plugs,wires, distributor cap, rotor, also changed oil and filter. Started the motor it still idles rough and when I drive it and press down on the accelerator the motor runs very rough and makes a ticking noise I'm not sure if it's a lifter or maybe I cracked one of the heads. The error code reads P0300 random misfires.

Any help or suggestions would be appreciated.

thanks
Jim

 

Welcome to the forum.

Not good to drive eight miles w/ overheating as you now know. Couldn't you pull on to the shoulder? Was the t-stat stuck closed?

I suspect you might have a warped header or leaky head gasket. Do a compression check.

 

important question,
is that ticking noise come from top or from bottom?
Is the oil clean or "muddy" ?

 

Thank's I should have pulled over. It was dark and it's dangerous to pull over on shoulder I wanted to get of the freeway. There have been a couple of fatal accidents here where vehicles are rear ended by drivers not paying attention.
I'll check the compression. I did change the oil before I started it back up. The old oil didn't show any coolant in it. I'll go back and check the new oil for coolant. I don't hear any ticking at idle only under acceletration. I'm hoping maybe an electrical problem and not something serious. Jim
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Today I rechecked all plug wires and pulled the plugs and rechecked the gap at .060" Then I did a compression test all cylinders showed 75 to 85 psi except cylinder 4 and 6 which showed zero psi.The engine oil looks clean no sign of coolant in the oil. I talked to a couple of auto shops and they said I probably have a blown head gasket between the 4 and 6 cylinder. I'm wondering if I get the heads rebuilt will the engine be reliable or should I spend a little extra and replace the engine with a rebuilt unit.
thanks for any advise

Jim

 

I think once you get the heads off you will be better able to answer that question...

 

<style></style>First, 75-85 psi is pretty low compression. Possible causes are head gasket as stated, burned valves/seats, and/or cracked/warped heads.

Since this engine has seen extended hi temp, I'd advise replacing if you intend to keep the truck for awhile.

I wouldn't just pull and overhaul the heads on the existing engine and rely on that fixing it. The rod and main bearings and rings/cylinder walls may be damaged. Even the crank may be hurting. By the time you overhaul/rebuild the whole engine, you'll probably have the cost of a rebuilt tied up.

 

it only has 100k miles, the bottom end should be good, just check the heads and cylinder deck when changing the heads for warpage or cracks