Valve Rattle in Pickup

[Bullbuyer]

I don't want to start a Chevy/Ford/Dodge debate - just want some honest opinions from folks that are more mechanically inclined than I am.
My 98 Chevy pickup has a little over 200k on it with a 5.7 liter and automatic - 4 wheel drive. I've been noticing a little valve rattle on some hills and when accelerating (sp). Truck is very well maintained, excellent condition otherwise. I'm thinking that this may be the 87 octane gas or possibly time to replace the O2 sensor?
Thoughts, suggestions greatly appreciated. Trading is not an option right now -tax time!!!

 

[dun]

There's a difference between detonation sound and vlaves. Valves tend to sound more metalic. Try a tank or 2 of the higher octane stuff, not the crap with ethanol. If the noise goes away it's not the valves.

dun

 

[Nowland Farms]

I agree with Dun, sounds like rattling because of the Octane in the gas. You could also try some of the Octane booster for the gas.

 

[cfpinz]

I had a Ranger one time that would rattle you out of the cab on cheap gas, but the mid grade would keep it quiet. Cheapest thing to try.

I'm not much of a gasoline mechanic, but I'm wondering if your truck has a detonation (knock) sensor? The main function of the O2 sensor is to adjust the fuel/air ratio.

cfpinz

 

[tytower]

Another vein - could be timing is out . Someone been playing with it recently?

 

[tom4018]

Carbon build up will cause that also.

 

[Bullbuyer]

Another vein - could be timing is out . Someone been playing with it recently?

Not that I'm aware of. We change the oil, filters, plugs - what I call 'bolt-on' things.
I did buy the better gas Tuesday and will fill up again tonight.

 

[skyeagle]

Could be a seized E G R valve. See if you can get your finger
to move the valve with the engine off.

 

[mountainranch]

Tom is probably right. I had the same prob. with my truck. Carbon builds up in the combustion chambers, and can get hot enough to glow cherry red. The hot carbon can act like a spark plug, igniting the fuel in the combustion chamber prematurely. This will cause clatter and eventually damage an engine. Get some seafoam, or similar engine cleaner, and squirt it into the throttle body intake ,with the engine revved to about 1500 rpm. Don't squirt in too much at once or you could hydrolock your engine. When you do this there will be lots of smoke out the exhaust. Take your time, rev the engine ,and use the whole bottle. It should get most of the carbon out. It worked for my truck.

 

[tom4018]

Tom is probably right. I had the same prob. with my truck. Carbon builds up in the combustion chambers, and can get hot enough to glow cherry red. The hot carbon can act like a spark plug, igniting the fuel in the combustion chamber prematurely. This will cause clatter and eventually damage an engine. Get some seafoam, or similar engine cleaner, and squirt it into the throttle body intake ,with the engine revved to about 1500 rpm. Don't squirt in too much at once or you could hydrolock your engine. When you do this there will be lots of smoke out the exhaust. Take your time, rev the engine ,and use the whole bottle. It should get most of the carbon out. It worked for my truck.

One of the best ways to put seafoam in one is thru the pcv valve hose. I also suggest running a can of it in the gas after putting some thru the hose.
The basics need to be checked to, timimg , knock sensor, etc.

Even had one doing this the owner thought it was vale rattle but was a blown head gasket.

 

[Bullbuyer]

I have a noticable improvement in the truck after running nearly two tanks of 89 octane through it. I was wondering about that sea foam stuff - read a little about it and the possibility of locking the engine worries me a little. Any advice on how to use it and minimize the chances of really messing up the engine?

 

[Earl Thigpen]

Plain old water will work just about as good as any other de-carbonizers.

Check your knock sensor, check the timing. One or both could be on the fritz. If both check out OK then it's probably carbon build up. Either way you need to get it fixed or you will be spending a lot to replace the pistons. Detonation will chew up pistons faster than you can spit.