Clacking noise in overdrive?

[00sport4x4]

Today I noticed a light clacking noise coming from under the hood while on the highway. it only does it while in overdrive say about 65mph and you push the gas pedal to accelerate a little more it starts making the noise. If I floor it from a dead stop its fine no noise until it drops into 5th gear where it accelerates slower. No engine codes thrown, seems to run fine. Could it be a little bad gas causing spark knock? I run 87 octane.

 

[Glacier991]

Sure sounds like preignition to me

 

[00sport4x4]

i'm going to try high octane to see if it will fix it,but if it doesnt do I adjust the timing or change a sensor to fix it and which sensor?

 

[Glacier991]

Usually preignition is caused by carbon deposits in the combustion chamber. Try running a tank of high octane and see if the problem goes away... use branded regular next and see if that helps... You can use one of the mukltiple vacuum lines on your Ex and run a little water into the engine at a FAST idle... like 1200 RPM ....and clean out carbon that way.... The first gens had an "octane shorting bar" you could pull out to change the engine timing.... don't know if yours has that. Timing is not adjustable per se. Hope I've been some help.

 

[00sport4x4]

I always run BP gas only and its funny that you suggest carbon because I had just stated in another posting about the lack of carbon in my exhaust system. I've never heard of the water in the vaccum line trick. Would a engine flush possible help? I've also changed the oil every 2,500 miles since i've owned the truck.

 

[Glacier991]

Carbon deposits are not something you can really prevent, it is more fate. I'd suggest you go post with a title "Cleaning Combustion Chamber Carbon - HOW ?" The seafoam guys will be all over you like stink on a skunk. If not ...PM me and I will walk U thru the water trick.

 

[00sport4x4]

what is seafoam?? a product. Plus I think it sucks that a vehicle with 60,000 miles is doing this.