Detonation or just valvetrain rattle

[DTT92LX]

Hey,
My stock 1992 5.0 AOD makes noise under load in OD when the rpms are low. Like going up a hill before it downshifts.

I've heard this noise in other older cars.

Detonation is usually described as shaking a can of marbles but that's kind of what this sounds like.

I don't think it's detonation since timing is stock (at least it should still be), fuel is 87, etc. but it does sound like a can of marbles...

Think it's just the valve train making noise? Should I be going in there to replace stuff if it is?

Thanks,
Dave

 

[Daggar]

Easy to find out... at your next fill, fill your tank just half way with 89 or 90 octane and see if it goes away. If it does... run your car on that grade of gasoline from then on.

 

[kndyblucapri]

pinging

detonation is like a pinging noise yes definatly bump up the fuel octane and see if that goes away and check timing if you get a chance

 

[HISSIN50]

yep, it sounds like the trans is shifting too early and bogging down (do you hear it at ~1500 rpm?).
double check your timing to make sure the hold down did not come loose. while upping the octane is a good choice, lowering timing is more precise in terms of diagnostics.

good luck.

 

[TrickStang37]

sounds like pinging to me. why run 87 octane? how much do you really save over a course of a year with it?

 

[HISSIN50]

why run 87 octane? how much do you really save over a course of a year with it?

have you checked gas prices lately? im just messing with ya. with my 15 mpg, i would notice the difference. backing timing down or more octane is should fix it. one is free, the other isnt.

 

[TrickStang37]

i would just buy a beater car then. my bro bought one for $900, gets 30+ mpg. will pay for itself in a year probably.

 

[Daggar]

i would just buy a beater car then. my bro bought one for $900, gets 30+ mpg. will pay for itself in a year probably.

Don't forget the cost of insuring the thing. ACK

 

[hllon4whls]

I agree that definately sounds like predetonation. I would suspect that you have a carbon buildup on the pistions and the combustion chambers. GM sells a top engine cleaner that may be a quick remedy to your issue. You run this stuff through a vacuum line until the car dies. Then you let it sit for a few minutes. After that crank the car and let it blow all the chunks out the tailpipe. Cadillac mechanic told me about this.

It might be a good idea to unbolt the cats just to be on the safe side, but that is up to you.