Detonation or just valvetrain rattle

DTT92LX

New Member

Oct 28, 2003

185

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Downingtown, PA

Oct 22, 2004

#1

• Oct 22, 2004

• #1

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

 

D

Daggar

New Member

Jul 19, 2004

3,902

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Oct 22, 2004

#2

• Oct 22, 2004

• #2

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.

 

K

kndyblucapri

New Member

Feb 17, 2004

22

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0

NY

Oct 22, 2004

#3

• Oct 22, 2004

• #3

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

"How long does it take to get help in here?

15 Year Member

Nov 29, 1999

31,179

34

129

Oct 22, 2004

#4

• Oct 22, 2004

• #4

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

New Member

Oct 17, 2004

292

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Oct 23, 2004

#5

• Oct 23, 2004

• #5

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

 

HISSIN50

"How long does it take to get help in here?

15 Year Member

Nov 29, 1999

31,179

34

129

Oct 23, 2004

#6

• Oct 23, 2004

• #6

TrickStang37 said:

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

Click to expand...

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

New Member

Oct 17, 2004

292

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Oct 23, 2004

#7

• Oct 23, 2004

• #7

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.

 

D

Daggar

New Member

Jul 19, 2004

3,902

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Oct 23, 2004

#8

• Oct 23, 2004

• #8

TrickStang37 said:

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.

Click to expand...

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

 

hllon4whls

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Jan 17, 2002

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Covington

Oct 23, 2004

#9

• Oct 23, 2004

• #9

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.