YACT: What is causing my engine noise?

[lastig21]

Ok car gurus. Normally I would just take the truck to the mechanic, but I am in a new town and am not sure I trust taking it some place where they could rob me blind if I have no idea what the problem is. I am also poor and would like to fix small problems myself.

I have a 92 GMC 1500 with a 5.7L engine. My truck is making a knocking noise that seems to be coming from close to the cab. Usually, the noise seems louder in the cab then outside the truck. I guess this is because of the background noise outside. It is louder than inside if I open the hood and listen.

The truck only makes the noise when I first start it, or when driving very slowly (less than 10mph). If I have driven it for a few minutes it won't make the noise at idle for the most part. If I turn the truck off and start the engine again, the noise will re-appear. The A/C makes the noise more apparent, and will sometimes cause the noise to start if it had stopped. Turning also makes it knock while driving down the road.

That is about as specific as I can be, but please give me some suggestions on potential issues.

 

[XZeroII]

No clue.

 

[Ladies Man]

have you tried higher octane gas?

engine my be pinging...

 

[Fiveohhh]

have you checked your oil? also try 92 octane like ladies man says.

 

[lastig21]

I use and have used 93 octane as long as I have had the truck, but maybe the pumps were switched at the station. Would the ping only occur at low speeds?


Oil level is fine

 

[Pepsi90919]

Originally posted by: Ladies Man
have you tried higher octane gas?

engine my be pinging...

at idle?

 

[Pepsi90919]

Originally posted by: lastig21
I use and have used 93 octane as long as I have had the truck, but maybe the pumps were switched at the station. Would the ping only occur at low speeds?


Oil level is fine

are you sure that's what the owner's manual calls for?

 

[lastig21]

Originally posted by: Pepsi90919

Originally posted by: lastig21
I use and have used 93 octane as long as I have had the truck, but maybe the pumps were switched at the station. Would the ping only occur at low speeds?


Oil level is fine

are you sure that's what the owner's manual calls for?

Its what the aftermarket performance chip called for.

 

[Pepsi90919]

Originally posted by: lastig21

Originally posted by: Pepsi90919

Originally posted by: lastig21
I use and have used 93 octane as long as I have had the truck, but maybe the pumps were switched at the station. Would the ping only occur at low speeds?


Oil level is fine

are you sure that's what the owner's manual calls for?

Its what the aftermarket performance chip called for.

k, cuz all i can think of here is like a fan making noise or something. unless your rods were knocking but you could tell that pretty easily.

 

[lastig21]

It seems to be coming from farther toward the cab then the fan, but I'll give it a check later.

How obvious would it be that my rods my were knocking? Would they make noise all the time, or just at low rpms?

 

[notfred]

Typically a car will start pinging at high speeds, but f you've got some junk "performance chip" in there, that could be doing it.

Of course, a pinging engine doesn't make a knocking sound.... it's more of a rattling sound.

How's the oil pressure? If the oil pump is going out, it's usually worst at idle. You could be hearing a rod knocking...

 

[lastig21]

Originally posted by: notfred
Typically a car will start pinging at high speeds, but f you've got some junk "performance chip" in there, that could be doing it.

Of course, a pinging engine doesn't make a knocking sound.... it's more of a rattling sound.

How's the oil pressure? If the oil pump is going out, it's usually worst at idle. You could be hearing a rod knocking...

The chip has been in there for several years now. I wouldn't think it would cause the engine to start pinging all of a sudden, but I could be wrong.

The sound could be more a rattle, I wouldn't really know the difference. When I hear it, I think that something is loose and is bumping into something else pretty frequently.

The oil pressure is good. About 45-50 psi at first start, and about 25psi at idle when it has warmed up. While driving, it is usually 40psi or above.

 

[Pepsi90919]

you would hear the rods knocking at idle. go listen to any mid-80's chrysler K-car for an example.

 

[lastig21]

Are rods knocking a bad thing? How long can an engine continue to run like that?

I crawled underneath the car while it was idling, and the sound seems to be coming from above the oil pan. Does that mean anything?

 

[Pepsi90919]

i hesitate to think that engine knocking is your problem since you seem to be describing it as coming from the cab. rod knock is usually terminal, but it usually gives lots of warning.

 

[lastig21]

Thank all for the help. Sounds like a trip to the mechanic is in my near future though

 

[CFster]

Cracked flywheel or flexplate.

 

[thedarkwolf]

Originally posted by: Pepsi90919
you would hear the rods knocking at idle. go listen to any mid-80's chrysler K-car for an example.

That isn't the rods. Those engines make a lot of valvetrain noise. In 88 they got rollar cams and most of that went away.