Engine serious rattling pinging noise

claudio123 · 07-03-06, 12:47 PM

Engine is making sound that is like when bearings go out in water pump when I rev engine. The engine runs fine for about 5 minutes til it warms up then it wont go past 2000 rpm. At this point water temp goes up but not over heated. The noise is not comming from water pump but more like valve area.
This is a 1990 corvette with 90,000 miles. The injectors went out about 3 months ago but car ran fine after changing injectors.
was running fine till this problem. I was on the freeway when it happened and after it happened I could only go about 10 miles an hour. The car had only been running for about 5 min. There is no oil in water and no water in oil. The engine starts normally and idles fine even after loss of power. Oil and water levels are good.
I don't have money for major engine work at this time so I have not had a mechanic look at it, but since it idles good I'm not sure that it is a major engine problem.
Anyone have any ideas what might be the problem?

tyrel · 07-03-06, 04:04 PM

Did you remove the serp belt and listen as you spin each belt-driven accessory? It helps to listen with a mechanic's stethoscope when you do this. The sound you describe could be anything. I had a rattling sound, turned out to be the cat converter, although other metallic sounds in my car over the years have been various things: clutch bearing on a/c compressor, air pump, alternator, water pump.

SPANISHVETTS · 07-03-06, 04:55 PM

If you are lucky it could be the cats but it doesn't sound good. Auto or 6 speed?

What is the Oil temp? Does the oil heat up faster than the water?

I think that you can rule out the accessories. Any load that slows a L98 to 2K would cook the belt in a few seconds.

Jeb · 07-03-06, 05:54 PM

Just a guess but I think I'd start looking into the timing chain area. You could have lost a tooth and slipped a few more, throwing your valve timing way off.

Don't drive it.

claudio123 · 07-05-06, 12:57 PM

Water temp increases before oil temp. The car has automatic trans.
How does one check the cats? I used a long screw driver to my ear but could not find any place where the sound was coming from. All temps stay in the normal range But I am getting a wierd smell.

gmjunkie · 07-05-06, 02:49 PM

Quote:

Originally Posted by claudio123

Water temp increases before oil temp. The car has automatic trans.
How does one check the cats? I used a long screw driver to my ear but could not find any place where the sound was coming from. All temps stay in the normal range But I am getting a wierd smell.

Well I believe that my brother Spanish is on to something here!! "If you are lucky it could be the cats but it doesn't sound good." Timing chain hardly ever jump anymore since they started using all steel gears with no plastic teeth,they get loose but hardly ever jump!! Put a vacuum gage on it, if the manifold vacuum is real low at Idle some times thats a sine that the cat's are plugging up!! Drive it around the block a couple times at night, and park it where it's real dark and let it idle and Look at the Cat's and exhaust manifolds,If there Glowing the cat's are on there way out!!!!!

SPANISHVETTS · 07-05-06, 02:51 PM

Quote:

Originally Posted by claudio123

How does one check the cats?

You could check the backpressure in the exhaust manifold but the easiest way to check the main cat is just to pull it off and see how the car runs without it. I guess that the pre-cats could be plugged up as well but they are so small I think that they would just burn up and blow their bits back into the main cat. That is what happened to my pre-cats.

How does the transmission fluid look/smell? I have seen a bad torque converter load an engine down.

Can you send a sample of the oil to a lab?

Before you throw time and money at the problem go back to square one, check the vacuum, fuel pressure, etc., etc.

If everything else looks OK pull the valve covers off and adjust the little buggers. Mine were way out of adjustment after less than 20000 miles. (Thanks to gmjunkie for pointing me in the right direction.)

gmjunkie · 07-05-06, 03:24 PM

Quote:

Originally Posted by SPANISHVETTS

If everything else looks OK pull the valve covers off and adjust the little buggers. Mine were way out of adjustment after less than 20000 miles. (Thanks to gmjunkie for pointing me in the right direction.)

I've forgot bout that!!

I slept since then!!!!

But that would be a good thing to check!!!!

claudio123 · 07-09-06, 07:31 AM

Thanks guys. I figured that there was a good chance that it was cats after all the replys and that was something I could afford. I had it towed in and sure enough it was the cats. $720.00 later it runs like new. They showed a box of rocks that they said were from the cats that were blocking the exhaust from exiting. They said they checked exhust pressure which should read 3 and mine was reading 11. They said all the noise was from the rocks rattling around. I had put a long screw driver to my ear and touched every thing that I could think of but never could really pinpoint the source of the noise. I guess the only way to check if its the cats is to check the exhust pressure. I asked him how to check but he acted like it was some kind of trade secret. They replaced replaced two cats with the y pipe. If some one knows how to test for this problem it would nice to post so other back yard mechanics like me could test for them selfs.
Thanks guys

78SilvAnniv · 07-09-06, 11:02 AM

Quote:

Originally Posted by claudio123

I asked him how to check but he acted like it was some kind of trade secret.

They place their hands in front of the exhaust outlets and "feel" it.
That was how I felt my problem...one of my valve springs broke and I could feel the 'space' in the exhaust note with my hands. With plugged cats, the exhaust wouldn't push at your hands. Other than that, I don't know how they actually measure between 3 and 11 pounds.
Heidi

G Winter · 07-09-06, 03:34 PM

You can check cats with a vacuum gauge. Hook the guage to manifold vacuum port. start engine, using the linkage on the throttle body bring rpm to about 1800 and hold the throttle steady. If cats are plugged the vacuum and the rpm will begin to drop. Remember the throttle has to be in the same position throughout this test. Results will show in a matter of seconds, most likely less than 30 seconds.

Glenn