1991 350 engine noise

[kennedys22]

I have just got my 1st vette and I have an engine noise (69K). After a 2 hour ride, the engine, at idle, would sputter and was making a metal on metal sound from the motor. I thought maybe a pump but it sounds like the motor. The following day the engine was quiet - although I always get a sound when I turn off the motor which I believe is a related sound. The sound, to me, is similar to the sound an automatic transmission makes if someone puts the car in park when you are still going 5mph. Any thoughts? Thanks!!! Jim

[Bill Burkholder]

Shot in the dark, from 92 up an opti spark problem can make the engine run funny and the timing seems to go off..... Look for a small leak around the water pump. Tony may be able to chime in, he's good with C-4's.

[DanS711]

Is it an automatic or stick. Could be a cracked flex plate if it's auto. Does it keep time with the engine. How is your oil pressure when it is hot? Is it a rattle or more of a knock. Take a long screw driver and put one end on the engine and the other up to your ear, move it around and see if you can get a certain area it is coming from.

Dan

[92RAGTOP]

This sounds very similar to something that happened to my 90. On a long ride the EGR malfunctioned. The check engine light never came on although it should have. The failed EGR sent unburnt gas vapors to the exhaust system turning the pre cats cherry red. The pre cats fell apart internally. When I shut the engine down the remaining peices rattled insdie sthe pre cat ounding like someone was banging on the engine block with a ball pean hammer. If this is the case with yours and it is a long shot. I would remove the pre cats weld a stainless steel pipe in it's place and replace the main Cat conv. with a good performance type. Good luck Guy keep us updated.

[kennedys22]

I forgot to mention I have a manual. A friend thought it may be clutch chatter and told me to see if it still made the sound with the clutch in. Interesting thought about the exhaust. I may need help to determine if this is the case. The oil pressure is at 3/4 on the gage when running, and it drops to about 1/3 at idle. The temp is at 1/2 the gage so these appear fine. I will try the screwdriver, that's a good tip. I think it is more of rattle than a knock. When it was noisy it sounded like metal on metal to me. Not really a loose valve, it sounded deeper in the motor. The idle seems to hiccup, and it is in time with the sound. It may hit some resistance when the sound occurs? No coolant leaks - it was in for a new intake gasket and I developed a leak at the thermostat housing and this was replaced. Is this the leak you're refering to - or vacuum? Many vacuum houses appear ready to be replaced.

Glad I joined CCDV and this forum. Looking forward to meeting everyone. Thanks so far!! Jim

[kennedys22]

I took the car for a good ride yesterday. I wasn't hearing any noise but after awhile I heard some chatter at a light. When I got home I let the car idle in the driveway. It was quiet. I inched forward, still quiet. I inched again and I heard the noise. I then depressed the cluth and the noise is gone. I think I am hearing the transmission (my friend said a bearing). I feel relieved that the engine appears okay. I'd appreciate any thoughts on the subject. Thanks everyone!

Jim

[Tony B.96LT4]

The ZF transmission, although a great tranny, is noisy. The early transmissions from 89-91 or 92 had square cut gears and tend to be noisier than the later year trannys. The noise could also be coming from the dual mass flywheel. If it's shifting good and the clutch is not slipping then I wouldn't be too concerned. Here is a website to find out all about the transmission and related parts.

www.zfdoc.com

[92RAGTOP]

Another common problem with those transmissions is that they have a dual mass clutch. This dual mass will make a metallic clang if your engine has a miss in it.However I thinks this only happens with the clutvh depressed or in neutral. I'm not 100% sure about the neutral mode clutch in I can understand.:confused:

[kennedys22]

Thanks Tony and Don. The website is great. I found a few tests to try. It sounds like I'm fine and can enjoy the ride.

[kennedys22]

I was ready to post a reply as to the results of my engine noise. Sean at the Vette shop did not check out the car because of a coolant leak. Bergey's in Colmar put a intake gasket and thermostat housing in recently. I am going back to them tonight (weather permitting) to have it fixed. I will post a reply after Sean checks it out.

Great day in Warminster - but I never met Frank!

[DanS711]

Jim,

As Tony noted above the ZF trans is normally noisy. Any uneven firing impulses in the engine will be amplified through that trans making it rattle. That was the reason they went to the dual mass flywheel, to quiet them down. Will be interested to see what you come up with.

Dan

[kennedys22]

I have been trying to ride out my engine noise so it would be repeatable for a mechanic. I took a friend for a ride and he thinks it sounds like a rattle from the exhaust. The engine occasionally idles rough and the rattle coincides. I will put the noise aside and will take the car on a long run to hopefully fix the idle, and I'll check underneath with my ramps for something loose. Thanks all!

[92RAGTOP]

still might be the pre cats see post #4

[kennedys22]

The Vette shop diagnosed my car - one bad injector. The sound was the engine almost stalling and catching up. Installed 8 new injectors and it has never run so good. Hoping to drive it next Thursady. Thanks again to everyone for their help. Mostly - thanks to Sean at the Vette shop.:)