koshe2

I just bought a 91 ZR1 with 115K miles. 6 speed Has this knock when its cold, at engine speed. It goes away for the the most part when its warm. Does not rattle at idle, but seems to start at 2000 RPM under load. Sounds like a lifter, Injectors have been replaced at one time.

I live near St Paul MN and would like to have this checked out. I am not super worried as it calms down when warmed up. Oil pressure looks just fine.

Where do I start? Suggestions??

Not sure what oil is in it. Not sure what to uses. 10-30 mobile 1??

Jim

randy ransome

Most of your questions can be answered here; zr1netregistry.com

Good Luck with your car.

Rkreigh

need a bit more info. for sure get the factory service manual and a mechanics stethescope to listen and track down the noise.

the tranny and dual mass flywheel can make a racket. And the car could have single mass flywheel which will sound like a light rod knock.

mobil 1 10-30 is ok. Marc Haibeck in chicago and the FBI gang *Pete* are up that way.

Best thing to do is join up with the ZR-1 net registry and seek out the ZR-1 faithful in your local area to give a listen and help you.

A bad coil pack / spark plug wire or plub can make a noise like this too as the car will run on 6 or 7 cyl and make quite a racket.

The dual mass bangs around with mis fires

Z51JEFF

As stated a miss will cause the cam chains,flywheel to make a racket. If your not positive about the injectors being replaced might want to look into that. I prefer Amsoil and the Bosch filter to Mobil 1.

ZR1Bob

As others have noted, some more sleuthing is in order. Could be as simple as piston slap, which is common on LT5s until the engine warms up. And if someone had installed a lighter single mass flywheel, that will create a lot of rattling in the transmission, but usually only at idle in neutral with the clutch out. One way Marc Haibeck minimizes SMF trans rattle is to make certain that the idle is absolutely smooth, and a bit higher than normal. A misfire due to coils and other factors can also create unexplained noise. If you get a chance to bring the car down to Marc, he can diagnose it for sure. --Bob

Dynomite

I was going to suggest Piston Slap but then koshe2 said "seems to start at 2000 RPM under load"

By the time you put on a load at 2000 rpm Piston Slap usually has disappeared

ZR1Bob

Certainly true, Cliff. But I was a Marc's shop a couple of days ago and saw an engine apart that had been brought in because of a noise in the engine, a rattling. With the heads off, Bob Haibeck showed Marc that if he pushed on opposite edges of a piston it would rock back and forth noticeably, almost as if it was a bit too small for the bore. Now it was a 402 of unknown origin so who knows what was put into it, but I think that one had a piston slap issue a bit farther up the rpm range. They will send it out to their honing expert and have him order a set of pistons that fit properly. But as I said, a bit more investigation is in order for the OP. Not clear if anyone might have worked on the engine in its 116k miles of life. --Bob