HELP! Engine Vibration

[jrtoffroad]

Since I purchased my car (91' ZR1) I've noticed a vibration that increases with speed (particularly above 80), but does not always seem present. I thought it might just be the tires flat spotting a little since it often improved with driving.

Today I noticed the vibration, but it seemed more sever than usual. Also, it seemed tied to engine rpm. Now that I have the car home it's idling a little rough and the vibration is very noticeable in the shifter, getting quite bad above 3k rpm (no load, clutch in or out).

I recently installed a set of MSD coils (had a stock one go bad) and while the plenum was off I removed the secondaries. The car has new spark plugs, fuel pressure is good, relatively new plug wires and injectors.

Any ideas??? I don't think the roughness is due to a miss since the power feels good, and most of the related components are new.

THANKS!
Jordan

[Ccmano]

Did you change out (modify) the chip to compensate for the removed secondaries?
H
:cheers:

[Kevin]

what do you mean by "removed the secondaries"

[VetteMed]

Probably removed the secondary throttle plates, shafts, and actuators, and associated plumbing.

[jrtoffroad]

Probably removed the secondary throttle plates, shafts, and actuators, and associated plumbing.

Correct. And yes, the chip was retuned by Mark H.

Just pulled the plugs to see if any looked light or dark. All look perfect. Also tried to look at the harmonic balancer and, from what I cand tell, the rubber looks ok.

Does anyone know how tight the belt tensioner should be? I was able to slacken mine with my bare hand (took a little force, but no 1/2" ratchet required). I found the idler pulley bearing is a little worse for wear, but sadly this is not the source of the vibration, it still exists when running for a sec with the belt removed.

[tomcat]

Since I purchased my car (91' ZR1) I've noticed a vibration that increases with speed (particularly above 80), but does not always seem present. I thought it might just be the tires flat spotting a little since it often improved with driving.

Today I noticed the vibration, but it seemed more sever than usual. Also, it seemed tied to engine rpm. Now that I have the car home it's idling a little rough and the vibration is very noticeable in the shifter, getting quite bad above 3k rpm (no load, clutch in or out).

I recently installed a set of MSD coils (had a stock one go bad) and while the plenum was off I removed the secondaries. The car has new spark plugs, fuel pressure is good, relatively new plug wires and injectors.

Any ideas??? I don't think the roughness is due to a miss since the power feels good, and most of the related components are new.

THANKS!
Jordan

I hope it wasn't 91 #649 that is having the issue

Manfred E........:fahne:
91 #906

[jrtoffroad]

USAFPILOT (http://www.zr1.net/forum/member.php?u=1054) had a similar vibration recently. I am not sure if that was resolved.
http://www.zr1.net/forum/showthread.php?p=99011&post99011

Thanks. Sent him a PM.

[jrtoffroad]

I hope it wasn't 91 #649 that is having the issue

Manfred E........:fahne:
91 #906


No, my car is 1643 (last 5 of the VIN right?)

[USAFPILOT]

sounds similar to what I have, but mine has not been solved. I hope whatever it is it breaks so I can fix it.

[Z51JEFF]

I hope it wasn't 91 #649 that is having the issue

Manfred E........:fahne:
91 #906

Whats the story with #649?To the op,the belt tensioner spring is either weak to start with or dies over time.I replaced mine at 8500 on the car.The original was bouncing around quite abit.

[Pete]

I would suggest changing the pilot bearing.
Cheap and easy.


Pete

[Pete]

Of course once they clarify when it vibrates.
But if it vibrates with RPM/revving motor while parked.

Could be what i mention on my previous post.
or
I recall stock flywheels have fluid in them,could be fluid leaked out.

Pete

[jrtoffroad]

Thanks for the great responses!

In my case the vibration occurs with the vehicle at rest and increases in magnitude as engine speed increases.

I am out of town now, but will be working on the car this weekend. I sure hope it's not a pilot bearing, the car is supposed to have a fairly new clutch, but who knows.

I'm in AZ now and saw a dealer on Craigslist that has a couple ZR-1's in stock. I'm thinking about running down to look at one, I'd love to see how smooth the engine is compared to mine.

[USAFPILOT]

Mine does it with the clutch in our out and in neutral. It is more pronounced in gear revving up above 5K. It is a very similar problem though. If you redo the clutch and that fixes it I guess I know what i need to do.

[tccrab]

Thanks for the great responses!

In my case the vibration occurs with the vehicle at rest and increases in magnitude as engine speed increases.


So this narrows it down just a bit, but still leaves plenty of room for problems.

Starting from the front of the motor, possible suspects are:
Harmonic Balancer
Engine related, i.e., dead hole or misfire, possible causes include fuel or spark or compression issues.
Flywheel
Pressure plate
Clutch

Smoking gun seems to be pointing at the flywheel/clutch/pressure plate.

Good luck!!

TomC
'Crabs