Help me diagnose this vibration

redcoupe86 · 08-01-2006, 07:28 PM

My car runs fine while under power. There is no "feelable" vibration. The only time I can feel the vibration is if the car stoped (clutch in or out - does't matter). If I rev the engine I can feel the slightest shudder though the cabin, but it goes away after 2500 rpm or so. Its a lot more noticable when you just barely crack the throttle ane let the rpm climb slowly.

Things to know:

The engine has never been rebuilt (117,000 miles)

Compression is all with a few % except for one cylinder (number 6) that reads about 10 lbs higher than all the rest (cant figure this one out)

engine mounts are the originals

transmission mounts changed recently

plugs and cables are new

Things I have coming:

new engine mounts

new coil (probably don't need it but cant hurt to change it.)

Any ideas?

Steve@Rennsport · 11:16 PM

Hi:

Assuming for the moment that the engine is running evenly on all 6, I'd vote for a clutch PP or disc problem.

Eagledriver · 08-01-2006, 07:55 PM

Sounds like a dead cylinder to me. I'd do a leak down and check all the plug wires.

-Andy

redcoupe86 · 08-02-2006, 02:35 PM

plugs are new, wires are new (and in the correct order).

I do have a ticking valve that needs adjustment. Could this be the culprit. Its not too bad, but there is a definate tick once the car is up to temp.

I dont' really feel any vibration through the shifter, and I have no propblem engaging gears. Smooth action on the clutch, no judder.

I know the timing is set on the distributor on a MFI car, but if the car has 117,000 miles on it, could the timing chain stretch over time causing the car to loose timing? Not that this has anything to do with the shudder.

As for a missing cylinder: I have had the car run without one plug fully connected causing a definate miss, and this doesn't feel anything like this. this is a slight shudder that goes away soon after 2500 rpm.

I know there could be several causes, but Im trying to eliniate the easy ones first. Thats why I'll be replacing all mounts and the coil. If that doesn't cure it Im not sure what to check. I suppose a leak down test. At what % would you typically start to get symptoms like a shudder? 10%? 15%? 20%? And how would compression come into play?

stlrj · 08-02-2006, 09:42 PM

Did the vibration happen right after you replaced the ignition cables?

redcoupe86 · 08-03-2006, 04:26 AM

I see where you are going with that question, b/c I thought the same thing too. So I switched back and forth between the new and old cables and the problem still persists.

stlrj · 08-03-2006, 12:14 PM

It could still be the cables if they caused a plug to foul then the good set of wires would not be able to unfoul that plug. That would make going back and forth to the old ignition wires seem not to make a difference when, in fact, you still have a bad wire.

redcoupe86 · 08-03-2006, 12:31 PM

Thats a good point, but when I put on new wires I also put in new plugs, and the old plugs didn't look bad to me - all had a light grey brown color with no build up.

However, I should probably pull them again (plugs are now less than 500 miles old) and give a look just to be safe.