engine vibration

redcoupe86 · 10-29-2006, 02:56 PM

I've been having this vibration that seem to begin to appear around 1200 rpm or so and last till about 2100 rpm or so. Its only a slight vibration, but you can feel it in the seat of your pants.

This would happen with clutch in or out, moving or not moving.
It would happen on acceleration and deceleration. And you don't seem to feel the vibration through the shifter or accel pedal.

The engine is sound mechanically and compression is withen 10%.

Engine and trans mounts have been changed.

Ignition system and wiring is up to par. Though the injectors have not been checked.

Clutch as replaced by PO

The interesting thing is, while fiddling around under the car the other day I noticed my Fabspeed exhaust (with cat bypass) was loose where the bypass pipe goes into the muffler. You could wiggle the muffler and the pipe wouldn't move. It was also loose too at the connection braket to the engine. Before I tightend everything up you could just take your hand and shake the muffer and exaust pipes around very easily.

Now that that is all tightend up the vibration in the engine is different. Now it feels like it comes on instantly at 1750 rpm or so and stops at 2000 rpm or so and it feel more intense (though only slightly so). Its like an on and off switch the way the vibration now feels.

So either the loose muffer was acting as a damper or maybe the pulses of the exhaust are somehow causing the vibration. Is this even possible. Is it possible that the engine would have a natral harmonic. I think it migh actually be a Pressure Plate alignment thing, but with the vibrations so on/off in there manner, it just don't seem like that would be it. I would figure a vibration from an out of balance PP would slowly lead in with a vibration, peak and the lead out. But I've never actually felt an out of balance PP before. Maybe somebody can shed some light?

redcoupe86 · 10-30-2006, 04:12 AM

early morning bump

redcoupe86 · 10-30-2006, 08:52 AM

mid day bump

redcoupe86 · 10-30-2006, 07:38 PM

one more time for posterities sake.

slodave · slodave's Garage

I had a vibration earlier this summer. I replaced my clutch and PP. The flywheel was resurfaced. When all was back together, I noticed a vibration at about 2000 RPM that could be felt throught the body. I ended up taking the pp/starter ring and flywheel back the machine shop. He balanced all three at my request, but the were all within tolerance anyway. He did tell me that there was some old crap stuck on the flywheel and once cleaned, the pp fit much better. I paid attention the second time eveything was reinstalled and now there is no more vibration.

I never found at what RPM the vibration went away.

Has the car always done this or has it just started?

Dave

redcoupe86 · 10-31-2006, 03:41 AM

I think its always done it. I've only put about 1500 miles on it since i've bought it.

slodave · slodave's Garage

Have you made sure all that all cylinders are actually getting a spark and that the injectors are working? Could be the pressure plate. I had mechanic friend come out and check mine out. He determined the vibration to be rotational. Anyway, hope you find the problem.

Dave

redcoupe86 · 10-31-2006, 07:14 PM

I've pulled all the plugs and they all read exactly the same (with correct color). I don't know if this can "prove" spark across the intire rpm range not.

jstobo · 11-01-2006, 11:56 AM

Shoot, why worry about it. Only time I'm under 2000 RPM is when I am starting off. Rev it higher. You big displacement guys baby your engines too much. At 1700 RPM my car stalls except in first gear. Rev it Up!