Ok, I just got done putting my new 383 in the car. When starting it and revving it around 1800 and higher it gets a vibration in the WHOLE car. The shifter and body vibrate bad. It's almost like the car has a miss to it. I've already diagnosed a few things and here are my conclusions.

All spark plug wires are plugged in correctly and they are firing like they should. (checked with timing light)

I doubt it is the rotating assembly. Balancer spins true as does the flywheel. And there is NO vibration in the motor. It sits still and you cannot feel the vibration in the motor when it is being revved.

The flywheel, balancer, and pressure plate were all balanced with the rotating assembly and being how picky the engine builder was, he got it damn near perfect.

There is nothing touching the body anywhere so that could not be the problem.

Now here is the weird part, when hooking up a fuel pressure gauge, the pressure stays around 40 PSI at start up and as you give it gas the fuel pressure DROPS. When the motor is around 2400 the pressure is at around 36 PSI.

My next steps are to change the coil, ICM and possibly the opti to see if that is the problem.

Could it be my fuel pump or pressure regulator ****ting out on me? The pump is a 255 LPH Walbro and I don't know how long it has been in the car.

ANY suggestions or help would be appreciated.

 

anyone?

 

anyone?

 

a shot in the dark but if everything checks out like u say and all balanced, maybe a bad /broken/forgoten bolt in the clutch/flywheel, but sounds like its is starving for fuel.

 

I wouldn't think that a fuel pressure drop to 36 psi would cause a dramtic shaking like you describe. It would be down on power but delivery should be smooth.

How close is the exhaust to the body. If it's smooth at idel and gets rough when you rev it, maybe the engine movement brings something in contact with the body.

 

My drivers side header used to come in contact with the car and also the y pipe used to hit the floor on that side as well and it did just what you describe when it was like that. I used a very large hammer to "adjust" everything and no more vibration.

 

I took out the tranny and everything last night. All in all it looked good until I got the clutch off. There is a groove in my flywheel that wasn't there when I installed it. Almost like the clutch is dragging really bad in one place. This groove was made by only running the car for about 20 min so it had to have been something major.

Also, the exhaust is not hitting the body anywhere, I checked everything before I pulled it off and it was fine.

 

i was thought it would be something with the clutch and flywheel the way u discribed the shaking and the engine was fine. was there a bolt missing that could of came out or lose that could of done it?

 

I see that it is flywheel/clutch related as we had discussed 97Formula...Were the pressure plate bolts tightened in small increments at a time in a star type pattern to ensure that it was seated properly against the flywheel?

 

Its normal for the fuel pressure to drop in proportion to intake manifold vacuum. Without the vacuum line connected, it should read 43.5psi (GM accepts 41-47psi as within spec). At idle, the pressure will drop 6 to 8 psi when you attach the vaccum line. At high vacuum (closed throttle decel) the fuel pressure will drop even more. At WOT the pressure should approach 43.5psi (or whatever your "no vacuum" reading was), with anything less than 40psi being a problem.

Your fuel pressure doeds not appear to be the problem.

 

I'm almost positive that they were. I guess if anything when I stick it back on that I will make sure that I tighten them down that way.

There were no bolts loose or any bolts that came out. The weird thing about it though, was that the flywheel just fell off as soon as I unbolted it. Usually I have to pry off the flywheel after I take out the last bolt. I guess it could have just been because it was only on the car, running, for about 30 min.

That's what we kind of concluded. I had someone tell me the fuel pressure should not be dropping when the RPM's go up, but there is no load on the motor, I am revving the car on jackstands so since there would not be a load on the motor that would explain why the pressure was dropping.

What else do you think it could be Fred? I was hoping you would post up some ideas.

 

Since you have the tranny out, put only the flywheel back on and fire it up(bolt up the bellhousing and support the back of the engine with a jack and wood block against the bellhousing).

See if your problem is still exists.

This was one way I helped to narrow down my unbalanced pressure plate issue....however that never shook the car as you are describing(it was bad...but not that bad).

 

See I should have done that last night when I pulled the tranny. Oh well, it's not like it is hard to install the flywheel and pressure plate again.

I am taking the flywheel and PP to the guy who balanced my rotating assembly to make sure those are balanced good.

 

Do not depress the clutch without the clutch/pressure plate/bellhousing and slave cylinder being hooked back up. If you do..it will destroy the slave cylinder.

 

Did the clutch disk get put in backwards?!?!?!?!?