88 Eagle 258 vibration issue

[j2sax]

OK, so I have an 88 Eagle my son is driving has a mega engine vibration issue. I did the Nutter bypass

http://s834.photobucket.com/albums/z.../Eagle%20Tech/

This is NOT a driveline issue as it occurs at idle and when I am driving down the road I can throw it in idle and rev it and the vibration increases greatly, so it is not related to wheel speed. Seems to hit around 2000 RPM. Everything is stock except for the Nutter bypass. It starts and idles fabulously!

I know what it feels like, but I am hoping it is something else... your opinions are valued... please don't say to check the ujoints... remember it happens when sitting still at idle. I had previously replaced the Dist, Rotor, Wires and plugs. Checked firing order twice and the engine times nicely after the bypass. Vacuum advance working great.

I am pulling the plugs 2mrw to see if a carbon chunk has flattened out a plug electrode. I can hope, right?

Have a great weekend

Jesse

[Mudrat]

Is it noisy (knocking) or just running rough?

Have you listened to the engine (stethiscope or long screwdriver) to maybe see which CYL or the top/bottom end?

Could be a bad plug :crossedfingers:, stuck valves or worse, on the bottom end.

[tufcj]

What's been done recently? Plugs, wires, cap? Have you verified firing order (swapped wires)? Is the timing right? Vacuum lines and valves working? EGR stuck open can cause a very rough idle, as can a vacuum leak.

Lots of things to check. Start with the simple stuff.

Bob
tufcj

[j2sax]

I addressed what was changed/checked in the original post.

EGR... hadn't considered that, but it' s a good suggestion. I don't know that it would cause this type of vibration especially since the engine otherwise runs so well without detonation.

OK, so here's an update. I thought maybe one of the plugs might have gotten pinched by some carbon buildup. Pulled em, gapped em and made sure the firing order was right again. They all looked good. Rotor/cap are fine as well.

So to put a finer point on it; when I rev the engine, it vibrates/shakes harshly on the way up past around 2000 rpm, then smooths out, when you let off the gas, it vibrates/shakes at the same RPM on the way back down. This is not exact RPM as I do not have a Tachometer.

When I bought this car, the starter was loose. Replaced, it and drove the puppy home. It has done pretty well for us, other than the distributor ground wire going bad and this vibration.

I discovered that one of the torque cnvrtr bolts was occasionally hitting the inspection plate, causing an intermittent scraping sound. I tightened all the bolts and bent out the inspection cover, which almost eliminated the sound... normally only happens when under load in reverse.

Now I am wondering of the flexplate was broken/cracked due to the misaligned strarter. I am going to pull the inspection cover and do a little inspection of the flexplate. Not looking forward to the potential!

Other ideas are welcome. I am thinking the Harmonic Balancer might be the another prime candidate.

BLAHST... thought I got away clean with this one!

[ironman_gq]

If its not the flexplate it could be the transmission. If you cant find anything I would drop the oil pan and check the thrust bearing.