i just put a another 2.8 in my 87 berlinetta and she starts and runs fine but there's a lot of vibrating going on. it gets real bad when i rev her up, i don't dare go past 4 grand cause it feels she's gonna shake herself apart. anyone know why it would do this? i think i might not have tightened the engine mounts all the way...could that be it? i made sure the drive shaft was put on the same way it came off but could it be unbalanced some how? transmission mounts are nice and tight, the torque arm is a little loose but i don't think that's it....i gutted the cat too and theres a big exhaust leak right before the muffler? i dunno...help me!

 

loose engine mounts, yes.
did you replace the mounts ($9 bucks ea) or reuse the old ones?
is the harmonic balancer from the new motor or old?
exhaust leak by muffler = new cat back set up

 

yes i reused the old mounts, i used the harmonic balancer that was already on the engine, i don't have money for new exhaust right now but i read a post a while back about some guys car vibrating after he gutted the cat....but he had an auto and it only happened during idle

 

old mounts may be bad, and if there loose well... pray your frame rails can take the abuse.

 

Sounds to me like Harmonic balancer or flywheel off balance. when you did the swap did you make sure the pilot bushing in the crank was ok, if the pilot bushing is wore or missing it can cause the clutch disk to get off centered sending the balance of the engine off. I am assuming you have a manual tranny.
Or it can be something as simple as two plug wires crossed.

 

I was thinking the same thing (about the plug wires), '55. I'm also wondering about the timing- have you checked it with a timing light?

Maybe something happened with the fuel injectors. Did you remove them, and reinstall them, WITHOUT replacing their o-rings? That can cause an "air" leak... and you might even get puddles of fuel on top of your intake manifold (don't smoke in that area)!!

Have you "read" the spark plugs yet? By reading them, you can tell which ones are firing (look normal), and which ones aren't (look wet, smell like gas), and which ones are firing half-assed (look wet with tons of deposits on 'em).

Have you done a compression test?

Have you checked for exhaust leaks at the manifold-to-block sealing area?

Have you checked all vacuum lines for a leak?

My vote is for timing or ignition, though.

 

I did a engine swap/replacement on a 2.8 S-10 about 3 months ago. I sold it to a friend of mine, and he called last week about a vibration problem. I had him bring it by the house the other day so I could look into it for him. Seems the bolts that hold the tranny and engine together came loose, that truck was vibrating so bad, the whole dashboard was a blur !!
What I'm getting at here is, check ALL the bolts, make sure EVERYTHING is tight.

 

I was reading another thread with the problem you are describing. My 1988 has the same problem as yours. The problem is most likely that you are using the wrong flywheel. If you used an earlier engine it is externaly balanced (weights on the flywheel) You should have also changed the flywheel when you changed the engine.