I recently swapped out a 3.4l 4A to an lt1 6M
the body is a 95. The engine is a 96. The PCM including wires are OBDI 94.

I went from Miami to Key West over the weekend to test this bad boy out on the highway, and I couldn't keep it in 6th gear. I'd jump into the gear and try to keep it steady at 80 or so, but the car just shook violently. I dont know where the root of this problem is.

Any suggestions?

 

What gears do you have? Mine with 3.23's is a handfull to get to 6th gear...only 80+ is really worth it.

If you have the 2.73's, thats probably why.....

 

3.42's came with the rear end upon the swap

 

Sounds like a burnt plug wire or possibly a cracked plug. I had 2 burnt plug wires after my first header install and it did exactly what you are describing.

 

Sounds exactly like a miss.

 

I'm guessing it runs fine until it's in sixth, right?. If so than why would it miss only in sixth and not in the other gears

 

Mine is currently doing the same. I changed plug wires but its doing it again My guess is that putting the engine under a load like low rpm 6th gear the weak spark to one cylinder is causing it to stumble? I don't know, I'm replacing the coil next and crossing my fingers

 

yeah....it seems to be a spark plug wire issue...i have to get that **** handled i guess.

Thanks for the responses....the fact that LT1's are so easy to diagnose is great.

 

hsyr is right. 6th gear is where it's most notciable due to the load on the engine

 

It does sound like a burnt plug wire... it only shakes under load correct?

Try shifting the car from first to fourth around 20mph (as if you had skip shift enabled) and see if the car still shakes once its under heavy load. If so, its definately a plug wire/plug.