i have a 94 camaro (a4) that i relcently swapped a low milage stock lt1 SB into. car has a cc503 cam, stock heads, 1.6 rr, long tubes, and a 10" 3600 stall convt. every since the swap my car seems to have a very noticable stumble/miss in only OD less then 2500rpms and starts to smooth out after 3000rpms. car feels fine at half-WOT throttle. i have all brand new ac delco plugs. opti is an ac delco which was on my old setup and worked fine. could this be the torque converter? o2 sensor? maybe rockers out of adjust?

 

I have a similar stumble, happens under the same conditions, but my cam, TB and intake are stock.

It seems to get better when the plugs and wires are new. A good fuel injector cleaning would help. The biggest thing I did to help mine was new O2 sensors. They were not setting a code but they were original to the vehicle, so I replaced them and picked up 4mpg's and no stumble.

I would also check the coil and ICM.

In your sig I see a ported lt4 intake. Is it mated up to the LT4 heads? That might also be part of your problem. The lt4 has raised runners. So the airflow through the intake into the heads might be running into a wall on the top part of the runner causing lower air velocity. I could be wrong about this, but it def makes sense.

It could be something simple or a couple of things on top of each other.


Its been about 10k miles since I replaced my plugs, wires, coil and O2's. Just reciently I noticed my stumble starting to come back. What rear ratio do you have. Mine are 2.73's, which I think is contributing to it as well. Being a low ratio, I believe it puts more load on the engine in lower rpm's, which may or may not be part of it.

 

Who tuned it for the cam?

When the converter locks up, you'll notice a misfire more. And it's going to miss at low RPM if you try to load the engine, if there are any weak ignition components..

You can't correctly bolt an LT4 intake on LT1 heads without machining the top of the intake runners, or the valve cover rails on the heads. The taller intake port metal hits the rail.

 

pcm4less tuned the car. the lt4 intake is just an lt1 intake ported. when i made the sig i made a mistake. the intake and heads are same from previous shortblock so they arent the issue. the only things that have changed during this shortblock swap was the torque converter, plugs(all new ac delco), tune. the new TC i have is a 10" 3600 stall. i double checked all the plugs and they are all good. wires have no signs of any failure as well. im kinda lost here.

 

No chance you cracked the porcelain on a plug when you installed it?

 

i just went thru them all this morning and pulled each one and double checked. no cracks on any.

 

my cc503 had the same "miss,stumble" cruising rpm range. WOT was fine as well as shifting through gears. pcmforless did my tune (waste of money horrible experience awful customer service) anyway i had it dyno-tuned and it was fixed, cam surge the tuner told me. runs perfect.

 

This is an outside chance but trying disconnect the EGR , and plug the vac line. You can leave the electrical connection in place. This helped to solve a problem similar to yours on a friends '94.