When I rev the car around 2K RPM's it shakes the car pretty good. It sounds a little rough almost like it's misfiring. The car runs fine and has a lot of power, but feels like it should put out much more power than it does.

I have unplugged each spark plug wire and heard a difference from every cylinder, I am not throwing any codes although I had a P0300 pending but have not seen that in a while, the STFT is within specs, the LTFT is normally +5 (lean) also within specs, the O2's were just replaced with no difference, new fuel filter, platinum platinum plugs and new wires, the IAT wiring was messed up so I made a jumper to fix it, cleaned all the sensors and EGR.....

The visible mods are headers, removed cats with some sort of resistor on the post cat connector, single performance muffler, bored TB, DIY CAI mod and that's all I can see.

I don't know if the ecm has a tune, but maybe the mods are effecting the ATF ratio?

What do you guys think?

 

Never pull the plug wires on these cars. If the spark has no place to go then is will bore its way out of the coil. This will leave a carbon track and in the future the spark will follow that carbon track instead of the plug wire.

Your spark plug test sounds hooky. I would still think a weak injector or something in your secondary iginition system is failing. Possible a bad coil. There really is a lot of things it could be. Maybe it time to get it put on an engine analyzer? There should be no guessing at that point.

 

what motor?

edit: just saw that its a LS1

 

I tested each headers temp and all looked about the same. I am thinking its a lean afr since my ltft is at 5% lean. I also need to check for vacuum leaks and maybe switch my plugs from platinum back to copper. I also have a compressio gauge i should pull out...
I dont have the money for a mechanic to find the problem but there must be a way to isolate and fix this issue.

 

are you sure nothing is coming lose on the pulleys, or the driveshaft?

 

5% lean will cause you to fail emission testing. It will make the car run a little hotter and a little faster. Ever heard the term "Lean is Mean"? It should not cause a stuble unless it is very lean. You have to remember when you looking at O2 sensor data you are looking at a result. A single O2 sensor is averaging together 4 cylinders. If you get a small injector leak you know have one cylinder a little rich and 3 cylinders lean so you really cant take the results of an o2 sensor at face value.

Start with the basics Fuel pressure and is the spark hot enough. One of the most common GM issues is a failing coil. Any parts store should have a spark tester and Fuel pressure gage. If you lucky and have a Harbor freight they can be bought real cheap.

 

Ill start with the spark plug tester and go from there. Thanks for the help guys