4.3 Vortec runs rough under load
 

Hey guys, My name is Lee and I need some help with my 4.3 V6 Vortec in my buggy. This motor was not swapped by me, wasnt pulled by me. Its in a tube buggy, not a chevy vehicle, so I dont have much to go on other than what I can find on here.

I had a vacuum leak that I plugged. You can see where that was in the picture. I think this went to the brake booster on a stock truck? Either way...before this was plugged, it would have a rough, surging idle and was tough to keep running. I plugged it and its fine at idle and not under any load (in park) It also revs perfectly when in park. When I put it in drive it will still idle fine and move the buggy fine, AT IDLE and SLIGHTLY above. Any load, speed, uphills, rocks, anything will make it bog down, sputter, backfire slightly, and just run like crap in general. It cant keep 25mph.

I am at a loss...I have no idea about these motors (the only ones I've ever worked on have been propane powered 22re toyota 4cyls) and need to find out why it runs beautifully at idle and not under load, but wont run to save its life once you actually put some power to it.

Could this be another vacuum leak? One related to the vacuum port i found before? What should I start with?

Please help!!

Picture to show where the port was: The intake has been pulled off so you can better see...

http://webwheeling.com/gallery/d/893...00201-1911.jpg

This is a computer controlled engine do you have a diagnostic terminal where you could install a Scan tool to monitor the engine? It could be a ECU issue, a fuel injector problem, an Idle Control Valve problem, a vacuum leak would be more problematic at idle. I would not know how to do the trasfer with all of the computer inputs required. Are all the ECU connections to the transmission and engine correct?

I dont think it is a serious "mis-install" or anything. This motor ran perfectly when it was swapped in and it ran for a couple of years in the buggy. Its only got 40K or so on it.

I dont know if there is a plug in for a computer...I doubt it. The computer/harness was sent off to Jims Performance and flashed there, I dont know if there is a plug in when it comes back from there. I could try and find out though.

have you check you compression on your cylinders

I havent. I dont have all of my tools here. I need to take it to someone who can run a compression test and some other diagnostics i guess. I was/am hoping that it is something super simple that is going to make me slap my forehead and call myself an idiot.

could the fuel filter be a culprit (summit racing filter off the fuel cell)? I'm going to swap in my spare filter tonight and see if that changes anything.