1992 Dually

firewireal · June 28, 2010

Hello, I have a 1992 chevy 3500 5.7tbi stock that ran really good. Now it has me scratching my head on what went wrong. Here the story. I added a cold (open) air intake on it about 5 months ago. slightly inproved the performance, then thought I would add a set of side pipes to her and that gave her a little more kick, but with the stock manifolds i kept getting leaks at the couplers. I decided to install a set of headers to fix the leaks, and while I was waiting to receive my new parts, i started overheating (not to the point of boilover) but really hot 215 degs pulling my boat. I figured while I was installing the headers this past week end I would also due a complete flush and filter change of the transmission, install a trans cooler and new radiator complete with hoses and thermostat, new cap and rotor, new wires, and new plugs. Well something has happened to this once powerfull SB. Here are the problems Im having:

Starts right up but with a stumble ( checked and double checked wires and even set the timing)

During Idle, little viberation (believe it the side pipes hard mounted to the body)

During acceleration, feels as if it is getting to much gas (floor it and it seem to clear up for a bit)

Power during towing: while trying to climb a med grade hill trans worked as advertised shifted down to 3rd but kept loosing power with RPM's at 2200. didn't want to push it for fear i did something wrong or tear it up. (P.S. I was towing a boat up to the lake when this happened)

Motor temps never got over 190deg the whole trip and it was 109deg ambient here in AZ that day.

No codes from the ECU either.

I thinking it might be the air to fuel mixture not being set right with the headers and intake.

what else can I look for that might be causing these problems shy of putting all the original equipment back on.

Any thoughts or help

Thanks guys

Blue_Z71 · June 28, 2010

I'd say too much fuel. My '95 350 got wayyyy too much fuel after I changed throttle bodies. Changed back to the old TB and it quit. Would idle a little rough, wouldn't gain speed, and went absolutely nowhere when you floored it

firewireal · June 28, 2010

Thanks for replying so quick. I think I'm going to start with the basics and reinstall the stock aircleaner to see if the ECU correct Air /fuel mixture. I haven't done anything to the TBI since it wasn't given me a problem before all the work was done. also might loose the sidepipes and go back to a set conventional dual exhaust.

Thought: reprograming the ECU help or maybe a bigger set of injectors? I know from my carb days that more air in and more flow out meant HP gains by adjusting the jets. I also know that the TBI is great and allmost problem free, just trying to get the three to work together is where I'm lost.

firewireal · June 28, 2010

Well I believe I found the problem. No 6 spark plug was broke at the ceramic insolator. I must have cracked it on the header installation. I thought I was carefull enough not to hit any of the plugs. So I went ahead and replaced all eight just incase any other plugs were damaged too. Got my HP back and then some. Sometimes its the simplest of things.