ok I was wondering if you guys could help my out here with a few questions on my friends 91 GMC 350.
He has already had it bored *40 over an has a cam(not to sure exactly what size, but it has a big lope to it) an it has all the bolt-ons to. But anyways, the problem is? At idel you can really smell that its running rich, that might have to do something with the cam, but atleast we know its getting fuel. But the main problem is once he gets on it an the truck shifts to 2nd gear its like the truck just wont really pick up any more RPMs, or it will atleast take a long time for it to tach out. Its like it leans out once you get it really opend up. An yes he does have the old TBI injection. So what would you guys say is a problem with it. He was told lastnight by another guy that sometimes the performance chips will cause it to not get enoghf fuel. Is that really true? We were going to try an remove the chip tonight an see if that helps any. But what would you guys say might be a problem or something diffrent we should try?

 

come on guys help us out here

 

where is everybody at?

 

I used to run a TBI on my S10 with cam/heads/intake. They could never get my chip burned right- rich at idle, wouldnt rev, ...... Anyway, I used an adjustable map sensor to control fuel, and it worked great. I had 220/230 cam with .510 lift and 200cc heads, and I easily passed emmisions. You can buy one at Turbo-city. If your friend is interested, I still have mine because I switched to carb.

 

What size of cam is it, because TBI does not like big cams or even mild ones.

I would recommend getting a custom prom to get it right. I use to have a 1990 RCLB 4.3L and I swapped in a 355 using the same TBI unit. I had all kinds of problems trying to get it to run right, mostly because I was running a cam (208/214 .422/.423) I drilled out the fuel pressure regulator screw and adjusted it to the max, elongated the holes in the TP sensor, and had the map sensor vaccum teed in to the PCV valve, and it would still run lean. I think bigger injectors may be needed if your running alot more hp than stock, 43 lbs are stock I think for 4.3/5.7, biggest ones are like 80 lbs from the 454 and they will only support around 360hp.

 

dude i had the same problems with my 93 4.3. you need some one to do a custom chip and you need bigger injectors. aint cheap for either. Street and Performance used to do the chips but i dont think they do any more. good luck. Suggest switch to TPI off of a vett or camaro 87-89. i have an injection system off an 87 vett sitting in the shop. if you want it pm me. it is complete with computer and wiring harness. it will give quicker throttle response and more tunability, because it is not MAP it is MAF.