I recently finished the TBI conversion on my 86 Chevy G20, with the parts from my Donor 92 Yukon. This was a complete engine rebuild, and then harness installation of the TBI system into the previously carb'd van. I retained the transmission from the van as well.

I got my van out on the road yesterday after double checking the timing (which i thought to be causing this problem), and the problem still occurs. Only happens under load.

At idle to 1/4 throttle, the engine runs smooth. When i reach 1/4 to about 1/2, 3/4 throttle it chugs bad, acts like it's missing/got no power. I can muscle it through if i give it closer to full throttle, and it'll come out of it and runs pretty well.

Under no load, it runs smoothly.

The suggestions that have been given to me already are disconnect the EGR, that it might be hanging open or dumping too much; or that it could be a problem with the map sensor.

I logged some with TunerPro and didn't see anything that looked too out of the ordinary, except for the O2 sensor readings (I converted to 4-wire, so may not have the wiring correct, going to test), and it wasn't going into closed loop at all. I have a log available if needed.

The only other issue I can think of, is that I do not have the transmission feed wire connected (park/neutral switch on ecu), and i no longer have the speed sensor, and have not yet installed a chip to disable these (if possible). Do I need to ground the trans wire?

thanks for the help.

 

Sounds like a low fuel pressure problem, did you run new lines when you did the conversion? Feed line should be 3/8. Return is 5/16.

 

I'm pretty sure it's not a fuel pressure issue, as it runs ok at WOT. if it was low pressure it'd struggle at WOT as well.

It's running better now, I fixed the O2 sensor last night, and am now getting the correct readings and getting closed loop during operation. It still has a little hesitation from time to time though, but i'm guessing that's from either a fouled plug from running overrich with incorrect O2 readings, or that it's still adjusting fuel trims in closed loop.


Back to my original question, do I need to do anything with the trans park/neutral switch feed on the ECU? Also I don't have the crank signal wire hooked up, I'm guessing that's just a starting enrichment wire?

 

Im chasing the same deamon sir, exact same to the T, and I wasnt even searching for it, go figure!! I drive the car 2 hours daily to work, passing speed seems a lil slower,

The search and researches continue!


Curious if you found a solution?