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Old 05-03-2009, 08:21 AM   #1
Join Date: May 2009
Location: idaho
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4.3 tbi running rich

ok here is the story, I've got a 1991 4.3 tbi with some recent engine work done, short block bored .40 over, it is a roller motor, I put a comp cam kit in it # CCA-K09-412-8 from summit, added some comp roller rockers, 1.6 ratio, an edelbrock intake, and msd offroad ignition box. the motor is mated to a 700r4 with a stak mini 3 speed behind that. the motor harness and tranny were pulled from a 91 s10 blazer which ran fine. I've put the setup in a 1950 cj3a. its running way rich,,,,,,,,

I've replaced the o2 sensor, fuel pressure regulator, injectors, and throttle position sensor. the fuel pressure at the throttle body is 11psi, took it to a local performance shop and they burned a new chip as to make it run leaner, and to remove the speed sensor, didn't help. they said it was the computer, tried two other junk yard computers (service #1228062). can't find any vacum leaks, idles rough but arround 500-700 rpm

as for the wireing harness, I took the stock one and weeded out what didn't need to be there, but there are a couple wires that went to the digital instrument cluster I'm not sure if they need to be hooked up, a white one I believe the tack from the computer, and a blue one, may be the speed sensor, anyway, I put in autometer gauges and ran wires from their sending units to them, not sure if the computer also needs those sending units, like the coolant temp, I believe the one in the front of the intake manifold is for the computer, where as the one in the block below the passinger side head is for the gauge, dont' think the computer needs the oil pressure. the vss I'm using in the stak t-case is from a jeep and is hooked to the autometer speedometer (ATM-1291) which puts out a 5v square wave. so can I hook this to the stock computer without messing it up?

any thoughts on where to go next with the rich running.

O'yea, no engine codes,

my next steps:
try a new Idle air control motor
painless wiring harness 60101 or something down that line.
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Old 05-03-2009, 08:41 AM
Posted in reply to 1950cj's post "4.3 tbi running rich"
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Wiring harness I don't think is going to fix the problem. Do you have the datalogs to show that it's running rich?

Could be IAC, but they usually don't have problems.

VSS helps on some setups, but I suspect properly removed, setups will run ok without it. If it's not programmed out via the chip, unless its an early TBI ECM, it's likely to cause problems. My '88 *TPI* runs horrid with VSS disconnected.

DRAC is what GM used to translate the signal from the VSS on the t-case to the ECM, but no clue if it's 5V. Check www.jagsthatrun.com for the VSS chapter they have online, it might help.
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Link to "square body" manuals http://67-72chevytrucks.com/vboard/s...d.php?t=545416
"1985" K5: Vortec Headed Roller 355/MAF TPI/32 spline 465/205/10B-14SF/3.42's/33". Will be converted to MAP TPI in the future.

1987 K5: 350/TBI/700R4/208/10B F/R/3.73's/31" Someday will assimilate the "1985" drivetrain.

The answer to your carburetor problem is fuel injection.
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Old 05-03-2009, 09:10 AM
Posted in reply to dyeager535's post starting "Wiring harness I don't think is going..."
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I don't have the datalogs, and the harness, well I'm not sure if I didn't cut out a ground or another wire that should have been there or if there is a bad wire in the thing causing all this, it ran fine in the blazer,but that was an engine rebuild and transplant ago.
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