1991 GMC Suburban Swapped TBI to Carburator

JUSTJOSHIN83

MEMBER
1991 GMC SUBURBAN

Transmission problem
1991 GMC Suburban V8 Four Wheel Drive Automatic n/a miles

Vehicle had 454 with TBI, motor was removed. I installed a 350 with a carburator. Obviously creating many problems. This vehicle has a 4L80E transmission. Transmission does not shift properly.

Wiring harness is intact and connected to transmission but the computer is almost completely bypassed. None of the sensors are being utilized. No TPS, no MAP or MAF, no camshaft position sensor, no crankshaft position sensor.

Is it possible to improve shifting? If so, how?

4 Replies

MHPAUTOS

MECHANIC
31,937 POSTS

Hi there,

I feel that the lack of input to the ECU is causing the transmission control system to go into conflict, I don't really see how you can over come this problem.

Mark (mhpautos)

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Tuesday, November 10th, 2009 AT 3:21 AM

JUSTJOSHIN83

MEMBER
3 POSTS

After checking around I found what I think may be a relatively inexpensive solution.
Many performance shops/sites have Manual Valve Body kits for GM transmissions. I understand this would not allow automatic shifting. These kits range from $150 to around $275. Any opinions, especially those of people who have used a manual valve body, are welcome.