Low power, tire-spinning 1-2 shift... HELP!

[bfcg30518]

Picked up a 96 C1500 for my son a few months ago. We got it with a bad transmission, so I have no idea how it ran before.
$2300 later, we have a fresh transmission that seems to drive and shift just fine under normal driving conditions. No issues whatsoever, other than what feels like a weak engine.
I've already replace the spider injection with the upgraded MPFI style spider, new MAP sensor, new TPS, new MAF sensor, new IAC valve, etc...
Also did a complete tune-up, plugs, wires, cap, rotor, fuel filter, etc...


im about ready to yank the whole injection system off and install a holley 650, edelbrock intake and HEI distributor.
I feel that would correct the low power issue... but still have no idea why this truck will literally burn rubber on the 1-2 shift @ WOT.
Trans shop is pretty well respected in the area and he said he did a few upgrades to the trans for firmer shifting and to hold more power for future upgrades.

Anyone in the Dawsonville GA area want to make a few bucks fixing this thing ?

I am old school and not much of a computer/electrical troubleshooter.

Any advice is much appreciated !

 

[Erik the Awful]

Check your fuel pressure. Check your O2 sensor readings. Have you plugged a scan tool into it? It's going to be a matter of diagnosis, and parts-throwing isn't going to get you there.

 

[0xDEADBEEF]

Did they install the Corvette Servo? I have the same behavior in my LS swapped truck. The WOT 1-2 shift will spin the tires like crazy. Even at light throttle it's a very firm shift.

 

[bfcg30518]

"Did they install the Corvette Servo? I have the same behavior in my LS swapped truck. The WOT 1-2 shift will spin the tires like crazy. Even at light throttle it's a very firm shift."

Yes, I'm pretty sure he installed the Corvette servo.

 

[bfcg30518]

Check your fuel pressure. Check your O2 sensor readings. Have you plugged a scan tool into it? It's going to be a matter of diagnosis, and parts-throwing isn't going to get you there.

Fuel pressure check is next. Havent done that yet but it feels really lean and lays over pretty bad.
It does have a CEL for O2 sensor issue, but I assumed that was due to gutted cat.

Also learned that it's a 305 Vortec and not the 350 that we thought... so that just nixxed any upcoming mods and morphed into a future 383 build instead.

 

[Schurkey]

feels like a weak engine.


im about ready to yank the whole injection system off and install a holley 650, edelbrock intake and HEI distributor.

I feel that would correct the low power issue.

learned that it's a 305

So it's running as expected, then.

Carb-swapping is a terrible way to "fix" a fuel-injected engine.

 

[GoToGuy]

O2 sensors, are important as this is one of information inputs the PCM uses to determine fuel factors. All before cat sensors are information for mixture ratio to pcm. All after cat O2 sensors are monitoring cat health. If cats removed or nonfunctioning the PCM needs to adjusted for that condition.
Well functioning pre cat O2 sensors are 1 part of well tuned, good running truck.

 

[L31MaxExpress]

Having owned a couple 305 Vortecs, they haul butt. A little less torque than a 350 Vortec, but I would not call them low on power by any stretch of the imagination. They also respond very well to bolt on parts like headers, higher flowing exhaust and a Volant air intake. You will want those parts to let a 383 breath anyway, so might as well put them on the 305 now.

 

[bfcg30518]

Fuel pressure was 55-60psi... so I left fuel pump alone and replaced all 3 O2 sensors with new Bosch units since it had multiple O2 sensor codes and CEL.
It seems to be running much better but still feels like its laying over pretty bad when I wring-out 1st gear. Theres still something "not right" going on here.
The cat was gutted, but still no check engine light.
Maybe the new MAF sensor is bad.

 

[bfcg30518]

Ive also swapped in a set of 3.73 gears and a posi unit pulled from a Suburban. It made a big difference.
Today I mounted a rear sway bar from the same donor truck. Had to lengthen the end links and weld the pads on the axle tube but it was otherwise a pretty simple job.
The truck handles much better now.