...well, got the engine back together and in the car, new Trickflow 23 degree heads, SLP 51006 cam and 1:6 roller rockers installed. Port matched the heads and 58mm throttle body to the SLP t-ram intake, and installed a new SLP 600-800 over stock torque converter, new plugs and wires. The car now pulls extremely strong from 1500 rpm to the redline, but stumbles coming off of idle. Timing is dead on, all parameters look good and the computer is not throwing any codes. I'm thinking that maybe with the higher lift cam I'm not getting the proper vacuum at near idle rpms, and maybe need a new chip for it. Also wondering if I may have a bad injector, although you sure wouldn't think that the way it runs once the rpms come up. Anyone have any other ideas or areas to check.

TIA for your help...

jimb0

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jimbo

Mosquito Coast F-Body Association (MCFBA)

1991 Formula SLP350
1999 Trans Am Firehawk

 

It could be a PROM problem as long as you've ruled out there isn't a boogie in your TPS or MAP sensor at those transistions.
...ed

 

Yeah, check the TPS voltage setting. You can actually adjust it to make it a bit richer from idle. The computer will handle the closed loop control.

 

jimbo,

If everything else is dead on then you have the dreaded 'off idle stumble' due to heads/cam and upgraded intake. Basically, your cam pulls less vacuum and therefore you are running rich at idle (checking your BLMs will confirm this). However, just off idle you will be lean. The fully upgraded intake allows a massive amount of air to rush into the engine. This requires a PROM change to fix. Only problem is ... I doubt that a standard PROM guy could fix it. Specifically...

1) You need to adjust certain portions of your lower VE table to decrease the amount of fuel at idle.
2) You need to INCREASE the pump shot table. This table is the table that acts like an accelerator pump on a carb.

I had symptoms similar to what you are talking about and eliminated them very easy through PROM changes. BTW - do you have Diacom or a scanner?

Tim
2)

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• Program your own PROMs!. Read my article to get started!
• Research and Experiment before asking questions.
• This is not a chip store. Go to the classifieds if you want someone to sell you a chip or give you a BIN.

TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

Hey Tim...you are correct, I am running rich right now at idle. My TPS is currently set at .61. I don't have a Diacom or scanner, but the local speed shop does. I'm am in the process of contacting some custom chip companies to send them the pertinent specs and data...will definitely include your observations and suggestions.

Thanx...really appreciate the insight...

jimb0