Running lean or rich never perfect

[tdrewh]

Daily driving a 94 K1500 Z71 extended cab. I love the truck and I'm looking to get the best performance possible on a tightish budget. The engine was rebuilt mainly back to stock. The TBI was also rebuilt. The only upgrade was a 450 lift cam. the issue I'm having is my TBI just can't seem to properly feed that big cam. The truck was running rich, so I replaced the MAP, and now it's running lean. Acceleration and top-end power are suffering greatly and I have no clue what to do about it. Any recommendations on things to try. I'm trying to get smooth and reliable power (nothing extreme) without completely swapping EFI systems.

Thanks,
tdrewh

 

[df2x4]

Has the PCM been tuned for the new cam? If not you're going to need to do that. Being a pre-'96 is going to make that more difficult. @PlayingWithTBI and some others here can probably point you in the right direction, there are people on the GearHead EFI forums who do tuning on the older PCMs as well.

 

[BNielsen]

PCM Of NC can tune TBI trucks via mail or in person I believe;

 

[PlayingWithTBI]

The only upgrade was a 450 lift cam. the issue I'm having is my TBI just can't seem to properly feed that big cam. The truck was running rich, so I replaced the MAP, and now it's running lean.

.450" is a fairly mild cam, you should be able to get it running right. A Q&D trick you can do is jack up your fuel pressure a couple pounds or ~14PSI, and advance your base timing to ~4 degrees (with the EST wire disconnected). Do you have a scanner that tells you it's running rich/lean? If so, you should be able to see timing too so you'll know if it's too far advanced and the PCM is seeing KCs and pulling timing.

@PlayingWithTBI and some others here can probably point you in the right direction, there are people on the GearHead EFI forums who do tuning on the older PCMs as well.

Yeah, Dave W (Old School EFI) has helped me in the past among others there. If you do want to go into "tuning" you'll probably want to convert your PCM to an emulator so you can flash your calibrations as you data log and update each time. Software like TunerPro RT v5.x is great for this stuff.