Low Gear Stumble/Lean Problem
 

Here are the details of the car first. It's a FI LS6 with a small cam and headers bolted to a 350 turbo with a small converter all stuffed into a 76 Camaro.

I had it tuned yesterday on a Mustang Dyno with HP tuners. The guy fixed lots of issues I was having with lean and power loss. It appeared to be all good on the dyno pulls but he started having some problems with the eddy current brake before we got done.

Well, we took it down the road to see how the car felt. Right off the bat, the car stumbled in low gear and the AF went to 16.4. Stayed there for a short time, then it came alive and the AF went to 12.5. This was happening before the tune but it was going to 19.5 during the stumble then. It just kills the low gear power. The car felt like it shut off once just as it shifted to second. The log file didn't show anything really wrong.

The guy went thru the tune and everything looked ok. He felt like I was having an electrical problem. I'm wondering about a fuel pump or supply issue but the duty cycle on the injectors looked OK. Gounds?

Any ideas I should check out?

Could be anything.

Is there an MAF on the car?

I would check the fuel pressue with a gage and see if it drops when going to WOT. Have the tuner check to see how quick the power enrichment is coming in... not sure what base tune you had, but maybe there it too much delay.

It does have a MAF, thought about that but I do have fuel pressure drop. I'm going to change the pump and try it again.

He did change the FE tables to try to fix the problem.

you don't happen to have bosch 02's do you?

Is it leaning out when you go WOT? If it is, first thing to do is log commanded A/F, and see if it's going into PE right away.

BTW, I'd ditch the MAF and go 2 bar SD.

One is a Bosch and the other is an original GM

It goes to about 16.5 during the stumble, then drops to 12.6 and the car comes alive. This just happens in low gear. The dyno pulls in high were OK with no stumble or AF issues at all.

I'm guessing the VE table is off - but I could be wrong.

Push the whole VE table up 20% and see if the stumble goes away. If it does, then have him adjust he VE table again.