Preface parts list: 243 heads, 226/234 .612/.595 112+2 cam, LS6 Intake, SLP Lid, potz ported stock throttle body, 38# Lucas injectors, racetronix 255 fuel pump w/ hotwire harness, 1 7/8" long tubes, denso O2 sensors, high flow cats

I'm not getting any traction in the other subs so I figured I'd try here. I've taken my 2000 Pontiac Trans Am to the same tuner twice trying to figure out why it wont start up right on the new tune. The car was previously tuned for just a cam and long tubes. It started up and drove fine. I then put in a racetronix fuel pump and hot wire and it drove fine still. Finally, I swapped heads, put in a new similarly sized cam, added a new ported stock throttle body, and it started up and ran fine. I then took it to the tuner to have it fully tuned. They had no problem with the street tuning or dyno tuning. However, getting the car to idle right when you first start it has been a total failure.

The last information I received from the tuner when I told him I had nothing but the fuel pressure regulator left to check was:

"I can't think of anything outside of fuel on the start up issue as the file you came up on originally the car started fine, but was also pulling 25% or more fuel to maintain stoich. As soon as the maf is turned back on and within +/- 2% trim it has this issue. I have often heard of issues with cavitation in the tank on the stock system with bigger pumps, but that shouldn't happen with start up, just under high loads or fuel demands. It's only on start up is the issue. Everything else is peachy with it."

I just had the 38# Lucas injectors flow tested and cleaned and they passed. The rails, lines, filter, and regulator are stock. The regulator is the only part of the fuel system at this point that hasn't been changed or certified to be in working order. I tested the fuel pressure and get 60psi prime, 46psi key on engine off, and 60-62psi engine running. The fuel pressure needle bounces a bit while it's running. I've posted two videos below. One is the current startup condition. The other is after it has settled into a warm idle.

http://vid1288.photobucket.com/album...pssk5y7fb6.mp4

http://vid1288.photobucket.com/album...psvhgee8sv.mp4

The first time they had a problem with the start up idle they couldn't get it catch itself at all. You had to give it a little throttle and it would eventually settle out. It would then hunt for idle when coasting to a stop with the clutch pedal out in neutral sometimes. They thought it was vacuum or iac related. I smoked the motor and verified it has zero vacuum leaks. I also replaced the IAC and TPS. In the end I had to raise the throttle screw to a tps voltage of .80 to get the car to catch itself, but it would still idle up when stopping occaisionally. This is when I returned to the tuning shop. Now they think it's a fuel system issue. The way he explained it to me in person was that at first start it would seem a little lean and then go way rich for a moment and eventually settle out. If he immediately restarted the car it would be fine. If you let it sit for a few seconds and try again it would be all over the place again.

Has anyone experienced these problems before? Could it be the fuel pressure regulator? Is it in the tune? I feel like I've been on a witch hunt for parts that end up being perfectly fine.

 

Should hold the 60 with key off after key on. No way to know if it is the tune without seeing it.

 

The problem is your tuner. You said the car started fine until you took it to him. He changed the tune and now it won't start. He said that when he turned the MAF on the problems started. That reads airflow, so it has nothing to do with hard parts sending fuel to the motor, so his comment about tank cavitation makes no sense. If your account of what has happened is true, you need to run far away from this "tuner".

 

It's been a long time since my cam swap and I can't recall
everything I had to mess with, but I know it included the
cranking VE table, afterstart enrichment and the profile of
how demanded airflow backs out after startup. In retrospect
the biggest deal was getting the VE tables right(ish) at the
RPM below where motor runs steady, which takes some combo
of eye-for-the-curve and blind stab * repeat. If you've got
too much fuel then everything else struggles, and cam swaps
almost guarantee you've got a false-high VE at low RPM (and
worse, the lower you go, including the stuff you can't see on
a scan tool because it doesn't scan while cranking).

 

Can you explain this part? I am SD and whenever I tune my VE table with STFTs, it keeps having me take so much fuel out that by the time they are close to correct, I have lean tip in, and when I first crank it warm, the on board AFR gauge flatlines around 18 AFR......
When I compare the VE of my "modded" H/C car against other cars tables, mine is a LOT lower in the lower portions of the VE table.

 

At low RPMs the cam overlap really cuts the pumping
efficiency of the motor, letting intake blow through to
exhaust or exhaust back into the cylinder & intake, and
the real VE is less than it was, and what was modeled in
the factory tune. So in the tune VE is now unrealistically
high for the hardware. This makes the PCM deliver fuel
to match (which is not really needed).

You may want to play with fuel trim cell boundaries. The
Gen4 Camaros, they lump everything below 2500 into one
set, 2500-6250 in another, and put two sets of FTCs out
of play. Especially cammed, there's a lot of change in how
the motor behaves between idle and 2500, and you can
end up with that "blob" being dominated by what's going
on off-idle and doing something inappropriate at the other
end of the range. With trims covering a wide range the
odds are that you'd apply this gross correction factor and
have it be really right only where the bulk of (or the most
recent) trim learning has gone on.

Slicing the load-space finer and using all of the cells can
make STFT-based tuning more accurate and cut down on
"endless tail chasing". You don't need any of the main
cells to extend past PE enable MAP or PE enable RPM
(although you can't keep at least one RPM column and
one MAP row, from overlapping PE space, you certainly
don't need three of the four RPM columns covering a place
where trimming doesn't happen).

 

Thanks for the detailed answer.
Sounds like I need to do some more scanning

 

Took it to a new tuner this weekend. He fixed everything and then some. I kept telling myself it couldn't be the car but I was reluctant to gamble on it. I had finally had enough and paid for a second tune at a different shop. It was worth every penny.

 

Good to hear, but this is a prime example of people who charge for a tune, who shouldn't.