kernelPanicked

Hi all,

Just got done a winter (and spring I guess) project. I have a 2000 C5 Coupe M6, 103,000 mi, which already had ARH LTs and Vararam, and was running good. Now it's got 2002 Z06 Heads + Cam + Intake + TB + Injectors, new OEM valvetrain parts, and U/D pulley. I also got a mail order tune from a reputable tuner, based on an Z06 with the same bolt-ons.

Startup went fine mechanically, but it was very rough idling. The car was driveable, and idle smoothed out as well, but soon started throwing P0171 & P0174 at the same time. I have Torque and an OBDII scanner...I cleared the codes a few times but they keep coming back, and I've only put about 35 miles on the car now. I am seeing very high fuel trim values, like this:

LTFT1/2 : pegged at 25 in all conditions
STFT1/2 : At a hot idle, creeps up to 40%; at cruise/low load, 10-15%; about the same at higher load. Sometimes spikes to 20%.

I tried a couple things, none of which fixed anything...MAF cleaner, re-torqued intake manifold...I had damaged my EVAP line clamps during the job and replaced that today with a fuel hose...I've checked every PCV hose I can put my hands on (which isn't all of them). Nothing obvious.

I am content to keep looking, as there might be something lurking behind the intake (it's kind of a mess back there), but I'm wondering if some of you all with tuning experience can answer a few questions:

• Given this is just an upgrade from LS1 to LS6 specs (+ bolt ons), is this much fuel trim even possible from a tuning problem? It's possible that there was some miscommunication when I ordered it. I don't know much about tuning but it would seem like unless he tuned it as a Geo Metro, even a bone-stock LS1 tune wouldn't be this far off.
  
• One thing I'm worried I haven't done right, and its hard to see, is the dipstick install. It is in and seems to give a sane reading, but it didn't quite meet the header mount like I thought it should. Is it possible for a loose dipstick to cause this much of a problem?
  
• I installed EGR/AIR, even though I'm pretty sure the LS6 doesn't have it. It feeds into the Vararam, I figured it couldn't hurt. Am I wrong?
  
• I tried the old trick of yanking off a hose to see if things got worse. This was the PCV hose on the passenger side of the TB. Didn't seem to change much. Is this confirmation I have a major leak somewhere?
  
• Any way other than battery d/c to reset LTFTs? Might be useful to see what is going on without the computer trimming around it.

Thanks for any answers or tips. I've got some ideas but I'm not sure where to start on this right now.

2xLS1

iTrader: (25)

Did you replace the coolant H style crossover under the intake with the LS6 front crossover and rear plugs?

kernelPanicked

I did not; I removed the casting fins from the intake. Do you think the h-pipe might be lifting the intake anyway?

I decided on modding the intake because I wanted to keep the crossover function, arguments for it were good...but obviously if it's breaking the car I will spend the few bucks for the LS6 pipe/plugs.

EDIT: Just ordered them. I think I am going to be pulling the intake anyway to check for leaks. I'd rather rule out this possibility then get any kind of small advantage from more crossover flow.

2xLS1

iTrader: (25)

The green plastic clips that hold the knock sensor wires to the crossover pipe need to be removed too. I won't get into the argument that the small amount of coolant that flows through that pipe can have much if any effect on cylinder head temps.

kernelPanicked

Yeah let's not touch that one. I like not spending money, and it was a supposed (small) advantage, so I went with it. I did remove the green clips as well.

Any opinions on the magnitude of the trim? Can we say definitely that something is leaking/broken, or could this big of a problem result from just from an inaccuracy in the tune?

2xLS1

iTrader: (25)

How can anyone tell without seeing the tune?

kernelPanicked

Just thought I'd ask, I don't really know what the differences in tune would be given the relatively minor mods (no cam/FI). If there was miscommunication about the tune, it would have been about injector poundage, EGR, or something like that...which I would have expected to lead to minor fuel trims, at least not enough to throw these codes. Your answer tells me there's nothing definitive about this amount of LTFT to say "tune's fine, your motor's broke".

Sorry to ask a stupid question, but I at least try not to ask it more than once.

Thanks for the help, sounds like the best thing to do is just pull the intake, fit the LS6 coolant tubes, and check everything else (PCV, etc) out.

2xLS1

iTrader: (25)

Didn't mean to sound harsh but until someone can look at the tune in your car no one can know. Anyone can make an unintentional error editing a file.

ScarabEpic22

iTrader: (1)

I agree with 2xLS1, without seeing the tune (if the tuner will allow you to post it, Im not sure of LS1Tech's policy) it's very difficult to say what's wrong. To me, sounds like it needs to be tuned again, if your LTFTs are maxxed out at 25 and STFTs are very positive, the tune isnt delivering enough fuel (or even close to it).

kernelPanicked

Talked to him today. He made an interesting point, I have almost all of an LS6 except one part -- the MAF. I have the older LS1 design. He tuned with the LS6 MAF table. He thinks that might be the cause of it. Certainly, it should be corrected. I'm going to get that MAF swapped out. Think I may still pull the intake to check for leaks, this all seems way out of whack.

kernelPanicked

Just to add, running with the MAF unplugged, the fuel trims all zero out, and the motor runs smooth. I think MAF mismatch is the issue. Will update if a new LS6 MAF doesn't do it.

BLK02WS6

iTrader: (2)

The MAF would be the issue for sure...