86 IROC

iTrader: (14)

I have had a problem with my car that has grown worse as time goes on. It started first w/ a sort of "hiccup" around 5400-5500 RPM, right before my 1-2 shift. I had initailly been told it was a broken 1-2 shift accumulator piston. Well, yesterday debunked that myth. My transmission is prefectly fine, and that piston was not broken. However, my issue in 1st gear has worsened. The car sputters and stubles through 1st gear now. It acts like bad detonation or a misfire. It only does this in 1st gear, the car runs fine through all of the other gears. Right now I am now thinking possibly the fuel pump is crapping out. But, I'm not sure... it's something I still need to investigate.

The specs on my car is as follows: 2000 Z28, A4, 3.42 gears, HPP3 to correct speedo error & turn fans on sooner for 160* stat. Pacesetter LT's, QTP 3" OR Y-pipe, electric cut out, SLP dual/dual, LS6 intake, ported TB, MSD 8.5mm wires - approx. 17K miles on them, NGK TR55's gapped at .052" - approk. 5K miles on those. Car has approx. 64,500 miles on it. Hasn't been tuned, fuel filter was just done for the 2nd time about 3K miles ago.

Right now I'm really stumped and frustrated. Hopefully someone here has had a similar problem and knows the fix. I thank everyone in advance for any help/suggestions they may bring to this thread.

2_wacko

iTrader: (2)

Well it might need a tune with the QTP's.

86 IROC

iTrader: (14)

The car does need a tune, however this problem existed prior to the LT's/ORY, LS6 intake, and pulley. It's only worsened over time.

86 IROC

iTrader: (14)

I am now thinking it could be my fuel pump or fuel pressure regulator. I am going to verify the exact fuel pressure, and see how long it holds pressure before bleeding off. Does anyone know what the range for fuel pressure should be on a 2000 LS1?

Cstick

Just a thought... Are you sure you are not hitting the rev limiter in 1st. I have mentioned this before, after I put a shift light in my car I was amazed how far off the factory tach was. Especially in 1st gear when the engine revs quicker. The tach does a crappy job of keeping up with the RPM. Gets better through the gears.
I set the light to like 5900, and it was flashing when the factory tach was at like 5500. I doubt you really have a problem.

nikon1999

iTrader: (22)

if it was fuel system it should do it in every gear?

86 IROC

iTrader: (14)

That's what I'd think too.

As for rev limiter, the car shifts the 2-3 at 5800-5900 w/o incedent. This really has me stumped.

Davd901

I had a similar problem. I was told to clean the MAF sensor... I did and it worked. You've got to be careful; it's very fragile.

86 IROC

iTrader: (14)

Hrmm... I'll try that. I was running ported ends for a while. I'm back to running my stock ends w/ the screen currently. I have never had a K&N type filter, I use the old standby FRAM paper filters that I replace with every oil change.

Davd901

Use a soft nylon (acid) brush and denatured alcohol. Let it air dry. Gotta be careful.

86 IROC

iTrader: (14)

Where can I find/buy these things? Drug store? Grocery store?

nikon1999

iTrader: (22)

they have the stuff at hardware stores... Yes the maf is a good idea... my friends mustang had a bad maf and it fell on its face through first gear, but fine once it was going. Maf ends and then no maf ends, and your mods, tuning would definitely benefit your car.

86 IROC

iTrader: (14)

Haven't cleaned the MAF yet, however I did hook it up to a Tech 2 and test the FP. Results: FP is 51 psi w/ the key in the run position, but not running, running at idle I see about 60-61 psi. On the Tech 2, it showed 3* or KR right before the 1-2 shift. If I set it to shift lower or higher, it doesn't matter the 3* of KR follows suit. My LTFTs were 2% - 3%. I replaced my plugs even though they weren't that old, they looked extremely lean and had some signs of detonation - white spots on the electrode. I don't hear any detonation, and the Tech 2 showed no signs of detonation until the 1-2 shift. With 3* of timing being pulled, I am only seeing 17* of spark advance at WOT right before the 1-2 upshift.

I will try getting the few things mentioned previously and clean the MAF hoefully some time this week. Other than that... I am out of ideas. I'm about ready to de-mod the car and sell it.

Edit: also, forgot to mention, when scanning w/ the Tech 2... it wasn't learning the fuel trims I was told. Not sure it that means anything or not.

86 IROC

iTrader: (14)

Well, two new theories have surfaced. I have a HPP3 that I use for speedometer correction, fans, and upshift points. It says in the manual supplied with it - that it should be "returned back to stock before going in for warranty work." It went on to say that it might cause false readings, etc. Also it made note of "if you have an issue w/ your car and it stops when you remove the HPP3, call the 1-800 # for warranty and exchange info."

So now I'm kind of curious if my HPP3 may be causing this, I intend to test this theory soon.

Next, the guy who let me use the Tech 2 told me he saw a TSB for hummers w/ the 6.0L that called for replacing the knock sensors for a problem similar to mine. It cited corrosion on the KS as the culprit.

I'm skeptical of that one because I've never heard of a knock sensor going bad on one of these cars. I'd hate to spend the money & do the work only to still have this problem.

Any thoughts or ideas about either theory? I'm going nuts trying to fix this.

86 IROC

iTrader: (14)

Well, been trying to wear out the search feature on this matter. It seems I am the only lucky SOB who has ever had this issue. However, I did find a thread about something similar. In this thread, someone stated that if you unplug the MAF and the problem goes away - the MAF is either bad or diluted.

I went out tonight and started my car, unplugged the MAF, and made several WOT blasts. Car shifted great. I then pulled over w/ the car running and plugged the MAF in. Did two more WOT blasts, the car shifted fine.

I think I am going to try and get the car to act up again tomorrow and then pull over and unplug the MAF, then retest.

Anyone ever heard of unplugging the MAF to see if it's bad or not before? It's new to me, but sounds reasonable. At this point - I'll try almost anything!

Davd901

That's how I found my problem. The car revs quicker with the MAF sensor disco'd, but this should narrow your troubleshooting. Cleaning it taked all of 10 minutes.