First of all, here's the car I have:

1994 Trans Am 180,000 miles

3 Weeks ago, got it back from the shop which installed:

MAC midlength headers and y-pipe
Car-sound California-legal cat
GMMG cat back
4L60E to T-56 conversion
SPEC stage 2 clutch
Strange 12 bolt rear w/ 3.73's

These have nothing to do with my problem but I'll put them in anyway:

Koni's, panhard bar, LCA, subframes, and a-arms.

They flashed the computer for the M6, and 20,000 miles ago, I had the opti replaced with plugs and wires because it crapped out on me. I also did O2's at that time.

Today I took it on a 200 mile pleasure ride through the mountains with all sorts of twisty turney, up, down, in, out, high revving roller coaster type stuff then took down my scanmaster readings after coming back to idle. They are:

MAF - 03
SP - 19-20
LP - 1.5-1.6
RP - 1.4
DTC - 36, 44 and 91
LBL - 146 (during the drive was at 150)
RBL - 134
LIN - 128
RIN - 128
TPS - .58
IAC - 29
MAP - 10
BAR - 30
ACP - 1.08

Since I got it back from the shop, it's been running perfectly. No miss fires, no loss of power (just blew the pants off a BMW today) 25 mpg on the freeway.

First noticed the dtc 44 on the drive down here to SoCal from Seattle, about 600 miles into the drive at the end of a 250 mile non-stop stretch. First noticed the dtc 36 when I got here and had done some city driving.

I have a tuned computer from pcmforless waiting to be installed, I'm just waiting for my 17" wheels to arrive so the speedo is accurate. Hopefully that will solve the lean condition but hopes aren't high.

Do you guys have any idea what could be causing these codes and what can be done to fix the problem? Thanks.

 

For LT1 code meanings, always start with Shoebox's Tech Page:

http://shbox.com/1/Dtcs.htm

DTC 36 = Distributor ignition system (faulty high resolution pulse or extra low resolution pulse detected)

The PCM is having trouble getting a consistant low resolution pulse signal from the Opti. This may be the result of a failing Optispark distributor, or faulty wiring. Check the pins on the harness connectors for corrosion or damage.

This code can be active and not affect engine operation at all, other than a very minor loss of timing acuracy (= increased spark scatter). You might never know it.


DTC 44 = Bank 1 (left) Heated Oxygen Sensor (HO2S) Circuit (lean exhaust indicated)

The driver's side O2 sensor is reporting a lean condition, and the PCM is elevating the driver's side BLM (LBL) to compensate. Could be a "true" lean condition, indicating an air leak on that bank of the engine, etc., or a "false" lean due to faulty O2 sensor, bad O2 sensor wiring, exhaust leaks before the O2 sensors or misfires on that bank of the engine. With new headers, there can be problems with burned wires, and it will cause misfires, which cause the elevated RPM and poor running. If your headers are cera-metallic coated, there is a possibility that the initial burnoff from the header coating has contaminated the sensors. Just speculation, but a lot of people report O2 sensor problems about a week after installing coated headers.

Both sides are running a bit lean at idle.... the drivers side is adding 14% extra fuel, the passenger side is adding 4% extra. 4% isn't a problem, but 14% extra is. And, the fact that the left and right banks of the engine don't have BLM's close to each other is a problem.

What Cell was the PCM when you recorded the 150 LBL while driving? Or were most of the Cells indicating that value?

Also odd the the integrators on both sides are exactly "128". Were they staying at that value the full time at idle, or were they moving around constantly? If the PCM is in closed loop, the INT's should be moving rapidly above and below 128, with an average value of 128, not a steady 128. A steady 128 would indicate it is still in open loop. Did you restart the engine shortly (< 3 minutes) before you took down the ScanMaster readings?

DTC 91 = Skip shift lamp circuit

When you did the A4->M6 conversion, did you add a "Skip Shift" light to the dash and wire it up? This will not cause any operating problems.

Why do you have to wait for your 17" wheels to arrive before installing the new pcmforless tune? If you selected the correct tire size, to maintain the stock tire diameter, there is no change required in the "tune". Even if you changed the outside diameter of the tires slightly, the impact on the "tune" would be small, maybe 1 or 2% on the speedo readings.

 

Thanks Injuneer, this is just what I needed

The LIN and RIN were shifting rapidly between 127 and 129-130, sorry didn't think that mattered.

No, I didn't see what cell the pcm was in while driving, I only saw 16 at idle.

 

I went ahead and installed the new computer, thanks for the heads up on the wheel situation. The dtc's 36 and 44 are gone however the LBL/RBL are still high and the RIN/LIN are higher. Here are the new readings after coming back to idle.

MAF 04
SP 22-26
LP 1.4
RP 1.3-1.4
LBL 142 (was at 150 while driving, the CEL was 06)
RBL 140 (also hit 150 while driving)
LIN 131-133
RIN 131-133
TPS .58
IAC 38
MAP 9
BAR 30
ACP 1.16

Car performed perfectly again with definate sotp improvement. The headers were coated so I'll try some new O2's and see if that eliminates my lean condition. The smell that usually followed a WOT punch hasn't shown up for a while so hopefully it's all burned off now.

 

I replaced the O2 sensors today and went driving for a while but the lean condition is still there. I was hoping the burn off from the headers was interfering with the 02's, guess not. I'm going to set my sights on the vacuum system unless someone has a different idea.

The codes are still gone at least.

 

If the numbers you reported for the MAF sensor are in grams/sec, they look too low. 3 or 4 gps at idle is very low. Perhaps the sensor is dirty, or there is air leaking into the system without going through the MAF sensor.

 

I'm going to keep updating my situation in this thread for the sake of someone doing a search for the problems I'm having, even if interest is low at this point.

I was checking for exhaust leaks yesterday when I noticed on the drivers side of the engine, the spark plug closest to the driver (don't know what number cylender it is) was arcing. The spark was easily seen in broad daylight and it didn't follow a pattern that I could tell, just kinda sparked randomly. I checked again at night and no other plug was arcing that I could see but I went ahead and bought some MSD 8.5mm wires along with clamps to route them OTVC.

Since the new 02's, the LBL and RBL are reporting values closer to each other, < 2, however the values are as high as 154 at idle and while coasting. When I give it gas they go down to about 142 but shoot back up as soon as I take my foot off the pedal. All cells seem to be indicating the high value.

Looked at the MAF, which is a Granatelli, and saw no dust or damage. Last year when I was home on leave, the pcm was throwing a dtc 48 which had magically disappeared when I came back last month. I don't remember the MAF value on the scanmaster though.

 

have you got your stock MAF?
replace with stock MAF and retest..

airdeano

 

So I just spent a total of 7 hours replacing my stock wires with MSD 8.5 mm OTVC wires, hoping that would fix my lean condition. It fired right up with no immediate problems however the scanmaster showed both banks move steadily toward 160 on the lbl and rbl and eventually max out, needless to say my excitement and celebrating were cut short. The wires had the opposite affect from what I wanted. I drove 12 miles from my buddies place to my appartment with no problems, both banks were between 155 and 160 the whole way back.

Once I got back I decided I'd replace the Granatelli MAF with a stocker I bought from a member of this site (good call airdeano). After it was snug in its new home between my 1LE elbow and CAI, I started the car again and watched the lbl and rbl. I watched in awe as right before my very eyes, both banks steadily made their way back down. I drove it to the store and back and at idle, lbl was 124 and rbl was 124. Lin was 127-129, rin was 127-129 and all other scanmaster readings were perfect (although the MAF was at 5 which is low I believe).

So there it is, the Granatelli MAF was the culprit the whole time. Oh well, even if the wires weren't needed, at least they still look cool going over my valve covers, and the old O2 sensors were two different brands so replacing them wasn't a total waste either.