Well, I recently swapped my GTA back to a T56 as it was before the previous th350. I've got tons of tunes and logs saved from over the years since I never delete things. (OCD I guess)

Anyways, car was running great before the tranny swap with no issues... actually completed and survived Hot Rod Drag Week last fall. Well, ever since the swap it keeps throwing p0107 MAP code. I'd usually delete the code right away after starting it since the MAP seemed to be working fine otherwise and I was trying to test out the new tranny.

I did some searching online for troubleshooting/diagnostic recommendations and messed with the car a little bit tonight. With the key on (engine off) HP Tuners shows less than 0.10 volts and about 10 kPa. As soon as the engine is started the voltage/kPa increase alot and they seem to read fine. I removed the MAP connector under the hood and checked for voltage and it seemed to have basically nothing. I have not removed the PCM connector yet and checked for issues on the 3 wires that run from the MAP to the PCM. I know I need to do this yet, but what I don't understand is why would it basically show no voltage with the key on (engine off) but show/read/work fine once the car is running? As a sanity check, I logged my '99 TA convertible and with the key on (engine off) it shows about 4.9 volts and 100kPa as I'd think my GTA should.

As another sanity check, I looked back through my logs from over the past 5+ years and noticed on them that anytime I was scanning before I started the car, the MAP showed about 10kPa which would equate to no voltage... same condition I have now. It started to drive me crazy and then I realized that maybe one of my previous tuners had disabled the MIL/SES for p0107. I then realized that my current tune is one of my old T56 tunes I used as a starting point now since I went back to a T56. I compared it to my previous auto tune and the p0107 was disabled in the previous auto tune. That explained why I wasn't throwing any engine lights with the auto but it doesn't explain or resolve the issue. The car has always seemed to run fine, but I am open loop speed density (OLSD) so I'd really like to not have MAP issues. lol

I am running a '98 setup which concerns me at times, and we have been having some issues getting the tune lined out now.... trying to get the TPS to stay at 0% at idle, idle issues, etc. I'm really starting to question this old '98 PCM and wondering if this MAP issue is telling me something.

Ideally I want to repin and swap to a '99-'02 PCM but I want to correct this issue first and get the tune lined out before introducing any other changes with the car.


Sorry for the long post... just trying to get all the info I can in here. Its a 402ci LS2, 90/90 setup, CNC'd 317s, big cam, LT's, OLSD '98 PCM, etc.


Thoughts or comments?


Thanks!
Jeremy

 

Anyone?

Back TTT

 

This may sound silly but have you made sure the map sensor wires didnt get pinched between the block and the bell housing? I have seen that and the map sensor wires pinched under the intake on several cars over the years.

 

Yep, that was my first thought. lol No issues there.

I still need to check the wires from the sensor back to the PCM but apparently I've always had the issues since the code was previously turned off.

I don't understand why the MAP "system" seems to work ok once the car is fired up though.

 

Update... finally got a chance to work on the car.

I disconnected the MAP sensor and once again confirmed voltage at less than 0.10v key on engine off. I probed each wire on the connector back to the PCM. All were confirmed good with no issues.

I then decided to check some other 5v reference stuff like the EGR and the TPS. The TPS showed 5.1volts at the disconnected connector with key on engine off.

Then I remembered I was using the 5v reference EGR wire to supply voltage to my alternator to turn it ok on. My harness is a '98 and when I did the swap into my '91 I initially had a resistor inline to drop the voltage to my alternator since I didn't have the dash light like a '98... otherwise you'll fry alternators really quick. Anyways, I disconnected that EGR wire at my alternator and checked it... 5.1 volts like the TPS. Then I went probing around some more... MAP wire now had 5.1 volts... WTF?! ...but only when the EGR/alternator wire was disconnected.

Now I'm trying to figure out why.

I also am using my EGR position wire as a way to feed my LC1 wideband voltage back to HP Tuners so I can realtime log AFR with a custom pid. I'm not sure if that in combination with using the 5v EGR ref wire as an alternator exciter wire is somehow causing an issue.

Thanks for any feedback... I'm not an electrical guy... just trying to figure this out. I think I'm there if I just figure out another way to excite the alternator. I've had charging issues at WOT (11.5-13) and alao aome TPS and idle issues. Starting to wonder if its all related and I caused it with the EGR/alternator wire.