MAP Sensor Issue - Mass Confusion

[pwmin]

I finally got my L67 top swap done on my 99 Grand Prix GT, but I'm having an issue that I can't figure out with the MAP sensor. I followed the vacuum diagrams that I found for the swap and fixed a leak that I found. I got it running with the L36 MAP temporarily and it would start and run fine for at least a half dozen times, but then it decided it didn't want to start sometimes. So, I hooked up an L32 MAP and it was producing the same issue. Unplugging it would allow the engine to start every time. I thought maybe it was the MAP, but after installing another one it starts every time. Problem is it's defective and constantly reads the same kPa and voltage. I also tested the other L32 MAP and it reads 5V input and reference voltage decreases when applying vacuum. Why would it start every time with a bad MAP but not with one that's testing okay?  

 

Also, I am trying to make an adapter harness to run an L67 MAP so I don't have to cut the factory L36 wiring but I'm having trouble finding the female connector everyone uses for their adapters the sell, like ZZP, Casper's and others. Casper's hasn't been able to help me so far. Anyone have a part number for it or knows where to get it?

[pwmin]

This is just insane.  I went to drive the car home last night and it would start, but idled horribly and kept stalling.  I put an older tune back in it and it ran fine on the bad MPA sensor.  After talking to some people on a tuning page, they told me I needed to take a GTP bin and put the GT transmission files in it.  I tried that at first, but it would not write, so I had to write a tune with a GT bin as a base and copy everything but the transmission files from a GTP bin.  I finally got a base GTP bin to write and then wrote the the modified GTP bin to the PCM.   Would not start with either MAP.  I unplugged the MAP, started the car and then plugged it back in and it idled smoothly.  Now I'm getting P1336, so i'm going to try a case learn to see if that code still comes up afterwards.  I'm so perplexed. 

[pwmin]

I seem to have gotten it to work okay with a combination of a certain tune and a certain MAP sensor.  It's only reading like 2 psi boost max and 12 psi vacuum.  It should be reading 100 w/ key-on, but it's reading 84.  That's the closest any of the 4 2 bar MAPs I've tried. (NAPA L32 162 kPa, AMZ L32 185 kPa, other L67 168 kPa).  Offset for GT is 10.33 and GTP is 7.99.  Someone on the DHP/HPT fakesbook martinsplace group got pretty snappy with me trying to convince me it's a wiring issue.  I have 5V input and ground.  The reference signal is controlled by the MAP.  I'm confident that it's an issue with all of my sensors.  The NAPA one brand new $70 unit won't change readings with vacuum applied.  That dude is still in my head, though.   I don't want to change the scaling and offset this sensor being off, but it looks like that's what I'm going to need to do.  I talked briefly with the guy that tuned my Forester and those were his initial thoughts, too, that the scaling was off.  I'm going to flash it to the same tune it's running now but with an offset of 10.33 instead of 7.99.

Edited February 9, 2021 by pwmin

[pwmin]

https://ecutek.zendesk.com/hc/en-gb/articles/207575639-BRZ-MAP-Sensor-Re-scaling

"The factory ECU uses an offset and multiplier function to calculate manifold pressure from sensor voltage, when the sensor is changed the output voltage will calculate the measured manifold pressure incorrectly. This may cause non start situations as well as DTC's and poor SD tuning."

this looks like fun:

 

Edited February 9, 2021 by pwmin

[pwmin]

I have read that it should be 100 kPa with key on, but atmospheric pressure at 5000 feet above sea level is around 84 kPa, which is what I'm getting.  I think maybe my issue was that the other 3 sensors were reading above the maximum kPa allowed by the PCM (160).  Other modified tunes I have had that increased to 200.  So, when the PCM saw that kPa was above the threshold, it would cause it to not start.  Only just after loading the bin it would start because it didn't have a "good" reading to go off of yet.  160 kPa is approximately 8.5 psi, which is more than I'm going to get w/ a 3.8 pulley and the mods I have.  I bet if I would run any of the bad sensors with a max setting of 200 that it would start.  The signal wire is reading 1.9V with key on, but it should be reading around 0 if I'm correct.

Edited February 9, 2021 by pwmin

[Robbie]

I had my 3800TPI absolutely F*CK with my head for months. Checked all vacuum lines, cleaned all kinds of sensors, plugs, and contact points. It would run fine while cold, but start surging at idle in Park while up to temp. It would also stall when going into reverse. I was SURE it was MAF-related...

Nope,

It was the g***amn o2 sensor. My brother was the one who figured it out, after going through many of the same steps I took.

I've never had any other car react so severely to a bad o2 sensor, ever. It was very blind-sighting. Exhaust never smelled particularly rich or lean, either.

Edited March 22, 2023 by Robbie

[pwmin]

3 new sensors bad out of the box.  Had to mess with the MAF settings in the bin file, too.