Help Please. PCM not seeing MAP output.
Thread Starter
Drifting
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From: Ok! So you don't believe in conspiracies, but will you acknowledge the possibility of there being coordinated activities in secret places? Texas
Help Please. PCM not seeing MAP output.
Had to do the 2 Bar MAP and OS conversion on my 1998 C5. Used 2 Bar MAP part#12569241 and HPTuners' 2Bar OS. My MAP sensor will not read using the following test method:
Disconnect MAP from intake, but keep it plugged in
Connect HPTuners Scanner to OBD2 port
Connect Mitey Vac to MAP hose barb
Turn ignition key to ON position
Connect and start scanning with HPTuners
Pull vaccum or apply pressure on MAP sensor by pumping Mitey Vac
With multimeter connected to the middle "MAP signal out" wire at splice point between the MAP sensor pigtail and the car's original MAP sensor wiring, the voltage sweeps (0-5v) as I change the MAP sensor pressure with the Mitey Vac. It never registers on the HPTuners scanner. I verified that the sensor has 5v power. I don't know how to test the ground, but at the connection point to the car the MAP seems to be working properly.
Is it possible that my PCM is bad?
What else should I be checking?
Thank you for any help!
I started this testing because while scanning the car I noticed that while driving the MAP reads 65kpa.
Disconnect MAP from intake, but keep it plugged in
Connect HPTuners Scanner to OBD2 port
Connect Mitey Vac to MAP hose barb
Turn ignition key to ON position
Connect and start scanning with HPTuners
Pull vaccum or apply pressure on MAP sensor by pumping Mitey Vac
With multimeter connected to the middle "MAP signal out" wire at splice point between the MAP sensor pigtail and the car's original MAP sensor wiring, the voltage sweeps (0-5v) as I change the MAP sensor pressure with the Mitey Vac. It never registers on the HPTuners scanner. I verified that the sensor has 5v power. I don't know how to test the ground, but at the connection point to the car the MAP seems to be working properly.
Is it possible that my PCM is bad?
What else should I be checking?
Thank you for any help!
I started this testing because while scanning the car I noticed that while driving the MAP reads 65kpa.
Tech Contributor
Joined: Dec 1999
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From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Had to do the 2 Bar MAP and OS conversion on my 1998 C5. Used 2 Bar MAP part#12569241 and HPTuners' 2Bar OS. My MAP sensor will not read using the following test method:
Disconnect MAP from intake, but keep it plugged in
Connect HPTuners Scanner to OBD2 port
Connect Mitey Vac to MAP hose barb
Turn ignition key to ON position
Connect and start scanning with HPTuners
Pull vaccum or apply pressure on MAP sensor by pumping Mitey Vac
With multimeter connected to the middle "MAP signal out" wire at splice point between the MAP sensor pigtail and the car's original MAP sensor wiring, the voltage sweeps (0-5v) as I change the MAP sensor pressure with the Mitey Vac. It never registers on the HPTuners scanner. I verified that the sensor has 5v power. I don't know how to test the ground, but at the connection point to the car the MAP seems to be working properly.
Is it possible that my PCM is bad?
What else should I be checking?
Thank you for any help!
I started this testing because while scanning the car I noticed that while driving the MAP reads 65kpa.
Disconnect MAP from intake, but keep it plugged in
Connect HPTuners Scanner to OBD2 port
Connect Mitey Vac to MAP hose barb
Turn ignition key to ON position
Connect and start scanning with HPTuners
Pull vaccum or apply pressure on MAP sensor by pumping Mitey Vac
With multimeter connected to the middle "MAP signal out" wire at splice point between the MAP sensor pigtail and the car's original MAP sensor wiring, the voltage sweeps (0-5v) as I change the MAP sensor pressure with the Mitey Vac. It never registers on the HPTuners scanner. I verified that the sensor has 5v power. I don't know how to test the ground, but at the connection point to the car the MAP seems to be working properly.
Is it possible that my PCM is bad?
What else should I be checking?
Thank you for any help!
I started this testing because while scanning the car I noticed that while driving the MAP reads 65kpa.
I will have to break ouyt the 98 schematics to get down to the nity gritty details in the MAP circuit.
Bill
Race Director
Joined: Apr 2007
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From: South Western Ontario
Did you verify that the 5V signal is making it to the PCM connector? Measure from the sensor ground wire and the sensor signal wires at the PCM. You could also ohm meter between the PCM connector and the MAP sensor connector.
As for the ground. The ground wire is fine if you measured from the sensor ground wire to the signal and +5V wires and got the proper readings.
As for the ground. The ground wire is fine if you measured from the sensor ground wire to the signal and +5V wires and got the proper readings.
Thread Starter
Drifting
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From: Ok! So you don't believe in conspiracies, but will you acknowledge the possibility of there being coordinated activities in secret places? Texas
I appreciate the responses. I have not verified the signal at the PCM. Sounds like that may be next on my list.
Thread Starter
Drifting
Joined: Feb 2006
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From: Ok! So you don't believe in conspiracies, but will you acknowledge the possibility of there being coordinated activities in secret places? Texas
Hello Guys. I did more testing today and verified that I do have MAP voltage at PCM. I found a MAP Voltage PID and reverified after probing the wire at the PCM connector. The MAP PID still doesn't read in the scanner though. If I scan MAP Vaccum it reads, but inversely. Meaning as I increase actual pressure the MAP Vaccum decreases as voltage increases. So wiring is good. Could my OS be corrupt? I reverted to my old 1 bar OS and the MAP reads V/kpa 0.14v/38.2kpa and 4.78v/82.2kpa. When I go back to the 2bar I can scan the MAP voltage, but can not read the MAP kpa.
Last edited by Mister Peebody; Mar 26, 2013 at 11:46 PM.
Safety Car
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Likes: 520
From: Da U.P.
Hello Guys. I did more testing today and verified that I do have MAP voltage at PCM. I found a MAP Voltage PID and reverified after probing the wire at the PCM connector. The MAP PID still doesn't read in the scanner though. If I scan MAP Vaccum it reads, but inversely. Meaning as I increase actual pressure the MAP Vaccum decreases as voltage increases.
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Thread Starter
Drifting
Joined: Feb 2006
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From: Ok! So you don't believe in conspiracies, but will you acknowledge the possibility of there being coordinated activities in secret places? Texas
Okay. I am sweeping the pressure with the sensor connected to a hand pump. While scanning with HPTuners I can see the MAP voltage sweeping as it should when I increase pressure the voltage increases. When I pull vacuum on the sensor the MAP voltage decreases, at no time do I see the actual MAP kpa move unless I go back to my old OS then the MAP reads kpa but 4.8v only yield about 88 kpa. This is all being done with a 2bar sensor installed.
Safety Car
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From: Da U.P.
Well it's definitely not a wiring issue then. I wasn't seeing how it could have been in the first place as you're using all GM sensors, aren't you? Are you using the correct PID (or whatever HPTuners calls them)? I know for knock on EFILive, there are a few different ones to choose from. Same for MAF. I think MAP is all the same on EFILive, but I wonder if HPTuners is different? Is there a tutorial on their forums that mentions this? On EFILive there's a MAP scaler which is where you tell the OS if you have a 1 bar, 2 bar, etc. Even if you missed that, the KPA value should still be sweeping. And the 2 bar does sweep on the original OS, correct? 88kpa at 4.8V seems off unless they read higher than 5V. If it's linear, then 5.0V corresponds with 91.6 kpa where they're supposed to read to 105 kpa according to the maps in EFILive.
Thread Starter
Drifting
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From: Ok! So you don't believe in conspiracies, but will you acknowledge the possibility of there being coordinated activities in secret places? Texas
I am using a GM 2bar sensor and yes it does sweep on the original OS. On the 2bar OS the voltage sweeps, but the pressure won't. I have tried all that I know to do as far as setting up PIDs.
Safety Car
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From: Da U.P.
When you're observing the MAP PID on the new OS, does it require that you monitor a different PID than your old OS? Have you tried firing the car on the new OS or did its not running lead you down this path?
Thread Starter
Drifting
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From: Ok! So you don't believe in conspiracies, but will you acknowledge the possibility of there being coordinated activities in secret places? Texas
Scanning for tuning purposes revealed that the car always registers 65kpa. My car, being a 1998, supposedly uses thes same PID for both OSs. On newer computers there is a seperate specific PID for 2bar MAP.
Safety Car
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From: Da U.P.
Have you tried the other one for shjts and giggles? I recently had a similar problem, my car (Corolla) kept idling at atmospheric, but it turns out I'd knocked my MAP sensor's vacuum line loose when I was monkeying around with the intercooler pipes. Is that OS compatible with your year PCM? When you're logging and observing a table based upon your VE or spark (whichever actually uses MAP and not MAF), is that where the MAP remains constant? Or is it only when you're observing that PID by itself and driving?
Thread Starter
Drifting
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From: Ok! So you don't believe in conspiracies, but will you acknowledge the possibility of there being coordinated activities in secret places? Texas
Have you tried the other one for shjts and giggles? I recently had a similar problem, my car (Corolla) kept idling at atmospheric, but it turns out I'd knocked my MAP sensor's vacuum line loose when I was monkeying around with the intercooler pipes. Is that OS compatible with your year PCM? When you're logging and observing a table based upon your VE or spark (whichever actually uses MAP and not MAF), is that where the MAP remains constant? Or is it only when you're observing that PID by itself and driving?
When you say "tried the other one" are you meaning try another MAP sensor?
The HPTuners 2 Bar OS is compatible with my year's PCM.
When I scan the VE vs MAP it only fills the 65kpa row at all of the various RPM columns, so the MAP remains constant when scanning "xxx vs MAP" and when scanning MAP PID only.
Next question, Is the fact that the MAP works with the old OS, but not the new OS telling?
I have scans, but sounds like you have EFILive
Safety Car
Joined: Jan 2012
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From: Da U.P.
Yeah, I don't have HPT, but if it's free for download and straightforward I might give it a shot. I do know that when my logs stay in 1 cell, it's an indication that I've selected the wrong PID. For it to be stuck at 65kpa though, that's an odd value as it's a part throttle acceleration value. Idle should be closer to 30-40 IIRC. I think I was getting at MAP sensors, have you gotten the 1 bar MAP to operate correctly with the new OS? If you're boosted, I'd just give it a whack in your driveway and see if it'll idle right with the single bar MAP. Also, despite the logs reading wonky, will the car run with the 2 bar?
Thread Starter
Drifting
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From: Ok! So you don't believe in conspiracies, but will you acknowledge the possibility of there being coordinated activities in secret places? Texas
Car runs well with the 2 bar OS. No bad behavior whatsoever. I have not gone much over 20% throttle, but AFR remains good. The problem is, I can't scan enough for my tuner to to see what may be "off". I am on a starter tune now. I have not put the 1 bar MAP sensor back in for testing.
Thread Starter
Drifting
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From: Ok! So you don't believe in conspiracies, but will you acknowledge the possibility of there being coordinated activities in secret places? Texas
But if the MAP value that the car sees is a constant 65kpa, it would run fine, right?