Unique Issue while Scanning - Solve it and be my Hero!

[Mister Peebody]

My car and ECU are 1998 models. My engine is a 2004 LS6 with cam and blower. I have upgraded my OS to the HPTuners Custom 2 Bar OS and I have installed a 2 bar MAP. Car has OBD2 gages in it so I can read many of the ECU's parameters without the scanner.
Now my issue: Car runs fine. Idles fine at about 13.5:1 afr, MAP about 65kpa, UNTIL I plug in and attempt to scan the car. When the car is plugged in to the laptop to scan car is not drivable, idles rough at about 10.5:1 afr, and MAP reads 102 to 105 kpa. While plugged in to scanner any throttle input makes the car stumble. It smokes and fouls plugs. It is repeatable over and over. I have already erased the "vcm scanner.cfg" file and let it load a new one, but the issue persists. It's like the scanner is giving the car commands seperate from the tune. I've looked and the VCM tools are off.

Has anyone else had or heard of this issue?

[ingsteve]

check ground connections...do not use 12v car power supply for the laptop while you are scanning

[Mister Peebody]

Car is on it's battery power or charger and laptop is on it's own battery power.

[Bill@HPTuners]

How are the "obd2 gauges" getting their data?

[planethax]

Can you disconnect your OBD2 Gauges then rescan and check.

[Mister Peebody]

The OBD2 gauges get their data thru the OBD2 port. I can't be connected to the scanner and the gauges at the same time. They are the Aeroforce Interceptor gauges. I connect the scanner, car runs bad. I disconnect the scanner and plug in the gauges, car runs good.

[c.u]

Hows it run when you have nothing plug into the obd2 port.

[Mister Peebody]

Hows it run when you have nothing plug into the obd2 port.

Like garbage! It runs with nothing connected just like it runs with the scanner connected. Thank you for asking. I had not checked that.

[Mister Peebody]

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. 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.

[Mister Peebody]

ttt

[Mister Peebody]

Good day

[Bill@HPTuners]

No idea what you are trying to do to be honest.

The manifold air pressure(SAE) pid is the one you need to log.

[Mister Peebody]

I am trying to tune my car with a 2bar OS for the 1998 Corvette. With the 2bar OS loaded the MAP always reads 65kpa. Again with the 2bar OS loaded and my 2bar MAP sensor attached to a Mitey Vac, the kpa stays 65 but the MAP voltage sweeps as it should. When I revert to the old original OS, the MAP reading fluctuates as it should, but the scaling is incorrect, as I suspect it should be since it is a 2bar sensor. Could it be a corrupt 2bar OS?

[mowton]

Like garbage! It runs with nothing connected just like it runs with the scanner connected. Thank you for asking. I had not checked that.

Then I would say the guage setup/wiring to OBD2 connector is providing some signal (voltage or ground I would think) that the PCM needs that isn't connected. Hooking up the guages seems to "complete the circuit" needed to make the PCM operate ok.

Check the PCM wiring.

sorry can't be anymore help

Ed M

[Bill@HPTuners]

As stated the pid is working properly, not sure how else to explain it.

[Mister Peebody]

Then I would say the guage setup/wiring to OBD2 connector is providing some signal (voltage or ground I would think) that the PCM needs that isn't connected. Hooking up the guages seems to "complete the circuit" needed to make the PCM operate ok.

Check the PCM wiring.

sorry can't be anymore help

Ed M

Ok, I found the issue with the OBD2 gages.
Question: Is the fact that it works with the original OS, but not the 2bar OS, important to this troubleshooting attempt?

[Mister Peebody]

As stated the pid is working properly, not sure how else to explain it.

So when you say, "the pid is working properly", does that mean the 65kpa is real?
Will you help me understand how MAP voltage sweeps with pressure change from Mitey-Vac, but not the MAP kpa reading?

Sorry if I seem dim, but in this situation I am since I am not knowledgable of the inner workings of the PCM. I am not being argumentative. I am seeking information.

Thank you for your help.

[Mister Peebody]

All good now. Thanks.

[mowton]

All good now. Thanks.

So after all the above....what was it and how did you fix it?

Enquiring Hero's want to know

Ed M

[Mister Peebody]

When I installed the 2bar MAP I tapped into the middle 5volt signal wire and ran it to the 5v input on my OBD2 gauges to supply boost reading. Looks like I formed some type of loop that caused the MAP to not read properly since there was a 2nd ground wire involved also. I disconnected that signal wire from the gauges.
Now I can't seem to get my histograms that use the MAP sensor reranged. They only read up to 105kpa. I read that the histogram range should mimic the range of the VE table of the OS, but it does not. The 2 bar OS VE table's MAP range is 15kpa-210kpa, but the scanner histogram MAP range is 15kpa-105kpa. How do I fix it? Thank you in advance.