To borrow a phrase from Rossane Rosannadanna, "If its not one thing its another". My scan gauge is reporting 14 psi of boost at idle. The XZT is totally disconnected from MAP sensor. I recently installed heater core and had batteries disconnected for several days. Whats up with this?

Its reading barometric pressure.

The XZT is totally disconnected from MAP sensor.

Remove the Quadzilla XZT from the truck and rehook the MAP sensor back to the ECM stock lead. If the value is still off then it might be a bad MAP sensor. If removing the XZT from the truck fixes it then the boost fooler is bad in the XZT.

I recently installed heater core and had batteries disconnected for several days.

Disconnecting the batteries does only one thing. It wipes out the APPS sensor calibration. As for resetting error codes or software it will not do that. To reset the software you only need to turn the key off and back on because the ECM goes through a full reboot process.

Its reading barometric pressure.

Absoloutly. The MAP sensor reports ambient pressure which is 14.7 on a standard day.

Well now, that's within a few tenths of what the scan gauge is reporting. So, because the scan gauge is reporting the same boost value with XZT as it does without XZT, the boost fooler must not be working.

I would think so. I never used my SGII for boost because it reads in absolute.

I didn't even know my scangauge would read boost.

My bad... :doh:I've got a old ScanGauge II my software doesn't even report the MAP correctly. But from what Pepsi1971Ocean told me there is a a boost gauge founction that does report true boost numbers in PSI not PSIa. But the MAP would be PSIa and ~14.x PSIa is about right for 0 PSI.

My bad... I've got a old ScanGauge II my software doesn't even report the MAP correctly. But from what Pepsi1971Ocean told me there is a a boost gauge founction that does report true boost numbers in PSI not PSIa. But the MAP would be PSIa and ~14.x PSIa is about right for 0 PSI.

I guess I have the old software too, no boost just MAP.

Ah ha! Michael, that gave me an idea. I went through the menu on the SG and there is an option that lets you choose whether to read MAP or boost. Even though it was on boost, I thought maybe it needed to be reset. I changed it to MAP, backed out of the menu, then changed it back to boost. It now appears to be reading actual boost. I think we all learned on this one!