LB7 Possible sensor issues

[Harshman]

Just finished a complete rebuild of engine and trans. I am seeing 7 psi boost with key on or with engine at idle. Unplug it and see the same thing. I had a new sensor laying here that I thought was correct for the truck. It reads 14 psi. I have 5 volts, I have ground. Truck does run good. It does show about 28 psi when on it. This isn't normal is it? Also with key on the MAF is reading 3.39 g/s.

 

[Ron Nielson]

What tool are you using to get those readings?

Our trucks use 5V for all of the engine sensors, and a ground, and sometimes a return from the sensor. MAP measures pressure at the intake, MAF measures density of the charge going to the turbo. BARO measures atmospheric pressure. Boost is a calculated number, basically MAP minus BARO.

Key on engine off, MAF should read about 40 gm/sec if the EGR valve is closed (or not present on the engine). MAP and BARO theoretically should read the same, but I note that mine are a little different from each other. Your truck has an external BARO sensor.

 

[DAVe3283]

Key On Engine Off the MAF should be 0, or close to it. I think the value the OP saw is fine. Idling should be about 40 g/sec.

Depending on the scan tool, some display MAP but call it boost. At sea level, MAP would be around 14.7 PSI.

Sent from my CPH2655 using Tapatalk

 

[Ron Nielson]

Key on engine off, MAF should read about 40 gm/sec if the EGR valve is closed

OOPS!
Thanks for the correction.

 

[Harshman]

 

[Harshman]

Also with the same tune in it that was in it before the rebuild it is hard to start most of the time. But will run and drive great. With Rob's SAC45 tune it starts fine except it will fire and stall a time or two. Don't know if that is from the lower idle speed. Runs good with this tune also.