Map sensor reading low

[Chrisv23]

Hi my map sensor is reading low. My map is at 12 psi and my baro is at 14 psi. My truck feel very sluggish and barely goes over a hill I changed ecm and map sensor still read the same,I changed map sensor and still read the same,I checked the wiring and the volts and it seem good. I also returned to stock tune and the map sensor still read 12 psi. Does someone have had this problem before? This is all on key on engine off

 

[JoshH]

What year and engine is your truck?

 

[Chrisv23]

It’s a 2008 gmc serria slt and engine is a lmm Duramax

 

[JoshH]

I moved it out of the intro forum to the LMM forum for you.

The problem is either going to be a wiring/connection issue, ECM issue, or sensor issue. Since you have already changed the ECM and sensor, it's safe to assume you're dealing with a wiring issue. You will need to verify correct continuity on all the wires from the connector at the ECM to the connector on the sensor and make sure you don't have any shorts anywhere.

 

[Chrisv23]

I checked the volts. The 5v ref is 5.02 volts the signal is 1.000 volts and the ground is 5.00 volts. This is key on engine off

 

[2004LB7]

Ground at 5 volts?

 

[Chrisv23]

Yes I use the map 5v ref wire as my red and ground wire as black

 

[Ron Nielson]

See the attachments. Might your ground wire be shorted to the 5V ref?

 

[Chrisv23]

How many volts should I see on ground wire

 

[2004LB7]

5 volt reference should as you tested be at 5 volts. Signal should be 0 unless there is a sensor attached sending a signal which will change depending on the signal. And ground should be 0 volts. Ground should also have a low resistance to battery ground or other good reference ground. You should be testing the voltage with black on a group point and prob the wires with the red. Also a good idea to disconnect the connector on the ecm side and prob the continuity through the whole harness, connector to connector pins, wire to wire and wire to ground to look for any wire to wore shorts or wire to ground shorts or breaks in any of the wires. Load testing the wires too to see if there is any corrosion or loose connections

 

[Chrisv23]

I checked the ground wire again but black to battery ground and red to ground wire and it read close to my battery volts

 

[2004LB7]

Something is wrong. Should be zero volts

 

[Chrisv23]

So I was doing it wrong sorry. I got 13.5mv on ground is this normal

 

[2004LB7]

That's probably fine. How many ohms?

 

[Chrisv23]

It turns out everything was good I was reading absolute map instead of the map2 on the pids but I still have sluggish acceleration I noticed my calc load drops when accelerating is this normal?
It would go to 22% then go down then back up

 

[JoshH]

What is your MAF reading?

 

[Chrisv23]

At idle I’m seeing 38 g/s

 

[juddski88]

There's no codes to lead you in any direction?

 

[Chrisv23]

No codes i also notice when driving my first gear will rev up a lil to try to get to 15 mph but I a drive slow it will go to 1/2 at 10 mph. It feels like I’m not getting enough fuel

 

[Chrisv23]

at 5 and 6 gear the truck feels normal it’s fast but at 1/2/3 gear it feels slow
1 gear rev a lil up to 15 mph. if I drive slow it will shift 10mph
2 gear shift around 20mph
3 gear barely hit 28 like it want to get up to 30mph
4 gear will hold until to get to 50 mph but will shift around 48