Reduced Power at Half Throttle 5psi Boost - Turbo LS2 E40 Trailblazer SS 2 bar MAP

[GMBlair]

We're in the process of calibrating a turbo Trailblazer SS. It works great in vacuum and at wide open throttle, with both 5 and 8 lbs of boost. The problem is around the 55% throttle area. Watching the log, it happens at about half throttle when the MAP is 20ish psi. At this point the MAP voltage peaks at 5 volts. The PCM puts up with it for about a half to 3/4 of a second then goes into reduced power mode. It has a LSJ 2 bar MAP sensor with proper scalers. Watching the scan tool, the PCM is seeing a positive pressure (130ish kpa). I'm stumped by how a 2 bar MAP is maxing out at 5lbs of boost when it should handle 3 times the boost, or another 70kpa... any help is greatly appreciated.

P.S. There is NO knock activity nor are the fuel trims outside of the 25% (correct me if I'm wrong) areas which trigger this reaction. The fuel trims are -17ish, but a couple minutes after this post that will be fixed.

[5.7ute]

Does it read the correct map pressure key on engine off. To me it sounds like the sensor is faulty. Can you post up a log with this occuring?

[swingtan]

+1 for faulty sensor
+1 for posting a log

Simon

[GMBlair]

Here is the log. The MAP is a little off, at 15.1 psi baro, the weather website shows 29.77 inhg. I am suspicious of the sensor as well. It does look like it is off, with 2.5v being around 8 psi. That looks like a 1 bar to me (or maybe the pressure/voltage relationship is not linear). Think we got a 1 bar instead of a 2? On a 2 bar it should read 15ish psi at 2.5v, shouldn't it? If this is the case, does anyone know a part number for the new style 2 bar MAP?

Thanks

[swingtan]

Are you sure that that is not just the boost coming in, then you're getting "reduced power mode" and it cuts the boost?

Take a look at C0309 for the air flow and C0404 for the max MAP values.

Also look at C0803, C0805 and C0806. All of these will set "reduced power mode" if the values are exceeded.

Simon

[GMBlair]

C0309 is maxed at 512 from the factory. After checking and adjusting the others, it's perfectly driveable again. Now it's time to clean up the calibration. Many thanks for the help!

[swingtan]

Great news. Glad to help.

Simon.

[mowton]

Resurrecting this old thread for some help. Here is the link to my thread in Gen IV -- http://forum.efilive.com/showthread....0-lb-injectors. Had a P0106 code, but didn't think that set reduced power (per Gearchatter.com)?

Have a copy of the tune and log where the dropout occurs in the linked thread. Only difference is mine ocurrs at WOT.

Haven't gotten back to the car yet but any help would be appreciated.

Ed M

Update -- after reading this thread and checking out my tune in this car, I think changing C0405 from 70C to 125C will fix my problem. Will try this when I get back to the shop next week. Thanks for the info

[mowton]

Resurrecting this old thread for some help. Here is the link to my thread in Gen IV -- http://forum.efilive.com/showthread....0-lb-injectors. Had a P0106 code, but didn't think that set reduced power (per Gearchatter.com)?

Have a copy of the tune and log where the dropout occurs in the linked thread. Only difference is mine ocurrs at WOT.

Haven't gotten back to the car yet but any help would be appreciated.

Ed M

Update -- after reading this thread and checking out my tune in this car, I think changing C0405 from 70C to 125C will fix my problem. Will try this when I get back to the shop next week. Thanks for the info

Thanks for the thread...great info. C0405 fixed our problem