Serious lag...
Moderator
Joined: 01-23-2009
Posts: 26,448
From: Fredericksburg,VA
I was referring to the gas pedal part; lag then let off then all is good.
The instructions that come with the GMTU show how to rotate the sensor but, that requires a GM technician to look at directions. LOL (Lot's Of Luck)
The instructions that come with the GMTU show how to rotate the sensor but, that requires a GM technician to look at directions. LOL (Lot's Of Luck)
Senior Member
Joined: 12-05-2014
Posts: 3,330
From: Northern Ohio
The current thinking is to always use pigtails to install the MAPs, but the dealer may not have gotten the memo, and crimped per directions. Apparently, tiny changes in resistance as those connections age cause trouble. The fix is to make new connections, and solder, grease, and shrink tube.
Moderator
Joined: 01-23-2009
Posts: 26,448
From: Fredericksburg,VA
Since it is a relatively new installation (6 months) do you think corrosion caused by age would be a cause? The lowet MAP sensor is a problem if the installer didn't bother to read the instructions about rotating the connector out of harms way. It involves removing the registration tab with a knife or file.
Platinum Member
Joined: 12-06-2009
Posts: 11,718
From: Alabama
Actually Don, if the tab is removed and the Tmap sensor installed, the wire plugin will point directly to the compressor.
There is no mention of turning the sensor in the original GMTU instructions.
Turning it may have been mentioned in a later TSB.
There is no mention of turning the sensor in the original GMTU instructions.
Turning it may have been mentioned in a later TSB.
Moderator
Joined: 05-01-2014
Posts: 8,499
From: California
There is a tab on the sensor itself that must be trimmed off in order to install it and have it seal.
Then there is a bar on the lower charge pipe that prevents the sensor from rotating. If you don't trim this, you can rotate 180 degrees. I trimmed that also to rotate it slightly, about 45 degrees. It's all in the how-to that I linked to above.
It may be that the sensor wasn't trimmed, and so it isn't sealing.
Then there is a bar on the lower charge pipe that prevents the sensor from rotating. If you don't trim this, you can rotate 180 degrees. I trimmed that also to rotate it slightly, about 45 degrees. It's all in the how-to that I linked to above.
It may be that the sensor wasn't trimmed, and so it isn't sealing.
Moderator
Joined: 01-23-2009
Posts: 26,448
From: Fredericksburg,VA
Maybe we should consider that it was not a GM dealer that installed the kit am=nd maybe whoever did did not replace the Tmap or even did the firmware upgrade correctly. The last discussion about the GMTU I remember is that A.) GM does not sell it anymore and B.) they would not install a third party item.
Senior Member
Joined: 12-05-2014
Posts: 3,330
From: Northern Ohio
Possible the lower map sensor was not installed correctly. But…
What octane fuel have you been using? (As you know, 91 or better is mandatory with the GMTU.) Before taking it back, I would try some racing fuel and see if it still does it.
Possible that due to a more aggressive spark advance, an accumulation of carbon deposits is causing a knock. When that happens, knock sensor signal tells the ECM to roll back the timing.
I have a GM car (not turbo) for which 91 is “recommended.” If I feed it 87, I get the hesitation similar to what you describe. With 93, no problem.
What octane fuel have you been using? (As you know, 91 or better is mandatory with the GMTU.) Before taking it back, I would try some racing fuel and see if it still does it.
Possible that due to a more aggressive spark advance, an accumulation of carbon deposits is causing a knock. When that happens, knock sensor signal tells the ECM to roll back the timing.
I have a GM car (not turbo) for which 91 is “recommended.” If I feed it 87, I get the hesitation similar to what you describe. With 93, no problem.
