ive got a 2001 z28 i recently fried the auto tranny in it, i had it rebuilt with a b&m shift kit and a new torque converter of course, now when the car shifts into second gear and sometimes third it retards the timing significantly and it will not put timing back in until you let out of the throttle. checked actual values on a generic scanner and it appeard that the map sensor was doing the opposite from what it was supposed to be doing i.e. the vaccum would increas if the throttle was opened and decrease when the throttle is closed. not sure if this is a problem with the scanner or what. there are no codes stored or current in the car, i checked to make sure that nothing was making contact while under hard acceleration couldnt find anything. just wondering if anyone has some input. was thinking it may be a knock sensor but it is rather inconsistent. was also thinking it may be a maf but stft and the ltft are still pretty close to normal. according to actual values the tps seems to be working correctly too.

 

Sounds like torque management is pulling timing during shifts. Do a search in this section on 'torque management' and you'll find lots of information. You say you have a scanner....do you have tuning software as well? If so you can eliminate/reduce torque management in your tune.

 

MAP sensor reports Manifold Absolute Pressure, not manifold vacuum. Barometric pressure minus manifold vacuum equals manifold absolute pressure.

(Sea level:101.3kPa)-(Idle ManVac:~70kPa)=(MAP:31.3kPa)

(800ft:98.5kPa)-(WOT ManVac:~2kPa)=(MAP:96.5kPa)

As for timing, you need to log the "EST" pids. I'd start with the GM.EST_RUN_DMA and the GM.EST_XMSN_DMA pids and compare them to the SAE.SPARKADV pid to see if you can verify where the timing is truly being pulled from. Then, go into the tune and see if there's anything you can do about it.

Also, check your connections on your trans. Make sure there's not anything gunked up between the contacts in the connectors.

 

that makes alot more sense, the scanner was reading in inHg which is vaccum when it should have been reading pressure instead. thanks for the info.

 

Inches of mercury (inHg) is a measurement of pressure just like kilopascals (kPa). Look under pressure here:

http://www.pmel.org/unitconv.htm

70kPa is equal to ~20.7inHg (varies based on temperature).