Need help with AC causing stalling
05-22-2011, 01:18 PM
#1
Need help with AC causing stalling I'm having a difficult time with the A/C causing the idle to overshoot when coming to a stop, and either causing a rolling idle or more often outright stalling the motor. I sometimes need to turn off the A/C to restart the motor and it'll idle fine, but if I blip the throttle it overshoots and dies.
Current calibration is attached. What do I need to log and how do I apply that data to the available tables to resolve this issue?
Thanks!
Jim
Current calibration is attached. What do I need to log and how do I apply that data to the available tables to resolve this issue?
Thanks!
Jim
05-22-2011, 08:07 PM
#6
11 Second Club
You still got that car?
I had that problem. From cruising down the street to stopping at a stoplight, my car had trouble finding idle w/AC engaged. About a third of the time, it'd stall. And it was worse on hotter days... you know how hot it gets here.
Now... I don't know if this will apply to an LS3, I've never worked on one. And I don't know what cam you've got.
My problem was a combination of the cam I was running and the erratic vacuum signal the cam caused the MAP sensor to report to the PCM. It wasn't out of range, so there was no code. But it wasn't playing nice, either. The MAP sensor was having trouble reporting changes in load (i.e., going from cruise to a stop) to the PCM because of the lumpy cam.
Using a short piece of fuel hose just the right size, I made an extension for the MAP sensor. It's like adding a 1" straw to the sensor, then plugging it back in. The small column of air it creates between the MAP sensor and the intake manifold smooths out abrupt changes in manifold pressure caused by some cams.
Dunno if that's worth a darn to ya, but it cured my ills.
-R
I had that problem. From cruising down the street to stopping at a stoplight, my car had trouble finding idle w/AC engaged. About a third of the time, it'd stall. And it was worse on hotter days... you know how hot it gets here.
Now... I don't know if this will apply to an LS3, I've never worked on one. And I don't know what cam you've got.
My problem was a combination of the cam I was running and the erratic vacuum signal the cam caused the MAP sensor to report to the PCM. It wasn't out of range, so there was no code. But it wasn't playing nice, either. The MAP sensor was having trouble reporting changes in load (i.e., going from cruise to a stop) to the PCM because of the lumpy cam.
Using a short piece of fuel hose just the right size, I made an extension for the MAP sensor. It's like adding a 1" straw to the sensor, then plugging it back in. The small column of air it creates between the MAP sensor and the intake manifold smooths out abrupt changes in manifold pressure caused by some cams.
Dunno if that's worth a darn to ya, but it cured my ills.
-R
How the hell are ya, Roger?Trending Topics
05-22-2011, 11:01 PM
#8
11 Second Club
Sure do. Just polish it and tell it how much I love it now.
Good. Left my desk behind. I'm a technician now (not for GM).
With a scope. Seeing the waveform graphically will be more useful if this is your problem. Harder to see in a scan unless you've got a good scanner that can sample data at a quick enough rate (like milliseconds). Most just don't sample fast/constantly enough.
MAP signal should be around a volt at idle, around 4.5v when no vac is present (engine @WOT or OFF), and anywhere between for cruising situations. When I'd let off the clutch, mine would bounce all over the joint between 1-3.5v, which would affect IGN timing, and at a stoplight, the car would get confused - (am I idling or am I cruising along?)... throw in air conditioning as an added load and it'd stall. That little standpipe trick (+ a new MAP sensor for good measure) worked good. That was... jeez, probably five years ago now. I ain't gonna tell ya it's perfect (is anything perfect once ya start modding?) because it will still stall if I cut the AC on and the engine isn't good 'n warmed up, but it was much less of a problem. I could let the wife loose with it on a hot day and not worry if it's going to stall on her at a stoplight.
Good. Left my desk behind. I'm a technician now (not for GM).
MAP signal should be around a volt at idle, around 4.5v when no vac is present (engine @WOT or OFF), and anywhere between for cruising situations. When I'd let off the clutch, mine would bounce all over the joint between 1-3.5v, which would affect IGN timing, and at a stoplight, the car would get confused - (am I idling or am I cruising along?)... throw in air conditioning as an added load and it'd stall. That little standpipe trick (+ a new MAP sensor for good measure) worked good. That was... jeez, probably five years ago now. I ain't gonna tell ya it's perfect (is anything perfect once ya start modding?) because it will still stall if I cut the AC on and the engine isn't good 'n warmed up, but it was much less of a problem. I could let the wife loose with it on a hot day and not worry if it's going to stall on her at a stoplight.
