Timing advance - a/c compressor.

[Rockettman]

Sorry, it's not my Marauder, but my '91 Mustang; but you guys are the best, so I thought I'd pick your brains with this one. I'm at a standstill.

So when my a/c compressor comes on (with the defrost or a/c), it drags down the engine rpm - it doesn't bump it up in rpm like it's supposed to. Last night with the wipers/defrost/lights/etc. going, the lower rpms were troublesome!

Where should I start to investigate? What do I look at first, second, third??

Don't even know where to start, as I thought it was taken care of by the ECM.

Thanks.

[RoyLPita]

Stock alternator?

[RacerX]

Hmmmm... Out of curiosity, see if it does it when you roll both windows down and turn the headlights on at the same time. Unless you changed your tune when it started happening, it's not PCM related.

[Rockettman]

Stock alternator?
No. 3G upgrade. 130amps (not the stock 75 amps).

Hmmmm... Out of curiosity, see if it does it when you roll both windows down and turn the headlights on at the same time. Unless you changed your tune when it started happening, it's not PCM related.
Can't really change the "tune" on these. Only changing a "chip" does that in these. That has not been changed.
Lots of accessories on at the same time (lights/defrost/wipers). That of course, was the purpose of the alternator upgrade. To handle all this.

[RacerX]

Doh! 91... Battery? If it just started doing it recently and you haven't changed anything, battery or alternator.... I dunno, just seeing what sticks...

Btw, I believe when you turn on the A/C, the pcm allows a little more air to bypass the tb to raise rpms, not adding timing.

[Vortech347]

Moates/Quarter Horse.

Have fun with full tuning ability.

I love mine. :)