Goes extremely lean with fans on

[gunslinger]

Got it running pretty good, but when the fans turn on, it goes extremely lean.
I've verified fuel pressure and volume, pump drawing 7A, maxed the fan idle comp, tweaked the VE table, nothing seems to make a difference.
Voltage at alternator is 14V when it's acting up, so pump voltage doesn't seem to be a problem.

What am I missing???

Thanks,

Eric

 

[EricM]

Your map reading goes to zero when the fan comes on, so you have a wiring issue. Is your map sensor powered and grounded from the ECM? Also how is your fan setup grounded?

 

[gunslinger]

Grounds are factory.
I did the MAP reference voltage modification, but nothing to the MAP ground.
It all makes sense. I'll run a battery ground for the MAP ckt and see if it fixes it.

Thanks!

Eric

 

[EricM]

If using dual fans, the factory grounding can also cause problems. Try the map ground first and see if that does it.

 

[gunslinger]

That got it, Eric.
I ran a ground for the fans and the MAP sensor right to the battery.
I also extended and cleaned the other ECM grounds.
It's running great again, and there's no more weird electrical load related tune changes, and I can't even tell when the fans come on now.

Thanks for the support!

Eric