dmcrx787

I have an FD alternator in an S4, been there for years.

The voltage drops once the clutch is pressed if the rpms drop below 1400 rpm. Voltage drops to 13.0 volts.

This appears to have dire consequences to the output of my Walbro Fuel pump, as engine either runs extremely lean or dies.
It used to be 1200 rpm, so idle is set at 1400, but now even then it won't hold.
Blip the throttle, and it holds a perfect 1400 rpm at 14.2 volts

I'm going to check the wiring tonight, as I am not sure if I wired the S terminal to constant 12v+ (I installed this before the latest FAQ was even posted in 2005, lol)
Could this issue be related to the S wiring? Or does that only affect voltage leakage when off? (Car stays on a battery maintainer, so I wouldn't know)

Obviously this is not my daily driver. I'm just tired of remembering to blip the throttle every time I come to a stop, and I don't want to raise the idle. (I'd like to lower it)

dmcrx787

Check wiring.
R and B are correct. Still need to confirm L. Does L affect alternator performance? Or is it just an output to the CPU alt warning relay?
L shows a few millivolts with key to on, and while running, so I'm guessing the voltage regulator circuit is dead. I always have 14.2-14.4 volts at all rpms including idle or 12v at idle. Shouldn't it vary as the battery builds charge?

dmcrx787

Removed alternator, passed bench test.
B+ voltage 14.97
Ripple 0.3
Lamp on voltage 0.72v
lamp off voltage 13.78v.

Car idles at -31 on SAFC at 14.4v
-11 at 12v, which is where it drops if I press the clutch.
Raise the rpm past 2500 and it settles back to 14.4v at 1400 rpm.

smikels

I might not be able to help you, but here are a couple questions. Are you running stock wiring to the fuel pump? If so have you checked the actual voltage at the fuel pump? I would suggest maybe a fuel pump rewire. I did this on my car mainly just because I knew I would be throwing more fuel at my upgrades. Before then I would see only around 10 volt at the pump due to stock degraded wiring. There are lots of threads on fuel pump rewiring. If you can't find something on it shout out though.

Ohh and as far as 13 volts at idle that is not to bad IMO. I am running at Aeromotive 340 pump and have no issues even when I was on a stock alternator. I also had a walbro in before that with no issues either like the leaning out you are talking about. I have an ford tempo alternator in it now.

dmcrx787

Fuel pump is wired with big wire through a relay.

Voltage is dropping to 12v (battery voltage) at idle.

Emmissions and cold start have been removed, tb mod with secondaties removed.


​​​​​​I turned the BAC in from 7 turns out to 3 and that seems to have helped with the stalling. It still stumbles and runs lean if the voltage drops tho

dmcrx787

Dual alternator pulley is 2 5/8 od. I'm looking for a smaller, faster pulley.


​Adjusted BAC from 7 turns out to 3 turns out.

Now it just stumbles and runs lean at 12v at idle, til I blip the throttle. Then locks back on 14.2v or so and 13:1 afr happy idle.

Voltage only seems to have 2 positions - 12v or 14.2v