Higher amp alternator?
 

I have a 140amp right now that's pushing out 14.6 volts at the alternator terminal. After about 5 minutes the fuel pressure gauge fluctuates. And when I turn everything on, the volts drop to 11.5. The car has a FAST EFI, electric fan, electric water pump, electric fuel pump, Halo and LED lights all around (with correct conversion), a Gear Vendors OD, electric windows, and a defroster fan. Am calling Powermaster tomorrow but want to hear what ya'll are running.

Is after five minutes of running when the car really idles down? What speed is your alternator running at (pulley ratio)? More food for thought. Look into all your accesory amperage draws and add them up. It might be surprising how much power all those things need. This is where some guys are getting into pwm for fans and fuel pumps, it does cut down on power usage.

How big is your charge wire, more times than not I see too small of a charge wire that results in low voltage output to the battery.

I'm with Tim ---- might be too light of a gauge of charge wire --- BUT --- Always the big Butt!!

CHECK YOUR GROUND circuit as well!! Too light of a gauge wire -- or inadequate ground circuit will also be a problem with voltage drop and NOBODY ever thinks to check that side....


Grounded motor to chassis -- to body -- to battery....

Ok, it's reading 14.2 at the alternator and 13.9 at the battery in the trunk. I just bought another 4 gauge wire and ran it from the alt to the starter. The ground strap is a flat, metal 4 gauge with a clean ground to the frame. With the car idling at 800rpm and everything on, my laptop says 10.2 and my fuel pressure gauge is still fluctuating.
Should I get a regular 4 gauge round wire for the alt ground? Also, would it be better to run that red 4 gauge wire from the alternator straight to the battery in the trunk? Thanks again.

I've used the starter as a junction --- should be okay....


I'd check the body to chassis ground --- assuming you have an intank pump.... might be that your tank isn't making good ground

I assume this is a 1-wire Alternator? That's why I will run a 3-wire and have the sensing line read voltage right where all the accessories create the voltage drop.


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Pump is external and has a good ground.
Tried a different ground wire and different ground spot on the alternator and am getting the same readings. The guy at Powermaster said this alt was sufficient. In fact I'm spinning it a little higher bc I have a 7 1/2" crank pulley and a 2" alt pulley. Oh and this is a GM 3 wire.

GM 3-wire, the like the others said, ensure you have good grounds. Engine block to frame & engine block to body, battery to frame & battery to body.

Battery to body? Even if I have a unibody car? Also, since the alternator is working but it’s not sending the right volts to the battery, does that mean that the starter solenoid, or whatever it is, is not working?

How does the car RUN??


Could this simply be a fueling issue versus a voltage/amp issue? I.e., could your pump be cavating?


Does your system use a return line? Could it possibly aerating the fuel?


Is the feed side to the pump above the pump? Thus a "flooded head".


What size are the lines you're using?


Is there a pre-filter on the pump? Is it clean and obstruction free?


What size is the pickup tube in the tank? Does it have a filter? Is it clean?


Of course all of this only matters is the car isn't running well...... if it runs fine -- then are you just chasing a voltage drop you're seeing on the Computer -- or chasing a surging fuel pressure gauge reading??

Aight Greg, here we go:

The car idles great except for the fuel pressure fluctuating. Then when I start turning on accessories and then the electric fan kicks on, the voltage drops to 10.2. I mash the throttle and the car falls on its face and sometimes dies.
The entire fuel system is new from front to back. I'm using -10 feed line and -8 return line (overkill for now but planning on power adder in future). The pump is mounted about 6" higher than the tank above the rear axle, I'm using 2 filters, before and after the pump, the tank and pickup are brand new from Rick's.
The car only has 350 miles on it. I did have to replace an Optima yellow top because it couldn't hold a charge. Then soon after the alternator took a crap and so I sent it back to have it rebuilt. Man I'm pretty sure this is an electrical issue. Gonna keep trying again today. Keep that advice coming.

Good info.


The car possibly dies because most of the ECU's I've seen will fail to operate once a set voltage drops to that level. 10V's is totally unacceptable.....


Next question is ---- where is the power take off for your ECU?? Most aftermarket systems require you to take power directly from the battery... "Most" might be an overstatement - but I haven't seen one that doesn't ask for this type connection. The battery acts as a line conditioner - and has the reserve capacity for when the alternator is operating in "on/off" charging (think voltage regulator).

FAST has me running 2 positive connectors and 2 negative connectors to the battery. I also have 4 connections coming from the alternator. 2 for FAST, 1 from the alternator plug to the alternator post, and then I have a 4 gauge going to the starter.
Only thing I don't have is running the 4 gauge alternator wire to the battery per the Powermaster instructions, and a ground from the battery to the body. My car is a unibody and I do have the battery grounded to the frame.

That sounds goofy as all get out right there!


In all my days -- I've only ever seen ONE 12V+ and ONE 12V- POWER to the battery.... all else marked GND or 12V+ are connected to engine ground or to a relay or somewhere - but I've never heard or read where there should be more than just the power source connected to the battery. Of course -- it's so hard to diagnose what's going on without being there and seeing first hand etc -- but I'd certainly be checking your power connections and making certain you've done that part of the installation correctly.

Sent a text to the FAST forum to find out exactly what these wires to the battery are for. The instructions don't specify.
Could the starter post be faulty which is why the battery is not receiving the full 14 volts since the alt is connected there?

Thought you said you had 14.2 at alternator -- and 13.9 at the battery..... nothing wrong with that. Battery will only "accept" so much voltage -- and 13.9 is fully charged so it's not going to take the full 14.2 the alternator is putting out.

Ok...I ran a 1 gauge wire from the alternator positive side to the battery and only picked up .2 volts. My ECM is still reading 10.9 with all the accessories on and the car idling.
I'm not going to bother running that 1 gauge to the battery for only .2 extra volts. Any other ideas?