Alternator Voltage?

what's the voltage when the car is off?

DC voltage will drop through wiring as the longer the wiring the higher the resistance. So you shouldn't expect through factory wiring to get a full 14V at the pump. See what you are getting at the battery during idle even, should be high 13's at least. If you are getting that then the lower voltage at the pump is simply from the factory wiring being too small of a gauge and possibly the whole dual voltage circuit losing some voltage.

The solution would be run separate wiring directly from the battery to the fuel pump but you will lose your dual voltage that way and might get fuel pressure high enough to overrun your FPR at idle. It's kind of a toss up really.

So check your battery voltage at the battery first to see what you are charging at.

edit: I think i read that wrong, so you are saying you are getting only 12.5 max at the battery? I am guessing during idle? Maybe try measuring while driving around if you could.

If voltage at the battery is 12.5v at idle then you have a problem. Check voltage at the alternator to see if there is a drop between the alternator and the battery, if not then your alternator isn't putting out enough.

xezerax said:

If voltage at the battery is 12.5v at idle then you have a problem. Check voltage at the alternator to see if there is a drop between the alternator and the battery, if not then your alternator isn't putting out enough.

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Could also be a battery issue if the battery is going bad and drawing too much. That's why I asked about the voltage when the car is off. If it's far below 12V, then I'd look to the battery first.

Someone stole my multimeter, ill go find one and test at the battery while the car is off. Im hoping its the battery and not the alternator, but i havent had trouble starting the car which seems strange if it is battery related.

could a short be causing this kind of an issue?

nkbourgeois said:

Someone stole my multimeter, ill go find one and test at the battery while the car is off. Im hoping its the battery and not the alternator, but i havent had trouble starting the car which seems strange if it is battery related.

could a short be causing this kind of an issue?

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No, a short of any kind won't simply cause voltage drop. You would need a resistive (i guess inductive possibly too) load to lower the voltage that much.

A short would pop a fuse and/or fry wires if you had one not cause voltage drop.

okay, so battery check (free) and if thats not it then go for a new alternator?

Im reading online that our alternators put out 12v?... is that really all they put out?

No, all my logs show 14v consistently when the car is running, and 12v when the car is off. It's definitely 14v. Unless our logging is incorrect, it should be 14v.

Yup, everytime EvoScan starts a log it checks the battery voltage. Its normally around 13.7-13.8 if you just started the car, and in the 14's after its been driving a while

okay so i went to autozone and had my alternator tester/battery. everything was fine. 14.6v

what in the world is going on? I have no choice but to guess it is electrical based on the fact that i have replaced literally every piece from the pump housing to the injectors with no change.

I'm about to push this car down a big hill and just say goodbye.

I'm guessing those voltage issues now belong to the person who stole your faulty multimeter. At least it's not an issue with the overall voltage the car is producing. Time to cross that off the list and dig a little deeper. My next question is whether a single pump can support your mods at full tilt or whether it's time to just upgrade the fuel system a little further.

I would think the same thing except for the fact that my tuner has built many evos on set ups with single walbro 255s and made comparable power with perfectly normal afr's.
+I have turned my tune down a bit for saftey and now im still running out of fuel.

I might go replace all of my relays again just in case... but im sick of throwing money at this problem with no change. what could be draining power in the high rpm band once im making 14.6v?

I guess what you really need is a way to measure fuel pressure when this problem is occurring. There's a couple of possibilities I guess:
1. Not enough fuel coming to the rail, showing up as low pressure. Either because of a problem with the pump or maybe even something like a kinked line in the tank
2. Pressure is good at the rail but your injectors are maxed out. I know I've read that certain injectors had flow issues at certain fuel temps, but I don't think it was the FIC 1100's.

Without knowing all the details of your fueling issue it's really hard to say. Maybe time for a brand new thread for the fueling issue you're having. Surely the gurus around here will be able to weigh in and help you get this problem under control.