RB25 charging problems

[huafist]

I've got a charging issue that I can't figure out for the life of me. Car is an S14 240 w/an Rb25. The problem is that I can't get voltage over 12.8V, and at WOT, voltage drops quickly - by 7k voltage has dropped to 9.4v, and ignition shuts down.
I've had both battery & alt bench tested, and ran the Vsense wire from the alt directly to+12v with a 560R resistor. Same results. The only thing I know left to do is double check the grounds. Below are two short videos in which you can see the problem - one @ cruise and one @ WOT. Battery voltage is at the bottom of the display.
Ideas?


Cruise:
https://www.youtube.com/watch?v=5faTRNs9pW0

WOT:
http://youtu.be/llNPpIuYirg

[240z4u]

Is your battery in the trunk? Sounds like you've got grounding problems to me.

Edit; any chance your alternator belt is slipping under WOT as well?

[huafist]

Is your battery in the trunk? Sounds like you've got grounding problems to me.

Edit; any chance your alternator belt is slipping under WOT as well?

It is in the trunk ; I'm inclined to agree with you about the gruonding.

I suppose it could be slipping; I'll tighten it a tad tomorrow before I test it.

[240z4u]

I had a problem with my alternator charging at a higher than normal voltage, and adding a ground strap from alternator to chassis, and running a 4ga ground to the trunk cured all that goofiness.

[huafist]

So, I reinstalled the alt today, and cleaned up the ground contact points. At idle I'm getting ~13.2V now. Don't know how it's going to react under load yet, I'll find that out later and report back.

[huafist]

Added another ground from the block to the frame; that seems to have done the trick! Getting 13.2 - 13.7v consistently now.

[240z4u]

Great, everyone loves a happy ending!

[huafist]

Great, everyone loves a happy ending!

Once I figure out why it's falling on its face around 6500RPM, it'll be a VERY happy ending lol

[240z4u]

Are you hitting the revlimiter?

[huafist]

Are you hitting the revlimiter?

Nope - I've got the rev limiter set at 8k. Not sure what the deal is right now, but I'll examine the logs and figure it out lol

[huafist]

I'm inclined to believe at this point fuel pressure is dropping off. I'm going to put a z32 fuel filter on it tomorrow. If that doesn't do it, then I suppose it's fuel pump, even though it's a walbro 255. Of course, that doesn't rule out the pump being old & tired.

You can watch the IDC go all the way to 89% at 22psi, and the AFR jumps to 17.8 - this is on 880cc injectors. I don't see how it could be anything but a fuel restriction.

[huafist]

Yeah - I think the fuel pump is going out haha

http://youtu.be/L8rJoyG0SYA

[huafist]

Well, the issue was definitely the fuel pump. Replaced it with a z32 TT pump and all is well.