WOT voltage drop

[mr.prick]

My battery voltage at high RPM drops a good bit even after
replacing the lousy spring loaded tensioner with a solid one
and the wimpy 8awg battery cables with 2awg.
Does anyone have any suggestions on how to stop this?
http://i235.photobucket.com/albums/ee259/whitespar/Voltdrop.jpg

[ssvolvo]

That's ECM voltage??? Or battery voltage???

Two very different readings. Have you actually checked at the battery positive under full load/rpm?

Hear me out. Last year I swapped an LS2 in my Volvo with an EBAY fuse block meant for an LS1. I was having trouble getting enough fuel at high load/rpm situatutions so I started logging different things.

Here's what I found: An Amp Probe installed on the alternator power wire (to the battery) revealed the engine consumes 6 amps@idle and 58 amps @ 6500 RPM during driveway burnout. Laugh if you will but I burned out 2 sets of tires trying to remedy the situation!

My homemade wiring harness had ALL of the engines 12v switched (GM pink) power was routed through 1- 15 amp fuse. Less the fuel pump. I split these into 5 separate circuits to remedy.

Also logged fuel pump voltage drop with a digital volt meter. Drop was down to 10.5 volts at full engine load so I ended up running a 12 guage wire from the front of the car back to the pump to remedy the drop.

My problem with fuel starvation ended up being a faulty Bosch wide band that had gone narrow. Reason was I drove around with the LM-1 box unplugged...BIG mistake. I didn't have a fuel starvation problem at all actually.

Enough of my blabbering. Here's what to check: Load the alternator and be sure it puts out 100 amps or what it is rated at. Battery voltage during burnout or WOT dyno pull. Check with a meter at battery positive. If the battery is showing low voltage during full load then check belt slippage/ alternator output. If this shows good voltage then check the voltage drop through the circuit to the ECM. You could have a bad ign. switch or relay. Under full pull the ECM should only drop .1-.2 volts from battery voltage. You might not have a belt slippage problem after all.

Again. The engine requires almost 60 amps at full pull to run everything not including A/C.

What kind of vehicle? Stock or gin rigged? stock accessory setup?

Good Luck, John

Mr prick LOL...I love it!:cucumber:

[mr.prick]

This is logged battery voltage {GM.VOLTS},
I never thought of measuring voltage with a DMM while performing a burn out. :hihi:

Last night I noticed the lights dim @ WOT, fuel is good but
voltage drop changes all kinds of things
This is an 02 Fbody with an UD pulley, A/C, 200A alt, and 2awg cables,
no shenanigans with the wiring.
After replacing the tensioner I thought this was cured because
voltage did not drop as much as before.
I still suspect belt slip or maybe crank pulley slip.

[ssvolvo]

It sounds like your battery voltage IS dropping if the lights are dimming.

I'm running F-body accesories with a truck alternator. Stock tensioner. Underdrive pulley from Summit (their brand). I did change the alternator pulley to the smaller diameter.

Try a new belt. Napa belt has never slipped for me but it does squeal during wide open shifts.

[mr.prick]

Altho the belt is not very old or showing signs of wear
I guess that could be a factor.
thanks.

[dfe1]

Here's what I found: An Amp Probe installed on the alternator power wire (to the battery) revealed the engine consumes 6 amps@idle and 58 amps @ 6500 RPM during driveway burnout. Laugh if you will but I burned out 2 sets of tires trying to remedy the situation!

Not doubting your findings, but almost 10 times the current draw at WOT compared to idle seems excessive. I wonder what contributes most to current draw-- ignition load, injector load or fuel pump load. It would be interesting to do your driveway burnout test with a separate source supplying voltage to the fuel pump and with a carburetor instead of EFI to see how current draw changes.

[ssvolvo]

I need to clarify this.
6 amps at idle through through the ECM circuit, not at the alternator.
58 amps at WOT was with the amp probe around the alternator positive wire.
I will check the alt. positive wire at idle. I'm sure it is more than 6 amps.

4L60E was certainly some of the usage. I would have not beleived this but was told this on another forum and hey, if you see it on the internet it MUST be true right?

It was a learning experience to say the least. I'll have to make a video. Been thinking about buying a used dyno cause my driveway is in need of new pavement.:hihi:

John

[mr.prick]

I logged tonight and the drop was not as bad. :confused:

[joecar]

How many miles/years are on your alternator...?

[SSpdDmon]

My voltage issues last year (WOT voltage drops) were the result of a faulty regulator in the alternator. No problems since I replaced the unit.

[mr.prick]

Where they consistent, voltage dropped less last night and the alt is not that old.
It's a LoadBoss 200amp.
The odd thing is that I had my stereo on (non stock) and power inverter running,
post #1 just just shows voltage with the stereo.
AFR was a little rich but close,
the lower voltage makes me wonder about the upper end of my VE table.