Fuel Pump Bogs When Headlights Running

[risk]

Engine drops rpms and I can hear my fuel pump bog down when I turn on the headlights..

I know this is affecting the flow of the pump, which bothers me. I have gone lean under boost in the past and paid the price. Plus, I know the pump is working harder with less current, therefore it must be running hotter.

SO..
I have a 90 amp alternator from AA products about a year old.
8 gauge fine stranded wire straight from alternator to battery.
Stock size pulleys

Feel free to correct my math & numbers if I'm wrong.

Running these accessories:
?? amps = MS2 - COP - hiZ injectors
3 amps = Innovate LC1
3.5 amps = Bosch Cobra Water Pump
13.5 amps = Aeromotive A750 Fuel Pump
5.4 amps = Fan on intercooler radiator
5.4 amps = Fan on ext oil cooler

Total
30.8 amps

headlights are 55 watt H4
4.6 amp each @ 12volts, so around 40 amp total draw with headlights on.

Headlights are ran off the stock wiring.

Fuel pump is wired directly from the battery with 8 gauge and a heavy duty bosch 75amp relay.

So, should I try for a better alternator, or LED headlights, or??

[Dale M.]

What does voltmeter say when you turn on lights............

A funny thing in my dune buggy.... When I turn on my headlights as dusk approaches my programmable speedometer drops to about half the reading it should be, but voltmeter (dash mount not digital) does not seem to indicate voltage drop....

Your 90 amp alternator should be putting out more then enough... What does Voltmeter say... Typical out put of alternator is right at 14 volts (+/- maybe 0.25 of a volt)

What you may be chasing is a bad ground path.... People seem to forget the pan/body is a ground path for many electrical items in vehicle and tend to get very involved in the wire gauge and power side wiring and ignore grounds....

Dale

[Ol'fogasaurus]

As Dale says!

Adding everything up: when you have everything on are getting up there close to the ability of your alt and add to that the large draw of the lights to the potential of older wiring you could be pushing things a bit.

The ground issue is very important. Metal gets old and tired and who knows who has welded and how good things are (an assumption that some work may have been done in the past). If you are using the stock flat ground strap they are known to go bad due to the strands breaking.

I also recommend you put a circuit breaker on the line from the alt to the starter just for protection. VW did not do this but I, personallyl, think it should be done. Stock wiring also may be tired plus there is the thing about wire length (voltage drop). All things to be taken into consideration especially in an older vehicle.

Lee

Edit: it can also make a difference as to where in the system (circuit) you made the connection.

[Piledriver]

Using the factory fuse box and wiring? Expected.

Put a relay-switched and fused dedicated 12 or 10 gar power wire to your fuel pump.
Do the same for your headlights, use the factory setup to control a pair of headlight relays.
Ditto if you have AC.

Run these direct to the battery.

Add another relay for your ignition running right off your alternator if running stock style coil setup.