Orange Juice

iTrader: (3)

Car is at the tuners, can't tune wot because not enough voltage to push the fuel pump. Car was fine a year ago, I switched to a truck alt for the extra amperage since then. Car is fine at idle and light load, it delivers 13 volts but under load it drops to 11.
The car has a racetronics pump that had the hot lead installed but Im not sure if that is still in place. Lots of new exhaust work since the install. The car is a couple of hours away and no hoist in the shop so it makes it hard to try different things.
Any help of opinions would be great. I guess the first thing to try is getting the alt taken out and checked.

fleetmgr

Yup, testing the alt is step one. A bit of math will tell you if the truck alt is doing anything for you. If you don't have electrical loads totaling over 105 amp, then you're getting nothing from it, and wasted money on it. You normally wouldn't have that kind of load without a pretty serious stereo being involved. My bet is you have a bad diode.

Orange Juice

iTrader: (3)

I do have two amps that get some use so that was the reason for the bigger alt.

Daniel Richards

iTrader: (1)

Stupid question, but did you do the "Big 3" upgrade when you went to the truck alt? Was the truck alt a junkyard salvage or a reman from a parts store or somewhere online?

Orange Juice

iTrader: (3)

Maybe a stupid answer but what is the Big 3 upgrade. I bought the alt new using the part number for a SUV. I did the swap myself and just plugged in the new alternator never thinking I had to do anything else.

Majestic9C1

iTrader: (19)

bigger gauge wire going from Alternator to Battery, Battery to Starter and Battery to Ground.

check out the Innovative Wiring Big 3 wiring kit for the F-body.. its literally plug and play.

Daniel Richards

iTrader: (1)

Yup, bigger alternator won't matter much if you don't increase the size of the wires to handle the increased current output of the alt, infact increasing current flowing through the wire will increase heat and potentially melt the wire (worst case scenario) and as heat increases resistance increases causing voltage drops.

That said, this is something you need to resolve but I doubt it will solve all of your issue.