Voltage Drop Under Boost

[RKHiPerformance]

I did a search on this subject because I know it's been brought up before but I couldn't find any definitive resolutions.
According to the Scanmaster, the voltage in our car while driving normally ranges from 13.3 to 13.9. Under heavy throttle, the voltage begins to decrease from the 13's to the 12's and even into the high 11's. I don't have DS but I am concerned that this problem is affecting the fuel system in 3rd gear. O2's dropped to the high 600's through the traps on our most recent pass, and I suspect the pump was not receiving enough voltage to keep up.
We replaced the alternator with another Advance Auto Parts unit with no change. The belt is the correct one and it is new and tight.
I'd prefer not to use a volt booster because of the potential drawbacks and because of the fact that the results are inconsistent with aftermarket alternators.
Does anyone have any suggestions? How much voltage is required at WOT for everything to operate normally?

 

[Ormand]

Is the alternator the correct 120 amp alternator? If the voltage is dropping that much, something must be dragging it down, and if the alternator is not the original high output version, or equal, it may not have enough guts. The fuel pump pulls 12-15 amps, maybe. The ignition is another big load, but there should be plenty of alternator available, since it has enough "reserve" to run the heater blower and the lights and other accessories as well as the engine electrical loads.
Fuel pump curves at GnTType.org show the drop off in pump capacity as lower voltages. The ignition will get weak, too, if the voltage drops off, but I have no idea how much voltage is "minimum".

 

[suicide six]

I cant begin to tell how many times the junk these auto stores sell,Always keep receipts cause more than likely it will be going back.

 

[RKHiPerformance]

I'm skeptical of the alternator, too. The unit I have is 'supposed' to be the correct 120 amp unit from Advance, but the quality from these chain stores can be inconsistent to say the least.
Is there a good source for a reliable replacement alternator other than the dealer?

 

[GN1]

I Was Reading In Another Thread That Maybe Your Cable From The Battery Can Be Touching The Headers At Wot With All The Force So Check That The Battery Cable Goes Under The Header And To The Alternator

 

[SloGN]

what size injectors are in the car?


i experience the same problem with may car after i installed a modded ecm and a set of 55 lbs inj. and come to find out the fuse was too small for the load @ wot. It was drawing enuff current not to blow the fuse . but the fuse was acting as a resistor due to it's small rating.

your only @ wot for only a few seconds @ a time so the fuse is not going to get hot and blow that fast. the only way i could catch mine doing it was with a direct scan. cause when the voltage was dropping the duty cycle on the injectors would go up big time and all the values for the sensors would be out of range.

and since the scanmaster getting it's battery voltage reading from the ecm. if the ecm is losing power everything tied to the ecm with lose poer also.

sorry to be confusing it's just a thought . i just put a bigger fuse like a 20 amp.

 

[RKHiPerformance]

The injectors are just 42.5 lb Greenstripes, and the fuel pump is a Red's single unit.

 

[turbofrank]

what size injectors are in the car?


i experience the same problem with may car after i installed a modded ecm and a set of 55 lbs inj. and come to find out the fuse was too small for the load @ wot. It was drawing enuff current not to blow the fuse . but the fuse was acting as a resistor due to it's small rating.

your only @ wot for only a few seconds @ a time so the fuse is not going to get hot and blow that fast. the only way i could catch mine doing it was with a direct scan. cause when the voltage was dropping the duty cycle on the injectors would go up big time and all the values for the sensors would be out of range.

and since the scanmaster getting it's battery voltage reading from the ecm. if the ecm is losing power everything tied to the ecm with lose poer also.

sorry to be confusing it's just a thought . i just put a bigger fuse like a 20 amp.

which fuse.

 

[rodman99999]

Take the alternator to a GOOD automotive electrical shop(not a parts store). They can run it, load it, and tell you if it's putting out the rated amperage. Bet it isn't! A high cranking amp battery will help keep the volts up at WOT throttle too(at least over 12). It's in parallel with the Alt, so it figures in the equation.

 

[SloGN]

which fuse.

The ECM fuse. it's a 10 amp stock and i replaced it with a 20.