All of the sudden my fuel pressure is dropping when my truck cycles the grid heaters on and off. Lights dim as expected and voltage drops to 12v, but fuel pressure is only rising to 5 psi. when the heaters cycle off and voltage comes up, pressure will come up too to about 10 psi. pressure will drop again when heaters cycle until I hit 15-25 mph.

What could be the cause of this all of the sudden and more importantly, how can I fix it? I have a Fass DDRP to put on but it sounds like I'm having an electrical issue somewhere so I want to figure that out first.

 

there is a recent thread on this just a few days old on here. do a search for more info.

in a nutshell - the electrical draw is slowing down your LP, resulting in a momentary drop in FP.

 

There are two grid heaters which draw 95 amps each and when both are on there is a maximum draw of 2280 watts. Thats A LOT. So depending on how cold it is outside will determine how many grids are used and how long they will run. Which means that the electrical draw on the system is HUGE and any electrical device will not receive its normal dosage while these buggers are working. This is the main reason why you must have batteries that are in top notch condition. But do note that when you get above 17-20 MPH then the grids automatically shut off. If its cold enough out, it may be necessary to drive long enough to replenish the batteries, but I'm sure that would be in sub zero weather.

 

I have a FASS DDRP & mine does the exact same thing when my grid heaters cycle on....mine drops about 2psi.....I do have fairly new batteries in mine....I just replaced them a year ago.....From what everybody has told me it is completly normal for it to do this....It's just a huge draw on the power & I think it affects the lift pump...