Engine/Transmission (1998.5 - 2002) learning something new everyday about our trucks

[SSolderitch]

When the grid heaters cycle and the load on the alt changes the rpm, I noticed my mechanical fuel pressure gauge drops 1 1/2 psi from 17. I know at idle I have more than enought psi, but it tells me the voltage is dipping down on the truck and effecting the FASS pump output. Everyone knows about the headlights dimming, but the fuel pump never crossed my mind. I know srt-4 guys rewire the in tank pump with a direct heavy wire to supply the feed the pump... . just FYI. Going with one of the high output Alt should also help.

 

[telliott]

i always figured the slight drop in fp was because of the added load on the motor when the heater cycles. I only see a very slight drop and i dont think it's anything to be concerned about. I've got a walbro instead of a fass.

 

[JMetzger]

My Fass drops around 1 pd when the grid heaters cycle. It is because of the added voltage draw when the heaters are on. Everyone says that this is normal & not to worry about it.

 

[GHandt]

It wont matter how big an alternator you get you will still see a voltage drop when the heaters cycle at idle. Even a high output alternator cant put out enough power at idle to fully supply the grid heater and everything else on the truck. It wont hurt anything to lose a couple of psi in fuel pressure when it cycles.

 

[AH64ID]

The voltage goes from 14. 8 or so in my truck to 11. 8-12. 2 when the grid heater cycles... so a psi drop is not surprising. . Here is the walbro psi/voltage chart (a FASS will react similar). .

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And as far as a high output alternator it would have to put out 200+ amps at idle for no voltage drop. .