FASS 95 & cold weather

[Bill Weber]

Ever since I have installed my FASS pump I notice my rail pressure is low (8-9,000#) while driving in 30- 45F temps. When accelerating it drops to 6k. I guess it is because the fuel heater & original filter/pump is bypassed. Is this a problem? Can I run the FASS pump discharge through the original system to get some heat or will this cause too much pressure drop?



Bill

 

[steved]

Take this for what its worth, but I would look for other reasons for dropping rail pressures.



Personally, I would look at a failing FCA or a failed rail pressure relief valve.

...

 

[Bill Weber]

steved - Maybe so but this problem only occurs during cold weather. As soon as it gets above 45F the rail pressure comes back up. If I park the truck for a few min. and then start up the rail press is normal until I use up the warm fuel in the engine compartment - then the rail press drops again.



Bill

 

[CToney]

Where abouts you from Bill. 45 F isn't that cold. Check your connections to your fass and FCA. Give a shout out to Diesel Dan from FAss he will help you out. It has been -20F or colder and I haven't had trouble with my Series 150/95GPH. Maybe take the quad off and see what happens.

 

[JamesStevens]

steved - Maybe so but this problem only occurs during cold weather. As soon as it gets above 45F the rail pressure comes back up. If I park the truck for a few min. and then start up the rail press is normal until I use up the warm fuel in the engine compartment - then the rail press drops again.



Bill

I have the FASS 150 unit with the 3 micron filters, have it mounted along the frame. Last winter I left the stock heater plugged in, this winter I pulled the wire going to the stock fuel canister (I left the stock filtration on for warranty reasons) and it hasn't changed lift pump or Rail pressure at all. I live in Canada and we just had a cold snap go through where it was -20 C for a week. As others have said I would look else where. If U think the fuel is gelling, buy some additive, that will help trouble shoot anyway. One thing I did notice is my FASS gets quiet'er during the colder months, but doesn't affect pressure that I noticed. Sorry I don't have the 95 for exact comparison, have U changed filters on it?



James

 

[DaveHess]

I'm with James and CT here in ND. It has been below zero here for the last couple of days and the only abnormal gauge reading I got was the fuel pressure out of the FASS appeared to be about 1/2 pound higher that usual. I could be way off base here but I thought that to be the fuel, like oil, may be a bit thicker in the cold and pump pressure was a reflection of that. My rail pressure gauge read as advertised.

 

[Bill Weber]

Thanks for the input guys. I think I did not make myself clear. The FASS is working fine. 14#s + press. It is the rail press that is low, BUT, only when the weather is cold (I live in S. Texas - 28F is cold). As the temp warms up during the day the rail press comes up. Today the temp was 30F. At 70 mph rail press = 8-9K. Normally 14-15K. It appears that the CP3 does not like to pump cold fuel which really makes no sense to me. My rail press number is coming from my Quadzilla monitor which is picking it up from one of the factory harnesses.

The truck starts & runs fine - just a low rail press.

 

[Tinman]

I think your gauge may be bad.

 

[Bill Weber]

Tinman: Could be, but, which guage? Both fuel & rail are electronic signals and don't change as the engine warms up. Only a change in fuel temp seems to effect the rail press number. Could be the FCA or relief valve as steved suggested but they only fail when the fuel is cold. ?????



Bill

 

[TCDiesel]

With those drops the truck would run poorly??? if not the gage is reading in-correctly. . check Pressure with scan tool at OBD II

 

[AH64ID]

Do you have the FASS 95/95 or FASS 95/150?



What is fuel pressure when rail pressure is low?