daniel

well i went to my local diesel performance shop to have my fuel pressure checked it was idling 5 psi well i took the dive and bought a fass is there anything i should know about this system that could cause me a problem is there anything that i will need to do differently than i am now. any help would be appreciated.
Daniel

spyder3634

I sometimes get hard starts once the truck is warmed up and I turn it off. From what I have read, this is because the FASS is overpowering the vp44. My vp44 has less than 10k miles on it so I am pretty sure it isn't going out. So I normally turn the key and wait to start until the FASS stops running (you can hear it) then it starts up fine. Other than that it is a great system!

Diesel-Dan

You will love it! Here is a link to read up on the install if you want to read it.

The hard start issue is a hit and miss thing. Some trucks have issue with it, some dont. Its not really that the FASS is "Overpowering" the VP, its more how the ECM tries to hobble the FASS when cranking to lower pressure.

The stock fuel pump is a centrifical vein style pump. This means it has to have shaft speed to force the finger out to make contact with the outer housing to seal and pump fluid. The more speed, the more force the fingers have on the housing. What the ECM does to lower pressure when cranking is pulse the pump. It does so in a manner to reduce its duty cycle to 25%. This will slow shaft speed and allow the pressure to be dropped because the fingers are not pushing out as hard on the housing anymore. This is fine and dandy with the stock pump.

The FASS Pump is a Gerotor pump. It uses a gear in a gear to push fluid. When it turns, it makes pressure. FAST! So when the ECM tries to hobble the FASS (The FASS connects to the stock engine harness on the 98.5-04 trucks), the FASS will pulse burst of 15-18 PSI (Depending if it’s a HPFP or FASS) to the VP. The VP likes lower pressure to start. In most cases this does not cause a prob. BUT some trucks are sensitive to this situation and have hard starts, particularly when hot.

There are several different ways to combat this issues. A simple reflash at the dealer (Or via the Smarty) can fix the problem. This will give the latest and greatest from DC to flash the ECM. AND I believe this “Hard start when hot” issue was specifically addressed in the newer programs. You can also relocate the FASS trigger wire going to the relay if needed as well. I have this outlined on this "Fix" on another thread on TDR. I just drew up a diagram of what is involved in modifying the FASS harness to make this work. Ill post it up here when its approved.

I also need to make a mention that this also may be a sign of a weak VP as well. I would try all the fixes first and if you still have issues, you might need to bite the bullet.....

Other than that….should be a simple install…….sorry to get wordy!

BigBlue

Hmm, that would explain why my holley blue only goes up to 5 psi when I first turn the key and Charlie's goes to 18. The holley is a sliding vane rotor type thingy.

Diesel-Dan

Here is a schematic of the fix......best i could do with MS Paint......






ALSO....just to add....if you choose this way...might want to look into a switch like this.....this will cut fuel in case of a crash.