I wonder if you have a bad ground, bad sending unit, or bad gauge? Did you try a mechanical gauge to verify fuel pressure?
Fass HD Runs but low pressure
- Thread starter stibuilder
- Start date
Nothing seems to be on backwards, everything was working about 6 months ago when just going down the road the electronic gauge started reading really high, then all over the place and finally just went to crap so I thought. Ive tested with a mechanical gauge to prove the autometer is correct.
1. Replaced the spring in the return on the FASS with a shorter New Spring = Zero Pressure
2. Took original spring and stretched it out = Pressure randomly 5psi, only when engine is running but, without any type of engine load. Once load is added it drops to 0psi
3. Replaced the check ball in the return, and the pump motor and seals.
4. Replaced the feed line from the tank to the pump
5. Replaced the filter head with a new head, and oem filter
Still no pressure. Thoughts are now the CP3? Returning fuel?
Truck seems to run great, and if I i pump up the primer on the filter head pressure comes up on the gauge. WTF?
1. Replaced the spring in the return on the FASS with a shorter New Spring = Zero Pressure
2. Took original spring and stretched it out = Pressure randomly 5psi, only when engine is running but, without any type of engine load. Once load is added it drops to 0psi
3. Replaced the check ball in the return, and the pump motor and seals.
4. Replaced the feed line from the tank to the pump
5. Replaced the filter head with a new head, and oem filter
Still no pressure. Thoughts are now the CP3? Returning fuel?
Truck seems to run great, and if I i pump up the primer on the filter head pressure comes up on the gauge. WTF?
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The next thing I would do is move the AutoMeter sending unit to the FASS and see if it is making pressure at the FASS. If you are getting pressure at the FASS but not at the filter, you have a restriction in the line somewhere between the FASS and the factory filter head.
I put a manual gauge on the Lift pump today and turned the key and got 8psi, the filter housing was zero, looking at replacing the last run of OEM fuel line that could be causing an issue.
So the truck set a P0087 code this weekend after driving is and letting it sit for 30min I went to leave it almost died came back and tossed the code. I was only 5 blocks way from home, it made under its own power. This sounds like a fuel issue on the low pressure side also.