Spuratic fuel pressure

[440Rat]

While I'm waiting for FASS to return a call I figured I'd ask here as well. I changed my fuel filter last Thursday and ever since, my FASS 150 is all over the place for pressure. I noticed this morning that every time the grid heater cycled the fuel pressure would build to 15psi, then drop back down to 12-12.5psi. Running down the road it continues to bounce between 12.5 to 15 some times it will spike at 18psi, then drop back to 12.5. Driving style doesn't seem to effect it either, Sunday driver to hot rod it doesn't drop below 12psi. Before I changed the filter it ran a constant 12.5psi and would jump to 15psi at start up then drop to 12.5. I bought a new water separator after work today to swap out the one that's on there, and other than pulling lines to look for debris I'm outta ideas. FASS states these pumps are preset to run 16 to 18psi.....

[Mopar1973Man]

Check your voltage supplying the pump make sure its stable.

 

Then check the pressure regulator make sure its not hanging up or the check ball jamming into the spring. (If that what you got).

[440Rat]

Called FASS back and the guy told me its got an air leak some where. I pulled the return line and checked for debris, and pulled the fitting to get at the check valve. The rubber ball has a slight ring worn in it from the spring, so I rotated the ball 180 degrees and put it all back together. I also pulled the feed line to the injector pump (was kinda loose, but not leaking) and made sure that was clear. Put it all back together, and tapped the starter and the fuel pressure jumped to 16-17psi, and stayed consistent for the 15 seconds the pump ran. With the truck running it still reads 16-17psi but its got a slight pulse I'd say 1/2 psi. The positive battery terminal has some corrosion so I'll clean that up now and see if that's causing a voltage interference?

 

 I questioned the guy at FASS about the fuel pressures of the pump and he said anything above 9psi I should be ok. I went about a month without a pressure gauge so I don't know what it ran out of the box. I do know that when I hooked the gauge up little over a month ago it read around 14-15, and has slowly dropped since then. I'm assuming its because of that rubber ball being worn?

[440Rat]

You can hear the motor and that loud pulse is coming from the return line... drove it about a mile to see if the pressure would fluctuate and it dropped 1psi in 10 minutes. It appears I have a slight leak on the feed line, so that may be the cause for my pressing loss.

Pump.mp4

[joecool911]

Wrong answer from fass. You should never drop below 14.

[Dieselfuture]

If voltage checks out good, then it's more likely ball and spring. Mine acted up from being brand new and FASS sent me new ball and spring, I modified the spring a little so the ball doesn't get stuck in spring. My pressure been steady ever since, but I do have 1/2 line in an out of my fuel module, so minimum restriction on fuel cycle. and that grove on new ball appeared over night too.

[Mopar1973Man]

Always love every ones fuel pressure numbers. Fact is Dodge states 10 PSI as a minimum. As a group we state 14 PSI to keep the overflow valve open (Unofficial). But I love hearing the all the pressures ranging from 5 PSI to 10 PSI from all the different shops.

[440Rat]

I called a diesel shop here in town and told him my fass was making 18psi and he told me that was to much. and that the Dodge in tank pumps were a bullet proof solution and better than fass.

 

 I'm not 100% sure why the pump was running like it was, but I'm guessing it may have had something to do with my failing batteries and bad battery cables. Since I've replaced those items the pump runs pretty much steady at 18psi it shows a slight drop to 16.5-17 under load.

Edited April 20, 2015 by 440Rat

[Mopar1973Man]

I called a diesel shop here in town and told him my fass was making 18psi and he told me that was to much

 

Just right. 14-20 PSI of fuel pressure under normal road load conditions. Should be 7-12 PSI while cranking/starting.

 

that the Dodge in tank pumps were a bullet proof solution and better than fass.

 

 

  Time to pack up and run from that shop because he's clueless.

 

it may have had something to do with my failing batteries and bad battery cables.

 

Because the ECM, PCM and VP44 do not get grounds from the body or frame but directly from the battery cable themselves.

[Me78569]

That is how you know the the shop doesn't deal with older trucks.  The oem pumps in the late 3rd and 4th gen trucks were great for their need, however not for ours. 

 

 

 

I have often wondered if we could retrofit a late model lift pump into our trucks.

[440Rat]

I could be wrong, but i thought the 3rd gen and 4th gen trucks ran a much higher fuel pressure than the 2nd gen vp44 trucks. So wouldn't their in tank pumps be to much for the vp?

[Me78569]

other way around the lift pump needs, the cp3/s3 should have 10ish psi, I think 11 was stock, but it is not near as important as the vp44. 

 

The vp44 uses positive pressure from the lift pump to help advance the timing piston, where as the cp3 has an internal pump and uses electronic injectors to modify timing etc.