Fuel Pressure too high or too low?

[leathermaneod]

Hi all,

So I recently upgraded my ancient FASS lift pump to a Fuel Boss mechanical lift pump from Glacier Diesel Power. It has a bypass valve that allows fuel to return to the tank at a certain psi. I bought a "Tuning Kit" for that valve so that I could set the pressure exactly where I want it. I have been trying to get it just right but I keep ending up with it either a little lower, or a little higher than I want. I need help figuring out if I am looking for the wrong number or what, and where I should set it. I have in my head that anything over 20 is too high but at the same time I don't want it to get too close to 15 either lol. After messing with it for a few hours today I decided to er on the low side. I tried all kinds of combinations of the spacers and 2 different springs the come with the valve and tuning kit and can't find a happy medium. Everything is either too high or too low. I ended up with idle at about 17-17.5.  And IIRC that puts it at about 18 at 65mph. Those numbers are the approximate average between my two gauges. I have an autometer mechanical gauge with isolator on the pillar and a Vulcan test gauge from Geno's. The test gauge always reads about 1.5 psi higher than the autometer. Since the pump is mechanical, the pressure generally goes up from idle, but it does dip very slightly at first (about 1-1.5 psi) If i stomp on it or when letting the clutch out without throttle. Basically until the rpms catch up with the fuel demand. I wanted it just a touch higher but I just can't get it there. Next step up puts it at 18 or 19 idle and then it gets over 20 up to about 22-23 at 2400 rpms. That just seems too high to me. What do you guys think? Knowing that it will dip about 1 psi or so, would you go on the high side of 19 idle and 22-23 at 2400rpms, or would you go lower with 17 at idle and around 19 at that rpm? I just get concerned when it goes over 20 psi, especially since I know it rises with rpms and Im not sure how high it will go...I mean, what if it hits 25 or more? But I also don't like it anywhere close to 15 either. Anyway like I said, what would you guys do? I know Im worrying about this too much, but I'm really OCD and I need the opinion of someone with more experience.

Oh by the way, these numbers are all with my Smarty on SW5 so they might go up slightly with it on a lower setting. Its not much though.

Thanks!

Nate

[dripley]

As long as you are staying in the 15 to 20 psi range you should be just fine. My AD idles at 18.5 to 19 and at WOT I see about 15.5  to 16 psi with no issues.

[Buzzinhalfdozen]

Don't be concerned with your pressure readings. All of us with an electric pump see a pressure drop with increased rpm, while your just the opposite.  A little over 20 psi isn't going to hurt anything I say run it like it is. 

[Mopar1973Man]

Nice way of looking at it. Green good, Red Bad.

Most of us aim for 14-20 PSI.

Edited December 9, 2015 by Mopar1973Man

[leathermaneod]

Thanks to all for the helpful replies :-) I will mostly likely leave it alone then.

[IBMobile]

With my Fuel Boss mechanical lift pump system I see 15-16 psi @ idle on startup and go up to 20psi by 1500 rpm. After driving for 5-10 minutes fuel pressure will be 16-17 psi @ idle and still 20psi going down the road.

I'd leave the pressure on the low side. My truck sees 15psi for 30-60 seconds, no big deal.

Did you put in an electric "prime pump" and if so what type? 

 

Edited December 10, 2015 by IBMobile

[leathermaneod]

Thanks for the reply IBMobile. Nice to talk to someone with a similar setup. I have a mechanical only setup. No electric what so ever. Are you using the included bypass valve? If so did you tune it at all? 

Edited December 10, 2015 by leathermaneod

[IBMobile]

I'm using the 'bypass valve', which really should be called a fuel pressure regulator, that came with the kit. I've had to take it apart and clean it when the pressure dropped due to a small peace of rubber becaming stuck and held the valve open. That was right after I installed it and it's be trouble free since.  I am running it with the electric pump disconnected.

[leathermaneod]

I had quite a bit of trouble with mine. I had lots of dirt right after the install and then I continued to have trouble and had to add a fuel strainer right before the valve. Since I added the strainer its been ok though. I need to clean my fuel tank :-) Ive also taken it apart many many times trying to get it to just the right pressure without it being too high. 

[Hawkez]

My pressure sits right at 16-17 with my fuel boss.  I don't see the increase in pressure that others see with increased RPMs, my pressure doesn't move much at all.  The only time I had issues was right after I installed it.  My pressure sunk to about 5psi.  I cleaned the bypass and I haven't had any issues since.  Richard at GDP told me that the fuel line can have debree in them that will fowl that bypass.  I guess I should have blown it out before installing it.  You'll like the fuel boss, pretty trouble free.

[leathermaneod]

Does your fuel pressure drop a pound or two as you let the clutch out? Maybe I should ask if you start out in second and if you let the clutch out without giving it fuel? I usually start out in second and let the clutch out without fuel because I feel like it slips it less. When I do that my fuel pressure drops a pound or so. I assume thats because the rpms are slowing down just a bit. I do like the fuel boss very much, I am just overly OCD about having things perfect so I've had a hard time getting the pressure exactly where I want it. 

[Mopar1973Man]

As long as the pressure isn't below 10 PSI for any length of time I don't think you'll have much problems.

Between 14-20 PSI you should see optimal return flow. This insures good cooling and lubing of the pump. So if it does drop just a pound or two not a huge issue.