Irregular fuel pressure?

J

jvencius

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Dec 16, 2007
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Background: I've done the normal in-tank mods and have an AirDog feeding the OE fuel pump into an ITP regulated return system. Fuel pressure is monitored through a DiPricol Optix gauge

Today I just started noticing that fuel pressure in a steady-throttle condition (cruising down the interstate) was fluctuating between 60-70 psi when before it had been rock-steady at 64 psi. Since Dennis @ ITP has assured me the only part that could really go bad in his RR kits is the diaphragm and that is VERY unlikely to happen, what could be the cause of my wobbly fuel pressure? I'm almost positive it's not a lack of supply (new primary and AD filters 2K miles ago) and since fuel isn't spewing out the boost reference port on the regulator, could the flaky pressure be a sign of the main pump going bad?
 
I would first try a mechanical gauge on the regulator. Make sure it matches with your other gauge.
 
Wow--I just called DiPricol b/c I'm thinking that the gauge head itself might have gone bad (truck runs completely normally w/o any fuel leaks and the regulator hasn't grenaded--there's only one possible fail point, per Dennis) and I don't think Eric could have been less helpful. Here's a reasonably accurate transcript of part of our conversation.

Me: "Before today, my fuel pressure right on the regulator was rock-steady at 64 psi"

Eric: "Regulator--what's that?"

Me: "The fuel pressure regulator"

Eric: "What does that do--I'm not familiar with these things"

Me: "It controls the fuel pressure going to the engine"

The conversation didn't really go well after that...
 
So whats a regulator? LOL


IT FKING REGULATES!!!!!!!!!!!!!!!!!!!

Pumps go bad. You sure nothings in the tank though?
 
'Powerstroke7.3 said:
Pumps go bad. You sure nothings in the tank though?
Click to expand...

I might just order a Walbro 392 and swap it in since that's a lot more economical (trying to be a bit of a tightwad lately...) than the Fuelab pump Dennis sells. The OE unit has 92K miles on so I can't really be upset that it's failing, provided that it is failing...

I highly doubt there's anything skunky in the tank--the AirDog primary filter is new (put it on at 90K) and the water separator drained basically no water when I checked it this afternoon... I'd think that if there was sludge/trash in the tank, my fuel pressure would be uniformly low vs. fluctuating like it was, but I'm no great wrench so I may very well be wrong re: that.
 
The only sending unit in the tank (for fuel level, not pressure) is still there. I yanked the mixing chamber when I did the in-tank mods but the float is still there (and working properly).
 
If I'm due for a new pump, than so be it but I'm curious why the indicated pressure is fluctuating so much if the gauge is on the "out" side of the regulator? If it were before the regulator than I could understand it being kind of wobbly, but I don't understand the fluctuation after the pressure is supposed to be controlled...
 
Updates:

For background: the gauge is a ~4 month-old DiPricol Optix electric gauge and all the connections in the wiring harness were clean and snug when I checked them today, the primary filter on my AirDog and my bowl filter are both new 2K miles ago, and I haven't noticed any fuel leaks anywhere or any other type of irregular engine operation.

Yesterday I replaced the fuel pump with a brand-new OEM pump and once the air got bled out of the fuel lines, I still noticed the pressure fluctuation between 60-80 psi at idle, trending towards the high end of that range. While accelerating, the pressure would drop to 63-64 psi and stay there until I let off the throttle, after which the presure would increase towards 80 psi. Today I re-installed the mechanical gauge that came with my ITP regulated return system since the transducer for the Optix gauge was installed in that port and at idle, my fuel pressure was very irregular and actually broke 80 psi during a couple of fluctuations so I immediately shut down and started typing this message. Other than a bad regulator, which Dennis has said he's never had to replace, can anyone think of a possible reason for my fluctuating fuel pressure?
 
Just sounds like a bad regulator to me.

I personally see them go bad all the time. Just not on trucks. :bigsmile:
 
'Powerstroke7.3 said:
Just sounds like a bad regulator to me.

I personally see them go bad all the time. Just not on trucks. :bigsmile:
Click to expand...

I have to work tomorrow but on Saturday I'll probably disassemble the regulator to see if there's anything funky about it (i.e. torn diaphragm, debris, etc...) but if it turns out to be alright, the troubleshooting will continue. Dennis has speculated I might have a blockage in the return line from the regulator back to the tank, but I can't think of a single credible way that could have happened. I'm using a Racor bowl filter and between that and the pre-pump filtration the AirDog provides I don't know how debris or gunk from the tank could have gotten that far. Providing the bowl filter hasn't grenaded (unlikely, given that Racor is the OEM maker and not some made-in-China garbage knockoff...), debris getting into the system upstream of the pump and causing a blockage would be hard to understand.
 
Wow--I can't speak enough for Dennis' service or patience with me trying to fix this problem. While going back and forth with him via email, he suggested moving the return line where it attaches to the bowl since the older versions of that fitting like I have didn't have a "stop" machined into them to prevent the line from slowly vibrating in towards the bowl and partially closing off the return port. So, upon his suggestion, I loosened the nut holding that line in the fitting, pulled the line out maybe 1 mm., then retightened the nut and fired the engine up. By the time I got out of the driver's seat and walked around to look at the mechanical gauge on the regulator, the fuel pressure was rock-steady on 65 psi and didn't waver one bit for the 5 minutes or so I watched it. Before, the pressure would start at 64 psi and slowly ramp up to 80+ but since that didn't happen after I tried Dennis' fix, that idea of his solved my fuel pressure issue. I R one VERY satisfied ITP customer (as if I wasn't one before...).
 
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