Engine/Transmission (1998.5 - 2002) Fuel Pressure Guage Questions....Strange Readings

[dnesbitt3]

OK, after 180K and a new VP44 I decided to try and stay ahead of the curve this time by installing guages. Westach Fuel Pressure guage w/sending unit mounted on top of filter canister, Westach Temp Guage with probe in Trans Pan, and Autometer Pyro.



Here are my observations/questions:



1) At start up fuel pressure is 15+, at WOT 12+, then for no particular reason it will drop to idle 7 lbs, WOT 5 lbs. (random occurence sometimes it does this after 10 miles, sometimes 30 miles, sometime it never drops) When I floor it the fuel pressure will immediately go back up to 12-15 lbs.



2) Less frequently the fuel pressure will drop to 0-4 lbs. at which time the only things that "resets" it to the 12-15 lbs range is stopping and restarting the motor.



I guess my concerns are is the fuel sending unit screwing up (guage is a month old) or are there some other things I need to check?? Don't want to mess up my new VP44 and I'm getting ready to pull a load out of state this week.



Thanks for your replies,

Don



ps I really like the Autometer Pyro - had no idea the exhaust temp changed so much... .

 

[jpmutt]

I would suspect a transfer pump going south, or has been intermittently failing for some time.

 

[RHARVEY]

A couple of things could be going wrong,, Number one the lift pump could be on its last leg and needs to be replaced. Number 2 the electrical sending unit could be having issues. And number three the guage could be also having issues but not much chance of that. I have seen gauges stick but never have different readings like what you are seeing.

Number 2 is the reason that I dont like electrical fp gauges. Yes I do have live fuel running inside the cab but I also have a needle valve shutoff under the hood if a hint of diesel is smelled. Also the guage is located just the the right of the go pedal so its easy to see if there is a leak. .

I would also vote for a lift pump taking a hike!





Rick

 

[RustyJC]

The resistance-type Westach sender doesn't like vibration or pressure pulsations. I would mount it off-engine using the grease-gun hose method.



I have the dual combo Westach fuel pressure gauge (pre-filter & post-filter). The senders are firewall mounted using braided stainless steel-covered hose. I've probably lost 8 or more post-filter senders due to hydraulic spikes coming off the VP-44 inlet that aren't damped by the stainless steel-covered hose. I even use a gauge snubber on the inlet to the sending unit.



I guess what I'm saying is that one mode of failure I've seen several times with the Westach sending units is that the gauge readings go completely squirrely as you describe. I'd suggest verifying what you're seeing with a mechanical gauge before you condemn the lift pump. I'd also suggest carrying a spare sending unit or two (I do) as another mode of failure is a ruptured diaphragm which causes a pretty darned good fuel leak around the terminals! If that one happens, you'll smell it!!



Rusty

 

[Tcolesanti]

I had a lift pump do the intermittant thing on me for a while, I thought it might be the gauge, but swapping it for a FASS setup showede that it was the lift pump going south.

 

[BWillard]

Let me say, I just went through the same thing with my FASS! Guage was bouncing and after a few days went dead completely No big deal it's just the guage or isolator I said. So after 2 days of NO fuel pressure, I stopped off to see Doug@ADT. We swapped out the isolator... . still dead Swapped out the guage... ..... no reading Hooked up a Doug's mechanical guage... ... ... . OOHHHHOOOO! Guess what..... NO FUEL PRESSURE!!!! :{ So for 2 days I drove my truck around with no fuel pressure + drove it over an hour to ADT to find out the relay went bad on my FASS and it wasn't running :--) Moral of the story is: the FASS is still subject to failure so keep an eye on the guages.