i have dual fuel tanks on my truck. i'm only getting 15psi of fuel pressure at the fuel rail while the truck is running. (if it does run that is....) plus when i stop the truck i'm not sure how fast the pressure is supposed to drop, but i can actually see it drop right before my eyes.

this is no where near the expected 40psi.

i'm wondering which pumps (front or rear in-tank low pressure or the frame mounted high pressure pump) goes bad the most.

this would explain this code:
41 HO2S (sensor) System Lean Right Side

 

at 15 I'd say the high press is bad. I really don't know which ones go bad more often though.

 

I think I'de check the regulator before messing with the pumps.

 

My 96 F-250 dual tank work truck had the front intank pump fail, it would run fine when switched to the rear tank but when switched back to the front it would die immediatly. If your problem is happening with both tanks its probably the high pressure pump or something further up the line. Fuel filter ?

 

I have never replaced the rail fuel pump on my 88 f 150. In tank pumps have been replaced one time each. Put a fuel gauge on the shrader valve at the fuel rail and try each tank to narrow the problem. Also check you fuel pressure regulator. If you dont have good pressure ,carefully squeeze the return line and if the pressure climbs to around 40 psi chances are good it may be the fuel pressure regulator not working properly.

 

In your '89, the outside fuel pump provides the pressure. The in-tank pumps are there only to prime the system if you run the tank dry. You can run the truck without them.

Bluneon: Pull the vacuum line off the fuel pressure regulator. If you get gas squirting out of it, replace the FPR first. Then test the pressure. If it's still too low, or the FPR doesn't leak, then replace the frame mounted pump.

Your pressure is not supposed to bleed off like that. You either have a leaking check valve or an injector stuck open. What's your mileage like?

 

i haven't been driving this thing because of it's crappy running condition to even know the mileage. i've been trying to figure out it's idling problem ever since i bought the thing.

seems as though the truck only pulls from the rear tank as the fuel gauge never drops whenever the switch is selecting the front tank. i only see the rear tank fuel drop from running the truck.

 

Pressure should be around 30-45 psi at idle. You need to attatch your gauge to narrow the problem down . If you carefully squeeze the return line your fuel pressure can easily climb to 80 psi if the pumps are working. If that happens chances are good the fuel pressure regulator is not working. If the pressure wont climb above the 15 psi while sqeezing the return line the problem may be the pump on the rail if the symptoms are the same for either tank.If an injector is leaking the spark plug may be fowled up. It is going to take a little bit of checking.

 

bluneon

I think I would check the Fuel Selector Switching Valve on this one as that is where the check valves are and if it is not switching right you would get low fuel pressure.

Here is a Diagram of the Valve.

 

This one has me curious as well. My front tank on my 95 f-250 7.5L stopped working for awhile. On a recent trip that was higher altitudes than where I live I hit the switch to go back to the front tank and it ran great for the couple of days I was at the higher altitude. Came back home and it doesn't work again. I'm thinking about trying this experiment again before I dive in to make a repair. Any thoughts?

 

If it will not run at all I would look at the wiring and the grounds for the tank but still could be a bad pump. The 95 had the check valves in the pumps and did not have the above diagram.

 

I replaced the rear fuel pump. It was still working but constantly reading empty.
the floater has "sunk". Cost me $200 for another pump and that was the cheapest I could find, I could have probably replaced just the floater, a " 25 cent part."

but since I had the whole thing apart, (lowerer the gas tank is a b1tch)
I thought I might as well replace the whole pump.

 

today i went through the diagnosing steps in the FSM. i should have read it sooner.

i am reading 11.88 volts at the electrical connector for the high pressure pump. so i know it's getting a signal.

but it seems i'm now only getting 26 psi after i short the pump a couple times. there is no change while the truck is running. while shorting the pump and looking at the pressure gauge i did hear some noises from one of the fuel lines while the pump was running.

sure enough it was the fuel return line. i squeezed that line and the pressure shot right up like you guys said. FSM agrees with you guys and said the FPR is bad.

so off to the yards for me pretty soon. 90 dollars for a new FPR at the auto parts store seems a bit steeeeeeeeeeep.

let's see what happens....i'm getting the lean running code again so hope this goes away too.

BTW: any tips on how to go about removing the FPR quikly and easily??

 

If you can get a small allen key bit that fits the the 3 screws to work with a small ratchet it can save you some time and foul language as the srews are facing down and a bit of a pain to get at. The first time I did it with a allen key without the ratchet but it was a little slow. The noises you heard may be the fuel returning to the tank. Keep us posted.

 

turns out autozome sells new FPR's for 20 bucks. so i got one and popped it in. i'm now getting 40 psi primed-not running and while it runs it's around 35psi.

i'm not getting that lean running right side code anymore. so all is well, but the truck still has idle surges. and it's only throwing 1 code, and that's code 13, cannot control lw RPM during self test or something. but that's another thread.

thanks!