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Old 08-28-2022, 01:52 PM   #1
AppliedThinking
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Default 98 Sun Voyager 460 Ford No fuel pressure to fuel rails

Well I must admit, this is not the first time troubleshooting the fuel rail problem. I did change out the fuel pump, located in the fuel tank, about 10 years ago. Very low mileage on the rig 16k miles.
Two years ago I was have a similar problem with intermittent engine and generator starts. At that time, I rebuild the battery disconnect relays replacing all the solenoids with new ones (two primary large and two smaller ones). Now the generator will start but no fuel pressure for the main engine.
Aside from dropping the (very full) fuel tank, I was wondering where the chassis test points to trace the power to the fuel pump are and any recommendations. I do have a fuel rail pressure tester (harbor freight).


I am assuming the first step would be to pump the gas out of the tank. That's a lot of fuel! Divide and conquer.
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Old 09-04-2022, 11:48 AM   #2
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Originally Posted by AppliedThinking View Post
Well I must admit, this is not the first time troubleshooting the fuel rail problem. I did change out the fuel pump, located in the fuel tank, about 10 years ago. Very low mileage on the rig 16k miles.
Two years ago I was have a similar problem with intermittent engine and generator starts. At that time, I rebuild the battery disconnect relays replacing all the solenoids with new ones (two primary large and two smaller ones). Now the generator will start but no fuel pressure for the main engine.
Aside from dropping the (very full) fuel tank, I was wondering where the chassis test points to trace the power to the fuel pump are and any recommendations. I do have a fuel rail pressure tester (harbor freight).


I am assuming the first step would be to pump the gas out of the tank. That's a lot of fuel! Divide and conquer.
Mine had a fuel rail pump bolted to the inside of the frame under the drivers door area. It’s the booster pump, increases the file pressure to specs.
Now that I said that, I ended up installing a new “second” fuel tank pump. That cured the issue.
Note; the in tank fuel pump is a bunch cheaper than the fuel rail pump.
Yep! I replaced the fuel rail pump! Knowing I had installed a new tank pump not more than 5,000 ago.
To my surprise, it was the third in tank fuel pump.
1. First Was from factory.
2. Second A Ford dealership in Weed California.
3. Third Was replaced in Langley BC.

Remember not to cheep out and buy the lesser expensive one. Make sure “New Pump” comes with a lifetime warranty.

Mike R
Tulalip Washington
35 miles northwest of
Seattle
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Old 09-09-2022, 02:14 AM   #3
THenne1713
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FIRST CHANGE CUBE RELAY in front fuse/ relay box under hood, driver's side?
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Old 09-10-2022, 12:07 AM   #4
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Circuit is pretty simple from my memory on (most); INERTIA SWITCH and FUEL PUMP RELAY CONTACTS, F.P. RELAY COIL controlled by IGN and/ or PCM. The FP RELAY should be replaced anytime PUMP replaced and any time pump= suspect? Usually in the FUSE/RELAY panel Under hood, forward of driver on (many) chassis; your mileage may vary? DO THE RELAY BEFORE DROPPING TANK, IF IF NO LUCK, THEN CHECK POWER TO/ FROM RELAY. GOOD LUCK
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Old 09-12-2022, 07:29 AM   #5
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Good points all. I finally got the time to troubleshoot the RV fuel pump. I installed a fuel line pressure gauge on the engine fuel rail and confirmed that I had no pressure (supposed to be 35-40psi). I looked at the fuses in the power distribution panel and they all looked good. Also verified that all the battery disconnect relays (chassis and coach) were at the proper voltage when turned on. Pulled the fuel pump relay and ordered a new one from Amazon. There is another row of 4 external relays next to the ones in the distro box that is not shown in the ford chassis manual. No clue what they do. There is only three things beyond the fuel pump relay and that is the connector on top of the fuel tank, the fuel filter and finally the fuel pump.
I am praying its not the pump. I did try and start the engine and it did fire for a brief instant.


I did not think of adding an external inline fuel pump. I just happen to have one that I use to transfer fuel from portable marine tanks to the vehicles. Hmm food for thought.


BTW, this is a Class A


If it boils down to the in-tank fuel pump. I will have to figure out a way to empty a full tank first. Its not a hard job to drop the tank but a serious challenge with any fuel in the tank. Lessons learned 10years ago when I did it the last time.
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Old 09-12-2022, 09:43 AM   #6
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Originally Posted by AppliedThinking View Post
Good points all. I finally got the time to troubleshoot the RV fuel pump. I installed a fuel line pressure gauge on the engine fuel rail and confirmed that I had no pressure (supposed to be 35-40psi). I looked at the fuses in the power distribution panel and they all looked good. Also verified that all the battery disconnect relays (chassis and coach) were at the proper voltage when turned on. Pulled the fuel pump relay and ordered a new one from Amazon. There is another row of 4 external relays next to the ones in the distro box that is not shown in the ford chassis manual. No clue what they do. There is only three things beyond the fuel pump relay and that is the connector on top of the fuel tank, the fuel filter and finally the fuel pump.
I am praying its not the pump. I did try and start the engine and it did fire for a brief instant.


I did not think of adding an external inline fuel pump. I just happen to have one that I use to transfer fuel from portable marine tanks to the vehicles. Hmm food for thought.


BTW, this is a Class A


If it boils down to the in-tank fuel pump. I will have to figure out a way to empty a full tank first. Its not a hard job to drop the tank but a serious challenge with any fuel in the tank. Lessons learned 10years ago when I did it the last time.
Sounds like you are on the right path.
Note; you could pull the line to the booster pump and see it it’s getting fuel. But again, the booster pump has to get enough fuel to boost.
External electric fuel pump, if used needs to be mounted as close to the fuel tank as possible. Electric pumps are designed to push fuel “not suck fuel” so keep that in mind. If you go with external pump, make sure you put a fuze in the electrical wires going to it, maybe a separate switch too.
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Old 09-17-2022, 05:09 PM   #7
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The problem resolution could not have been simpler. Fuel Relay
A big relief for me as I was not looking forward to dropping the fuel tank. (full)


For the record. Turning the key on will give you about 5-6lbs of fuel rail pressure. With the engine running its around 25lbs.


Our 98 Sun Sport does not have a booster pump. However I will look into potentially putting one in to bring the pressure up to 35-40lbs. The only hang up would be to tap into the 12vdc fuel pump power line. I would do it with a shielded pair conductor.


I am guessing the 4 additional relays to the left of the power distro box many be related to either the 6.5kw generator or maybe the two A/C units on the roof. My service manual gives no reference.


All relays are FOAB-14B192-AA which have common replacements at Amazon or any auto store. It would be a good idea to have a spare on hand....
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Old 09-18-2022, 01:23 AM   #8
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Maybe it would be a good idea to start your coach turn everything on and pull the relays one at a time so you’ll know what they operate.
Just a thought.

Mike R
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Old 09-19-2022, 01:35 PM   #9
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The low fuel pressure kinda bothered me (25psi at idle). It runs fine. However, reading on other F53 chassis and superduty 460 engines suggested possible fuel regulator challenges. There was some references to an adjustable fuel regulator as well. So, I took off the engine cover again for a peak. There is No Fuel Regulator on the top of the engine. I do see two fuel lines going down from the fuel rails to a location on the chassis drivers side. The journey continues....
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Old 09-19-2022, 03:55 PM   #10
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The low fuel pressure kinda bothered me (25psi at idle). It runs fine. However, reading on other F53 chassis and superduty 460 engines suggested possible fuel regulator challenges. There was some references to an adjustable fuel regulator as well. So, I took off the engine cover again for a peak. There is No Fuel Regulator on the top of the engine. I do see two fuel lines going down from the fuel rails to a location on the chassis drivers side. The journey continues....
One of the fuel lines is a return line to the fuel tank. When the fuel rails don’t need the extra fuel, fuel gets sent back to the fuel tank.
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Old 09-20-2022, 06:31 PM   #11
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Yes sir, got it. Humble Pie here. I do have a fuel regulator as it is on the forward driver side fuel rail. There was a very good set of pic's on eBay for a big block fuel rail that led me to finding it. It is outboard and opposite of the pressure gauge connection. Looks to be the two bolt type. There is not a lot of clearance between the top of it and a hose run above it that would probably preclude the installation of an adjustable fuel regulator. We shall see.
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Old 09-21-2022, 01:29 AM   #12
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If your going to put an adjustable fuel regulator on your rig mak th please it where you can raise the hood to futz with it..
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Old 09-21-2022, 06:36 AM   #13
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Access is via the engine cover inside the RV held in place by 9 captive screws. I decided on just a OEM regulator (non T-series) from Rock Auto. I did notice that the T-series stated 48psi where the higher end part was 41psi. While doing the change out I will continue to poke around looking for degraded rubber hoses as that is a fact of life with older engines. And the engine needs a bath even with the low mileage 15.6k miles.
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Old 09-24-2022, 04:46 PM   #14
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Time to close this thread. I replaced the fuel regulator and filter with OEM parts. As aforementioned, I use the high end Standard part. I had forgotten how fun it is to get the fuel filter loose out of the clip along the frame. A big flat blade screwdriver had to be used. The fuel leads did not want to come off either. I used a two different release tools where the metal one finally did the trick.
The engine purrs like a kitten (a very big kitten). Time for some Techron fuel injector cleaner as well.
Thank you all for your comments, time to close the thread.
Best Regards, JohnF
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ford v8 460, fuel rail, power distribution

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