I appreciate your help!

I'm going to try and locate a gauge and hose so I can drive the truck around with gauge in hand to see what the fuel pressure does under load.

I did try unplugging the fuel pressure sensor and the truck seemed to run even rougher so I think the sensor itself is working. I also tried unplugging a vacuum hose that went to the intake manifold and sprayed some carb cleaner into the house to see if it would change the idle. It didn't seem to change much although the truck is idling so poorly now it's hard to tell. I know the engine was getting the carb cleaner as the truck was burning the carb cleaner out the exhaust.

A friend of mine pointed me to this link. These are the EXACT symptoms my truck has:

https://www.yourmechanic.com/article...-jamahl-walker

 

Got to work on this thing more last night with the help of a buddy with a more high end scanner.

The first thing we noticed is there is no schrader valve on the fuel rail of this truck whatsoever to hook a mechanical gauge up to get a reading. We pulled the upper intake hose off and looked / felt all the way to the back of both sides of the rail and nothing. I'm not sure if that's a 3v only thing, but unless we both missed it I really don't think there is one.

It makes me a little uneasy not being able to test the fuel pressure mechanically, but the scanner was able to read fuel pressure live. We fired the truck up and initially it started out at 30psi at idle, but within seconds it tapered off. It got as low 18-20psi and would drop even further when throttle / load was applied. We could also see where the PCM was trying to max out the injectors at 33.33% when this would happen which tells me it is definitely a fuel / lean condition.

We decided to check the Fuel pressure driver module. Like the fuel rail pressure sensor the FPDM looked brand new (dorman part). Whoever installed it actually did it right and used four studs with nuts between the back of the new sensor and the frame of the truck to keep corrosion away from the sensor. We bypassed the sensor by grounding it out completely and no change to fuel pressure under load at all.

We can audibly hear the fuel pump kick on, but I am still thinking it's a fuel pump issue. There still could be issues with the fuel pump internally not being able to maintain pressure. It doesn't appear to me that the fuel pump has been dropped anytime soon which was a good sign because if someone had tried to change the fuel pump out as well we would really be out of ideas. It seems to me like someone tried to change the easier external sensors, fuel rail sensor and FPDM.

Thoughts?

 

If you have not replaced the fuel filter with a new one already, I would do that. It's cheap and about 10 minutes of your time. It's located under the truck by the drivers side door.

Sounds like a fuel issue. There should be a shrader valve on the drivers side fuel rail.

Start with the fuel filter first. Then I would check the fuel regulator/replace before replacing the fuel pump itself.

Both the fuel filter and the fuel regulator are cheaper than an hour time at a shop.

 

I didn't personally change it, but the fuel filter looks brand new. I peaked at it last night. I planned on replacing it with the new fuel pump anyway, but I may throw it on first to see if that helps anything initially.

The driver side of the fuel rail does have the fuel pressure sensor, but there was no schrader valve I could find. Looked for a good 10 minutes all up in the engine bay

The fuel pressure sensor has also already been replaced. It looks almost brand new. It looks to me like the only thing that hasn't been replaced is the fuel pump (and I don't even know that until I get the tank dropped).

 

Oops, I typed drivers side for the fuel test port... It's actually on the passenger side behind the PCV hose. It's towards the rear passenger side of the fuel rail. It's tucked in there nicely.




Fuel Pressure Port on V10

 

Sounds like the pump, but before changing it what voltage is the fuel pump getting?
The fuel pump relay contacts may be corroded and not enough power is getting thru to the pump to run efficiently.
When the load goes up the power needed to run the pump will go up, too.
You can probe the PK/BK from the inertia switch to the fuel pump for a reading.
On our 2003 the fuel pump voltage reads .5v less than system voltage - i.e. system - 13.4v, fuel pump - 12.9v.
If the pump is getting under 12v that may not be enough.

 

I will check this tonight. Thank you for the direction! Were you able to test voltage under load?

It's just weird because when the fuel pump initially kicks out you can audibly hear it working. Both the new and old we could hear.

My buddy and I dropped the tank last night to go ahead and replace the pump / fuel filter. I knew it was bad news when I saw there was an OEM Motorcraft pump in the tank that was dated 11/2014. Must have been replaced fairly recently. Went ahead and replaced the pump anyway while we had the tank out as well as the strainers. The old ones looked pretty bad to be honest. No change whatsoever.

To try and eliminate more problems we uncapped the brand new motorcraft fuel filter on the engine side and hooked up a fuel pressure gauge directly to the outlet of the fuel filter. Cycled the key with the engine off several times and it never got higher than 20psi and was at 15'ish psi most of the time. It's definitely something with the fuel pump / sending unit side of the truck.

 

The voltage was the same under load.
I added a voltmeter mainly to watch the charging system and later added a source switch so I could also look at the voltage going to the fuel pump.
I had added a relay triggered by the OEM fuel pump relay and had a problem with the circuit breaker for the new power source.
Your relay contacts might be pitted so that 12v still goes thru, but not a lot of current.
You could try a test with a jumper wire from the battery directly to the PK/BK wire at the inertia switch.
Then jumper all the way back to the fuel pump.
You might have a broken wire with just a couple of strands left.
I once had a wire in a distributor get kinked and it ran fine until there was one strand of wire left connected.

 

Check the voltage AT THE PUMP when it's running and see what it's getting. If there is voltage drop in the relay, inertia switch, or wiring, it'll show up right at the pump.

 

The truck would always initially startup fine and after 20-30 seconds the fuel pressure would eventually drop off until the truck died completely. Having said that we verified a constant 13.2 volts at the pump (tank dropped with upper half of sending unit off testing wires at the pump) throughout this entire process.

While we had the upper half of the sending unit off the tank but the power wires and feed line hooked up we noticed we could hear fuel flowing back into the tank when cycling the key. There's this little bypass (I'm guessing that's what it is) that slips over the pump when it's in it's housing. This bypass, after 20-30 seconds of the truck running, was allowing all of the fuel being pumped to just flow back out into the tank. We plugged this to test our theory and the truck fired up and is running perfectly holding 40.xx psi at idle. Drove it for a good half hour last night and not a single hiccup.

So lesson learned I probably should have just replaced the sending unit.

 

Idle fuel pressure should be around 28-30, and 38-40 under load.

Of course, that's the 2-valve, I'm not sure about the 3-valve, but normal fuel injection is usually around those values.

40 sounds high at idle.

If two pumps do the same thing, and the bypass in your pic is included with the pump, than something else is wrong and it's causing the bypass to open.

 

The bypass in my pic is not included with the fuel pump. It is part of the sending unit assembly. With verification of proper voltage at the pump I'm not sure what other issue I could have besides something in that bypass or something within the fuel sending unit.

40psi at idle I don't think is too uncommon. A buddy of mine swapped an LS into his old chevy pickup and that thing runs at 50 something psi at idle. The scanner we used on the truck actually calls for 39.15psi fuel pressure at idle. At least that's what it's saying for desired fuel pressure at the rail.

 

Then I guess you need a new sending unit

Fords are usually 28-30 at idle, and 38-40 while under load. Again, not sure about the 3-valve, but I don't think they would change it much.

Either way, that bypass is probably your culprit.

 

I appreciate all your help guys!

 

You might want to consider replacing the entire bucket while you are there. I had a problem
on a mustang that took months to troubleshoot, ended up that orangeish
corrugated hose in your picture had a fine crack in it, would only leak when the pump
tried to bump up the pressure. Car would be fine most of the time but fall flat on
it's face when the blower would kick in.