Is your oil level good? What's the fuel pressure when cranking (minimum is 25psi at a minimum 100 rpm crank speed)? With the age of our trucks the pickup screen in the tanks are prone to disintegrating. The pieces then like to migrate into the fuel system creating problems/restriction in the fuel lines, tank transfer valve, etc. You may need to blow air back through the lines from the pump to the tanks and maybe hook up a container of fuel direct to the pump to see if it will start/run on that. The quality of fuel pumps these days is questionable, although I have not experienced problems with my replacements (I get OEM pumps from either RiffRaff or Diesel O-rings). Cheers!

 

That's really good advice. I would add, check to see if you have fuel in the fuel bowl and is there any debris in there?

 

You can leave the guts of the shrader valve in, you don't really need flow for pressure readings. The fuel lines that come up from the tank selector, one will connect to the pump with a short blue hose and the other will connect the Fuel Pressure Regulator (FPR) with a short black hose. You would want to blow back through the blue hosed one with low pressure air. The pump is a 2-stage pump, so the supply line will feed the low pressure side of the pump which sends it through the filter and then back to the high pressure side of the pump, which then sends it through the banjo fitting/lines to the rear of the heads (fuel rails). Excess fuel will return from the rails out the front of the heads to the FPR, and back to the tank(s) via the return line. See the attached. Cheers!

 

That's really good advice. I would add, check to see if you have fuel in the fuel bowl and is there any debris in there?

You can leave the guts of the shrader valve in, you don't really need flow for pressure readings. The fuel lines that come up from the tank selector, one will connect to the pump with a short blue hose and the other will connect the Fuel Pressure Regulator (FPR) with a short black hose. You would want to blow back through the blue hosed one with low pressure air. The pump is a 2-stage pump, so the supply line will feed the low pressure side of the pump which sends it through the filter and then back to the high pressure side of the pump, which then sends it through the banjo fitting/lines to the rear of the heads (fuel rails). Excess fuel will return from the rails out the front of the heads to the FPR, and back to the tank(s) via the return line. See the attached. Cheers! View attachment 799643

I think I'm following.. that diagram is pretty helpful. I'm assuming like 5-10 psi through? I don't want to mess anything up using too high pressure. Makes sense how to test the pump alone.

I just thought of this and maybe it helps? When I reinstalled my fuel bowl, I assumed when I turned on the ignition that that would "prime" it, filling the bowl with fuel. That's what I had heard from other videos, but the videos I found that showed priming were not with my 95 style bowl, they were slightly newer style. It did not fill, even with the ignition on for 2 full minutes. So, I filled the bowl manually thinking it was like a basic pump that needs liquid to start pumping.

Is this correct that it should not fill when the ignition is turned on, like to "wait to start" light? Seems like it should? I've found conflicting information about what exactly I should have on my year truck.

 

That I'm not sure of. Some of the folks that are more familiar with that year are better qualified to answer that. I know for the late 90s 7.3s it's not necessary to prefill the fuel bowl. I've never done it on my 99.

 

Since it's a mechanical pump, the engine has to be turning over (spinning) to move fuel. The later videos you see are probably the later SuperDuties that use an electric pump. Generally after changing a pump one would crank for a bit, push the shrader valve to let air out, lather-rinse-repeat until you get fuel. You can fill the bowl with fuel prior to help. 5-10 psi air should be fine. Cheers!

 

I'm pretty sure what I was watching was a sd. I thought all I had was a mechanical as you described, so that explains why I can't find these electric pumps on my truck that people talk about in other forum discussions. It's starting to seem like having a 95 is going to be tough to find bulk reliable info.

Block heater is on now, (I'm in Salt Lake City, UT), trying air this morning since I'm leaning towards a line blockage somewhere. If that doesn't work to keep it running I guess next step is replace the pump.

Thanks for all the help so far, hopefully I won't be asking more after today... fingers crossed.

 

There is no electric pump. I guess you could put an electric pump in, but generally they put out more pressure than the mechanical pump is providing (so the e-pump is not going to like that). There also would be no filtering of the fuel to the e-pump (it's not going to like that either). Most lower pressure e-pumps are not going to be compatible with diesel. I remember a guy that did exactly that, but at that point you might as well go straight e-fuel from end-to-end. Cheers!

 

There’s an e fuel setup for 94-97 that changes it all out for an electric fuel system like the super duties have. It’s a good upgrade but the kits aren’t cheap especially since there is a tank selector valve you have to deal with.

There’s an e fuel setup for 94-97 that changes it all out for an electric fuel system like the super duties have. It’s a good upgrade but the kits aren’t cheap especially since there is a tank selector valve you have to deal with.

Yea, I can't drop the cash on a new fuel system right now, and every thing on this truck is OEM, so I'll run the original setup as long as I can. I searched hard to find an un-modified OBS 7.3, so I'll keep it that way in as many ways as makes sense. I'm also no mechanic, so I want to know why it's acting up before I start bypassing things. Ford engineers are way smarter than I'll ever be.

So update, I had enough of hitting dead ends and used AAA to take it to a highly rated speed shop. Dude had a 95 just like mine for years so he's familiar with every bolt on it. I don't want to screw something up with stubborn ignorance..

Once I get the diagnosis and fix I'll post Incase it helps anyone else.

Thanks for your time everyone, will report back asap.

 

You would need a pre-filter for the pusher pump ("dirtier" than gasoline). Also, the pump would need to be rated for diesel fuel not gasoline (diesel will mess with the seals). The factory OBS fuel bowl is not meant to see the pressures that the SD fuel bowls are (remember the fuel bowl only sees the low pressure side of the pump. Cheers!

 

Yeah I know about diesel being dirtier and all that, after all I do own a SD and have a mechanical background. I guess I don't see why a system like is on the SD can't be retrofitted to an older truck. Surely it should be possible. Where there's a will there's usually a way, don't ya think? Maybe something needs to be eliminated, added or modified. I bet someone out there has probably already done it somehow.

 

You can do it, but you end up replacing the filter bowl, pump, lines, etc. At that point most folks will just go to an aftermarket or DIY setup with e-pump, regulator, pre and post filters. SD systems are also "dead-headed" where the OBS systems are not. Cheers!

 

It would be an interesting mod to do but how feasible it would be is something entirely different.

 

So, I got the diagnosis and it's something I didn't even consider...

Multi-part problem:

1. My fuel tank selector switch had some pinholes and was letting air in. I didn't notice the puddle, I thought it was just snow melt. We've had a lot of wet weather since it stopped running, so I didn't think twice about a puddle right where the bed meets the cab... which is pretty much where my selector switch lives.

2. The previous owner installed a low-quality ICP sensor, and it was malfunctioning inconsistently. Sometimes it would read fine, other times it wouldn't. Installed new quality sensor.

3. Put in the new Motorcraft fuel pump and fixed a leak from the old one.

So, all of that combined changed my fuel pressure from the previous 10psi to the correct 60ish psi. I didn't think anything of how it ran and drove since it's my first diesel, but apparently it is running WAY better.

Still smoking white a bit so I may have to tackle some injector work related to the lack of fuel pressure and non-atomized fuel for so long in the future.

Hopefully this ordeal can help someone trace what's going on with their rig.