Hey y'all, I'm in need of your infinite wisdom and guidance. I own a 1993 F250 7.3 IDI. Owned it about 11 months and it's ran and drove great since the day I got it. Yesterday I was driving the truck and it started and drove perfect as always until after I had been driving it for about 20 minutes. All of the sudden it starts lurching almost like it's misfiring or something. I get it to the shoulder and she dies on me. I get it to begrudgingly start and limp it a hundred yards further to a parking lot. This whole time I'm thinking that it must be fuel related. Now, as I mentioned I've had it for about 11 months. This whole time I've been procrastinating replacing the fuel water separator filter with a new 1 because A: I don't know when it was last replaced, and B: it's a Fram POS. I figured that I would have some warning before I had to replace it but I guess not maybe. ¯\_(ツ)_/¯
So I went, got a new fuel water separator filled it up with fuel installed it and it started right up. I feathered the petal for a couple minutes and then let it idle for 15-20 minutes to be safe. After which I was comfortable enough to drive it home. It ran and drove perfectly till about .5 a mile from the house and it started to do it again. I'm at a loss. I figured if it was the fuel pump, injectors, or the ignition pump it would do it all the time not after 20 minutes of driving. What do y'all think? Please help.

 

on the 93 .. the Fuel Filter Light "Should" come on when fuel filter is restricted and can often Illuminate if the lift pump is failing.

how much fuel is in the tanks ?

connect a Fuel pressure gauge and see if inlet pressure is dropping when it is failing IF not then it is most likely the IP. check the IP for leaks.

 

IF you have leaks on the inlet side and it is sucking air it will cause similar issues.
could be metering valve sticking, plungers sticking, or Tang Drive wear.

would be handy to test the Transfer Pressure and the Housing Pressure too.

it is not an injector Problem IMHO

 

How do I test the injection pump for this possible problems? All my life I've just thrown parts at vehicles until they are fixed and I'd like to get better at diagnosing so that I can confidently say what the problem is. With all my research and my general gut feeling I'm now leaning towards exactly that. Something injector pump related but I've got no idea where to start and I don't just want to buy a new one and put it on the credit card. I'd like to fix the one I've got if I can.

 

Definitely sounds like a fuel supply issue to me. It's sucking air somewhere or the mechanical pump has a cracked/broken diaphragm

 

the First thing to do is grab a copy of the Stanadyne DB2 Service manual.
this will explain the complete operation of the Pump including Troubleshooting and Repair.
You will need to make some special tools to work on the Pump as most of the tools are no longer available from Stanadyne, sometimes you can find tools on FleaBay

One tool is the 21900 this is the adapter to test the Transfer Pump Pressure <<<=== dang hard to find them nowadays but pretty easy to make (anyway just 1 example)

IF you haven't worked on them before they can be pretty tricky.

you might be able to get away with the ATF or diesel Kleen Fix... this is where you fill the filter then start the engine and run it for about 30 seconds then shut it down and let it sit for 24 hrs

As I said before you need to make sure the Lift pump mounted on the engine is working right and that you have no leaks on the inlet side.. the best way is to connect a Fuel Pressure Gauge.

 

here is trouble shoot in a Nutshell https://oregonfuelinjection.com/cont...leshooting.pdf

Everything else is covered in the Service manual

 

You can test the mechanical lift pump by disconnecting the fuel OUT and running a hose into an empty jerry can. Crank the engine with the 12V to the FSS on the IP disconnected and the mechanical lift pump should have positive flow into the jerry can. You can also put a clear vinyl hose between the lift pump and the fuel filter housing to check for air bubbles. If you see air bubbles then that's a sign of air intrusion.

 

Okay so now when driving I can't keep the gas pedal still. If I fluctuate the pedal between barely and floored I can manage to keep the truck from jumping, jerking like crazy. The rpm's are dancing anywhere between 500 and 3000. Please help me figure this out y'all. It was doing great, like she always has, till once again at the 20 minutes of driving mark she started lurching and jerking but I could get her to smooth out if I floored it. But the further I drove it the worse it got. Please help

 

Also, I pull it off at a parking lot because I think she's done for and won't go a step further and wouldn't you know it she sits there idling perfectly.

 

Really basic old school trucks. The odds are high of it just being a failing lift pump,a rusted out line,failing selector switch or a pickup issue in the tank.Just unhook the fuel pump from the tank to the pump line.Hook up a new hose that will reach into a jug a diesel and see if she'll run smooth off the jug.If so,then the problem is between the lift pump and the tank,if not,probably a bad lift pump or plugged fuel filter.Don't jump to conclusions of more expensive parts.It's human nature but resist the urge to think the worst lol.

 

Oh. Probably a bad lift pump.Do this first then:

 

I guess no one believes in using an Old Skool Fuel Pressure Gauge

you can install right on the Schrader Valve..... shoot, just remove the valve stem IF you don't have a Schrader Adapter slide the hose over the valve and use a Tie Wrap as a Clamp (it will hold just fine) a 0-10 PSI gauge is all that is needed...


I think the IP is toast JMHO
BUT you will not know until you do a couple simple checks, IF you cannot do the checks then send it to a Shop that can.

 

Well,it's more than likely he doesn't have one that's all.That why we offer the cheat methods too.Mostly millennials own these IDI trucks now.They be like,what's a fuel pressure gauge? Does it have a usb or mini usb port? haha

 

When you say lift pump are you referring to the mechanical fuel pump? Or is there another fuel pump that I'm unaware of? No rust on the truck at all, she's super clean. And both tanks are full so I doubt the pickup is the problem.