Dead 7.3 IDI Diagnosis

[Jackson Fronsdahl]

Hey everyone, I'm looking for some help with my 1994 F-250 7.3 IDI factory turbo.

For the past few months it's had an intermittent issue where it'll randomly shut off while I'm driving. When it happens, the tach drops straight to 0 RPM, but the dash and electronics stay on. Sometimes itll studder pretty hard whole idling and then go back to normal idle. It'll usually restart after cranking, sometimes running rough for a few seconds before smoothing out. I also had the fuel filter light come on intermittently sometimes, flicker realky fast or stay on steady then then off. I replaced the fuel filter, which seemed to help for a while, but the problem came back and the lights still intermenty coming on. When I replaced the fuel filter, I didnt put any diesel in it to see how fast it'd fill, and it was SLOW, very slow to fill, so my leading theory is that my fuel lift pump is going bad.

Now it's gotten worse. The truck died again while driving, but this time it cranks very slowly instead of at normal speed. The batteries and starter are both new.

I'm just trying to figure out where to start. Could this be an alternator or charging issue, bad battery cables/grounds, a fuel shutoff problem, air intrusion? Has anyone had a 7.3 IDI do this before?

I'm fairly well versed with engines, specifically building 4cyl motercycles, but this is my first diesel and its a bit of a different monster

Any advice or troubleshooting steps would be greatly appreciated. Thanks!

 

[Jesus Freak]

Im calling it bad battery cable ends. Corrosion will build up inside the cable ends and do what you describe. Power is shutting off to the fuel solinoid thus the engine instantly dies, so check the bigger 8 pin connector that goes from the firewall to the glowplug harness..... ive had issues there before...... you got this, keep us posted.

 

[Jackson Fronsdahl]

Im calling it bad battery cable ends. Corrosion will build up inside the cable ends and do what you describe. Power is shutting off to the fuel solinoid thus the engine instantly dies, so check the bigger 8 pin connector that goes from the firewall to the glowplug harness..... ive had issues there before...... you got this, keep us posted.

Thank you, I'll take a look at it when I get home. Trucks only got 206k miles so its not super high milage, but the wiring isnt in beautiful condition so thats something I was worried about.

 

[Jesus Freak]

Thank you, I'll take a look at it when I get home. Trucks only got 206k miles so its not super high milage, but the wiring isnt in beautiful condition so thats something I was worried about.

The battery cables can actually look just fine...... exemplary even..... but be green yuck inside the cable..... usually right next to the battery terminal. Give em a big wiggle.....

 

[Jackson Fronsdahl]

The battery cables can actually look just fine...... exemplary even..... but be green yuck inside the cable..... usually right next to the battery terminal. Give em a big wiggle.....

Will do, thank you!

 

[DaveBen]

Also check the other end of each cable. They can be corroded there.

 

[Jackson Fronsdahl]

The battery cables can actually look just fine...... exemplary even..... but be green yuck inside the cable..... usually right next to the battery terminal. Give em a big wiggle.....

I'm fairly certain I'm looking at the right thing, the smaller female connection felt very lose when I was taking it off and I can see the actual connection moving.

 

[Jesus Freak]

I'm fairly certain I'm looking at the right thing, the smaller female connection felt very lose when I was taking it off and I can see the actual connection moving.

That's the fuel shut off solinoid and yes, that can be an issue. The larger connecter is the fuel shut off solinoid...... but theres a big Grey connector on the passenger side of the engine that connects the engine wiring harness to the harness on the fender, unplug and clean it too......

 

[IDIBRONCO]

I suspect that you have more than one issue here and they may or may not be connected. I'd say that you definitely have an electrical connection issue. Don't forget about your suspected weak lift pump though. You didn't mention the conditions that you were driving in when the engine died. Cruising with a steady, light throttle or during/right after acceleration. Another reason why you should still keep the lift pump in mind is that the fuel shut off solenoid (FSS) won't affect the idle. A weak lift pump sure can.

 

[Jackson Fronsdahl]

I suspect that you have more than one issue here and they may or may not be connected. I'd say that you definitely have an electrical connection issue. Don't forget about your suspected weak lift pump though. You didn't mention the conditions that you were driving in when the engine died. Cruising with a steady, light throttle or during/right after acceleration. Another reason why you should still keep the lift pump in mind is that the fuel shut off solenoid (FSS) won't affect the idle. A weak lift pump sure can.

I do think its more then one issue, I'm currently even trying to get it to start. Both batteries read 12 41v but its cranking incredibly slow. So I think its having more then one issue, which is phenomenal lol

 

[Jackson Fronsdahl]

That's the fuel shut off solinoid and yes, that can be an issue. The larger connecter is the fuel shut off solinoid...... but theres a big Grey connector on the passenger side of the engine that connects the engine wiring harness to the harness on the fender, unplug and clean it too......

I found the big gray one and connections look solid, not to wiggly nor corroded. I'm trying to get it to even start, both batteries read 12.41v but its cranking super slowly.

 

[IDIBRONCO]

Both batteries read 12 41v but its cranking incredibly slow. So I think its having more then one issue, which is phenomenal lol

I'd guess battery cables here. One end may be loose and you haven't noticed it yet. Maybe it's the engine end of a ground cable.

 

[Jackson Fronsdahl]

I'd guess battery cables here. One end may be loose and you haven't noticed it yet. Maybe it's the engine end of a ground cable.

Yea, idk at this point. I checked and cleaned the big gray connector, the fuel shutoff solenoid connector, and the battery terminals. Both batteries read about 12.4V at rest, but while cranking they drop to around 8.6-9.1V. The starter engages and turns the engine, just extremely slow, like weak batteries. The fan and belts are turning, so the engine isn't free-spinning. The starter, relay, and both batteries are all fairly new. The truck originally died instantly while driving with no sputtering, but now it barely cranks. I also tried jump-starting it with no real improvement. Is there a specific voltage drop test or cable test I should do next, or does this point more toward a bad cable, ground, or a defective reman starter?

 

[Jackson Fronsdahl]

That's the fuel shut off solinoid and yes, that can be an issue. The larger connecter is the fuel shut off solinoid...... but theres a big Grey connector on the passenger side of the engine that connects the engine wiring harness to the harness on the fender, unplug and clean it too......

At this point I'm not sure, there's likely more then one issue. I checked and cleaned the big gray connector, the fuel shutoff solenoid connector, and the battery terminals. Both batteries read about 12.4V at rest, but while cranking they drop to around 8.6-9.1V. The starter engages and turns the engine, just extremely slow, like weak batteries. The fan and belts are turning, so the engine isn't free-spinning. The starter, relay, and both batteries are all new. The truck originally died instantly while driving with no sputtering, but now it barely cranks. I also tried jump-starting it with no real improvement. Is there a specific voltage drop test or cable test I should do next, or does this point more toward a bad cable, ground, or a defective reman starter?

 

[asmith]

You can try and check the resistance in the main battery cables. I dont know what the max resistance that is allowed, but I would want as close to 0 as possible.
If you have been cranking it a lot, its possible to burn up a brand new starter pretty quickly. If it were me I would trow the batteries on a charger overnight and get new battery cables. From there I would see how it cranks, if it is still slow it may be the starter.
The other part to the hard starts is making sure you don't have air in your fuel lines and your glow plugs are working. Once it is spinning fast enough, I would look into those things. With an air tight fuel system and working glow plugs, mine lights off in what seems like one revolution, its pretty amazing.