Fuel leak
More Turbo
Joined: Oct 2014
Posts: 696
Likes: 82
From: Alberta Eh
Check the return line the goes between the back two injectors (7&8), it dips down out of sight and it’s usually dark and dirty back there. It’s 5/16 hose if it needs replacing. There’s a lot of places for these engines to leak fuel from lol
More Turbo
Joined: Oct 2014
Posts: 696
Likes: 82
From: Alberta Eh
OP I think I’m wrong, it would be 1/4 inch hose back there. Going down from the brass T to your hard line back to the tank is 5/16.
lonewolf I’ve had fuel leak onto my starter, and also fuel pour onto the exhaust pipe crossover when that short piece of 5/16 hose cracked. I was just pulling out of the yard thankfully. The original hose lasted pretty good.
lonewolf I’ve had fuel leak onto my starter, and also fuel pour onto the exhaust pipe crossover when that short piece of 5/16 hose cracked. I was just pulling out of the yard thankfully. The original hose lasted pretty good.
Cross-Country
Joined: Oct 2020
Posts: 75
Likes: 11
From: Bellingham
I just did all my fuel return hoses and injector caps yesterday. If you find fuel is leaking from one of those, be advised that there are two different sizes depending on the year. Make sure you get the correct parts kit. Split was around '89. This article proved to be very helpful 6.9L & 7.3L IDI Diesel Fuel Injector Replacement Procedures (dieselhub.com)
The fuel heater can also leak and I could see that maybe blowing back onto the starter if it's leaking heavily enough. It's on the passenger side on top of your fuel filter.
The fuel heater can also leak and I could see that maybe blowing back onto the starter if it's leaking heavily enough. It's on the passenger side on top of your fuel filter.
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There does not seem to be fuel on the valley pan.
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It is definitely diesel
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OP I think I’m wrong, it would be 1/4 inch hose back there. Going down from the brass T to your hard line back to the tank is 5/16.
lonewolf I’ve had fuel leak onto my starter, and also fuel pour onto the exhaust pipe crossover when that short piece of 5/16 hose cracked. I was just pulling out of the yard thankfully. The original hose lasted pretty good.
lonewolf I’ve had fuel leak onto my starter, and also fuel pour onto the exhaust pipe crossover when that short piece of 5/16 hose cracked. I was just pulling out of the yard thankfully. The original hose lasted pretty good.
Posting Guru
Joined: May 2015
Posts: 2,036
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That hose goes to a t back there. Some of them had an olive in there and would just loosen up..
4th Gear
Joined: Jul 2021
Posts: 4
Likes: 0
Same issue
I know this is an older thread, but I figured I’d give it a try. Currently having the same issue on a 94 7.3 NA. Replaced all the return lines including the crossover that dips into the valley pan. Doesn’t seem to have fixed it. Also installed an electronic fuel pump and blocked off mechanical pump with a plate. Fuel only drips when the engine is running, not when the fuel pump only is on. Not noticing any fuel in the valley pan.
On a side note, I replaced the fuel tanks and fuel selector valve, and also some sections of line that looked pretty rough. I can’t keep the fuel bowl primed. Obviously getting air somewhere, but no fuel leaks other than the one mentioned above. Truck runs fine when drawing fuel from a Jerry can on the ground. The leak above existed before any of the fuel tank/lines were done.
Any ideas offered are appreciated!
On a side note, I replaced the fuel tanks and fuel selector valve, and also some sections of line that looked pretty rough. I can’t keep the fuel bowl primed. Obviously getting air somewhere, but no fuel leaks other than the one mentioned above. Truck runs fine when drawing fuel from a Jerry can on the ground. The leak above existed before any of the fuel tank/lines were done.
Any ideas offered are appreciated!
Tuned
Joined: Sep 2024
Posts: 486
Likes: 121
From: Ougadougou
I know this is an older thread, but I figured I’d give it a try. Currently having the same issue on a 94 7.3 NA. Replaced all the return lines including the crossover that dips into the valley pan. Doesn’t seem to have fixed it. Also installed an electronic fuel pump and blocked off mechanical pump with a plate. Fuel only drips when the engine is running, not when the fuel pump only is on. Not noticing any fuel in the valley pan.
On a side note, I replaced the fuel tanks and fuel selector valve, and also some sections of line that looked pretty rough. I can’t keep the fuel bowl primed. Obviously getting air somewhere, but no fuel leaks other than the one mentioned above. Truck runs fine when drawing fuel from a Jerry can on the ground. The leak above existed before any of the fuel tank/lines were done.
Any ideas offered are appreciated!
On a side note, I replaced the fuel tanks and fuel selector valve, and also some sections of line that looked pretty rough. I can’t keep the fuel bowl primed. Obviously getting air somewhere, but no fuel leaks other than the one mentioned above. Truck runs fine when drawing fuel from a Jerry can on the ground. The leak above existed before any of the fuel tank/lines were done.
Any ideas offered are appreciated!
As to your side note I am not sure what you mean by keeping the fuel bowl primed. Do you mean fuel filter? AFAIK there isn't a fuel bowl on the IDI.
4th Gear
Joined: Jul 2021
Posts: 4
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Fuel leak
Yes, fuel bowl = fuel filter in my poor vocabulary. Apologies for the confusion. IP is new, and I cleaned and inspected everything on install. I don’t see anything indicating that as the source. I hooked the Jerry can back up yesterday and everything ran fine, fuel leak aside. I’m wondering if it’s possible that it’s leaking from the injector itself? Can it leak somewhere that it would run down the passenger side of the back of the motor but not be visible from the top?
Logistics Pro
Joined: Jun 2017
Posts: 3,954
Likes: 509
From: Edmond, OK
Injectors can leak. Either from the returns, or between the injector and injector line. Did you replace the injectors when you put on a new injection pump?
Last edited by Olds64; Oct 26, 2025 at 12:22 PM.
Tuned
Joined: Sep 2024
Posts: 486
Likes: 121
From: Ougadougou
Yes, fuel bowl = fuel filter in my poor vocabulary. Apologies for the confusion. IP is new, and I cleaned and inspected everything on install. I don’t see anything indicating that as the source. I hooked the Jerry can back up yesterday and everything ran fine, fuel leak aside. I’m wondering if it’s possible that it’s leaking from the injector itself? Can it leak somewhere that it would run down the passenger side of the back of the motor but not be visible from the top?