1991 F250 7.3 no start

[David A Hodson]

guys it’s been way too long since I work on an idi.
Son bought a 91 F250 with a 7.3 Ida that had sat for several years. After a bit of work I got it running but I never felt it was right. Lacked power and throttle response. Well the return lines developed a leak and the son decided to replace without me and got a set for a 6.9 and ever since can’t get it running. Inj pump not even pumping fuel too injectors. Also have high pressure coming out of return port of fuel filt.
At my wits end

 

[Thewespaul]

Likely if you look out how he routed the return, it’s not like stock and the ip isn’t getting enough return flow. You need a 7.3 return line kit for a 7.3, not a 6.9 kit. If the return is blocked for the pump it will not move fuel to the injectors because the housing pressure is equal to the transfer pressure, and the plungers displace nothing because it’s at equilibrium.

 

[Selahdoor]

Sounds like you have to fix what your son fixed.

It was running before. It isn't now.

Go step by step through what he did, with a fine toothed comb. Don't just assume that things are fine, because "he already did that".

 

[David A Hodson]

Thanks.
I forgot to post that I redone his mistake by installing a 7.3 kit. Could having the wrong kit screwed up something.
Also I don’t have any fuel out of the return fitting on the pump.

 

[Thewespaul]

Okay you’re a step ahead already. I assume you’ve cracked all the lines and you’re not getting any fuel anywhere, when you crank it and push the Schrader valve on the fuel filter head do you get fuel coming out with no bubbles?

 

[David A Hodson]

Schrader has very little bubbles. If you pull the return off filt fuel shoots way past dose of truck. All injector lines are totally loose

 

[Selahdoor]

Can you take off the air cleaner, and give us a few pics of the return line systems.

Also, with you getting no fuel through the return line to the IP... Makes me wonder if there is a clog somewhere in the return system.

If the return line down from this system, to the tank switch and then back to the tank is fine, (Blow on that. Yourself, not a compressor.), and clear, it wouldn't take much of a clog near the IP, to send all the return fuel back to the tank, and none to the IP.

Last... What did he/you lube the o-rings with? Grease? Did you maybe get something in the holes on the sides of the injectors?

 

[Thewespaul]

Aha! There’s your issue. Your regulating spring in your filter head is stuck. Pull the return fitting off the filter head and plug it with an 1/8” npt plug. Reroute the return line to tee into the return for the injection pump. Pressurized fuel will go the path of least resistance, with that return stuck open all the fuel is just getting pumped out the return there.

 

[David A Hodson]

Can you take off the air cleaner, and give us a few pics of the return line systems.

Also, with you getting no fuel through the return line to the IP... Makes me wonder if there is a clog somewhere in the return system.

If the return line down from this system, to the tank switch and then back to the tank is fine, (Blow on that. Yourself, not a compressor.), and clear, it wouldn't take much of a clog near the IP, to send all the return fuel back to the tank, and none to the IP.

Last... What did he/you lube the o-rings with? Grease? Did you maybe get something in the holes on the sides of the injectors?

Okay tad confused. I have fuel return from #2 inject to pump but I thought I should have fuel coming from pump as extra from the top housing going back to the tank not from the return side of injectors to the pump.

Lubed o-rings with fuel and clean oil mix

 

[David A Hodson]

You must be registered for see images attach

 

[Selahdoor]

Aha! There’s your issue. Your regulating spring in your filter head is stuck. Pull the return fitting off the filter head and plug it with an 1/8” npt plug. Reroute the return line to tee into the return for the injection pump. Pressurized fuel will go the path of least resistance, with that return stuck open all the fuel is just getting pumped out the return there.

A quick test for this would be to pinch the line with a pair of vise grips. If it's new line, it shouldn't be damaged, if you are not abusive with the vise grips.

 

[Selahdoor]

Okay tad confused. I have fuel return from #2 inject to pump but I thought I should have fuel coming from pump as extra from the top housing going back to the tank not from the return side of injectors to the pump.

Lubed o-rings with fuel and clean oil mix

Not completely sure about that, myself, to be honest.

My own experience... With the engine running, if I pull the return line off of the top of the pump... Fuel comes out the line. Not out the pump.

 

[David A Hodson]

I use a set of hose pincher and pinched off the line off filt and #2 inj to pump then pulled line off pump and had son crank eng. Have fuel coming out of top fitting on pump. Reinstalled said line.

 

[Thewespaul]

Keep the line from the filter head blocked and prime the system, should start now.

 

[Selahdoor]

Wes, can you answer the question of whether the fuel should be coming out the line or out the pump? Thank you.