"91 m923A2 won't start after sitting overnight....

[shorty53]

As title says, truck won't start after sitting overnight.
Replaced lift pump (didn't need to!).
Can get to start if I manually pump up fuel at lift pump, with injection pump "return" line cracked open, until I get stream of fuel.
Where is my probable "air leak" causing the IP to lose prime?
Thanks

 

[wilmart01]

As title says, truck won't start after sitting overnight.
Replaced lift pump (didn't need to!).
Can get to start if I manually pump up fuel at lift pump, with injection pump "return" line cracked open, until I get stream of fuel.
Where is my probable "air leak" causing the IP to lose prime?
Thanks

I had problems with air in the fuel line, the mechanic couldn't figure out, now I keep my tank full all the time and the problem went away.

 

[Ue413]

I do two things.....take off fuel filter housing, top off with diesel and replace. Take one of the fittings off the tank and with an air hose, inflate tank until you hear a burp, then replace fitting before air leaks out. Make sure your batteries are charged, shut-off is not engaged and crank.

 

[wheelspinner]

That's way too much work every time you want to start a truck, mine sits for weeks and fires right up. You have a hairline crack in the fuel line somewhere. Try filling the tank completely, if it starts, your problem is the line inside the tank. If it still does not start, its between the tank and the engine. Rubber line is cheap to replace. Its there somewhere.

 

[73m819]

Also the tank selector valve is a KNOWN issue, the O rings dry and crack, then suck air or allow prime to be lost.

 

[Ford Mechanic]

Also the tank selector valve is a KNOWN issue, the O rings dry and crack, then suck air or allow prime to be lost.

No duel tanks on the 923a2 so no selector valves.

 

[mcmullag]

pin hole size or smaller size hole in a fuel line sucking in air. Wish these trucks had intank fuel pump like a deuce and pushed the fuel to the engine instead of this set up that pulls the fuel from the tank to the engine. mine was the line from frame to filter, got a new hose made at at PH hydraulic place since it had those pressed on hose ends like hydraulic hoses do.

 

[73m819]

Yep, saw that AFTER I posted, I "read" 931, but was still drinking my first cup of coffee AND did not have my glasses on.

 

[Suprman]

The hose between the big fuel filter and the lift pump is a common culprit. The way that hose sits it can rub thru over time.

 

[trooper632]

Yep fuel line from lift pump to the fuel big fuel filter can. Replaced mine and starts every time, the hose didn't look bad either but it was

 

[Csm Davis]

Guy's come on these trucks are 30-40 years old replace all the rubber fuel line, and if you have that tiny inline filter replace it with a big military or civilian spin on type you will be happy you did.

 

[shorty53]

thanks everyone,
Csm Davis, you talking about small filter located on rear, left, side engine above lift pump?

 

[Cape Coastie]

Hey Shorty, my truck had the same issues and replaced filter and rubber fuel lines. Didn't really change anything. I decided to pull the pickup tube from the tank and touched the tube at the fitting and it just about fell out of the fitting. Resoldered the tube to the fitting and reinstalled and solved the problem. Used to have to prime every time to start. Now it can sit for a week and have no problems with prime. Starts right up. Good luck.

 

[Csm Davis]

thanks everyone,
Csm Davis, you talking about small filter located on rear, left, side engine above lift pump?

No, on all 939A2's they were built with an inline small silver fuel filter like you would find on a jeep. They were such a failure that the guy's would take boxes of them with them and the military issued a replacement kit with an old style big canister filter and hoses. The filter on the engine is on all 8.3L that I have ever seen.