1992 F SERIES 7.3 IDI STARTS AND THEN DIES

[ChristopherH]

I was just wondering if anyone has any suggestions out there about this problem. This truck is a 7.3 idi w/o turbo. It will start and run for 3 seconds and then die. It does this with a hot or cold engine. After doing this a few times it will start and run normally. The engine runs well when it is running. I have checked for battery voltage at the fuel cutoff solenoid during the concern and it is good and does not drop out. The injector return tees and o rings have been replaced. There are no fuel leaks found. I am suspecting possibly an aeration problem or fuel bleed back issue. Any common problems that anybody remembers on this?

[Bruce Amacker]

Have you checked fuel pressure or supply volume? These things were notorious for the mechanical pumps failing. The way I checked the pump for bleedback was like this: (labor intensive) Remove lift pump. Block the outlet with your thumb. Stroke the arm, operating the pump 2-3 times. If it hisses through the intake port (tube), the pump is bad. We found the majority of them bad. Use a pair of 3/8" studs to mount the pump, and if you want to put bolts back in, do so after one stud/nut is tight, as they are not super easy to get at. A floor jack and block of wood under the engine to stretch the motor mount a bit will help with clearance to access the FP, as it's stuffed against the crossmember.

 

Make sure the return line is clear to the switching valve: Pull the return hose off of the top of the injection pump and apply 5psi regulated air to it. Remove the fuel caps and verify there is air coming out of one of the tanks. KOEO, switch the switching valve and verify air flows from the other tank. I've seen the switching valve go bad causing weird starting problems by blocking the return flow. If the return flow is blocked completely, the truck will still run, but start hard.

 

If FP pressure/volume/fuel quality looks good, try a huge dose of additive in the FF. The injection pumps are commonly bad and additive may show an improvement if it is.

 

On the top of the injection pump there is a brass return fitting. Remove it from the pump and look through it, it should have a glass check ball held by a spring. Stick a toothpick or something similar in there to make sure the spring is not broken. if there is junk collected in the return valve that looks like coffee grounds, replace the injection pump.

 

If FP/return is good, put an injection pump on it.

 

I'm surprised I still remember all of this crap! We made LOT of money of these engines......

 

Good Luck!

 

[eastendpowerstroke]

Every thing Bruce said and if/when you take the lift pump off look inside at the cam lobe and ensure it is in fact still a lobe I've seen many that that acted like a bad lift pump but the pumps were fine, turned out to have a grove worn in the lobe and not pumping the arm.