7.3 V8 normal aspirated Diesel engine problem

[dmetalmiki]

Well here's one for the book..this problem is driving me NUTS!.

(AA) The vehicle. 1989. F350 ambulance with international 7.2 V8 normal asperated Deisel.
The Problem. Starts fine..Runs for 5 seconds and stops!
rectification.
1) new heater control relay. 2) new timer) 3) new heater plugs. 4) new fuel filter.
5) fuel drained replaced.
Further recification. Bypassed heater realy assembly. to manual switch.
Starts fine runs 5 seconds stops!. (curses kicks tyres, starts fine runs 5 seconds stops)
New piping from the mechanical lift pump. after pipe off test,pumps like a gusher!
IT will NOT start once it stops. BUT the tinyest wiff of ether and WHAM starts runs fine.......(.and nope! ) Carries on running just fine. drives good starts and runs fine from then on. BUT let it stand 1 hour and it starts fine STUTTERS struggles and then just keeps going. then.. starts runs everytime and drives fine.

Let it stand for Anything over an hour and...Go back to sentence (AA )!.
This is driving me nuts , so ANY ideas or simolar experience with this model engine (which has done only 9000 kilometers.) appreciated> I need another "viewpoint". anyone.

 

[DodgerRoger]

Sounds to me like it losing its prime, IE its getting air in a fuel line. Stop ethering your engine. Try to run the truck off of a bucket and also watch the fuel lines for any sign of leaking. Brake clean everything clean and blow it dry before you start.

 

[fsearls92]

I have an 89 F-250 with the same engine but it is a 7.3 liter diesel. On the visor it says to hold pedal fully depressed in temperatures under 32 degrees F and half throttle down for temperatures above 32 degrees F. It is the factory sticker and my truck does the same if I don't hold the pedal down as instructed on the visor.

 

[dmetalmiki]

ok but

I have an 89 F-250 with the same engine but it is a 7.3 liter diesel. On the visor it says to hold pedal fully depressed in temperatures under 32 degrees F and half throttle down for temperatures above 32 degrees F. It is the factory sticker and my truck does the same if I don't hold the pedal down as instructed on the visor.

The throttle settings work as you say. When floored the fast ifdle is set and kicks off when the tempreture rises. As mine is plugged into the engine heater its allways warm and the problem persists if cold hot warm or anywhere. I used to have a pre prime pump and you could hear the exess fuel going back to the tank ok..removed that aand what puzzles me is why the slightes TINY wiff of ether and it starts up straight away. (after its cut out). and holding the heaters on makes no difference at all. (the heaters are NOT used with the ether puff.) still starts fine. Just without that it can crank all day= no start. Im puzzled because of the high pressure delivery from the machanical fuel pump. and why it stops after 2 seconds no matter the throttle setting but with the mearest smell of ether it starts runs goes good!. its allmost as if the fuel was not combustable. (on cranking). but then why run fine when it does start without missing or slugging?. As a last measure i will try the "can" feed tommorrow and report back. And yes it is the 7.3 truck engine.

 

[73m819]

Sounds like you are running it out of fuel by SUCKING air.

 

[5tonman1971]

Sounds like your sucking air or loosing compression/low compression causing it to die. From your description it seems like when it gets warm it runs fine.

 

[Jeepsinker]

I'll just put it out there since no one else will: It's because it's a Ford. Stick a bow tie over that blue oval and it'll start fine.

 

[Jeepsinker]

In all seriousness though, you must be sucking air as others have said. Reinstall your pre- priming pump, and then PLUG YOUR RETURN Line, pressurize the lines with the newly reinstalled pump, and watch and wait for a drip or wet spot to form on lines or connections somewhere. That's the best way to find your air leak.

 

[Gunzy]

Look at the injectors and see if any are wet or damp. They have "o" rings on the fuel return caps that tend to leak. Also check the back of the injection pump for leaks.

 

[Jeepsinker]

Also, fwiw it sounds like it is sucking air upstream ( engine side) of the fuel filter. So that may or may not help you find the suck.

 

[dmetalmiki]

Tried it again today with free of can fuel. and same. 2 or 3 seconds Dies. Its just as though the electric cut off switched off every time. The maddening thing is why it sarts and runs fine after the second start with the MEREST sniff of ether, No ether no go! if there was an air leak it would surley keep stopping after such a small start crank time the second (allways) try. I will investigate further tommorrow and try the tips offered as well Thanks all anyway. I will report back. (now if ONLY I could find where murphy's hiding!)

 

[shovelheadi]

What does the oil pressure do? If the lower pump is having trouble, it won't make oil pres. Mine will start and die, then will have to spin until pres comes up. It then runs fine. Just saying watch oil while cranking. If no pres, no fuel from injector.

 

[youngunbd]

These IDI's are fun and work great when they are working. You might want to put new O-rings and return lines on it, the kit is 45 bucks. I'd leave the injectors in and not do the copper washers just yet. Pop all the return lines and plastic caps off, pick both O-rings off the injector. lube with grease or diesel, slide first O-ring on, lube 2nd and slide down over first to the 2nd groove. Set the cap on and use a socket large enough and hammer to seat it all the way down. Seating the caps is important! Hook up all the new lines with new clamps then bleed the air out by cranking with your foot all the way down on the go pedal. Might as well replace the fuel filter if you haven't done so already. Make sure the glow plugs are good also. If the return line kit doesn't do it, post here and we can keep trying. I have an 86 f250 with a 6.9 IDI, I love it. If you want to build a good solid motor, you can do it with an IDI, the performance market is growing so fast right now!

-youngunbd

 

[F18hornetM]

Its been many years since I worked on these as they are all gone now from the fleet. but here are some thoughts
From reading the post I doubt any issue with glow plugs as it starts! Glow plugs should not cause it to shut off after a few seconds. Also plugged in and nice and warm, Glow plugs are really not needed. I also cant see why return lines would be an issue with not continuing to run. They would just leak. they can be left off and it should still run, however messy. Low compression cant be an issue if starts then stops. Low compression may cause hard cold starting, but once started will run, even with low compression.
If you think there may be a suction leak. You can go back near tank, and temp install an electric fuel pump, or use regulated air pressure. Somebody mentioned it but this will pressurize the suction side of the fuel system. Or use a container of fuel on the suction side of lift pump and will eliminate any suction leak between lift pump and tank. If you say the lift pump has good flow, then I doubt a suction leak. Have you tried bleeding air from injectors? Make sure no bubbles come from lines.
The 6.9 and 7.3 were pretty reliable engines. Not as much power as the newer 6.4's and 6.7s, but a whole lot more reliable and inexpensive to repair. Good luck.

 

[dmetalmiki]

This problem is now Resolved, and the cure..after pondering in a late night dream!..WHY does the engine "go out" after 5 seconds every time? The consistant factor was (is) the timer delay relay AND my attempts to start it using (aproximately) the same timing with a bypassed timer. For first time every time good start I held the heater activation switch ON untill the engine fired and ran smoothly. which it did (does) now by holding the heaters on longer. Wish i had thought of this with the cheyennes we had had (nothing but) trouble with. I am now so pleased with this truck (A fully fitted out and functioning Ambulance ) I shall be looking to present at shows and events this years season.

 

[Jeepsinker]

If you need commonly available( in America) parts, I would be happy to acquire and ship them to you if you ever find yourself in need.

 

[dmetalmiki]

If you need commonly available( in America) parts, I would be happy to acquire and ship them to you if you ever find yourself in need.

Thank you kindly for that offer..and I will gratefully accept it next time we need parts. It has new heater plugs new timer and relay (now bypassed!) Side steps wheel arch flares , additional lights..I think it looks better now for it. thanks to everyone that took time out to contribute to my problem,,I hope the resolution hepls someone else with a similar problem (with similar or diss similar trucks)

 

[F18hornetM]

That's awesome you found the problem. Thanks for sharing what you found. Those were good motors.

 

[youngunbd]

I'd beware of using the glow plugs longer than 15 seconds. If you do decide to go back to using the controller, one of the screw in solid state controllers has worked flawlessly for me for quite a long time. Usually these trucks only need about 8 seconds of lit glow plugs in 40 degree weather and it should fire right up after that.

I hope it continues working well for ya, they are great motors