Truck Don't Start

Help, my truck won't start. Been running okay but wouldn't crank this weekend. Turned over normally, full of fuel. Ran okay weekend before and parked normally but now nothing. Where to start? First diesel and ain't much of a mechanic even when standing under a shade tree. 1988 F450 7.3 IDI rollback truck. I did find fuel to the filter (valve) but it did not run out of fuel anyway. Any help is appreciated...

"Wouldn't crank", "turned over" and "nothing" all indicate conflicting conditions. Is the engine turning (cranking) when you turn the key? If so, next thing to check is FSS. Disconnect, turn the key to RUN, and check for voltage at the connector. Then disconnect/reconnect (key still in RUN), you should get a "click".

Any smoke from the tailpipe while cranking?

Is it cranking any slower than before?

Answer these questions and maybe that will tell those watching this whats wrong. If the engine is not cranking fast enough you will never start it. If you have a standard trans you might push start it too. The faster the engine cranks the hotter the compression is and the hot air ignites the diesel when it injected into the engine. When air is compressed slowly it will not gain heat. But compress it fast and it heats way up. Diesel requires 942 degrees to ignite.

First, thanks for replying.

Truck does not start though the motor is turning over as fast as it has been, cranking speed is normal.

Okay so I googled FSS and it is a fuel shut off solenoid. Will try finding it, disconnecting and testing it next.

I don't recall seeing any smoke while cranking but by myself so not sure. I'll try googling a pic of the FSS.

Thanks again fellas. New2diesels is more than just a catchy nickname ;-)

The fuel shut off solenoid in found in the top of the injection pump cover. You really can only see the wire connection for it. The wire you need to remove to check if its working is the large spade connector. Its the wire closest to the radiator end of the truck. The back wire is the internal electric advance.

You could also do a SO simple test that will allow you to check for Diesel fluid delivery to the injectors to get her going . Get an open box wrench 9/16 or 5/8 ( can't recall the Size ) and loosen one of the injectors cap nuts loose Pick one outa the 8 . Go inside the truck and crank it up go back under the hood and check for diesel poring under that cap or all over the place . If you see diesel all over then your pump doing it's work or at least supplying .

You could have some air got into the system and by doing that you doing 2 things , 1st verifying you getting diesel delivered to the system , 2nd letting any possible air to escape out ( bleeding the system in a way ).

5/8"

Okay, I found power to FSS wire with key on, FSS clicks when wire replaced with key on. Cracked front left (driver side) injector line and got fuel there. Note the key switch no longer turns starter but shorting across from top post turns starter. Found some frayed wires at this point (starter relay?) and after messing around with that the key no longer activates starter. I think I caused this problem jiggling wires, so I think this starter relay may be bad and will replace and repair frayed wires too.

I'm not sure what all these wires control but could non-start be due to one of the frayed wires controlling "run condition"? Well it's off to the parts store for a new relay. I least I got a three day weekend to try and figure this out. Any more helpful hints are appreciated.

That fender mounted solenoid controls most if not all power to the engine. Find the large wire harness bundle that feeds the engine. Now locate the big coupling disconnect. It will be near the passenger fender well. Open that up and look for corrosion. This is a known issue with this plug. Any corrosion in there will melt it and cause fires. Now see the very end of said plug. There are 2 yellow wires there. Those supply power to the glow plug controller. Many times this are melts and you will not have power to the controller so there is no glow plugs to start a cold engine. Plenty of information on bypassing this plug too. But remember this. Those yellow wires are hot all the time with 12 volts and about 2000 amps. Same with the alternator heavy wire. Just trace these wires back to the solenoid and you can see they end up back at the hot side of the batteries.

Okay guys some form of success! The sweet sound of a running diesel but I had to jump it from the solenoid to turn the starter. The big electrical coupling was greasy and filthy but some electronic spray cleaner cleaned it up and now she runs. Note the big yellow wires had previously melted the plug somewhat and the PO must have pulled them out separately when he ran the manual glow plug push button.

Right now the truck still wont turn the starter by the key, so I'm still trying to track that down. That was not the original problem but something that happened as I tried to figure out why the truck would crank but not run. I've got some of the dash panels pulled down to look around but how do I track the key start function either from the key end or backwards from the opposite end.

Note I just put in a brand new starter solenoid. The small wire to the top of the solenoid should be the "key start" signal to the solenoid, correct? With the key in start mode I should get 12 volts there it seems. Note there was no wire going to the small solenoid post on the bottom.

Thanks guys for the advice, any help with this new problem is appreciated. This is a great forum!

I am only receiving .01 volts at the solenoid when turning the key so either the switch just happened to go bad while working on other problem or I've rubbed a wire the wrong way somewhere during my poking around. Back to searching...

When you turn the ignition switch to the first section does your dash warning lights work? Then when you turn the switch to the start section on the ignition switch does all the warning lights turn off? Easy way to check if the ignition switch is functioning is have the radio turned on. Set the ignition switch to the first part so the radio is heard. Now push the ignition key to the start. If the radio stops playing your switch is probably ok. Most every electrical item that is hot when the ignition switch is in the run position will hot be hot in the start position. All cars and trucks are designed this way. You need ALL the amps and voltage going to the starter motor for a good start.

You only have one wire going to the start relay/solenoid, it's gounded internally. The key switch is at the bottom of the steering column, there is a rod from the key switch to the electrical switch, sometimes the little hook at the key breaks off and it won't trigger the switch at the bottom, or the switch can get loose and the rod won't move it. Look there. how to set it, pic below.