I've got a 1988 7.3 IDI that refuses to start. It cranks well but won't start. Black smoke is coming out of the tailpipe when I try to start it so I'm pretty sure it is getting fuel and spark. Any ideas?
Of course this happens the day I'm scheduled to pick up hay.

 

Could it be that your glow plugs are not working? Have you tried a little bit of ether?

 

Good suggestion. I just checked to see if the glow plugs are getting voltage and they aren't. I'm thinking maybe the Glow Plug Controller. I can hear the relay clicking. Any one know how to test the Glow Plug Controller?

 

Ether is bad ... Especially in a Glow Plug motor!

Been more than one occasion that GP's have ignited the Ether and ka-boom!

If you can hear the relay clicking then the controller is doing it's job...

I would test the relay.

The picture is pretty self explanatory.
You should get power where is says Glow Plugs (green) when the GP are activated.

The white wire is the signal from the controller and is a grounding circuit!
I believe the white should not be grounded unless the controller is telling the relay to energize!

If the controller is bad, and the relay is good, You can remove the White wire and hook a wire to it's location, then to ground via a Manual Push button switch!
Something I detest! I am not a fan of Manual Glow Plugs for these systems.

Any questions ask away!

Somebody slap me if i got it wrong!

-Enjoy
fh : )_~

 

Yes, ether is bad.. Good to know about possibility of explosion with hot glow plugs. When I got my truck the glow plugs were toast and the only way to start it was ether... If you have to use it, maybe the best thing to do would be to disconnect the glow plugs to be sure...?

As I have mentioned in other posts, I put a button switch into my glow plug power line because my relay was staying on and the glow plugs stayed on enough to drain both batteries. Two sets of plugs blown and several battery drains before I figured it out... New switch eliminated the problem and also is a nice theft deterant. Plus, if I ever need to use ether, which is very rare, I just wont hit the button. Once I brought it to get inspected and failed to tell the mechanic about the new switch.... He replaced the glow plugs again... ouch... $$$.. I guess he then traced the wires and found my switch.... He failed to own up to it and give me my old (and probably good) glow plugs. Since that expensive mistake I alway print out starting instructions when I get it inspected and tape them to the steering wheel...

Anyway, when my plugs were blown the motor would crank, white smoke out the pipe, but it would never fire.

 

I'm thinking the glow plugs are ok. They were replaced about 2,500 miles ago with Motorcraft. Also, I'm not seeing any voltage to the Glow Plugs.

I'm thinking it may be the relay. I called the parts store and they say that the relay and the controller are combined in one unit on 1988 models. Is that true?

 

yes the controller comes with the relay bolted on it but you can get just the relay

 

Yes, Unfortunately that is true.

Though I believe someone mentioned that you can get just the relay, but I am uncertain if true or not, or even where to get one.

The pic above is a pic of just the relay that is mounted on top of the controller.

Did you test at the relay to ensure it's not a bad wiring connection between the relay and GP's?

[edit]
I just looked on Napaonline and it appears they have just the relay.
[/edit]

-Enjoy
fh : )_~

 

I've been digging around the forum trying to find out how to test the relay but it's like drinking from a fire hose. There are so many posts out there and I haven't found one yet.
How can I test the relay?

 

On the newer style, like the above picture.

All you can do is check the power terminals for power ... Full time 12v+ at the yellow location, and Ignition Switched power at the red location.

Then remove the white wire, apply ground to the relay where the white wire was, then test for power on the Glow Plug (green) side of the relay.

The only way I know of to test the controller is if the white wire becomes grounded when the glow plugs should be on... ie: cold motor (below 112F deg.), ignition switch on.

-Enjoy
fh : )_~

 

Engine temp has little to do with the glow plugs on the new style system 87 and later.

As for the relay, the relay on top of the controller is the same relay the 86 and older diesels used on glow plug system that was mounted on the inner fender.

Testing the solid state controller, either the white wire goes to ground as soon as power is applied to the ignition terminal or it don't.
Since it is encased in epoxy, the only thing you can check that would stop it from working is,

Do you have power at the battery terminal at all times?
Do you have power at the ignition terminal when the key is on?
Do you have a good ground connection for the black ground wire?
Are the glow plugs all good?

The last one is usually where the problems come from because the glow plug resistance controls the glow time.
If you have two or more burnt out glow plugs, the relay may not even close to send power to the glow plugs.

First check is always are the glow plugs ALL good.
Test light method is a good fast test.
But the best test is with a multimeter, check the resistance of each plug.
Since the controller is looking at circuit resistance, each plug ideally should be between .5 and 1 ohm resistance.
A digital meter is best for this test.

You can check power through the relay by checking the green glow plug terminal and using a jumper to ground the white wire terminal with the key turned on.
But be aware, when you ground the white wire the relay will close and stay closed until either the key is turned off or the jumper is removed.
10 seconds is all the time you have to check, any longer and you will be burning out glow plugs.

The voltage from the battery terminal and the other large terminal on the relay should be very close if you check both while the relay is closed.

Remember 10 seconds while checking though.