I bought an 88 F-250 with the 7.3 two days ago and It's got a starting problem. when I turn the key on the WTS light comes on for about 7 to 10 seconds and goes off like it should, but the glow plugs are not heating up. I tested all the GP's and the lowest resistance I got was 4 ohms on only one, the rest were 5 to 6. checked the voltage on the wire at the GP's and it's only .1 volts til the WTS goes off then it has nothing. I've got power at the relay on all wires (except ground of course). I'm hoping someone can point me towards something to check next cause I'm running out of ideas. I know that the GPS on the 7.3 is different than the old 6.9 but I dont know how it works to heat the glow plugs. does it ground itself to kick the relay on or does power run straight to GP to heat that way. If someone could shed a little light on this, It would be greatly appreciated. I'd like to get it fixed soon cause I don't like using either to start it in the mornings.

thanks,

 

Your readings sound familiar to somone holding the test leads on the GPs with their bare fingers ( the body gives an ohm reading too). Do the test light routine, 12v positive for the clip and touch the probe on the bullet top of the GP with the electrical connector off, you should get a light for a good GP. One other point was the engine stone cold when the GPs were tested.

Click on my name and email me and I will send a test for your controller.

Here is some good info...

If you have 2 or more bad GPs, the controller may not cycle at all.

Two problems that occur with the solid state ( 1987 to 1994 IDI engines ) GP systems. If a GP burns out ( circuit resistance goes up ), the controller cycles the GPs at a faster rate which doesn't let them get to max operating temp. If 2 or more GPs fail, the controller may not cycle the GPs at all ( very rapid or no clicking heard ). When you check the GPs, use an ohmmeter. A high resistance ( not necessarily burned out ) GP can cause circuit resistance to go up and the controller will then cycle the GPs too fast. You probably will not find this problem with a test light. Resistance spec for GPs = .5 to 1 ohm cold. Second problem. A poor controller ground ( black wire attached to valve cover stud ) will cause the controller to leave the GPs on longer, often damaging or failing them. If you are having mulitple GP failures, I would check closely the controller ground. Now the confusing part. Bad ground --> longer GP on time ( slower cycling ). Burned out GPs --> faster cycling If you have both situations, it may appear that the controller is cycling the GPs at the proper rate. Bad ground slows it up while the burned GPs speed it up ---> normal cycling. The system acts/sounds like it's working normally, but you have a hard starting concern.
DieselDon

Glow plug torque is 12 ft lbs, I always use antisieze on the threads.

 

This is the problem, it should be 6 volts.

 

Check the ground wire....... althought the GPs are 6 volt they get 9 volts on the wire I think..

 

OOPS! You are right, they are 6 volt glow plugs, but they are supposed to get more voltage fed to them (12V?). Regardless, .1V is NOT going to work!

 

The only reason the voltage reading at the glow plugs is less that 12 volts is the large load the glow plugs are drawing. This causes a voltage drop in the wire.



The battery wire should have battery voltage on it at all times.
The ignition wire should have battery voltage when the key is ON.
The ground wire should go to a good ground.

The controller grounds the white wire to energize the relay, you would see voltage on it when the glow plugs were not heating.

The glow plug terminal should only have voltage on it when the glow plugs are heating.

Also there is a connector in the wiring harness from the truck to the engine near the dip stick tube. That connector has about 10 wires in it, the two large wires (yellow is the color as I remember) are the battery power to the glow plug controller. That connector often overheats and causes a bad connection so you get low voltage to the glow plug controller.