I have developed a bit of a problem with my faithful old Ford service truck. The truck after 350,000 miles my old 6.9 was burning more oil than Diesel fuel. Every time it left a stop sign there was an embarrassing cloud of blue grey smoke. Since I make my living fixing Diesel engines this was becoming a bit embarrassing. I put in a 7.3 and solved the problem. The problem I have now is with the glow plugs. After having the new engine in for about a year. The engine suddenly became hard to start. I checked the glow plugs with an ohmeter and found that the resistnace was at maximum. Not being too bright I put in a set of glow plugs swithout checking the voltage. The new glow plugs lasted about one day. This time I checked the voltage to the glow plugs and found that I HAVE 12.8 VOLTS. The book says 6 volts. Is there a set of glow plugs that will fit in the 7.3 that will take 12 volts? I have the bayonet type ends on my glow plugs not the bullet type ends. If there are no glow cplugs available what must be repaired on the control circuit? Thanks for the help.

 

I sound like you used the old style 6.9 GP system on the new 7.3 engine is that correct....... Which GPs did you install ......... Beru/Motorcraft, Autolite, Chumpion......

 

You are correct I used the old 6.9 GPS.

 

You are correct I didn't do anything to the glow plugs. I don't know what make of controller the truck has. How can you tell?

 

Mechanic, did you install the glow plug controller in the rear of the passenger side head?
First, what year was the truck and engine originally?
The glow plug systems changed between 86 and 87.
83 thru 86 was the old style system, Only use Motorcraft/Beru ZD 9a glow plugs in it.
87 thru 94 was the new style system with the bullet connector, Motorcraft/Beru ZD 1a glow plugs in it.
The other brands are garbage, don't use them.

All the glow plugs are 6 volt, that is why they heat so fast.
When you have 8 good plugs in it, the voltage drop will get it down to around 8 or 9 volts. Since you have bad glow plugs now, the voltage drop is not happening.

 

I don't remember changing anything in the glow plug relay circuit when I changed engines. The truck is an 85. The glow plugs have the bayonet type ends on them. Let me see if I understand this the glow plug circuit runs on 12 volts open circuit voltage. When the glow plugs cycle due to the amperage draw. The voltage drops to eight or nine volts. Thus you can use 6 volt glow plugs. I thought that I had discovered why the glow plugs only lasted two days when I got the reading of 12 volts open circuit and knew that I had 6 volt glow plugs. Does anbody have any idea why the glow plugs only lasted two days.

 

I just checked and there is no controler on the passenger side head.

 

How are you getting voltage to the glow plugs?

On the old style system there is a relay behind the passenger side battery down on the inner fender well. Power straight from the battery to one terminal with a large wire, usually red and on the front most terminal. Two smaller terminals, the one closest to the fender is black and has a slide on stud connector. The one closest to the engine is purple and also has a slide on stud connector, this wire goes into the chassis harness and then into the engine harness. It emerges near the rear of the pasenger side head. The controller screws into the water jacket through a 1/2" hole in the back of the head, stands straight up and down, in a very hard to get to place. To see it you almost have to be on top of the air cleaner with your head by the firewall.
The fourth connection on the relay has two large orange and white stripe wires that feed the glow plug and a small black and pink stripe wire that goes to the "Wait to Start" light in the dash.

The controller senses the coolant temp, the glow plugs should not even turn on if the coolant is above 115 degrees or so. Bad thing is, when the controller fails, it either does not turn them on when it is cold, or it may turn them on while driving. The later will burn the glow plugs up in a very short time.

I converted mine to manual control when my controller failed and like it much better.
Remove the purple wire on the relay.
Run a 14 AWG wire into the truck cab off that terminal.
Connect it to a push button switch mounted in a convienent location.
Connect another wire to the other connector on the push button and run it to a switched fuse in the fuse box.

To operate the glow plugs,
Turn the key to ON
Push the button for 10 seconds
Start the engine.

Nice thing is, if the engine is warm after running it in the past couple of hours, just get in and start it. No glow plugs needed. This saves them for when you do need them.

If you don't have a controller, I am wondering if the wires are shorted together and the glow plugs are on all the time. They won't last long like that. You should have voltage on the glow plug harness for under 20 seconds after you turn the key to ON. With the warmer weather, 10 seconds after the key is on the glow plug circuit should go off.

Also the Motorcraft/Beru plugs only is very important. Champion, AC, Lucas and several other less known names are likely to swell when the burn out. If you break then off trying to get them out, you may be removing the heads to get the tips out.

 

Thank everybody for the help. I wired my glow plugs to a spring loaded toggle switch so I can't leave them on and everything works fine. It is embarrassing in my line of work to sneak up on your truck every morning with a can of ether in your hand. Thanks again.

 

When I turn my key to start, the wait to start light goes off but it makes a clicking noise under the hood for about 5 seconds afterward. Usually I wait till it stops clicking and then start it. It starts and runs fine but what is that clicking noise and is it damaging my plugs?

 

That is the glow plug relay kicking on and off.
Normal operation.

 

Dave i think you have your numbers reversed. i thought the ZD 9 were in the 87 to 94 trucks

 

Remember guys the key is turned to start with foot 1/2 to the floor when the WTS light goes out...........do not wait untill clicking stops. The clicking is the controller cycling to maintain the correct GP heat in the precup for the start. When the clicking stops and no start is accomplished, turn the key off then back on again and start the proceedure all over again.

6.9 system........ZD1 with spade connector (12v GP)

7.3 system........ZD9 with bullet connector (6V GP)

Note: extremely late build 6.9s, some did have the 7.3 system.

 

You are correct, I did reverse the numbers.