Got a 7.3 IDI 1993 dually. I've refurbished/upgraded some components already, but the glow plug system is taking a toll on me.
I've tried many things and the GPR clicks for about 15-20 seconds when I turn the key to on.

I've replaced:
1. Glow plug controller
2. Wiring harness
3. Each glow plug with Motorcraft ZD9

Before replacement, the wait-to-start light never illuminated.
After replacement, the wait-to-start light would only flicker for a very short second and then turn off, while the GPR began to click and continue for 15-20 seconds.
Now, the WTS light doesn't even illuminate when I turn the key, GPR still clicks when the key is first turned and does it's long click cycle.

I've double checked all of my connections but still having issues when cold starting.

Where should I start checking? I think it's something between the WTS light going to the GPR..

 

That's the symptom of burnt out glowplugs. Double check your glowplugs with a test light. You might have gotten a damaged glowplugs or counterfeits.

 

motorcraft switched from ZD-9 part number to ZD-29 to slow down the chineseum counterfeiters.
if you put in "new" ZD-9's, it is very possible you were sold counterfeit chinese plugs.

 

This counterfeiting thing angers me. We can only hope thier military uses the same quality parts...
Anyway......
Yes, the controller will cycle the relay continuously if one or more plugs are bad or not properly connected. It also cycles normally under certain conditions (temp) as an attempt to lower exhaust smoke when first running (thank the politicians for that).
The Wait To Start light gets +12 from under the dash and the controller provides a ground. You can disconnect the wait to start light connector attached to the controller by the firewall and ground it to see if the light comes on. The actual bulb sockets can get flakey from corrosion and that can cause flickering. I always clean all the sockets with contact cleaner, WD40 works also.
If you hear the relay "flickering" or your testing the light is OK, then the controller might be defective.

The whole scheme shortens the life of the plugs with them coming on sometimes when the engine is pretty warm and the after-start cycling.
Just like many others on this forum, I eliminated the controller.
Disconnected all of its wires coming out of the controller and tuck them behind .
Small +12 wire from truck wiring harness remains connected to small terminal on relay.
Push button on dash has one terminal grounded, long wire of other terminal goes through firewall near steering column and connects to the other small terminal on relay. Relay is receiving +12 from harness when key is on, push button supplies ground to make it close. Also, connect the Wait To Start wire I mentioned earlier to that same terminal as the push button, and it will illuminate when button is supplying ground to it and solenoid.
I suggest leaving controller unit in place to serve as a mount for relay and the big wavy Ballast that's on it. Do Not bypass or eliminate that Ballst resistor or too much current will be supplied to plugs and harnesss.

Red is fat cable from RH fender (battery)
Yellow is +12 from ignition it doubles back and connects to fuel shut off on injection pump as well
Blue is wire to Wait To Start light with....
White from pushbutton
No wires from controller circuit are involved.
The gray wire lying there plugs on to top of Oil Pressure Sender

 

the temp sensor shuts the controller off when engine engine temps hit around 110 degrees.
so if the controller is coming on when engine is warm, the temp sensor may very well be failing. my controller has a little under 5000,000 miles on it. all original.

 

Mine has who knows how many!
All the potting material turned into some kind of hard crystalline stuff that I thought was a Wasp's nest when I first saw it
Printed Circuit board practically fell out when I unbolted it from manifold.
Despite all the degradation,:it still worked fine.
I just bypassed it because of that cycling nonsense.
And yes, be very careful that you get a proper Glow Plug Relay and NOT a starter "solenoid"! Both are actually Relays, it's just nomenclature
They're wired differently internally.
The glow one has both ends of the coil appearing at the small terminals, as most any other relay has.
The starter one has one end of the coil connected to ground and the remaining small teminal becomes hot +12v when its actuated. This might just kill the big transistor on the controller circuit board and render the controller scrap!
The reason I want an IDI is simply because no electronics are under the hood.
I'm an electronics engineer, and despite being one that can deal with any onboard electrical / electronics issues, I know that failures are so random and usually in the wrong place at the wrong time. In the case of these old controlers, I'm impressed with thier longevity, but they dont have Chinese Semiconductors in them. All the later stuff is pretty much the same as a Hyundai
Engine is a 93, aging gracefully but tired. Really thinking about a 7.3 Powerstroke truck, but then I'm back to electronics under the hood. 6 Grand to replace my IDi is kinda tough and I have no way of pulling it. But I like my OBS
Tonka Toy of my adulthood!

 

I disagree. The temp switch has no influence over the operation of the glowplugs controller. Inspecting the 1994 wiring diagram, the temp switch taps power from the glow plug controller harness to operate the idle-up solenoid and the advance-solenoid, but it has no control over the glow plug controller.

 

Two kinds of controlers.
One type, on my '86 6.9 screwed into manifold
Other type, on my '93 7.3 is rectangular ans bolted into manifold That's the one I've been discussing here.

 

maybe it aint the temp sensor.... all i know is the glow plugs on the solid state controller stop working once the engine reaches around 110 degrees.

 

Tom on mine it does not seem to make any difference what the engine temp is, when starting as the WTS light comes on. Not near as long as a cold startup though. You can see the volt meter cycle a couple of times also so I do know they are lighting up. I have often wondered why and I have only owned the truck for 5 months now. Wonder what is correct?

 

When I first got my truck I knew it had at least on bad glow plug from the way it started. So got a set of EBay, I found out the hard way that what is advertised as ZD9's on EBay are not always the real deal. After installing those all the controller would do was short cycle. After much hair pulling, thinking and some testing I finally clamped an Amp meter around the gp harness to find out they were only drawing 100 amps. Everything I could find says around 200.

I than happen to run across an article that told you what to look for to determine if the glow plugs were OEM or not. Checking what I had installed were not. So I got a set from O'Reillys (ZD29's). Those draw right around 200 amps. The controller went back to working as it should.

From my understanding when the amperage drops down around 100 or so the controller believes the plugs are warmed up and the reason for the short cycling until it times out..

Not sure if you could rent an induction amp meter from a parts store or not but makes for a very quick easy way to test the system.

 

something in not working correctly than. do you have the controller bypassed with a pushbutton?

 

No I do not. Fast idle and I assume timing advance both work like they should.

 

I changed to manual push button simply to increase life of plugs. After manually activating the plugs for a while, one learns just how long to glow depending on temperature outside, how long it's been shut off, etc. Basically engine temp. I find many times, such as leaving truck for over an hour on an 85•f day, the controller would stupidly cycle the plugs, despite no need for them. This was both on my '86 with the original and brand new controllers, and my '93 with existing controller. I get no smoke without the unwanted cycling, here in this warm climate anyway.

$5 Amazon

Hole was already there when I bought truck and it turned out to be the perfect location.

 

7.3 type -- controller came from DieselRx -- it doesn't click -- Z9 plugs are all motorcraft - wait to start comes on for about 10sec -- then voltage stays down for another 10sec -- then voltage rises above 12 -- that's when I usually hit the key to start -- she don't click -- she don't click talk........