Are you positive the GP are only on for a few seconds, cuz they will stay on after the light goes out for a few seconds to help with smoke.

Sounds to me like you have the common air intrusion problem on your return lines.

 

I would guess yes!

Did you test them new GP's before installing?
It is possible you got some bad ones ...

I like to hold them with vise grips and quickly touch them to 12v and see if they get hot first ... CAREFULLY!
They can heat up quickly and burn out doing this, so don't leave them attached any longer then a few seconds!

-Enjoy
fh : )_~

 

That is not exactly true ... When the WTS goes out, They go off, then cycle a few seconds later.

By the book, you start as soon as the WTS goes off leaving them cycling after the motor starts for faster heat build up thus reducing unburnt fuel smoke.

-Enjoy
fh : )_~

 

i have never trusted the wait to start light. i have seen with my 88 where the light does not come on but the plugs work, and other times where the light comes on but no power goes to the plugs. that is why i have a small 12 volt light (now an LED) hooked to the glow plug relay output. if the plugs are getting power, my light is on and i know they are working.

 

It is controller operated so ...

I have a different problem ... I have a switch breaking the white wire so I can turn the key on without heating the GP's, I forget to turn the switch back on!

Embarrassing as heck when all the buddies show up to head out and it don't start!

-Enjoy
fh : )_~

 

I thought air intrusion as well for the rough starts. I opened the Schrader valve with my nephew cranking it and fuel came out right away. That was after it sat overnight. I'm going to check it tomorrow without turning it over to see how strong the stream of fuel is. There should be about 10psi, correct? I don't have a pressure gauge to read how much pressure there is.

 

1/3 pint in 10 seconds at ~6lbs

The first thing to do in the AM is pull the filter, If it is other than full, fill it, you have drain back likely caused by air intrusion.

-Enjoy
fh : )_~

 

Thanks for the tip. Never thought to pull the filter but we need to put diesel kleen in it anyway.

 

[The GP's were still cycling 2-3 seconds. The brand of GP's were unknown to us but the tops looked different than the ZD9's in my plow truck so we ordered a set of ZD9's. Thankfully we did because the truck had garbage Autolite GP's. 6 came out easy and two had to be worked out. They had all started to swell and 5 of 8 were reading open and 3 were 0.8 ohms. We got them changed and still only 2-3 seconds. The truck seemed to be turning over fine but I threw a battery charger on it and it was only reading about 25-30% charged so I'm hoping that is why the new ZD9's are still short cycling]

I am wondering if you bought gp's for the 6.9. I haven't had to work on mine but I know it has spade connections, and has an auto relay and operator variable timer. So non standard.

Now if I remember correctly and not having re-read the GP stickies. ( new/old type) isn't there a voltage difference?

 

Other than the connector the ZD9 and ZD1A are interchangeable ...

-Enjoy
fh : )_~

 

They're ZD9's for a 7.3 with the round tip, not spade. What I meant was the old GP's were slightly different in design compared to the ZD9's in my plow truck so I knew they were likely one of the crappy brands and needed to be changed regardless of functioning properly. I was right(Autolites) with 5 bad and all swelling. Thankfully only two had to be worked out and no broken tips. Thunderstorms today so further investigation will have to wait uintil tomorrow.

 

Heres my take on your problem.

The ignition switch located on top of column is coming apart. This is caused from the actuating rod connected to key lock. The switch has a plastic circuit board thats retained by four tabs on housing. After years of use the switch starts to push apart from actuating rod. The common symptom is shaking the column and it works. If thats the problem, all needed to fix is bend the tabs back down. After reinstalling adjust so it doesnt repeat the problem.

Your glow plug situation is likely a wire in the harness is shorted to ground. A two second short will cause glow plug regulator to cut out just like if heating the glow plugs alone.

Thats my diagnosis on your description given. Use at your own risk. Void where prohibited. Not licensed in California, New York or Washington DC.

 

actually it sounds more like it has tilt column and the 3 or 4 attaching bolts are loose, causing the actuator rod to not fully pull the ignition switch when trying to start.
moving the steering wheel side to side will make the rod longer or shorter, which in turn will cause the ignition switch to start, or not start the truck.

a separating ignition switch will make the truck have a mind of it's own, with it just shutting off when the key cylinder is touched, or if you hit a bump while driving down the road.

 

Since I fixed the loose zigzag resistor on the GPC it hasn't had the issue with the steering wheel. The GP's still come on for 5 seconds with the truck cold, 2 seconds when the truck has been running and warmed up. My nephew has been driving up in the fields with no issues. It does however still have the rough start issue. Sometimes it fires and runs with no issues, sometimes it runs rough at first start. But once running, it runs great with no hesitation or stumbling. It's going for a safety tomorrow and then when we get it back were going to pull the fuel filter to see if we have air intrusion and to run some diesel kleen through it. I did notice the original drain spout on the bottom of the fuel filter is spinning freely but I don't feel any diesel leaking from it. One injector fitting looks a little damp but not wet so it may be a source of air intrusion as well.

 

If you have fuel leaks in the return system you have air intrusion ... The structure of fuel is larger than air.

Short glow cycle is due to too much resistance in the glow system from the beginning of the ZigZag resistor on ... Typically bad glow plugs, sometimes a loose Zigzag resistor or bad harness.

EDIT
See red!

-Enjoy
fh : )_~