This is a new one for me... 93 7.3L. As soon as the key is turned on the glow plug relay 'twitches' or clicks extremely fast - about 15-20 times per SECOND. The WAIT TO START light never completely illuminates - just a dim fluctuation. Strongly suspect the controller but just not sure.

 

Can't say I've had that one yet either. Maybe a loose connection on the module/solonoid, if not, like you say, bum Controller.

 

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.

 

More info... plugs currently never come on long enough to get to start temp. Also, about three weeks ago, went to start engine - apparantly normal gp cycle, WAIT TO START light went out, when key to start position no starter action but everything in truck dimmed significantly, seemed like a huge current draw somewhere. Opened hood and tapped on gp controller and tried again - started right away.

 

............seemed like a huge current draw somewhere..............

Or a really bad connection somewhere............ Since you stated things worked well after tapping the controller, I would start there. Remember there are "Very Live" wires there so I would disconnect the batteries before poking...........

 

Hi rpillers,
watch that controller closely,mine went on several times while driving a few years ago and fried some plugs,tips went down in the cylinders,what a mess!!!
I went with a manual switch since,no more problems:You can find the diagram here: Mike

1986 6.9 4x4 F250

Controller bypass

 

So, at this point I am assuming that nobody has seen this before?

 

When mine fluctuaded while driving it was too late!!!Like I said,watch it ever so closely!

 

Saigon the difference between your 86 and the 87-94 trucks is night and day. The controllers in the newer trucks are solid state and when working fly circlres around the 83-86 setup. The controller bypass is very much needed on your 86 and would be advised yes.

One point to remember Beru Motorcraft GPs only should be used, they can be priced at $9-10 at Autozone stores/internet, IH and other fine places.

Also the older trucks can be upgraded to the solid state system for <$250.

 

Well,I get smarter everyday!!!I am not too knowledgable about newer trucks,all it know is that it works on mine.

 

To complete the thread, I thought I would post the outcome. I went through the INTERNATIONAL glow plug controller troubleshooting chart and determined that the controller was indeed bad. Found one on the internet for a great price (~$95) and installed it. STILL NOT WORKING!!!! Turns out the batteries were bad... I know, I know, I should have checked them first, but, the troubleshooting chart said to just check voltage at the controller and if it was over 10 Volts that to proceed. I should have known better... voltage gives NO indication of current delivery ability of a battery. To my defence, I have had batteries go low before and it never exhibited the rapid clicking relay symptom before. With egg on my face, I hope this helps someone...