We've been getting a LOT of the "I need help with my glow plugs" posts lately. And some of these new members aren't finding what they need in the glow plug stickies. Rather than constantly repeating the same ol over and over I just wrote up a long winded tutorial that'll bore you to tears. I'll post it here in a second, I think I covered it pretty well, but feel free to add whatever input is needed.

 

Glow Plugs 101

Disclaimer, use my advise at your own risk, I am not an electrician, but I play one on the Internet.

There are two kinds of glow plug systems used on the IDI engine. The old style (OS) is on the 1983 to 1986 trucks/vans. The new style (NS) is on the 1987 to 1994.5 trucks/vans.

Both systems consist of a controller, a relay, and the glow plugs (GP). The controller determines via engine temperature when and how long the GPs need to be on prior to engine start. The controller then sends a signal to the relay activating the relay and thus providing power to the GPs.

On the OS, the controller is screwed into the rear of the driver’s side head. The relay is on the passenger side inner fender:




Red circle is the GP relay, yellow circle is the starter relay.

OS Controller & GPs:





On the NS the relay is mounted to the top of the controller. The controller is behind the intake manifold:




Blue arrow is the rely, red is the controller.


Diagnosis is your friend when working on anything, guessing and throwing parts at a problem is a waste of time and money. Let’s chase down your problem.

On the NS if there is more than one dead GP by design the controller cycles rapidly. The reason for this is for each GP that is burnt, the power that would have gone to is instead goes to the remaining working GPs. The increased load then will burn out the good GPs.
So if your Wait To Start (WTS) light is cycling quickly, begin by testing the glow plugs.


Testing glow plugs, both OS & NS.

This is a simple procedure using a test light. (Note: all tests here require the engine OFF. And key OFF.) Disconnect the wire going to the GP. Put the clip of the tester to the positive side of one of your batteries and touch the probe to the end of the GP where the wire hooks up. If the test light lights up your glow plug is good. Repeat the procedure for each glow plug.

If your WTS light does not come on at all and your engine is not warmed up then your problem is more than likely the controller. The controller tells the relay and the WTS light to come one.
However if the WTS light doesn’t come one when you turn your ignition on, but your amperage gauge shows a significant draw for 10 to 15 seconds then your system is working the WTS light itself is faulty.

If your WTS light comes on and appears to cycle properly but your GPs aren’t warming up then you have a problem with the relay and/or the power going to or from it. (You’ve tested your GPs by this point, right?)

The GP relay gets its power from the battery side of the starter relay. On the OS this short wire can be a fusible link. Test it with your circuit tester for power on both sides. At the time of this writing I am unsure if the NS has a fusible link or not.

CHECK YOUR CONNECTIONS!!!! Oh, I know, some of you are rolling your eyes right now, “it can’t be the connections, that’s never the problem, something failed. My connections aren’t burnt and they appear tight.”
Okay naysayer, you don’t have to believe it, but a connection doesn’t have to be loose or burnt to be bad. Most of these trucks are 20+ years old, the others are getting there. These GP systems draw a lot of power, that’s why the wire for the system is such a heavy gauge. It’s a pretty primitive system if you think about it, a GP really is just a short in an electrical circuit. The short gets hot and burns your fuel to get the engine started. The connections have had a lot of work and time to get bad.

Disconnect your batteries. Pull all the connectors from your GP relay and the starter relay where it feeds the GP relay. Use a small wire brush and make the terminals, connectors, washers, and nuts shine. Reassemble. Do one at a time so you don’t jumble up the wires on reassembly.

Testing the system for operation:

Put the probe of your light tester into a GP connector. Put the clamp on a ground. When the system is activated the light should light up showing power to the GPs. The light should stay on for the entire cycle. 10-15 seconds.

Tester hooked up, key off:



Tester hooked up, key on, engine off:





Manual Glow Plug Switch





Many of us have opted to wire in a manual switch inside the cab instead of replacing the costly and often unreliable controllers. You leave the controller in the tuck when this conversion is done, but it no longer plays a role in powering the GPs. You, the operator, become the controller telling the relay when and how long to power the GPs.
Before you jump on this band wagon though, there is an important question to ask yourself to determine if this is the right choice for you.
Do you share your truck? Does your spouse and/or girlfriend drive your truck? Your neighbor? The guy that’s your best friend when he needs something? Does any shop ever do any work on your truck? Do you use valet parking at the Grand Hilton?
These are all people that could potentially hold the button in for way too long or often and burn every GP in your truck. Or not know how to use it and fry your batteries and starter trying to get your truck to start. And in frustration ruin your engine with Liquid Engine Destroyer (quick start). So if this is potentially a problem for you, you might just want to get a new controller and avoid the head ache.


If you’re still here then you must want to go with the manual switch, so here goes.

NS, super easy, disconnect the white wire from its terminal on the relay. (White circle in above picture.) Tape wire up and set aside. Run a wire from the terminal on the relay to the inside of your cab to the push button switch. Run the second wire from the push button switch to a good ground. You are done.

OS, still easy, just a bit more involved. Disconnect the purple wire from its terminal and set aside. (Red circle, pic below.) Run a wire from this terminal to the button switch. Run the second wire from this switch to the hot side of the relay, the side getting its power from the starter relay. (Yellow circle) You are done. It is advisable to install an inline fuse where your new wire gets its power at the hot side of the relay. Unplug the factory electrical connection at the controller and tie it aside; even if the controller is dead. This system has a habit of failing in the "on" position and will burn out all your GPs in short order.







I hold the button in on mine for 10 seconds and that has always been enough for my truck, but I do not have the cold winters some of you have. We get in the low 20’s here, very rarely we’ll see the high teens. Those of you in the more frigid climates may have to go to the 15 seconds.

Hope this helps.

-Niles

 

Nice write up!!! Thank you for taking the time to write it !!!!!

 

Thanks Vic, I appreciate that.

 

####ßCHECK YOUR CONNECTIONS!!!! Oh, I know, some of you are rolling your eyes right now, “it can’t be the connections, that’s never the problem, something failed. My connections aren’t burnt and they appear tight.”
Okay naysayer, you don’t have to believe it, but a connection doesn’t have to be loose or burnt to be bad. Most of these trucks are 20+ years old, the others are getting there. These GP systems draw a lot of power, that’s why the wire for the system is such a heavy gauge. It’s a pretty primitive system if you think about it, a GP really is just a short in an electrical circuit. The short gets hot and burns your fuel to get the engine started. The connections have had a lot of work and time to get bad####

That means grounds two! And I use spray on battery wax keeps all connections nice and clean,if its a plug use dielectric greese a little cleaning pays dividens when trying to fire up one of these bad boys on a frosty morning! And will save SSS money not buring up starters and batteries

 

thanks! good pics with highlights always helps this diesel newbie Tip Ive learned on my old broncos is polish any ground and keep a small can of clear spray around. Once its polished and re installed coat it with the clear makes a huuuuge difference

 

Nice work -- thank you. Wouldn't hurt those of us who aren't exactly newbies to give it a once-over too.

 

this is a good one Niles!
here's some more to complement your write up.

for those with the newer system '87+ here is some more (and some of the same as Niles posted worded different too) from Haynes diesel tech book #10330


wiring harness check
engine OFF > remove wires from GP's > test continuity with your ohm meter between the test terminal (this is the one with that flat metal plate that folds/coils downward.) > repair any wires that are open.

you may need a new controller,but there are a couple more things to check before testing that.

check the ground for continuity.
you want 0 or a max of 1 ohms.

supply voltage test
with the engine & ignition OFF
there should be 10+ volts to the power supply terminal (the big red wire,which is hot all the time?)
recharge batteries,or repair this wire if less than 10 volts.


ignition switch voltage test.

ignition switch ON /engine and all accessories OFF > test the voltage between the ignition terminal and ground.
less than 8 volts or more?

if less than 8 volts,repair the wiring/ inspect-replace the fuseable link.

if more than 8 volts;

control function test
(which is likely where your trouble is.but hey,its best to check everything out first right. )

engine and switch OFF > connect test light to test terminal (the metal Z bar) and of course ground >

temps to time duration:
temp of control unit (F) - WTS (wait to start lite duration) - TL (test lite duration)
-20 / 7-15 WTS / 35-70 TL
0 / 7-12 WTS / 25- 60 TL
35 / 5-12 WTS / 15- 35 TL
70 / 3-5 WTS / 7-15 TL
105 / 1-3 WTS / 3-5 TL
140 / 1 or less WTS / 1-3 TL

if your durations are correct,it's ok.if not,you need to replace it.

wait to start light lamp diagnoses

if the WTSL remains ON
unplug the connector at control unit.
turn ignition switch ON.
if the WTSL goes OFF,disconnect the ground cables to batteries and replace the control unit.
if the WTSL remains on,trace out and repair the wire to the indicator light.

if the WTSL doesn't turn on
unplug the connector at control unit.
connect a jumper wire from the harness side to ground.
turn ignition switch ON.
if the WTSL remains OFF,replace the bulb or trace out and repair the wire.

if the wait to start light flashes rapidly
happens when two or more GP's are burned out
test for continuity (or via the test light method as noted by Niles above) and replace as needed.



caution!!!
it is strongly advised by the masses to replace glow plugs with motorcraft (they are made by BERU in Germany) only.

motorcraft glow plugs (GP's) can be purchased online much more affordable than at your local ford stealership.
do not be tempted by other store/house brands.not only do they not last,many of them swell up becoming stuck in the engine head.often requiring head removal to remove them! there have also been reports of them swelling up,braking off,and cleaning out the top of pistons which leads to full engine reman or replacement.
do as you wish but,you have been warmed!

need to save up for a set of beru's and thinking of buying a cheap set to get you by for now?
reconsider.try doing one these temporary starting aids instead;
use your block heater,or even just a blow dryer shot down the intake for 2 minutes will help start the engine right up if you can't wait for the block heater or it's not working either.
if your not by an e-outlet,then consider unplugging the gp harness and carry a gallon of gas with a rag.dampen the rag not enough to drip and hold it over the intake,the fumes are said to help start a diesel engine this way.
or last but not least,just disconnect the gp harness and use starting fluid (preferably while cranking the engine as you spray very short burst to help it fire) until you can afford to buy a set of beru gp's online.
i would do any of the above before i even thought about screwing an off brand gp in my engine fwiw.
do as you wish but,you have been warmed and informed of alternative temporary starting assist aids!

 

Thank you for the info! I will certainly be referencing this and the sticky up top when I get around to diag'n my problem. Not enough time in the day for all the issues I've found and trying to work

 

Nice write up...excellant Job!!

 

Really like the glow plug write-up. read the comment about Liquid Engine Destroyer... Just bought a '91 7.3 and while cleaning it out - found several caps which appear to be from ether cans (down in the wheel well/firewall area). what's the long term effects if this is the case? can effects be reversed? have a JD 410G w/ ether button - have always understood if needed just a quick pulse. also understand the JD ether is super strong - what's anyone's take?

 

regarding previous question... have always used highly flammable brake cleaner in my two stroke toys understanding that there is lubricant present that isn't in ether. has anyone used brake cleaner in place of ether on a diesel. my thought is that the lack of lub would etch cylinder walls. tried pulling up effects of ether on aluminum but they wanted $41 to view the article. does it burn/pit the cylinder/piston top?

 

Most cans of "quick start" that I see today are labeled to have 'upper cylinder lubricant' in them.

The massive carnage from Liquid Engine Destroyer is immediate and fatal to the engine. It happens when the ether ignites prematurely while the piston is in an upward stroke and grenades the piston/rod. Think of it as a massive, violent pre-ignition.
Obviously the chances of destroying a glow plug engine are greater since even just warm GPs have a really good chance of igniting such a highly volatile fluid.

 

Great right up, I just got my 1989 7.3L a week ago so I'm learning how to work on it real quick and this def helps. Question though, is it normal for the GP controller to start clicking (until you turn the key to start) after the WTS light turns off?

I got a new controller and new GPs but I'm waiting to put them in until I do some more research. I also might do that push button thing for the GPs after I put the new Motorcraft ones in so they don't get burned up. What should the switch be rated for amperage wise?

 

yes thats normal.you want to start the engine as soon as the light goes off.this way those extra clicks are done while the engine is running.this is called afterglow and helps reduce white smoke,and keeps it running smoother when cold.
there is no need to install a manual push button for the newer style unless the truck isn't worth replacing the controller due to condition,cost or if funds don't allow.
if the truck is still in decent shape and will be around for a while and you can afford to replace a failed controller,that's best.the early style wasn't worth fixing.too failure prone and would fail often in the ON position which burnt out your gp's.not a common issue with the newer system.