Ford 7.3L IDI Glow Plug Relay Testing Procedure

[@wgiles51]

The ribbon type deal is called a shunt resistor. A shunt resistor is used to measure current. The voltage drop across the shunt resistor is proportional to the current flowing in the shunt resistor. As the glow plug resistance increases, the current flowing through the shunt resistor will decrease. When the controller senses the decrease in current, it shuts off the power to the glow plugs. When the glow plugs fail, they fail open and the current flowing through the shunt resistor is reduced. I have no idea whether the controller can sense the number of operating glow plugs or not. If it can't sense the number of operating glow plugs, it may interpret the reduced current as a signal that the glow plugs are hot and prematurely shut off. That is why it is important to be sure that all of the glow plugs are good. The voltage drop across the shunt resistor will be very small, possibly tens of millivolts. Measuring low ohm resistors is very difficult with ordinary ohm meters, so it is important that the measured glow plug resistances are close to each other. If there are wide variations in resistance, there are probably some bad glow plugs. An incandescent test light is probably a good way to do a quick check for continuity. An LED test light is too sensitive and will show a high resistance as a good circuit. Connect an incandescent test light to the battery positive and probe the glow plugs. A bright light is probably a good glow plug. Dim or no light is a bad one.

[@robertgraves4963]

Been trying to figure this out for 3 hours at an Arizona rest stop with a horse trailer and family waiting on me thanks for the detailed information. Got me back on the road

[@FIREMANJAX]

Watched the video which helped out a lot in diagnosing my problem. As it turns out, my 1990 had a connector go bad in the wiring and I lost constant voltage from the battery via the two wires that ultimately connect to the battery side of the starter relay on the passenger side fender. In my case the wires coming off the glow plug relay were yellow but changed to black with a red stripe at the connector. The connector has many other wires going through it with these two stacked on the end. One of the wires burned the connector out and then the other wire wasn't long behind in burning out and melting the end of the connector. Since it's 25 years old now it doesn't surprise me this weak connection failed.I cut the wires out of the connector and used two yellow butt connectors to join them back. Instantly power was restored. The thing that threw me at first was that I had enough voltage at the glow plug relay to light my test lamp, but when the relay tried to engage, the light went out.

[@FordTechMakuloco]

Oh wow at least you found it all, sweet!

[@FIREMANJAX]

FordTechMakuloco I forgot to say that the relay module was clicking much like the glow plugs went bad. That's how I ended up on your video. I had replaced all the glow plugs a month or so before the problem surfaced so I was pretty sure they were not the problem. Another thing I took away from the video is that as glow plugs start to go bad, it will begin clicking near the end of the cycle.

[@larrymarkham6985]

You didn't show how to test it

[@ahillbillyredneck2375]

This video just helped me fix my 94 F Super Duty with the 7.3 IDI w/turbo. Thank you!

[@Mitim695]

Hello, I am having some cold start issues with my “92” 7.3L. I would rather repair it the way it is supposed to work opposed to bypassing the system with a switch to ground. I watched your video and have completed some trouble shooting. My solenoid turns on but clicks off around eight to twelve seconds than cycles close to open intermittently. I began by checking the glow plugs wondering if it could be a resistance related issue. I found two of them to be bad. The other six tested .2 Ohms or better. When I checked continuity on the posts of the solenoid I found the ground (white wire) to be acting as it was in a closed position when the key was in the off position. In you video you state that it is supposed to close when the system checks are ok. Although you said the solid state device seldom goes bad I am wondering if I might be one of the rare occasions. I cannot find anything on the web to check meter the device against. I would appreciate any advice you can give me I hate to randomly change parts. Thanks,

[@jasonosman925]

I have a question, the pole with the red wire when the ignition is in the start position, its voltage reads zero. did the unit fail?

[@oldviking6404]

yeah good info but maybe show how to test it? lol

[@ryanpaetz3643]

My wait to start light wont come on and GP are not working at all, do you think it's the controller under the relay is the problem? I've replaced the relay and all my GP (motorcraft) and havnt had any difference...so that all I can think of

[@ColeShaffer-c8l]

I’m probably not going to get a answer anytime soon but is the yellow wire supposed to be hot and that leads to the two wires for all the glow plugs?

[@nonamechannele]

Hello FordTechMakuloco ! I have a truck F550 7.3 Diesel 2001, and there is a problem when I'm driving slowly, it can turn off several times when standing in the parking lot , can turn itself off, but when i go quickly such a problem does not exist. (Starting good, no problem) maybe CPS sensor or not? Thank you so much! (Ssory for my English)

[@quantumprepper6715]

I just picked up a 1993 7.3IDI f350. Little by little I am going through the engine and removing as much electrical components as possible. Is there a way to manually turn on the glow plugs and bypass the relay?

[@mustangmadd3172]

I put in the push botton ground on the the ground terminal where the white wire is. Well anyway, now 3 years later it no longer works. So i checked it and my ground terminal has juice to it. That is not normal right? How could a ground also have juice to it? Im assuming the relay "solenoid" shorted?

[@SoporensGame090]

Good explanation of how the relay works, thank you for the video. Would a misplaced ground wire cause the wait to start lamp to only engage for >1 second, or would it be a bad solenoid in general?

[@Beaver7osrs]

Samsquanch Gaming did you ever figure the answer to that question out?

[@chad5128]

My shunt resistor does not have any fire when I put voltage tester to it

[@cassholuk5685]

my 1992 f-250 fuse #17 for the instrument gauges and transmission shifting just started blowing, any ideas of what could be the problem?

[@mustangmadd3172]

Hi I have an issue with my 1992 f250 7.3 idi. I bypassed the controller to a push button 3 years ago. Glow plugs worked fine. Until now, they will not work. I found that my ground that comes from my push button to the solenoid and hooks where the white wire is that you said is a ground. Well anyway for some reason when I touch it with a test light it is a hot until I push the button then light goes out. If this is a ground then why does it have juice to it. Is that normal or is there maybe some kinda short in my solenoid. Thanks in advance, Jason

[@adolfohdez31]

did u fixed ur problem man ? im having the same situation , im confuse its suppose to be ground but its hot on my...thanks

[@stevenrobertson1631]

did you ever get this squared?

[@stevenrobertson1631]

@@adolfohdez31 did you ever get this squared?

[@adolfohdez31]

@@stevenrobertson1631 yes thanks i removed that black box and put a switch

[@stevenrobertson1631]

@@adolfohdez31 you replace the whole module with just an on/off switch? I've been having a hard time with my truck as far as starting and I'm sure that I'm having an issue at the in the relay department. I saw this video and thought it would be a great fix. Is there a certain amperage you looked for or step down so you don't over do the glow plugs power supply?

[@chaunceylocklear3661]

Thank you for making this video! Much appreciated

[@davidk7544]

Hey, you'd know the answer to this - I cannot find an engine diagnostics port under the dash. Do the 7.3L IDI engines not have diagnostics? my engine is a 1989 s-series 1654 7.3 L IDI engine.

[@danvan4481]

OBD-II wasn't a standard until 1996. Your truck won't have one.

[@Kryochrysalis]

Would this device be on a 1990 F250 Lariat 7.3l V8? Friends having issue where batteries good, but when turning key will not turn over, but will click. Guy said it was the old worn neg bat blk cables were cause & need replace. Another guy said was starter or solenoid. Mobile mech checkin soon, will see what they say. Thanks for your timely & info packed vids.

[@FordTechMakuloco]

Kryochrysalis This will not cause a no crank but it will be a good symptom if it cranks strong but does not fire and there is plenty of white smoke.

[@chuk2795]

Kryochrysalis when I open my door the cab light is bright and when I turn the ignition on to warm the glow plugs it immediately drains the power like my batteries have been sitting for weeks is this the same problem you are having if so was it your glow plug controller

[@oshpunit987]

My cousin has a 6.9 that he had a glow plug problem with and he put a ground wire from the battery straight to the solenoid and bypassed the ignition switch and put a push button switch on the solenoid and then holds the push button for a few seconds and turns the key and it starts. Mine is a 93 7.3 and has that electronic box under the solenoid. I believe you said the ground comes from the electronic thing. I was thinking of bypassing the electronic thing and running a ground wire straight from the battery to the solenoid and bypassing the key switch too and using a push button switch to work the glow plugs. do you think that would work? Currently the solenoid clicks after being on for about 15 seconds and according to one of your other videos that is an indication of a defective glow plug effecting the resistance. This thing started fine this spring.

[@FordTechMakuloco]

Yews allot of people that own these have been doing the push button thing for many years now over replacing the whole assembly. I am sure there are plenty of write ups about this on the web as it is a very common fix.

[@larryeaton7384]

My 2002 7.3 glow plug relay was changed out without marking the wire connections. Now my harness was replenished and the connections are a puzzle to me. Any advice? Thanks. PS; I like your videos compared to a lot I have researched.

[@ZakarooNetwork]

have you ever considered bypassing the solenoid garbage to direct glow switch to simplify like the 6.9L?

[@FordTechMakuloco]

+ZakarooNetwork Many have yes, this being a customers vehicle at the dealer we are not going to be doing anything like that.

[@mmprop1]

Need help I have a 1988 F Superduty dump been sitting 3 years getting fuel threw the filter down to injection pump and nothing out of the injection pump which I just put on today brand new when I turn the key that relay clicks about 5 to 6 times

[@chuk2795]

mitchell markovich if your trucks cranking and your getting fuel to your IP then you should be getting fuel unless a line or injector is clogged

[@shinemccarver8868]

i replaced glow plugs/harness/controller on 90 7.3 . glow plugs come on for 2 sec and go off . any ideas ?

[@juansolis9409]

Dude i a m a follower, thanks man.

[@montwolfman]

Thanks for posting...very informative!

[@bopayne5323]

On my 1989 f250 7.3 idi i just replaced the glowplugs, because i just got the truck and the clicking noise, shoukd it still click when the key is on or would a bad relay cause this

[@johnkiefer4173]

No

[@fomoco1454]

Excellent video! Thank you!

[@patrickleckrone2308]

I have a 91 F250. I get the clicking noise after the ready to start light goes out. Once it starts it continues to click. Your thoughts?

[@FordTechMakuloco]

That was how this one reacted when I tested it after changing 7 glow plugs and ran the engine to get it hot to remove the 8th plug which was seized in the head. So I would say 1 or more plugs are dead.

[@topollillo4274]

my idi is reading 18volts when I gas her up I don't know why anybody knows or how to repair

[@yasmanybeitra444]

Probably a bad voltage regulator

[@topollillo4274]

will U know the location

[@Shroommduke]

well done!

[@vincentkohls830]

very good help. Thank you.

[@davidk7544]

this has a microprocessor?!

[@FordTechMakuloco]

no

[@hddm3]

great videos! thanks

[@neon1226]

You are good thank you for sharing

[@FordTechMakuloco]

neon1226 glad to help!

[@josephlacour9012]

Need hold camera better

[@manuelalfreso4694]

Si me puede proporcionar el video en español sería de gran ayuda para los latinos ggrasias

[@dieseltech_maniac2981]

Didn’t really give the test procedure

[@santoshsuryodaya2319]

Vds