Glow Plug Relay Test Question
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Senior User
Joined: Nov 2006
Posts: 294
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From: Northern New Mexico
Glow Plug Relay Test Question
1999 7.3L cranking but not firing. Glow plug relay was replaced last winter. So, I am wondering if this is the problem this year. The truck has sat for a time and it has been quite cold, below zero (F). Problem could be fuel gelling. To test the relay, I turned the ignition on and tested both of the large leads with a digital multi-meter. I am reading 10.36 and 10.41 volts on both large terminals. Shouldn't it be a 12 volt reading on both those leads? The batterys could be a bit low. I am guessing if the relay leads are reading close to the same on both sides, the relay is likely good. What do you think?
If the relay is good then I should test the glow plugs themselves?
Thanks is advance for any advice.
If the relay is good then I should test the glow plugs themselves?
Thanks is advance for any advice.
Logistics Pro
Joined: Jun 2005
Posts: 4,243
Likes: 16
From: AZ
1999 7.3L cranking but not firing. Glow plug relay was replaced last winter. So, I am wondering if this is the problem this year. The truck has sat for a time and it has been quite cold, below zero (F). Problem could be fuel gelling. To test the relay, I turned the ignition on and tested both of the large leads with a digital multi-meter. I am reading 10.36 and 10.41 volts on both large terminals. Shouldn't it be a 12 volt reading on both those leads? The batterys could be a bit low. I am guessing if the relay leads are reading close to the same on both sides, the relay is likely good. What do you think?
If the relay is good then I should test the glow plugs themselves?
Thanks is advance for any advice.
If the relay is good then I should test the glow plugs themselves?
Thanks is advance for any advice.
Thread Starter
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Senior User
Joined: Nov 2006
Posts: 294
Likes: 3
From: Northern New Mexico
Yeah, that is what I am doing. I checked the batteries and the meter is indicating about 12.2 volts. It should be around 14 volts for a fully charged battery, as I recall.
I should know better than to let the truck sit in sub-zero weather for an extended period of time without starting and warm up or at least putting a battery tender on it.
Thanks.
I should know better than to let the truck sit in sub-zero weather for an extended period of time without starting and warm up or at least putting a battery tender on it.
Thanks.
Logistics Pro
Joined: Jun 2005
Posts: 4,243
Likes: 16
From: AZ
That's the ticket! Once you get the GPR/GP solved and a good set of batteries on it and 5-40 syn oil you can easily start the truck down to subzero. Put an led on the GPR and you will know if it is working correctly and then wait until it goes out before starting.
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Senior User
Joined: Nov 2006
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From: Northern New Mexico
I am running 5W-40 synthetic Rotella and it sure helps!
Are you suggesting putting an LED light on the "engine" side of the relay and running that into the cab? That is a good suggestion for moitoring the GPR. Now, to find an LED light here in this wilderness...
Usually, I plug in the block heater as well in the winter. Anything to help out the starter. That is one part I would prefer to not replace for a very long time. I have owned the truck since new and it has the original starter.
Are you suggesting putting an LED light on the "engine" side of the relay and running that into the cab? That is a good suggestion for moitoring the GPR. Now, to find an LED light here in this wilderness...
Usually, I plug in the block heater as well in the winter. Anything to help out the starter. That is one part I would prefer to not replace for a very long time. I have owned the truck since new and it has the original starter.
Logistics Pro
Joined: Jun 2005
Posts: 4,243
Likes: 16
From: AZ
I am running 5W-40 synthetic Rotella and it sure helps!
Are you suggesting putting an LED light on the "engine" side of the relay and running that into the cab? That is a good suggestion for moitoring the GPR. Now, to find an LED light here in this wilderness...
Usually, I plug in the block heater as well in the winter. Anything to help out the starter. That is one part I would prefer to not replace for a very long time. I have owned the truck since new and it has the original starter.
Are you suggesting putting an LED light on the "engine" side of the relay and running that into the cab? That is a good suggestion for moitoring the GPR. Now, to find an LED light here in this wilderness...
Usually, I plug in the block heater as well in the winter. Anything to help out the starter. That is one part I would prefer to not replace for a very long time. I have owned the truck since new and it has the original starter.
Thread Starter
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Senior User
Joined: Nov 2006
Posts: 294
Likes: 3
From: Northern New Mexico
You can get a 12v led from RadioShack for a couple of bucks. Just connect to cold side of the relay and then ground the led under dash. When you turn the key on the PCM will command the relay to turn on for a certain amount of time (not the Wait to Start idiot light time) and the led will light. You then start when the led goes off, having full amperage for the starter. If you search for led in the forum you will find plenty of info.
Any other good ideas? I mean to keep this truck for the remainder of my driving days so improvements are welcome.
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Logistics Pro
Joined: Jun 2005
Posts: 4,243
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From: AZ
Extra tranny cooling, gauges, change/flush everything over to synthetic (tranny, gear oil, brakes, etc), AE to spot small problems before they become large problems...man I can spend your money 
! Do in-tank mods, AIS air filter...how much you want to spend? More?? A JW transmission...
! Do in-tank mods, AIS air filter...how much you want to spend? More?? A JW transmission...
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Senior User
Joined: Nov 2006
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From: Northern New Mexico
Guess I spent my modifcation money in the wrong places. I upgraded the springs, added better bumpers, fabricated a wood flatbed and tool box and side racks. The engine I left alone except for an off road extreme duty air filter assembly.
Fleet Mechanic
Joined: Nov 2010
Posts: 1,408
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From: Ringgold, Ga
By the way win you shop for a Led make sure its for 12V and not 110V.
I have this on the to do list myself. Just replaced my GPR and want 2 know its working.
Order those parts online and ship em. Here is a link on a write up.
https://www.ford-trucks.com/forums/7...wmriceman.html
Later
I have this on the to do list myself. Just replaced my GPR and want 2 know its working.
Order those parts online and ship em. Here is a link on a write up.
https://www.ford-trucks.com/forums/7...wmriceman.html
Later
Junior User
Joined: Oct 2012
Posts: 82
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I had the same type problem with my 99 7.3
found no problem with glow plug relay or glow plugs
would not start in cold weather plug it in for 15-20 min
start right up these engines need to turn over at least 120 RPMs
to start had the original starter with 370K on it replaced it and no more problems
found no problem with glow plug relay or glow plugs
would not start in cold weather plug it in for 15-20 min
start right up these engines need to turn over at least 120 RPMs
to start had the original starter with 370K on it replaced it and no more problems
Cargo Master
Joined: Oct 2007
Posts: 2,712
Likes: 107
From: BoCoMo
get a digital volt meter that plugs into the accessory port. It will show your what is going on with your electrical. Get one at Wally world for around 15.00
1) plug in volt meter and should show around 12.5v for batts.
2) turn key on and it should go to 11.5v as glow plugs come on (GPR). If it goes to 10.4 the truck will not start as it needs at least 10.5 to start. It may crank at below 10.4v, but it will not start because of low voltage.
3)start truck.... voltage will stay at 11.5 until GPR shuts off. At that point the voltage will slowly rise. It should settle around 14.4v. This is the output of the Alt.
Cheap little tool for checking several systems at once.
1) plug in volt meter and should show around 12.5v for batts.
2) turn key on and it should go to 11.5v as glow plugs come on (GPR). If it goes to 10.4 the truck will not start as it needs at least 10.5 to start. It may crank at below 10.4v, but it will not start because of low voltage.
3)start truck.... voltage will stay at 11.5 until GPR shuts off. At that point the voltage will slowly rise. It should settle around 14.4v. This is the output of the Alt.
Cheap little tool for checking several systems at once.
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