1999 7.3l PSD. with 162,000 miles. Truck was slow to start and batteries were getting old so I replaced them. Seemed to solve the problem until yesterday. It didn't start until 3rd try. With all of the problems I've heard about relay I decided to replace it. Truck will not start this morning in 25 F weather. I tested relay and got the following results. Please see picture links. Truck has original glow-plugs. I check all the Buss fuses and didn't find anything blown. Where do I go next. Any links with pictures on testing glow-plugs would really help.

Thanks, Kevin

 

Pluged truck into block heater for about 1.5 hours and it started right up, but ran rough for about 1 minute. Does this sound like glow plugs to you?

Thanks

 

Something is wrong with the relay, I think.
It may be carrying a heavy load, but you should see 12v at both large terminals when the relay is turned on. It should carry enough amps to be able to get a voltage reading at the large post without the boot.
Try crossing the two large posts with a screwdriver tomorrow morning and see if it starts any easier.

 

Here is a post I found posted by Megawatt00, and am saving in my file. It gives instructions for testing the GPR and GP's, kinda long, but i think it is what you are looking for. So read through it and see if it is what you are looking for. Hope this helps.
https://www.ford-trucks.com/forums/7...pr-system.html

 

I've got a quick question for you Kevin. I was sure you had burned all your glow plugs up, but when I looked at your pictures again, you've got red arrows coming from the big post with the rubber boot. Does this mean you placed one lead on this post and then placed the other lead on the other posts and gave us the readings?

If so, then you're numbers seem ok, just for future reference, next time place one lead on a ground, then place the red test lead on each of the 4 posts to get your readings.

If you want to test your individual glow plugs you'll need a multi meter capable of reading ohms. Locate the flat rectangular connectors on the inboard side of each valve cover. It's near the center right where the valve cover bolts to the head. Unplug the plastic connector and you will see 9 flat pins inside there. Place the black lead on a good ground (or battery ground) and use the red lead to check the ohms on the front 2 pins and the back 2 pins against ground. A good glow plug will read between 0.1 and 2 ohms.

 

My truck did that same sht for two years. Then one day the starter went out "suddenly" and it starts in zero degree weather and I haven't plugged it in once. Guess what...the starter had been gone ever since I owned the truck. You should hear how fast this thing turns over now.

I forgot. All indications (and threads) led me to gps and relays...not so much. You should do this so you will always know if it is working.

 

key in the off position looks ok. key in the on position looks ok, but the voltage drop should be more than 0.2v across the two large terminals. not sure about the after the relay trips, id have to see the elec schematic to see if the pcm leaves the ground open or monitors the ground path for the relay. the relay may be bad.
someone must have done these tests before.
any one able to send a schematic?

 

Great Pictures.. Especially the one with the key on.. You should see 0 volt accross the two large terminals.. the contact has been made, so the voltage would be the same. the meter wouldnt be reading much any difference.. You may want to now look at the actual glow pugs now.. do the pin out at the harness...

 

The small post where he reads 11.88v with the key on the the PCM ground. The PCM provides the ground to activate the relay for up to 2 minutes. If he's got a good ground signal coming in, and power going out the other large post, I'd say his relay appears to be working properly.

 

If you are testing across the terminals, the relay is working. Testing with a known ground would be better.

 

i totally agree, but in the last pic "after relay trips" why is he showing .04v at both small wires. whats the pcm's involvment with both leads when running. when the key is off, first pic. hes got a ground path at both small wires.
again i agree that it looks fine im just not sure why theres a pos signal at both small wires when running?
cheers.

 

But it is a good thing to check accross those terminal as well, if the contact is bad, there will be a heavy voltage drop accross them, you can read that with the meter....

 

That was in the off position,, and the volatge is there because the one side has not dropped out yet ( to ground )

 

True, but that differance will show up against a ground as well.

 

Do you get a lot of white smoke when it starts? If so, I would ohm out the male connectors at the valve cover.