Ok so i have a 2000 7.3L 269k miles, standard tranny
Here is the problem,
So WILL not start if not plugged in
My GPR has power to the constant, and no power to anything else with key off
With key on the constant has 12.2V both small posts have 12.2V and the other large post has 0.00V. So i replaced GPR tonight and SAME exact reading, what in the HELL is going on???
I have replaced
UHVC Gasket (both sides)
Intake heater relay
EOP sensor
EOP sender
Injector O-rings
Block heater

I am so damn frustrated with this truck, i mean once started she runs like a dream and if she is plugged in she starts like a dream!
PLEASE PLEASE PLEASE help me before i rip all my hair out
thanks in advance
Meg

 

Check the control wire to the GPR.

 

that is the big wire that comes off the the left side it you are looking at it from the front???
Yes that ALWAYS has 12.2V and when key is on it has 12.2V and the 2 smaller posts have 12.2V as well
The other larger post to the right has nothing EVER, even with a new GPR

 

No, the control wire comes from the PCM. It signals (Controls) the GPR as determined by EOT and AIT. You should NOT have any voltage tot he Control Wire once the vehicle has run from 10 - 120 seconds dependent upon ambient air temperature and oil temp.

You sound as though something is not connected properly.

Look this over:

 

This is what mine looks like

 

Meg,

Take a BIG screwdriver and jump the two large lugs on that relay. The draw is about 100 amps and it will give a healthy spark when you make contact. I don't think the key has to be on. Hold it for about 20 seconds then try starting the truck. If this works then your problem lies within the relay, if it doesn't then something else is wrong.

 

Where did you buy the GPR some are pretty cheap and go bad right away. I assume it doesnt click when you turn the key on? If so something has to be hooked up wrong or it was bad out of the box.

 

are you sure they gave you a glow plug relay and not a starter solenoid?
a solenoid uses a case ground, a GPR uses one of the small terminals as a ground. a starter relay will not work as a GPR.
to check the relay, remove the two small wires and connect 12 volts to them. positive to one, negative to the other. the relay should close and energize the glow plugs.
if it does not, it is either a starter solenoid, or it is bad.

 

Meg, you said both small posts have 12V when the key is on. When you first turn the key on, and only for the amount of time that the glow plugs need to run for, one of the small posts (I think it's the rear, but can't recall) should show zero volts. This is what Tom W was referring to as the Control Wire. This is what trips the relay to close, and that wire is controlled by the PCM (based on oil temp and air intake temp).

If your overnight temp is down around 50F, your PCM is only going to demand a short period of glow plug time, maybe 20-30 seconds. So, from turning key on, to checking that control wire voltage, you've gotta be a bit quick.

Some of those relays crap out faster than others, and it's entirely possible you got a bad one. Or, like the other Tom said, maybe they gave you the wrong relay.

If, as Walleye suggested, you short the two big posts (use a big screwdriver, and yes, it will spark, and the shaft of the screwdriver will heat up quick) of the relay for 20 seconds, and immediately hop in and the truck starts, you know it's either a bad relay, or the PCM isn't properly dictating when the glow plug relay should function.

If the control wire for the relay does indeed show zero volts (it actually gets shorted to ground, I'm just trying to make it easy for you to see with a meter) for the time the glow plugs should operate, but the truck starts if you jump the relay (with screwdriver), then the relay is bad.

You can also verify the relay by using Tom #2's method - disconnect the wires from the small posts, take your jumper cables, connect positive 12V to one small post, negative to the other small post, and the relay should give an audible click. At this time, you'd measure 12V on the big output lug of the relay, up until the time you disconnect one of the jumper cable feeds.

The other possibility is your batteries are toast. Using the block heater allows less juice to be sucked down by the glow plugs, leaving enough to start the truck. But no block heater is leading to big draw from the glow plugs, which is taking your battery voltage down to below the threshold needed to start the truck.

Let us know.

 

orange wire which should be the rear small wire, should be a ground from pcm when key is on, need pcm ground to operate relay, hope this helps

 

I would be cautious until you determine if in fact it is wired correctly. Sending 12VDC to the PCM will cost you!

Here is a wiring diagram I just made to help.

 

Im thinking they gave him the wrong part his looks like the starter solenoid I replaced on my 99.5 but they all look different so who knows

 

GPR Should look like this....

 

Thats what I was thinking. The one he has on looks just like the solenoid next to the gpr and the starter solenoid, it has the x in the middle instead of the "u" shape in your picture. Typical auto part "technician" mistake im sure

 

If it was a starter solenoid that grounds through the case, i would think both of the big terminals would have voltage with the key on until it burned up. That exact scenario happened to me before i found this group.He is showing voltage on the two small terminals because its not receiving the command to ground the relay from them .

Tom and Steve are right with the two tests. However, my truck lost the ground signal from the pcm for a while so it would never work. If you ground the small post that should be the ground command like they said, and it works, that could be your issue.


If it works when you ground the small post, it will most likely require a scanner. SPRINGERPOP i think used to have a really good guide to it but his personal page is down. I had it but lost it when my laptop crashed.

The gpr command on depends on a couple of sensors to tell it to work. EOT is one of them but I cannot remember all of them. I vaguely remember if you unplug the eot sensor, it will send a default command to power the GPR if the EOT sensor is bad but again, I am not sure. I know there is a fusible link in the wire that feeds the pcm. That was ultimately my problem. It took me a while to find it. In the short term, i wired a momentary push button to ground and would just energize it manually before i cranked it and then held it another 30 seconds or so after it cranked for good measure when cold. Now that i have a my Glow plug system working correctly with the led mod, its amazing how long the pcm actually commands the GPR to be on when cold.