How do you test the GPR
 

Another hard to start truck in cool weather, low 40*s to mid 30*s. Batteries check good. Want to test the GPR. Read a post saying to touch the two big leads with a screw driver, if it starts afterward then the GPR is bad. Man did the fire jump when I touched them together, that part was left out of the post. But the truck did start. Would like to be sure before replacing, so how do you test it?

Hook test lite to ground & touch side of relay going to GP or use voltmeter, should have same volts on both big lugs.

^^^^^^^^^Just as he said ^^^^^^^^^
on a cold engine, when the GPR should operate with the key in the on position.

https://www.ford-trucks.com/forums/a...3&d=1199723220
Terminal 2 is always hot. Be careful.

https://www.ford-trucks.com/forums/a...6&d=1262108414

What they said... take a volt meter and touch one electrode to the big terminal on the right side of the relay and touch the other electrode to a metal part on the truck. Have someone turn the key (do this when the truck is cold... otherwise, the PCM will see warm oil and won't charge the glow plugs). You should see 10v to 12v when the key is turned on. If not, then it's bad... very simple.

Used a test light. did not havea voltage meter. The post going to the Glow Plugs never lit up, one from battery was hot. Was telling the friend I purchased truck from and he has a new one he bought last winter. He never installed it because he did not no for sure that it was bad and he liked plugging truck up at night, which made it start easy. FREEBEE:-D

Good deal bud, P--- on that cord PIA. Mines been plugged in one time just to see if it worked.

There were two GPR's on my desk this morning when I got to work. A lot of our concrete trucks are International, these GPR's are International. International Parts dealer looks out for our mechanic.

HELP!!!!!!!!!!!!!!!!!!!!!!
 

Replaced GPR with the International one I was given, now truck want even try to turn over. The new GPRs looked the same other than the post alignment. Would a bad or GPR or wires being wrong cause it not to try to start??

Just curious...you only replaced the GPR relay and not the AIH, correct? Besides the relay wires, did you disconnect any other wires during the work? Maybe you left something disconnected? Here is a photo in case you want to check your wires.

(Note, my AIH has been deleted so that wire is missing).

Can't get picture to open. What does AIH stand for. I know there are two relays side by side, I changed the shorter one which is farther from the fuel bowl.

AIH is the Air Intake Heater. You changed the right one (further from fuel bowl). Check you wires, look at the pics of it Robin posted above.

YouTube - Glow Reley & Plug Testing

Older truck, connectors on the valve covers are different. But testing Glow Plug relay the same.

Did a little more trouble shooting, on starter solenoid I am getting power to post with heavy wire but not to the other large post when I try to start. Just replaced solenoid and it still does the same thing. Jumped across post with screw driver and engine turns over. Tried moving from park to neutral back to park and even wiggled gear lever while trying to start, nothing. Looked all around engine for loose wires and found none.

***Note: Last time truck was running the idle pulley broke and got my fan. While replacing fan I changed the GPR which was bad, and installed an Issopro Trans. Temp sensor. Gauge was installed a few months ago.

The absolute BEST way to test the glow plug relay itself is to do a voltage drop test across the high current leads. This will tell you whether or not your relay is in good shape, marginal shape, or "I'm surprised the truck even starts!" shape. Make sure the engine hasn't been run for more than 8 hours. This will give you plenty of time to see what the test results are because the PCM will keep the glow plug circuit active for more than 30 seconds.

Using a volt meter (set to DC volts and not ohms or amps!!!) with alligator clips on both leads, attach the red one to the side of the relay with the big black/orange tracer wire and attach the black lead to the other big post with the brown wires.

Turn the meter "on". It should read battery voltage. If it doesn't, you've either got an open circuit in the power feed (big black wire) or you have 8 burned-out glow plugs, an open in the wiring, or the fusible links in the glow plug wiring that are burned up. Once you've established that you have battery voltage reading on your meter at this point, go ahead and turn the ignition switch to "run". Don't start the truck though.

Run around to where you can view the meter display. What does it say? In an ideal world, the meter should read 0 volts. That means that there is no resistance (voltage drop) between the two contacts and the contact plate in the relay. Rarely is this the case - especially on an old relay. If you are dropping more than 1.5-2v across the relay, it is bad and needs to be replaced because you are losing that much voltage across the contacts and your glow plugs are not getting as hot as they should be. Heck, any more than .5-.8V is excessive......

If the meter still reads battery voltage, you need to find out whether or not the relay is even being commanded "on". Again, use your meter to check for voltage. This time, go across the two smaller terminals on the relay (control side). Turn on the ignition. Do you see voltage? You should. Is the relay clicking? If you see voltage on the control side and the relay does not audibly "click", then you need to check the resistance of the solenoid coil. Do this by disconnecting one of the smaller terminal leads and using your meter set to ohms ( the symbol looks like a horseshoe). You want to see about 5-10 ohms. If you see anything more than that, then there is too much resistance and a strong enough magnetic field may not be created to pull-in the contact plate. If your meter displays "OPEN" or "OL" or anything pertaining to an open circuit (an open circuit IS NOT 0 ohms...that is a short and is also a problem) then you have found your problem and the relay is junk. However, any value out of the range of 5-10 ohms, especially an open or short, means that the relay isn't happy.

If the relay clicks, but the meter still displays battery voltage across the big terminals when doing a voltage drop test, you need a new relay because there is no current flow through the relay when it's commanded on. Disassembling the relay will likely reveal to you that the contacts and the contact plate are burned very badly.

Hope this helps!

Use a test light on the small wire at the top of the solenoid (your truck is a 99-01 truck, right?) that has the push-on connector. Using a friend, see if you have power to that wire while in the "crank" position. If you do, then it's a solenoid problem (although to have the same problem with a new one would be kind of weird). You likely don't have battery voltage there during "crank".

Here are some fuses to check:

Fuse 20 in the underhood fuse block (50A)
Fuse 20 in the instrument panel fuse block (15A)

Other than that, all you have is the ignition switch, transmission range switch (mounted to the transmission shift shaft), and/or wiring issues.