several weeks ago Iwasn't getting any juice out of front large post on GPR,so I replaced same.Still no volts out according to test lite-juice to large post towards left rear and 2 small posts.Takes 4-5 turnovers of 10 seconds each to start on 32 degrees or below mornings.Plenty of gray smoke.If I put block heater on for about an hour and ahalf -turns over quickly and starts in about 5 seconds.Help!!! Thanx.99.5 F250,SD,Ex Ca,6spd

 

Are you testing for voltage immediately after the key is turned on? One large post should be hot, the other should be hot between 0 - 120 seconds after the key is turned on depending on engine temp, etc.

 

That post was a bit hard to read...but I think I got an idea of what you were trying to say. My question...do you have your key in the "ON" position when testing your GPR?

The GPR is a pretty basic relay..basically a big magnet that swings around to give juice to your glow plugs..one post has constant power, the other only comes on when your key is turned to the on position.

Looks like Chris beat me to the punch. You Marines...you gotta be so good at EVERYTHING?

 

Us sailors always kept our eye on the marines.Yes,with key turned on by a 2nd person and me with the test lite on the GPR.

 

Lead, Follow, or Get the H*** out of the way.

Do you have an always hot side on your relay? You might have a bad connection, corroded wire, short, etc. getting power to the relay.

 

Try jumping the relay with an insulated screwdriver. It's a sure fire way to tell if your problem is the GPR or not. The screwdriver will arc power from the constant to the other post and should heat up the GP's. If the truck starts easily, looks like you might take that new GPR and exchange it.

Otherwise, id take a good look at the wiring that leads to the relay and make sure nothing looks freyed.

Edit: good grief. Twice in one thread.

 

Post 2 should always be hot. Post 4 should be hot with key on. It should be hot for 1 to 1 1/2 minutes. It stays hot even after WTS light goes out. By hot I mean equal to or very close to your battery voltage.

 

I will have to check that.Will get back. Thanx (USN Ret)

 

When the Glow Plug Relay is turned ON, to supply current to the GP's, one of the SMALL terminals should have +12 volts, but the OTHER should be grounded, i.e., NO voltage, when the relay is energized. That ground is supplied by the Powertrain Control Module (PCM), and is timed for up to two minutes depending on temperature conditions.

When conditions call for the relay to NOT be turned on, the connection to the PCM should be OPEN, and you will read +12 volts on that terminal, the voltage from the other small terminal that is coming through the coil wire. Since you are reading voltage on that terminal, it's not an open coil wire inside to the relay.

If that SMALL terminal doesn't drop to almost zero volts for about two minutes when it's cold, it's most likely a wire open to the PCM, or it could be the PCM itself. Hope it's not the PCM.

If these conditions are met, only then should there be voltage on both LARGE terminals. One of them should ALWAYS have +12 volts. The other should be the switched power that goes out to the glow plugs.

You can always, as a last resort, manually control it with a push-button switch, but we can leave that discussion for later if necessary.

You NEVER should jumper the two SMALL terminals, as you will feed +12 volts directly to ground within the PCM. Ewwww....

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Same as previous post but with the terminal ID.

 

Post 4 has no power!!! This is the reason I changed it. When I turn key and check for power- post 2,3,5 have power and 4 dont.JUst checked it again.

 

Do you have another relay that looks similar right next to the GPR? If so this is for the AIH. Try swapping them out and see if you get voltage with the other relay. Remember new doesn't always mean good.

 

If you read my Post #9 above, you'll see that terminal #3 should NOT have power during relay operation. That's where to start the investigation.

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If the PCM post lites up,that indicates power from the PCM. Correct?

 

If you read my Post #9 above, you'll see that there is NO power FROM the PCM. It's supplying a ground.

The reason the test light lights up is it's seeing the +12 volts from the other small terminal through the relay's coil wire.

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