Great! Thanks MDB!

 

Only the mounting bracket is different. The relay itself is identical

 

OK, so yesterday I pulled out the voltmeter and ran some tests. With the key off, I only have 12 volts on the battery terminal, none of the others. With the key on, I get the same 12 volts on the battery terminal and around 11 volts on just one of the smaller terminals, and 11 volts on the big glowplug terminal, but only for a few seconds. Once the Wait to Start light goes off, the voltage disappears from the big glow plug terminal... I also can hear the relay click when the key is turned on. After about 2 minutes, I hear another click, abd now I have 12 volts on the other small terminal, 11 volts on the first small terminal and the same old 12 volts on the battery terminal. Still NOTHING on the big terminal going to the glowplugs. It seems like the only time the glowplugs are actually getting voltage is when the wait to start light in on! This is consistant with the way the truck starts. If I wait for the WTS light to go off, the truck won't start if it's below 40 degrees. The only way I can get it to fire is to turn it over while the WTS light is still on. Is it my relay or the PCM??

 

Anybody? Any advice would be appreciated!

Thanks

 

Sorry about the delay. I think you are saying that the GPR only stays on as long as the WTS light is on. Is that correct? If so, something is probably wrong with another sensor, such as barometric pressure or engine oil temperature. According to the manual these are the input parameters used by the PCM to determine how long to keep the GPR on. I suppose that the GPR only stays on a short time (the length of the WTS light) if it thinks they glow plugs aren't needed.

Either fix the problem or a simple solution would be to install a manual GPR control switch. This way it works whenever you want it to, as long as you want it to. Just wire a toggle switch to the relay, and disconnect (and tape off) the factory wiring if you are so inclined.

 

Thanks, yes that was the problem I was having, but since I didn't get a response, I went ahead and took the plunge and replaced the GPR. Problem solved! The only trhing I can attribute the problem to was the GPR was just worn out and not "holding". I would have to turn the key on and off several times in order to get the glow plugs on long enough to do any good. Then, it would only fire if I cranked it while the WTS light was on.

Now, it latches after I turn on the key and stays latched for about 2 minutes after the truck starts. The truck starts right up, there are no longer any big clouds of white smoke at start up, and all seems to be working as it should. A small 20 dollar investment made all the difference!

 

Hey MDB,
I have replaced my GPR about 4 times this winter and again today. You seem to have some electrical knowledge so I wanted to run this past you. I tested the plugs and all measure about .6 ohms resistance each. There is another wire on the load side of my GPR I suspect it's the intake heater, it measures about 1420 ohms. The current draw through the control coil is 4 amps. The ground side of the relay has about .47 ohms resistance to ground when calling for GPR closure. I bypassed the control ground with a wire directly to ground and the control coil current remained at 4 amps. I bypassed the power wire to the control coil and the current draw still remained at 4 amps. What I'm thinking is -Since there is less than absolute ground when calling for closure, the relay may not be closing completely and causng the relay to chatter and burn. I think this because when the relay stops working if I hook it up to a power supply and bang it in and out a few times, the contact make and it starts working again for a while(probably knocking the junk off the contacts) Ford is still giving me free replacement relays but I don't know how long that will last. I'm going to order a White Rogers for the next replacement just to see if it lasts longer than fords stock one. If my scenario isn't clear please ask me questions to clearify.
Thanks, Clem.

 

Wow, you sure aren't getting much life from those relays! I understand what you are saying, and you may be correct about the relay not pulling in properly. With DC current you shouldn't get any chattering (like you might with AC current), but it may very well just barely be pulling in the relay due to the high 4 amp current draw of the GPR.

If you take the relay apart you will see that it is nothing more than a heavy copper disk (about 1/8" thick) that gets pushed against the heads of the the copper input and output load bolts. This disk is supposedly free to rotate so that it doesn't burn in just one spot and evens out the wear on the contacts. In your case, my guess is that the relay disk isn't being pushed tightly against the bolt heads, which will result in arcing and progressively increasing resistance (read heat generation).

Once it reaches this point the relay contacts very rapidly degrade, usually melting copper from the disk and transferring it to the bolt head and creating a small point on the bolt head. This small point doesn't make good contact until it is knocked off, at which time the relay may work again.

The reason there isn't an absolute ground when the relay is energized is because the PCM uses a solidstate device as a relay to sink the current to ground and energize the GPR. It is extreemly reliable, but because it is solidstate it has some voltage drop across it, as do all solidstate devices (usually about 1 to 1-1/2 volts).

Another potential problem is that there is no way that this solidstate device can reasonably be expected to handle a 4 amp load for very long. It isn't that a properly sized solidstate device can't handle this much current, but to do so it must be a pretty good sized device and it will require a heat sink (remember voltage drop = resistance = heat generation) to prevent it from overheating. I am not familiar with the inner workings or design of the PCM, but those that are tell me that there isn't any solidstate device inside of it that is large enough to handle 4 amps on a continuous basis.

Enter the Whiter Rodgers relay, which draws only about 0.8 amps and has silvered contacts. Theoretically, the much lower amp draw should be much better for the current handling capabilities of the PCM's relay and allow a the GPR's electromagnetic coil to generate the maximum pressure between the GPR's contacts. This alone should result in greatly increased GPR life. The silvered contacts provide the added bonus of better connectivity by virtually eliminating arcing which also greatly increases the relay's life span.

Hope this helps.

 

Yea, Makes sense MDB. Thanks for your input. I found a White Rogers relay on line and will be ordering it. I'll see how long it lasts.

 

Sorry to bring up an old post, but hey this is GOOD reading. Having all the issues described above, I am picking up Grainger part # 6C017 on my way home from work tonight. It was $22.40 plus tax, and it was in stock. My local Ford dealer said it would be $92.99 and they were out of stock.
My question is to MDB or whoever may know, if the wires will go to the same locations on this new relay as they would on an OEM unit...
BTW, nice work MDB, you just saved myself, and probably countless others exactly $70.59! And as a bonus, I don't have to deal with the crabby parts counter guys!

Thanks!

 

Yes, the wires go in the same location. A SPST relay doesn't care which wire goes to which terminal, either for the control or circuit wire. Obviously, the heavy wires go to the large terminals, and the signal wires go to the small terminals, but that is all the really matters.