I just returned from a 4 week cross country trip of 6500 miles. The truck ran just perfectly. The only issue was in the colder area such as Montana, Wyoming, etc. I had a hard start after sitting over night. White smoke and then it would clear up after a few minutes warm up. It didn't seem like the glow plugs were doing their thing.. I usually hear the GPR click on but no longer hear the click sound. Thinking it was the the GPR I replaced it. Still no click when the ignition is turned on. Fuse is good. I checked the power to the gpr and it is on full time at the one terminal and the other terminal only has power when the ignition is on. As it is should be. Could I have two bad relays? Need your sage advise on how to fix the grp issue. I'm planning on another 6K mile cross country trip in another 6 weeks so I am hoping for a solution. Other than fuel prices being out of whack it was great to be on the road. Lowest price I paid for fuel was $4.25 but most hovered around the $5 mark. The independent stations seemed to have the best prices across the board. Pilot, TA, Flying J prices were generally 25 - 45 cents per gal higher. Sinclair, Maverick and Fast Trip seemed to be the better deal. Thanks in advance for your advice. Skip

 

If your glow plug relay is coming on, but you still suspect glow plug issues, then test the continuity of the harness between the relay and plugs, and then test the resistance through the valve cover gasket harness and glow plugs themselves. If all is well, your glow plugs are not the issue.

 

PCM grounds one small lug depending upon oil temps, use a DVOM or a basic test light to verify it is grounding it. Cold start will have alternator voltage on the other big lug. As you know, one small one is switched 12V and other is constant.

 

20yr ago I installed a kill switch in the primary ground connection to the GPR. The switch opens the primary circuit so the relay stays off. That way, even though the computer tries to turn on the GPs, the entire GP circuit stays off. The engine will start without GPs if it's warm. I still have the same set of UVCW harnesses I installed 20yr ago and they show no signs of wear or cracked/worn insulation. I recently replaced the GPR but it was 18yr old. It's not a DD but has 140K on the clock. Installing such a switch will add years to your GPR and wiring.

 

I thought I was crazy, as I always unplug my GPR once the evening temps do not drop below about 65-70F (late March usually in my area), truck starts up fine. 100% agreed less wear on the wiring and charging system.

 

i unplug my GPR when it gets warm out too, then it gets cold the next night LOL

 

I put a GPR disable switch on my dash because I got tired of changing GPRs. Now that I have the big GPR, it's not such an issue anymore.