Hey,

I am having problems getting my 7.3l to start without being plugged in. I changed out the GPR and GP about 10 months ago and had limited success for about 2 months. It was nearly impossible to start during the past winter even when plugged in. It has been 80 degrees for the last 2 weeks and I still have to plug it in to get it to start. I do live at 10K and the nights do drop to 30 to 40. Just not sure where to look from here. Thanks for any help.

 

Have you replaced the valve cover gaskets, that may be your issue as the juice from the gpr has to pass through them to the gps. Pull the gps and test them as well. Do you hear the click of the relay?

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for more detail....

Taken from Dieselmann PowerStroke Diagnosis

Hard start/long crank--cold only:
This usually indicates a problem with the glow plug system.
Disconnect the Engine Oil Temp (EOT) sensor at the rear of the oil reservoir. This will cause the PCM to energize the glow plug relay for 2 minutes, and set a code. Turn the key to the run position and check for any voltage drop at the outlet side of the glow plug relay. The voltage should be greater than 10 volts during the glow plug cycle.
There is a history of burned and melted relay terminals and a couple of updated relays. Most recent part number is F7TZ-12B533-CA and can be identified by a gold-colored base.
If there is no voltage out of the relay, check for voltage in at the main terminal as well as key power and PCM-controlled ground at the two-wire connector. On 97 and newer vehicles inspect the bank circuit divider shunt for damage. If the relay tests fine test the glow plug resistance to ground at the valve cover connectors. The glow plug terminals are the outer two on 94-97, outer four on 98.5/99. Resistance should be 0.1-6 ohms depending on engine temp. A high reading could be the result of a spread or damaged Under Valve Cover harness or damaged valve cover gasket; re-check any high readings at the glow plug itself. Damaged UVC harnesses can be repaired with kits F7TZ-14489-AA for 97 and -BA for 94-96 trucks or replaced with F4TZ-9D930-K for 94-97 trucks or F81Z-9D930-AB on 98.5/99. Resitance from the glow plug relay to the valve cover connertors is 0-1 ohm. If no other faults are found, allow the vehicle to sit overnight. Before starting the engine, set the scan tool to monitor data stream and pick the EOT and Intake Air Temp sensors. The EOT and IAT should be within five degrees of each other. Next, remove the level-check plug from the HP oil pump reservoir and check the oil temperature with a thermometer to verify the EOT reading. If the EOT reading is higher than ambient (IAT) temperature, the PCM may be activating the glow plugs for too short a time, or not at all. If the problem only occurs at high altitude, and there is no glow plug system failures, the BARO sensor is most likley at fault.
Some 97 trucks have experienced a check engine light on after starting with Glow Plug Monitor circuit codes P1391, P1393, P1395 and P1396. After checking the glow plugs and the harnesses as in the above procedure, install a breakout box and check the GPM circuit to the PCM--GPML, LH bank terminal to pin 34; GPMR, RH bank terminal to pin 9; GPMH, relay output terminal to pin 8.
If there are no opens or shorts, re-flash the PCM to a higher calibration level. Also watch for an intermittent no output from the glow plug relay caused by oxidized internal contacts.

 

Thanks for the information. I did change out the valve cover gaskets when I changed the gpr and gps, but I think that I should start with the glow plug system again. Would genuine ford parts be the best or is there a better quality part?

 

If it is your GPR, this is the relay you want to replace it with.

586 105111 White-Rodgers | Mouser

 

The FoMoCo GPR is a joke. If the GPR did crap out on you (which mine did) I would recommend replacing it with the stancor/rodger-white relay, not that much more than the stock relay but seems to work MUCH better.

Welcome to guzzle's Stancor GPR replacement Mod Web Page

I love mine.

PowerStrokeNation : Ford Powerstroke Diesel Forum - View Single Post - Stancor Relay, Glow Plugs, and UVHC Packages...


As far as hard starting it could also be the injectors so it might not be a bad idea to have them tested and maybe have a compression test on the truck just to be safe.