oil temperature sensor location - Diesel Forum

ford_7point3 · 12-10-2006, 09:55 PM

Hello, I'm working on a 2001 ford f350 with cold start problems. The motor surges untill it warms or I feather the trottle. This doesn't happen if I leave the truck plug to house 120 over night. I've troubleshot the gpr and found it and the glowplugs to be good. I found the ground to the gpr to not have ground with the key on and want to make sure the temperature is not affecting the results.... If i'm on the wrong track, please let me know. Thanks

**klhansen** · 12-11-2006, 02:20 AM

Here's a photo showing the EOT sensor. The sensor itself is pretty robust and probably just fine, but if there are high resistance connections between it and the PCM, it might affect timing and make the engine hard to start. Advanced timing counteracts the thicker oil in the HP oil system to assist with starting. You can try unplugging the EOT sensor and the PCM will go to a default mode. That will help you tell if the sensor or the circuits are an issue.

If you're checking for ground from the GPR on the small terminals, you need to know that the ground is thru the PCM, and if the oil is up to temp (above 131F), the PCM won't close the switch and turn the GPR on. The GPR "on" duration gets longer with lower oil temp, up to 2 minutes when oil temp is 14 F or below.

If you're seeing "romping", it's usually from oil issues, either needs to be changed because it's used up and foaming, or changed to a different viscosity.

ford_7point3 · 12-13-2006, 10:07 PM

Hello klhansen,

Thank you for your help. I do understand the pcm grounds the gpr. I asked about the oil temperature switch to confirm the location as well as the it's function. The problem I have is that the pcm only grounds the gpr for about 4 seconds with or without the oil temperature switch plug attached or disconnected. I have confirmed with a load that all the glow plugs are good thinking the glow plugs affect the pcm as does the glow plugs affect on the controller of the pre-powerstroke units. Is there a possibility of something else sensing temperature or ? that could be causing this greef? Thanks again for all the help.

**klhansen** · 12-14-2006, 12:00 AM

The PCM only activating the GPR for 4 seconds doesn't sound right at all. But if you unplug the EOT sensor, the PCM may not be getting the right signal. It goes into default mode and assumes an oil temp for starting and running as far as adjusting the injection timing, but I don't know how that would affect the GPR activation. You could use a resistor in place of the EOT to fool the PCM, but if you get the same 4 second results, I'd say something funky with the PCM. A 60 kohm resistor would be equivalent to 50F which should get you a fairly long ON time for the GPR.

The Barometric sensor also affects the time that the PCM turns on the GPR, but there's only one little blurb in the service manual that says "add 5 seconds to glow plug on time when above 7000 ft in altitude, but not to exceed 120 sexonds".

My wiring diagram shows 3 sensor wires on the output of the relay, but my truck only has one of those sensor wires. That's for California PSD's. They had the 3 sensing wires connected to a shunt on the output of the GPR so the PCM could compare voltage drop across each half of the shunt and compare current draw (and number of working GPs) on each bank. If the GPR is on more than 35 sec and voltage is within a specified range, the PCM would set a code if everything wasn't right.

At this point, you might consider just replacing the GPR and see what happens. Maybe the control coil in the relay has a heat affected open circuit that closes when the heat (current) goes away. That's only a $20 part, and may save you lots of troubleshooting time.

Let us know how it turns out.

ford_7point3 · 12-14-2006, 08:17 PM

Hello klhansen thanks again for your advice. I should have added that the gpr was replaced and had the same results as the original gpr. I can run a ground from the battery straight to the ground terminal for the gpr and after 30 or so seconds, the gpr is still suppling current to the glowplugs so long as my wire to the battery is connected. One more question concerning this I would like to ask. Is there a way to reset the pcm other than or including disconnecting the battery? Thanks again.