99 & up 7.3L Power Stroke Engine and DrivetrainDiscussion of the 99 & up 7.3L Power Stroke diesel engine and drivetrain in the 1999-Up Super Duty trucks and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 7.3L Power Stroke engine.
I have read that the both solenoid control wires should read 12V when not needed during high temperatures. Then when the PCM calls for the GPR to energize, one of them should ground thus energizing the relay (which one?). I don't get the ground from the PCM. There is no activation of the GPR.
My glow plug relay is not being energized. When I remove the control wires from the two small posts and apply 12V and Ground, the solenoid clicks. When the wires are connected and the ignition is first turned on there is 12V on both small terminals. No click.
Even though the solinoid clicks when manually energized, the large post side does not get 12V so I need to replace the relay. But that is not the question.
1. What tells the PCM to ground to complete the GPR circuit? Could there be some temperature sensor that's not working?
Last edited by rhinedogg; 11-11-2008 at 06:31 PM.
Reason: New information
I have a 2002 F-250 7.3L Diesel and just put two new batteries in last night. It was about 38 degrees when I was testing the GPR so I know that it should have been called to function.
How about this for overkill. I ran into a couple of short lived GPR's in the last two years. I have a voltmeter, and it will indicate the voltage drop when the glow plugs are activated, but went one more step. I installed a small led pilot lamp in the guage pod. It will light when the GPR activates, and go off when the glow plugs are turned off. It is a simple install. It would be a good mod, if you did not have a voltmeter. My GPR's seemed to fail when the weather was lousy. It must be Murphys law. The GPR at your friendly Ford dealer is an International part repackaged, and over twice the cost from IH.
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Ok..... I did some more checking tonight. There is 12V definitely on both small terminals and no voltage on the glow plug side when manually energized. Any ideas????
Do you have voltage on the battery side of the relay?
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Yes there is 12V on the first post. If I short the two large posts (with the small wires disconnected of course) the truck started right up tonight at 40 degrees.
What I meant by cold is 35 to 45 degrees. I did start the truck last week when it was 42 degrees with the wind blowing but it took about 5 tries.
GrampyJim, I'm glad that you know the exact operation of the PCM. So.... what inputs does the powertrain control module use to determine if the glow plug relay should turn on. Perhaps that will give me a clue where to look next.
Here's how the GPR is wired.
The large Black orange wire is from the battery (hot all the time).
The brown and yellow wires go to the glow plugs and should be hot when the relay is activated.
The small red wire is hot when the PCM power fuse is pulled in (key on).
The other small wire (pink & some other color that I can't remember right now) go to the PCM and is grounded to activate the GPR (internal relay in the PCM).
The GPR is activated when the key is first turned on if the oil temp is below 131F and will stay on for a variable amount of time (up to 120 seconds) depending on the oil temp. The colder the oil, the longer it stays on. If the oil is above 131F, the relay will not activate. The barometric pressure sensor also adjusts the on time (longer at higher altitudes, but never longer than 120 sec).
So it depends on oil temp, not air temp. If you just ran the engine and it got up to temp, the GPR will not pull in even if the air temp is minus 50F. (But at that temp, it wouldn't take long for the oil to drop below 131F )
Hope that helps.
From what you're describing (no voltage on the output when you jumper the small terminals?), then it's time for a new GPR. About $20 from International.
Great information! Thanks. If the oil temp sensor was bad, do you think there would be some notification of that? Like an engine light or not running properly?
Where is that sensor located and how to verify/replace?
Depends on the fault... If the concern is an "out of expected range" reading, there will be a DTC. Engine oil temp is the main precursor for glow plug operation.... As Kevin has indicated, if the EOT (engine oil temperature) on an F series is over 131F, the glow plugs will not turn on.... Add that 131 F IS an expected reading on this sensor and will not trigger a DTC.
If you suspect a concern with the EOT, the absolute best way to verify is to perform a sensor coherency test.... Leave the truck through a cold soak.... several hours without running and without the block heater being used. Access the live PCM data with a capable scan tool and compare EOT with IAT (intake air temperature).
The EOT sensor is located in the back of the high pressure oil reservoir (if you guys want to work on these trucks, I highly recommend a decent workshop manual as a way to truly save money and aggravation) and can be tested with an ohm-meter.... This method is open for induced concerns.
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