Cold Start PCM And Sensor(s) Question - Ford Powerstroke Diesel Forum
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  #1  
Old 11-13-2012, 04:18 PM
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Cold Start PCM And Sensor(s) Question

I have just installed 8 new Motorcraft glow plugs , a new glow plug relay , and two new Motorcraft 850cca batteries , and do not have voltage going to the load side large terminal of the relay with the key on , the battery side large terminal has 12.7v with key on or off . Both small wire terminals show voltage with the key on.
I think one of the small terminals is supposed to supply a ground when the key is turned on when the engine is cold . PCM is supposed to provide ground to the GPR during cold start . Which sensors supply the PCM info (signal) that the engine is cold and needs the glow plugs energized and how long to energize them for ???

truck is 2002 f250 4x4 7.3 powerstroke with 117,200 miles
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Old 11-14-2012, 06:16 AM
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Remove the 2 sm wires and test them individually (connected, they will Both show the 12v).

Determine which is the PCM side (you're understanding is correct as to how it works) and reconnect the the Other sm wire with 12v in it. With the key ON ground the sm term that went to the PCM wire and you should hear the GPR (relay) throw and supply power to the Load side.

If not you have a bad relay.

If so, see if the PCM wire is supplying a Ground Path (at first, on a cold engine). The PCM uses the EOT (Engine Oil Temp) sensor to know the status of the engines temp.

Have you looked at this thread? -> Troubleshooting GPR & GP's
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Old 11-14-2012, 11:58 AM
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SOME PROGRESS BUT not solved

Ok this morning truck had sat over night outside and temp is 28 degrees F . I connected a 12 volt test lamp between negative the battery post and the load side large terminal going to the glow plugs on the GPR , turned key to on and lamp did not light up, showing no voltage to glow plugs . So I repeated this test but this time I added a jumper wire from negative battery post to the small terminal on the GPR with the orange/violet wire to the PCM , turned the key on and the lamp lighted brightly showing voltage to the glow plugs . I kept the key on for 10 seconds after the WAIT TO START went off and then turned the key to start and it fired up immediately and ran great .

So now I know how I can get my truck to start when cold and not plugged in , but I still Don't know where the problem is ,the PCM , a sensor , or bad wire ?

After truck was warmed I shut it down and put the test lamp and jumper wire back on the same as described above . turned the key on and the lamp lighted for less than 1 second and turned off , I cycled the key a few more times and the test lamp did not light at all unless I waited 2 or 3 minutes before turning key on and then it would light for short blink .

So I think some temperature info must be getting to the PCM , because the GPR is disengaging the voltage to the glow plugs on the warm engine even with the ground jumper still connected .


Anyone know where the problem is ?
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Old 11-14-2012, 12:26 PM
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Your test makes sense to me, there's something different from cold to warm. But, I would refine it a bit and instead of looking for power at the Load side of the relay, look for a ground path from the PCM wire when both Cold & Warm.

Then if you find Ground in the PCM wire, with it unhooked, why would it not throw the relay when manually grounding does? Unless the path to ground from the PCM isn't sufficient to fully energize the coil...

If that's the case, I'd look at the corresponding plug on the PCM connector (maybe Ohm it out to the relay) and finally call the PCM bad (or at least that portion). You then have the option of Manually controlling the GPs, with a toggle sw to that wire that supplies ground, or getting another one.
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Old 11-15-2012, 04:55 AM
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NEED WIRING INFO

This morning after another cold engine test , the GPR would not send voltage to the glow plugs unless I install the jumper wire from a good ground to the small wire terminal on the GPR that goes to the PCM .

I have determined that the PCM is at fault (will not provide ground to the GPR) and I do not want to spend several hundred dollars for a new or re manufactured GPR , since this starting problem is only during the cold season and I don't use the truck as often in the winter , but do use it occasionally and may have to cold start it where it cannot be plugged in .

Can someone tell me the best way to wire a manually switched GPR , so I can control the glow plug system from the drivers seat position ?
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Old 11-15-2012, 06:09 AM
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Sure, it's actually pretty simple to do...

Take that wire (you said Or/Vi) and connect it to a toggle sw in the cab somewhere convenient and just Ground the other side. Then you supply ground to the GPRs coil and activate it. If it were me, I would get a sw with a light in it so you don't forget it's ON

You then bring 12v to the sw (for the light) and grounding the relay also provides a ground for the bulb so it comes on with the relay.

Below 40 degrees (F) switch it on for 30sec and crank, leave on for another 30sec.

Below 30 degrees (F) switch it on for 60sec and crank, leave on for another 30sec.

Below 20 degrees (F) switch it on for 90sec and crank, leave on for another 30sec.

You'd be doing the same thing as the PCM does. Do this even if it's plugged in...
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Old 11-15-2012, 06:36 AM
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glow plug relay

does anyone know if there are 2 glow plug relay on the 2nd addition 1999 powerstroke 7.3 L there is 2 similar relays in this location???
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Old 11-15-2012, 06:43 AM
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Should I keep the wire going to the PCM connected to the terminal on the GPR or disconnect it , when installing the manually switched ground wire to that same terminal ?
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Old 11-15-2012, 07:07 AM
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Quote:
Originally Posted by racer1234 View Post
does anyone know if there are 2 glow plug relay on the 2nd addition 1999 powerstroke 7.3 L there is 2 similar relays in this location???
One of the relays is the GPR (the one in back) the other is the, pretty much useless, AIH (the one in front of it) you don't have to worry about or even need...


Quote:
Originally Posted by headlayoutman1 View Post
Should I keep the wire going to the PCM connected to the terminal on the GPR or disconnect it , when installing the manually switched ground wire to that same terminal ?
I'm not sure why,,, but I would disconnect it from the PCM. Just use the wire from the PCM plug and extend it to the sw.
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Old 11-15-2012, 09:23 AM
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gow plug relay

thanks for the info
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