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Old 06-25-2013, 11:48 AM
tylerc82588 tylerc82588 is offline
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97 7.3L Glow Plug Relay Issue

We are having an issue with a 97 F-350 7.3L powerstroke. Its summer here and the truck started having issues starting. The first instinct was to check he glow plug relay. Upon testing, there was no voltage on the second post of the relay, so we replaced. Upon replacing, still no voltage and it still starts hard. You have to cycle it many times to get it to run and then it runs rough and smokes for the first minute or so. So, we tested all the wires on the glow plug relay seperately. Note: all wires were tested while unhooked from the relay. The large post (bottom left) tests 12V constant. The little post (bottom right) tests 12V when the key is on. The other little post (top left) tests .6V when the key is on. The other large post (top right) tests no voltage with the key on or off. This tests the same on the new and old glow plug relay.

Another side note: Originally when we tested all of this, the relay was clicking. Now it doesn't click at all. None of the voltages changed, just the clicking of the relay stopped.

The wait to start light still comes on and off with the key as usual.

Any help would be greatly appreciated! We're pulling our hair out here
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Old 06-25-2013, 05:43 PM
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Hussler Hussler is offline
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Reconnect the two small wires for troubleshooting. The RED/Lt GRN wire is what you indicated, 12 key switch ON. The other small wire PPL/ORG goes to the PCM and the PCM grounds that wire to activate the relay.

With both wires connected to the GPR and with key ON if each small wire measures 12 volts then the PCM is not pulling that wire to ground. As another test disconnect the wire that goes to the PCM, PPL/ORG and ground that relay lug to a ground. The relay should activate and if it does then the relay is working properly. If that is the case and from your description of the GPR cycling On / OFF I would suspect a bad PCM, unfortunately.

Also note during the troubleshooting if the EOT is 135* or above then the PCM won't activate the GPR at all so check with a cold engine.
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Old 06-25-2013, 05:45 PM
mojoman mojoman is offline
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get a Western Plow relay and be done with 12 volt rated relays...hth
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Old 06-25-2013, 08:24 PM
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You have a issue with wiring to the gpr but you also may have another problem cause you shouldn't really have problems starting in the summer
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Old 06-26-2013, 10:42 AM
tylerc82588 tylerc82588 is offline
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Thanks for the tip guys. Yes, its kindof strange that its starting hard in the summer. All ran well before this issue. If I cycle the key quite a few times it will fire, but it doesn't like it, and will smoke and groan for a bit.
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Old 06-26-2013, 01:16 PM
madpogue madpogue is offline
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If you're turning the key off when the WTS light goes off, you're wasting your time. The glow plugs stay on long after the WTS light goes off. Just leave the key in RUN for an extra 10-20 seconds.

And if indeed longer glow plug run time helps it start better, then you probably have weak glow plugs. It's also possible that the relay is closing, but still faulty, and providing insufficient power to the plugs. One other relay test - turn the key to RUN, then check the voltage, one at at time, at BOTH big terminals. Measure it down to the tenth of a volt, with a digital meter. The "always hot" terminal will probably read around 11V. The other terminal will be slightly lower, but should be close. If the difference between them (the voltage _drop_) is more than 0.3V, then the relay is failing, even though it's energizing the plugs.
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Old 06-26-2013, 01:36 PM
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Old 06-26-2013, 01:36 PM
 
 
 
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