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Discussion Starter #1
Sorry if this was already covered I’m new to this website
02 7.3 power to the glow plug solenoid 12v ground is good but only 1v to signal wire when I run a jumper wire the solenoid clicks and Carry’s the current through
I’ve replaced the left side plugs and harness all ohm out to .2 ohms right side ohms out to 1.2 ohms shows 12 volts to the connector that plugs into valve cover even before I jumped the solenoid but I didn’t load test it
773170
 

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1999 F250 7.3L Crew Cab
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What issues are you having to suspect glow plug system is bad? What ambient temps are you seeing where you live? I'm assuming you have a no start condition since you're chasing glow plugs.
 

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What issues are you having to suspect glow plug system is bad? What ambient temps are you seeing where you live? I'm assuming you have a no start condition since you're chasing glow plugs.
She’ll start around 60 but it dropped to 30s and lower and wouldn’t start motor seems good stout the second you turn the key off it dies and I’m not getting voltage across that solenoid
 

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First, you'got other problems if you're relying on the plugs at those temps (every Fall lots of people discover that their GP system hasn't worked in months and didn't start any differently). It doesn't sound like you're testing the relay properly though, there's no "voltage" measurements at the signal wire, it's across the two Lg terminals you look to see a drop (shows that the contacts inside aren't capable of carrying the current the plugs require).

One side of the sm. signal wires is hot with the key, the other supplies a path-to-Ground for that power to energise the coil inside to throw the Lg contacts together. Static, both signal terminals will show 12v because that coil connects them together (confuses a lot of people ;) ). That ground path is supplied by the PCM and it determines when and how-long it should be doing that based on the EOT sensor.

Have a look at this thread -> Troubleshooting GPR & GP's
 

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Discussion Starter #5
First, you'got other problems if you're relying on the plugs at those temps (every Fall lots of people discover that their GP system hasn't worked in months and didn't start any differently). It doesn't sound like you're testing the relay properly though, there's no "voltage" measurements at the signal wire, it's across the two Lg terminals you look to see a drop (shows that the contacts inside aren't capable of carrying the current the plugs require).

One side of the sm. signal wires is hot with the key, the other supplies a path-to-Ground for that power to energise the coil inside to throw the Lg contacts together. Static, both signal terminals will show 12v because that coil connects them together (confuses a lot of people ;) ). That ground path is supplied by the PCM and it determines when and how-long it should be doing that based on the EOT sensor.

Have a look at this thread -> Troubleshooting GPR & GP's
Neither small post has continuity to ground so it’s a pcm issue? Thanks for all the help and where is the pcm and how do I diagnose it?
 

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id start with the wiring harness from the pcm to the glow plug relay first, trace back wires look for chafing or loose connection at the drivers side valve cover, but to answer your question its down under the fuse box in the engine bay drivers side, near where the e brake is
 

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Neither small post has continuity to ground so it’s a pcm issue? Thanks for all the help and where is the pcm and how do I diagnose it?
No,,, neither post will have continuity to ground, it's the wire to it that will. But it's a little more complicated than that...


You can't determine anything without disconnecting the 2 sm wires from the GPR. Internally they are connected together through the windings of a magnetic coil used to draw the large contact together and pass current to the plugs (the 2 Lg terminals).

So, test it by removing both sm wires from the relay and determine which one has 12v in it with the key ON. The other sm wire that Does Not have 12v in it is connected to the PCM and is what it uses to activate the GPs by providing a path to GROUND.

When the engine is Cold, and the plugs are needed, you will find 12v passing to ground thru the wire that goes to the PCM. Use a meter and connect one side of it to the battery (+) and the other to the PCMs wire (disconnected from the GPR). When cold, and it should be using the GPs, you should see 12v flowing through the meter (make sure it's in DC, test it first across the batteries terminals). Depending on how cold it is you should see that power flowing there for from 30-120secs.

That will show you if the PCM is doing what it should in activating your plugs. Test the GPR by simply grounding the terminal on it that went to the PCMs control wire, with the sm 12v "supply" wire (the one that has power in it with the key on) connected back on the GPR. You should hear/feel the solenoid throw, when grounded, and now be able to measure the voltage on both of the Large terminals (compare voltage readings between the battery side and the plug side, they should be close to the same if the contacts inside are in good shape).

That will tell you everything you need to know about the GPRs function...
 
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