95 f250 7.3

while trying to figure out my cold starting issue, I tested the GPR. Had a constant hot post, as I should, but the other large post does not get power when I turn the key one, even just for a few seconds. Replaced it with a new one today, still no power. I found a not super clear forum post about it possibly being the control wire, and to unhook the two smaller posts and jump them to hot and ground to see if it clicks. It gives a loud form click when I do this. Does that mean I have a wiring issue somewhere? Truck is basically impossible to start if it gets below 50 deg overnight, unless I plug in the block heater.

My issue is I'm not really sure how to proceed. Like I said, the best thread I could find online wasnt super clear what the next steps were for troubleshooting.

 

You are correct in the troubleshooting technique. If disconnecting both small wires and jumper on one small post to battery then the other to ground and the relay clicks ON it's a wiring, connection or PCM problem. If you disconnect both small wires and key ON one of the wires should show battery voltage always through the ignition switch. The other wire is grounded by the PCM to activate the relay.

 

So if I'm reading my findings right, would the easiest thing to do just be wiring in a momentary switch in between the small post in question and a good ground? Because I really dont start tearing into crap to figure out why it isn't getting a ground from the pcm.

 

Actually, yes you can. But be sure one of the small wires disconnected from the relay is showing battery voltage with key ON. The other small post you can ground as necessary but if you forget to flip the switch to OFF you will burn out the GP's in short order.

 

Yeah, that's why I figured I'd go with the momentary switch, no chance of accidentally leaving it on. Although I just double checked my glow plugs, and it appears I have 1 dead. I'm leery of pulling glow plugs, because if the wiring quality is any indication, the PO likes to skimp on parts. So I'm afraid I will find swollen up Autolites when I crack em open, and I dont want the hassle trying to remove a broken tip. This is my first diesel, but would the engine start with one bad GP in a climate with fairly warm winters? Most nights it doesn't even get below freezing here in TX.

 

PCM sends a ground when oil temp is below a certain level. Nothing to tear into, you are way over thinking the complexity of this machine. The PCM was designed for this probably around 1990, it not earlier. Pin the two small wires at the GP relay...as stated one is a switched 12V other is PCM commanded ground to close relay. A simple test light will work for checking to see if you have this 12V signal...key on, engine off test. Check the studs at GP relay first. Then engine harness. Did you probe the output side of the GP relay to verify you have no power to the GPs? You may just have a ****ty starter. BTDT in the low 50s mine would have a really hard time spinning fast enough to light off and my GP system worked fine. Into the 40s? Nope unless plugged in.

Oil temp is just a NTC sensor...have you checked to see if it is good? Is it even plugged in? Should be on the HPOP reservoir.

https://www.thedieselstop.com/faq/94...an/stjmain.htm



What glow plug relay is on it? Pretty much everyone uses the Stancor tank, I do. Monster White-Rodgers Glow Plug Relay Most of the auto parts store ones are not very good.

If compression is good, it should start without GPs in this weather currently in the mid 50s. It will be smoky and take a while but will light. Provided your batteries are 850CCA and starter works well.

I would pull the driver valve cover, easiest to me, and pull one GP. See what brand it is. OR Use a cotton swap and clean all the oil away, see if you can find a brand name on it.

 

Yes, I checked the second large post, confirmed no power to GP. I know my OTS is good, I have it set to display on the dash of my scan tool. I'd be surprised if my starter was going, I have paperwork for replacement a year ago, and I would expect even a cheaper one to work that long. Batteries are both pretty fresh as well. Temps have been hitting the 50's in the sunshine near me, but when I roll out to go to work the sun is still down and it's only been a few degrees above freezing most days in the last week. I'm kind've surprised to hear you say the engine should be catching with completely non functional glow plugs at those temps. Again, I'm far from an expert, but I was under the impression the glow plugs were pretty crucial to starting when temps started to drop towards freezing. I suppose I can always drop a note on one of those bd high torque starters and see if it solves the issue, but I was assuming that Occam's Razor would bear fruit for me here, and that if I fixed the obvious problem it would help my cold starts.

 

Mine lit in upper 50s or low 60s without a glow when I was dicking with it, and that was before I shimmed my injectors. It even started off one battery with a short glow once, in modest temps around the upper 60s I think.

Fresh batts are good, but are they 850CCA? 700s have a noticeable difference in cranking ability. Wallymart ones seem to have more CCA up in the colder areas than down here in Texas. It is really odd.

Run a test to check the PCM output to that GP grounding plug. It is pretty easy to poke around, if DFW I can probably help.



https://www.ford-trucks.com/forums/1...ou-cranky.html

 

Easy way to check is with a cheap volt meter or trouble light. We know the relay works due to your troubleshooting. With both small wires connected to the GPR and key ON one small post will show battery voltage and the other just a few tenths of a volt because the PCM is grounding it. If both small wires show battery voltage then the either the PCM isn't grounding it or a bad connection - wire going to the PCM or a bad PCM. Of course all of this has to be done within a minute or so after key ON so be fast.

What often occurs is someone trying to troubleshoot without understanding the operation on the GPR circuit. For example if you were to put battery voltage on the small wire that the PCM grounds it would burn up the circuit inside the PCM that controls it, no fuse protection and excessive current.. If so there is no fix except to send the PCM in for repair or replacement.

A lot users have put a momentary switch on the ground wire side of the relay for more control, especially in warmer climates. If going that route just check that one small wire has battery voltage with key on, disconnect from the relay. Reconnect that wire to the relay and tape off the other. Use the other small wire terminal for the momentary switch to ground. IMO this should be a short term fix until you can find the root cause, but that's just me.

On cold starts with 1 bad glow plug the engine should start just fine. Don't be surprised if the exhaust smokes a bit as that 1 cylinder is still cold. Usually driving a block or so warms it up enough and the smoke stops. Good luck, post back with the results if possible.

 

Yeah, I've determined that it's for sure an issue between the post and the PCM. I got an offer from another member in my city to help out, so either the root cause will be addressed or I'll just say screw it and wire in a switch. Truck started right up jumping the ground post to the ground directly behind the GPR, the one with the ribbon cable attached.

 

I work for Miller Lite and Red Baron

 

I'm not even gonna lie man, the last contractor I was supposed to meet today was a no show, so I got bored and knocked together a push button on the dash to ground it. Thinking of putting together a Fury Road style ignition sequence next.

 

It was not me! I did not see a reply from your PM.



I will fix that ****, hit me up.

 

Haha, I'm sure I'll be hitting you up for one thing or another, and I'll keep your preferred payment in mind. I'm actual glad he flaked, he's my least favorite painter.