I wasn't sure if I should have put this in the excursion forum or the general 7.3 forum since really only California trucks and Excursions have the GPCM but here goes...

I have an excursion (7.3 2002) that wont start after sitting on the cold all night. I was able to plug it in then and get it home to the garage to work on it.

I first checked my glow plugs by checking the resistance at the valve covers and 7 of 8 glow plugs check out perfect (right around 1-1.5 ohms) so I know my GP's are good.

I then figured it must be the GPCM so I purchased a new one from Ford. I put it in and no luck. Now I'm questioning my wiring (what else could it be?). I have checked both plugs to the GPCM, they both have power on the bottom middle plug.

I then hooked the GPCM all up and went to the valve covers, unplugged the harness there and checked for power in the harness (by putting a test light on the tab for the GP and hooking the other end to the negative on the battery post). I get NO power here. So next, I move back to the GPCM plugs, I test the wires right out of the GPCM that go to the GP's - NO power.

I'm down to a few possibilities, maybe someone here can help. Either...
-my GPCM is still bad since it's not sending any power to the GP's
-my truck just isn't firing the GP's because it's warm enough already? (it's 48 degrees in my garage which is where it's sat for 24 hours off) how cold does it need to be so I can test this?
-some other factor (PCM maybe) that would tell the GPCM to fire the GP's is not working (how would I test this?)
-or i'm just not testing it correctly

Thanks in advance for your help!

 

Glow plug on time is determined by the PCM based off of oil temperature. You will have them on if the temperature is less than 131 degrees.

Here is a page I have been working on for Glow Plug Issues.

7.3L Glow Plug System


Here is a GPCM Troubleshooting guide

 

Also, with a tool like AE, you can run specific tests on the GPCM and the GPs that will help you diagnose if they are working properly.

Riffraff Diesel: AutoEnginuity Total Ford Enhanced Bundle

 

A GPCM is designed to throw a code and set a CEL if there is something wrong with the module or any of the glow plugs. If you don't have a CEL, it's time to start looking elsewhere for your problems. Does the truck start up better if you plug it in for a few hours first?

 

Yep, if I plug her in for one or two hours she starts right up. If you point me in a direction I'll check it out. To me it just seems if its a temp related issue I should be starting with the gp's. Where else should I be looking?

 

The easiest test would be to pull the valve covers and start the engine with the motor cold (it won't make a mess). Watch the oil discharge port at around 11o'clock on each injector. If you've got worn injectors, you'll have a few not spitting oil like the others, but as the engine warms up they will all start to spit the same amount of oil.

a buzz test on a cold engine can also tell you, but you need an expensive scanner like AE to be able to do that.

 

so youre sayin you think it culd be a issue of bad/worn injectors? i do plan on gettin AE...maybe now sooner than later.

if i do take the covers off, do i need new gaskets or wiring just because I took them off? if i do open em up and see what youre saying (not much oil movemnt till warm) then what? would that mean id need to drop the dough for all new injectors?

i recently upgraded to the semi synth oil and am not seeing any new leaks (was afraid i would in the cangefrom dino). would going to 5-40 help fix my prob?

 

The valve cover gasket is re-useable so nothing to replace there. The wiring is fine too. There are other things you can do while under the valve covers as a preventative measure, but if the injectors are worn it can wait.

If you do have injectors not spitting oil at first, but then they start to, that's a sign of worn injectors or injectors in an engine that has not had proper oil changes. You could technically only replace the injectors not spitting oil, but the others are likely in almost the same condition.

Changing to synthetic will not cause any leaks in the truck or break loose any gunk in the engine so you have nothing to worry about. Switching to a synthetic 5w-40 should help some if it is worn injectors due to the "5" weight rating of the synthetic.

 

I'm working on the same situation right now. This is where I am at...

I checked continuity on all driver side plugs and got 2.7 - 2.9 on all of them. Then I pulled the most forward one and tested it off the battery. It worked fine. Just to check one of the new ones to see if one was brighter than another and they both looked the same. Glowed the same at least. So I am stumped at this point. I checked power off my GPCM and wasn't getting anything with a test light. Turned the key on and stuck my test light into the plug end that goes into the valve cover and the light didn't come on. Any ideas? It's still a rough start when its cold out. And doesn't even want to start when it's cold out and not plugged in. I've tried replacing the GPCM and that didnt work. I am getting codes P0678,77,76,75,74,72.

 

Thank you F350 for your advice. I do feel like it may be the injectors as I have NO codes. My only question that seems to be nagging at me before I drop the $$ on AutoEnginuity is that I can't seem to test and confirm power FROM the GPCM.

On the plugs that go to the GPCM, I DO have power from both power terminals and also from the PCM terminal of the GPCM plug (3 total).

I've checked for continuity from the plugs through the GP's, all OHM out fine.

So given that, I have power to the GPCM and good circuits through all GP's. The GPCM is new from ford (and I tried another used one prior to this) so I think GPCM failure is ruled out.

My question is then... if all this is good, I should have power to the GP's but when I poke any of the wires from the GPCM to the GP's and put them to the negative battery post and then turn the key (so the GP's should be powered) I get no volts... why would this be? Am I testing it wrong?

 

As Ken mentioned previously the PCM will not operate the GPCM if the oil temp is above 131°. If the EOT sensor is faulty and always reading higher then 131° then the GPCM will not send power to the GPs. Before you go any farther you need to make sure the EOT sensor is working properly. Also make sure the EOT sensor connector is fully seated, the pins are clean and dry and the wiring is ok. It is mounted to the back of he HPOP reservoir and has a green connector.

 

I did all that as well. I tested for power going to the GP's buy disconnecting the harness at the under valve cover plug, stuck a mini flat head screw driver into each pin and checked for power with a test light. The whole passenger side of my motor had power, but not the driver side. I just got a new GPCM today and I am going to try to install it tonight to see if it works.

 

I've tried this with the EOT sensor unplugged which another post suggested. Per that post, it would make the GP's stay on longer as if the temp was low. Is that correct? If so, still no power from GPCM. Is there another way to test the EOT?

Can you see what the EOT is sensing through the in-dash readout if you hold the trip button and turn the key (to the "TEST" mode) so I can confirm it's working?

 

I installed a new GPCM last night. Got power to all my glow plugs, cleared the codes and now I am still getting a P0677,76,75 and 72.

But they all are working. So I dunno whats going on now.


By the way lalh20 have you seen this and followed this procedure?

https://sites.google.com/site/woodnt...attredirects=1

Its the test procedure for the GPCM and circuitry. Check it out. It was very helpful.

 

Oh and one last thing...

My truck started up in 20 degree weather last night without it even being plugged in! It would never do that. It would take me like 15 minutes to get it started when it was that cold. This morning I am going to try it again to see if it starts right up. Right now it is 12 degrees, feels like -1.