Another lesson learned for me recently...

Story begins about 18 months ago with the passenger side harness coming loose while away from home towing my fifth wheel through the mountains. $500 for tow and $300 for dealer labor and I am back on the road with the little plastic clip that is supposed to keep that from happening again.

8 weeks ago I have the same symptoms, this time near work so I opened up the valve cover and discovered a loose connector. Without a quarter and a grinder, I was forced to re-use the little plastic retainer clip that the dealer installed before and I was on my way.

About 3 weeks later, P1316 again. This time I went with the quarter fix and figured that ought to do it.

Last week the SES light came on again and only 1 bank working. Luckily I was around the corner from home so I just parked the truck and pulled out my meter to check the ohms and found the entire bank dead. Open circuit on all 4 glow plugs and all 4 solenoids. Pulled the valve cover and the plug is connected nice and solid. I figured the harness or gasket must be bad so I ordered new parts from Clay.

Per Robin's suggestion, I looked closely at the center pin and found it was burnt along with the associated plug. The driver's side still looks good so I can only assume the burning is a result of the plug coming loose and the current must be arcing from plug to pin. Even with a burned pin, it will still work for a while until vibration compromises the connection, which for me seems to take about 3 weeks to happen.

So, if your UVCH comes loose, check the terminals to see if they are burned before you put it back together or you might be doing all over again shortly. Maybe even multiple times like I did.

Since we all love pics...

 

Thanks Greg. This is a new one for me. I will take a look at the pins next time I have the VC's off. I hope it is a long time before I take them off again.

Reps for the pics.

 

Great advice Greg.. I have heard this happening before... arcing is a real possibility when then the connector is loose..

 

Thanks for the pics Greg. Great illustration of what I was talking about. The injector common pin is the power supply and when
it gets loose it will arc everytime an injector solenoid operates.

 

Interesting...
So, the center pin is the supply and the other 8 are return? I guess that simplifies things a bit....
I didn't know that. Thanks for the info.

 

Not really.. the code is :

GGIICIIGG...
G = Glow plug +
I = Injector +
C = Common Ground..

 

I dunno', Clint....

I believe more accurate would be:

GGIICIIGG...
G = Glow plug +
I = Injector (-) (minus)
C = Power (+) (common)

The signal out of the IDM to those center pins is called "Injector Feed" on my drawings.

From that alone we can't tell anything about the voltage polarity, but it tells me that it's more likely that Robin is correct. The IDM injector "returns" may be high-voltage open collectors.

Have you personally checked the voltage polarity to be certain? If so, I will add that note to my personal copy.

Thanks,

BTW, the center pin is the common (high or low??) for ONLY the four injectors on that side. The return for the glow plugs is through the block directly.

Nice photos, Greg. I have to spread the rep around first before I can thank you appropriately for taking them. Somebody else might want to see to that.

Pop

 

As far as the injector common being the power I got my info here. It would explain why 1 bad solenoid can somtimes take out the whole bank.

 

Now I feel silly. I have that tech bulletin as well and look at it often. Says right there that center pin is power.

I'll go home now and write 100 times so I don't forget....."Must not doubt Robin, Must not doubt Robin...."

 

That's going a little far Greg. I have stepped in it on this forum more then once.

Here's a PDF of the IDM pin-out. There are 8 switched grounds (pins 6-9 & 19-22), one for each injector
and 2 injector feeds, one for each bank (pins 23 & 24).
The IDM supplies a ground to each solenoid so the common must be power.

 

Gotta have a little fun ya know? After all, it is Friday. . (finally...)
Thanks for the IDM pin out, another candidate for "the Binder".

I think what got me confused is that someone (my uncle) once told me that the IDM made about 130 volts a/c to fire the injectors so when I saw the center pin was labeled as "common" then I assumed ground because that is how it is in a/c world. I later learned that the injectors get d/c power but I still had common=ground in my head.

So now it all makes sense because I was wondering why the glow plugs would need the center pin for ground when they are screwed into the iron head so they already have a great ground. If I now understand correctly, then the pins are G(pos)-G(pos)-I(neg)-I(neg)-C(injector pos)-I(neg)-I(neg)-G(pos)-G(pos).
This would also explain why the glow plug pins are so heavy compared to the injector pins (because they carry so much more current).

Pretty fun learning about how these engine work.

 

Something else that should be brought up is how the power and ground are controlled by the IDM. The IDM actually sends the power and the ground signal to the injector simultaneously. One would think that the 115 vdc is always applied to the common pin, but it is actually switched.

More good reading from GB Re-manufacturing about the 7.3L IDM OPERATION

 

Since I have been on this forum I had always assumed the injector common was a ground, until I learned differently.

Learning is one of many reasons I enjoy this forum.

 

Here is a good schematic of the whole Powertrain System



And attached as a PDF for anyone who want's to save it.

 

Very informative PDF, Ken! What I liked best was this: