OK, corrected the incorrectly installed IPR coil and tried to start it. Failed.
Removed the dptuner and grabbed the computer for some data collection. It was dark by now so I had my wife start the truck so I could check the tailpipe. Grey/white smoke.
Didn't get chance to check wiring yet or voltage at IPR coil leads.

 

That is a vast improvement - the engine is trying to fire. The Fuel Injector Pulse Width shows it adding fuel to the cylinders, and the smoke out the back is confirmation. Now you just need some heat - like shorting out your glowplug relay.

Once you have fuel, then you just need compression and heat. Take one away and you have a no-start.

Your IPR is pushing hard without a lot of response from the HPOP. I think the Cody test is still in order.

 

Thank you Tugly.

BTW, I can't tell you how much I have learned from your signature links - so very helpful!

Some years ago I installed the really heavy duty glow plug relay mod that I saw here and it has worked flawlessly, so far. I am an electrician by trade so I can test out to see if the glow plug system is faulty. Everything else except electrical is what I have been struggling with ;-) I can check that system out tonight when I get home.

I am very sure that some of the system is working because of the voltage drop, from 12.4 to 11.2 when the key is first turned on, after a bit the voltage came back up most likely because the 'on' time had run out on the glow plug relay.(witnessed on a different test ) But I'll check to see how many plugs are getting power.

I plan on doing the cody test Saturday when I have a day off.

 

Took current reading of glow plug power cable, peaked around 50 amps.
At this point I think the cody test is going to show some leakage. Will see Saturday.

 

Good job on "looking for sign"

Uh... you might want to ohm each plug (through the contacts in the VC harness), then ohm each GP cable to the relay post... and check all your connections while you're at it. I don't have the means to get a 50-amp read on a meter, but I use Ohms law to calculate it - and you aren't where I am. As the plugs age, they loose their resistance - and they are kaput at 2 ohms (48 amps on the system with Ohms law).

Now see there... your skills as an electronic technician, plus just a little diesel knowledge, will take you far with the 7.3L. This is where I have seen the world change so much - I used to keep my rigs up with wrenches, a timing light, and a dwell meter - now I have to use the multimeter, the laptop and OBDII adapter, and the USB O-scope. I'd be lost without my electronic career supporting my diesel (and boating) habit.

 

I got to admit it, I cheated. I borrowed the meter from work as my personal meter doesn't do DC current, just AC. I didn't have enough daylight to check each individual plug last night, and the wife is getting tired of me spending time under the hood instead of spending time with her - when I'm working outages our time (awake) is limited due to the long work hours, should be done with outage in a month, then she'll be glad I'm out of the house lol.

I didn't know they were bad at 2 ohms, thanks for that. What's a new plug ohm reading?

You're right about the change in requirements for keeping a rig running. It's a different world. I work on electrical devices all day and see how often they can fail, being in the field you've probably seen this too. While the newer technology is amazing at what it can do, the older technology is more serviceable 'on the spot'. Newer technology can be very difficult to troubleshoot as well due to the nature of electronic components, they can be very 'flaky'. I ride a 98 Harley because it has very little electronic components compared to the new ones. I've had for 17 years and just keep replacing parts as they fail or get unreliable. Mechanical components (and some electrical) can be fixed on the side of the road, electronic is another story.

I really don't like making vehicle payments, so keeping this ol' 7.3 going is pretty important to me. As a matter of fact, my plans are for this truck to last me until I start riding a rocking chair in the old folks home.

...."I'd be lost without my electronic career supporting my diesel (and boating) habit."

You have some good habits!

 

While I have seen a lower low number written somewhere, glow plugs should be anywhere from 1/2 ohm to 2 ohms each.

So I would expect to see anywhere from 50 to 200 amps though the GPR.

Since is is unlikely that all 8 GPs are at 2 ohms (theoretically possible and in spec, but unlikely), 50 amps through the GPR warrants more detailed inspection (ohm out all 8 GPs individualy).

 

Gotcha. Thanks! The meter peaked at 50 amps and started dropping off to the 30s before I took the meter off. (just a few seconds) This would indicate that I do have some bad plugs since the resistance value is going up as they heat up. By the way they are wired to the contactor I'm assuming that they are either all 'on' or all 'off'.

I'm beginning to think that if I take off the valve covers to replace some orings that I'm just going to replace ALL of the orings and plugs as well. There's 270+k on this thing and it's probably overdue. I'm usually of a mindset that if it isn't broke don't fool with it unless it's obvious that a failure is eminent.

I've never had the covers off on a diesel so I'll be probably asking some dumb questions if I can't find a thread with them already answered. Any comments or tips are more than welcome.

 

That is true for non-California trucks. California trucks have a Glow Plug Controller instead of a GPR which operates differently. And since you have a GPR (contactor), treat this info as trivia.

 

There is a lot of good information in the video below by the great Diesel Tech Ron.

 

Here's a question you probably wouldn't think to ask: "Can I run the engine with the valve covers off?" Surprisingly, the answer is yes. Oil doesn't shoot up when it's running - the oil shoots down because of the spouts. After I mess with injectors, I run the engine until warm, then I re-torque the injector hold-down bolts - and I get more spin out of the bolts. Warning - major suckage takes place while idling with all that air hardware off, so clear the paper towels and bungee the cat to the floor jack.

 

Motor-Craft glow plugs are self regulating which means as they heat up the resistance goes up a bit and reduces current draw. Last glow plugs I installed measured about 0.8 ohms each. With ohms law initial current draw cold should be in the 120 Amp range assuming 12 volts and 0.8 ohms each. It's dirt simple to measure each glow plug at the valve cover with a multi-meter. This will give you an overall view how each glow plug is working. And yes, if you have the covers off just replace them all for piece of mind. With good batteries, good connections, good glow plugs, good GPR and good valve cover gaskets it's amazing how fast these truck will start up in cold weather.

 

Clearly this diagram only refers to one side of the engine, but as you can see the outer 4 pins (2 on each side) of the valve cover harness are the glow plug connections.

Pins A, B, H and J in the diagram below are for the glow plugs on that side of the engine. You should be able to ground the black contact on the multi-meter (MM) and use the red contact to touch the pins on the valve cover harness and check for resistance on each of the glow plugs without removing the valve covers. Each plug should be below 2.0 and if they are not, they are bad. If you decide to remove the valve covers, then simply remove the connector from the top of each glow plug and touch the red contact to the top of the now exposed glow plug.

Same readings should be observed from the MM.

 

Thanks for all of the help, great information!

I ohmed out the passenger side plugs and found them to read good at .8 ohms. I will ohm out the other side this weekend. (Ran out of time) I think that I'm still going to replace all of them, cheap insurance while the covers are off. Funny thing is that there was 6 ohms from the glow plug terminal to the negative terminal of the battery but .8 to the housing of the alternator. Sounds like some of the ground connections on the engine need to be cleaned up. Will take care of this too.

 

Assuming the other 4 are also 0.8 ohms each, the entire set connected to and read from the GPR should be 0.1 ohms. And if they are all 0.8 ohms, the cheapskate in me says to leave them alone, they are fine.

Assuming a nominal 12V, the set should draw 120 amps.

That ground difference definitely needs to be fixed, it will also affect battery charge from the alternator. And 6 ohms of resistance will not allow the glow plugs to reach full heat. I also question the 6 ohms, check that again between the alternator body and the battery negative terminal. 6 ohms difference there would cause all sorts of problems. Check it to both batteries, maybe one (the one you checked) battery has a bad connection.

I also question it since you read 50 amps in the glow plug circuit, and 6 ohms resistance in the ground would limit the set to 2 amps.