Once again yesterday, I was assisting in the hard cold start diagnosis of an IDI. After determining that the return lines were not leaking it was clear to me that the glow plugs and/or GP controller was at fault. The truck in question is a '93 7.3. The owner had had the GP's replaced about 10K ago and said that it has been slowly getting harder to start as the cold set in. The owner said that he used a multimeter, as shown on this forum, to determine if he had a bad GP, and that all but one proved "good" using that method. The symptoms, however, suggested otherwise. The first glow cycle was pretty non eventful. WTS light came on, for what in my opinion, is the correct amount of time, then the engine was started. Sure enough it was a pain to start and I could tell that it had about four dead holes. Post glow was the interesting part. After the engine was running, the GP controller "post glows." The symptom here was that the entire dash would power cycle. Also the GP controller was cycling on and off at about 2Hz. The dash power cycle corresponded to the GP power cycle. I suggested we remove the GP's for further investigation. I had a hunch that he had several glow plugs that had internal shorts. We removed all the GP's. Next we verified the resistance of all the plugs. It corresponded to the previous verification, using the method on this forum, that seven were good and one was bad. I next used a jump pack to ACTUALLY test the GP's. We found that he had ONE truly bad glow plug, THREE GP's with internal shorts(within the body), THREE GP's the did not glow at the tip (2 midbed and 1 only at the body) and ONE GP that actually glowed where is was supposed to. As a note all the GP's were AC Delco(for information only). The point of this rant is to urge people to approach diagnosis logically. Don't just throw a new engine in when you need to change the oil, and don't assume that something you read on a forum is THE way to test something. While he had great intentions, the method failed him, and now his truck starts the way it's supposed to. 20 minutes $100 to diagnose and replace properly. He spent 10 minutes diagnosing two months ago and potentially damaged his batteries and starter as well as his alternator and GP controller and wiring. Extended cranks cause undue wear on the starter and batteries, and the three dead shorts cause undue wear on the wiring, controller and alternator. Not to mention the ECM's probably didn't appreciate it too much either. Burnout in NOT the only failure mode of Glow Plugs. and an internal short can read 0.3Ω just as well as a GP that glows where is isn't supposed to just as well as a good GP.
End of Rant
Have a Great day!!!!

As needed to prevent flaming, Photographic and/or Videographic evidence can be provided.

 

Thats good advice. I like photos/videos.

 

I hope this is OK, we only have dial-up way out here so video is much more painful.

Good plug:


Bad Plug:


Midbed Plug:


Internal Short:


I hooked all the plugs to my battery charger for the next series of photos. The maximum output on the charger is apparently about 22A as shown in the shorted plug photo. Also Pictures were taken at 10 Seconds for all and at 20 Seconds for the midbed plug to show the differences.

Good Plug @ 10 Sec:


Good plug close up @ 10 Sec:


Bad Plug @ 10 Sec:


Midbed Plug @ 10 Sec:


Midbed Plug close up @ 10 Sec:


Midbed Plug @ 20 Sec:


Midbed Plug close up @ 20 Sec:


Internal Short plug @ 10 Sec:


I hope this clearly illustrates the differences in performance of the plugs. The typical Glow cycle isn't going to be long enough for a midbed plug to be at the proper temperature.

 

Well Done.

Might want to put a copy of this in the IDI forum. That's something i sure need to remember...


and what model is your DC ammeter? I've been halfway looking for one...

 

I will probably let it lie here. Over there in IDI land, I have the feeling I'd be dodging a flamethrower. I'll let the search engine lead people to it. AS far as the meters are concerned, the Clamp is a Fluke 337 and the Multimeter is a Tenma 72-6203. I really recommend Tenma stuff. The Multimeters have Fluke guts just not the Fluke price. As an electronics hobbyist, I need good test equipment, I have a combination of Fluke, Tenma, and Techtronics. All really good stuff.

 

krog,

NICE write up!...reps sent your way!

Thanks for sharing!

Joe.

 

$300+ for a meter i dont need is a little high...

 

I know it's priced pretty high, but most good clamp meters are. I have noticed lots of them at my local pawn shops (I think we all know the origin of such products ) pretty reasonably priced. I also picked up a $600 portable oscilloscope at a local yard sale for $50 (I'll also bet questionable origin.) Anyway, keep your eyes open and I'll bet you'll find a good one sooner than later.

 

Yeah those pictures say a thousand words, each. Good work and I am going to rep you.

It must be nice not to have to remove the valve covers to get at the glow plugs.