Glow Plug Test--Before I Zap Myself or Fry Something

Ok, I'm about to attempt the in line fuse method glow plug test, as I am replacing the module and have easy access to that area of the van. Before I zap myself or fry something, I want to make sure I have it all down correctly.

I am using an inline fuse with a 20A fuse and 12g solid wire. I believe that is correct based on other threads.

I just installed a new glow plug module. The battery cable to the new module is connected and the battery is once again re-connected to the vehicle. In other words, the new glow pug module is fully installed and all the electrical is hooked up like normal.

I will pull the 5 port plug from the module. With my in line fuse tester I will place one end of the 12g wire(with a small flat connector at the end) into 1 of the 5 ports, each one corresponding with a different glow plug. I will then take the other end of the in line tester and touch it to the positive side of the vans main 12V battery. I will hold here for at least 10 seconds. If the glow plug is open/bad, the fuse will blow, if it is operating it will not.

Is all of that correct?

Thank you.

If the plug is open it won't blow, only a short will blow the fuse.

Midwestdrifter said:

If the plug is open it won't blow, only a short will blow the fuse.

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Got it. I had one fuse blow for GP3. On GP1, 4, and 5 the fuse was fine but I did notice that when I'd connect the battery end of the inline fuse to the battery I'd hear a little "tick" or spark noise. On GP2 this did not happen, and the fuse also did not blow. I'm guessing that means there is also an issue with GP2?

Yep, gp2 is open and non functional

Cool. I'm likely going to change them all between now and November just so I know they're all new, but it's good to know how to test and what the results mean moving forward.

Do you have the newer updated module? If not, the shorted plugs will have blowing the internal (non replaceable fuses). The newer updated glow plug control module has self resetting breakers.

Yes, I actually replaced it today and figured I'd test the plugs using this method while I had the grille and headlight removed. Bought the van Monday(a 2004, I also have a 2006), check engine light came on yesterday morning. Had a local shop run the codes(I have a code reader currently shipping to my house): PO380, PO672, 673, 674. After running a few errands the check engine light went away. After researching decided to change the module to the newer design and test the GPs. I assumed the original module was still in there and was a bit surprised to find out today that it was in fact already changed at some point to the solid state design. Replaced it anyways since it was all taken apart. Plan to order some glow plugs and replace all 5 in a few weeks, very carefully.

Alright, so I was able to get 4 of the 5 glow plugs removed and replaced using the methods many of you all have posted(kroil, kroil, kroil, let marinate, remove with warm engine). 3 of them came out as easy as pie, 2 of them weren't budging, so more kroil and waiting. I was able to get 1 of those two out eventually. After I was able to get it unthreaded, the body of the plug was still stuck in the block. I could spin it with a wrench, but I could not get it out for the life of me. Eventually, with some vice grips and pulling on it as hard as I could, it came. There was a lot more discoloration on the body this one. I am now at the same crossroads with the final plug: I have it unthreaded and it spins in the block, but I cannot get it come up and out. It is plug number 2 I believe, 2nd closest to the windshield, so I'm not able to get as good of a grip or put as much upward pulling force on it as the other one that was stuck--and in trying to get it out I snapped off the very tip of the plug(the part the connector goes on(luckily it did not fall into the void space around the plug itself)). SO...any further suggestions? I see there are different types of glow plug removal tools on the market though I have not done much research into how they work. I'm also not sure if they will actually fit under the hood to work as they are supposed to because of the location of this particular plug. Anything I should try?

Start the engine, it should blow the bits out.

Midwestdrifter said:

Start the engine, it should blow the bits out.

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Not sure what bits your talking about. I can’t get the glow plug out. It’s unthreaded, but I can’t pull it out.

RJV said:

Not sure what bits your talking about. I can’t get the glow plug out. It’s unthreaded, but I can’t pull it out.

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Start the engine then slowly rotate it.

But be ready if it shoots out! Cover it with a cloth or blanket!

Yep, I'd cover that sucker and fire it up. It should come flying out pretty hard.

Thanks all. Happy to report I finally got it out. In a last ditch effort I took a drive to the auto parts store and bought a different penetrant: Sea Foam Deep Creep. I used a compressor to blow the Kroil (and any small metal shavings that I managed to flake off the top of the glow plug when trying to pull it out) out of the cavity around the plug. Then I sprayed the Deep Creep and used the ratchet to just spin the plug back and forth. Almost instantly I could tell it was loosening up more than it had with the Kroil. I should state here, that I was using straight up Kroil--not the aerosol spray can. In retrospect, this may have been a detriment, though I was able to get the other 4 plugs out without too much hassle. The Deep Creep is a spray can FWIW. Anyway, after a few minutes of letting the Deep Creep work it's way in and twisting the plug around I was able to pull the thing out maybe a cm or so--so at this point I knew it was close to coming out. A bit more Deep Creep, a bit more twisting, and I was back to a stalemate as the thing would not come out any further. This was all before I saw your suggestions to cover the plug, start the engine, and blow it out. I had tried to do that earlier, I even drove about 50 miles with the thing unthreaded but it remained stuck. Now that I had finally gotten it to come out a bit I tried it again(didn't cover it, oops) and the "bits" blew right out! Luckily it just hit the padded firewall and didn't do any damage, take out a neighbors window, or kill anyone. I'm happy it's done and I didn't break one off in the block. I'm seriously considering just replacing the things on both my vans on a yearly basis just so I don't have to deal with this again. All in all, I probably spent 8 hours over the last 2 weeks getting the things out, don't really feel like doing that again.

Midwestdrifter said:

Yep, gp2 is open and non functional

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I'm confused above you said open fuse would not blow glow plug good and later you said fuse did not blow but because it did not spark or tick but fuse did not blow glow plug no good which is it? Could you not just check glow plugs with an ohm meter that is how I check them on my M.B. 300 SD.

There are three types of failure. On one type of failure the plug will test okay but fail once it gets hot. The other type of failure is an open plug, which will show up with a meter.

A happy glow plug is on the order of a half ohm ... and sick-but-still-conducting can be from one to two ohms.

Such fine discrimination at low ohmages is quite difficult to measure with a home ohmmeter and hand-held probes.

Both the (near zero) ohm "short" and "happy" are hard to tell apart (compare your glow plug reading with just touching the two ohmmeter probes to engine metal ... that would be a "short"), and the "happy" and "1.5 ohms" are hard to tell apart (a 1.5 ohm glow plug would still be getting pretty warm, but only a third as hot).

An open plug shows up quite nicely with an ohmmeter. (infinite ohms)

--dick (who uses a clamp-on ammeter)

Not to take away from Dick’s ohmmeter readings, but to put into 20-amp fuse test terms:

- a failed glow plug shorted to ground will blow the fuse almost immediately;
- a failed “open” glow plug will pass no current and produce no spark when disconnected;
- a sick glow plug will heat up but produce only a weak spark when disconnected (5-10 amp current hot);
- a healthy glow plug will heat up and produce a visible spark when disconnected (15-20 amp current hot).

A clamp-on ammeter is the most accurate tool to use to measure the individual currents, but if you can’t acquire one then the 20-amp fuse test will allow you to identify any blown, shorted, and perhaps weak glow plugs.

-dave

I wrote my post to give some help on interpreting (inexpensive) ohmmeter readings.

My only qualm about the fuse test is accurately judging the spark.

Many inexpensive voltmeters can directly measure 10 amps, so it might serve as verification of the "weak" current.
(but you might pop the voltmeter's fuse at a "good plug" 12 amps)

--dick