checking glow plugs

[gyroman]

I think I might have one or more bad glow plugs on my kubota so I put a ohm meter lead on the block and
the other lead on the glow plug terminal and it read zero. Is this a good reading or is my glow plug bad.
I appreciate any and all tips for checking them correctly.
Thank You.

 

[LarryT]

Do you mean 0 as in "no resistance", e.g. short, or 0 as in infinite resistance, or open. I would expect a glo plug to have a little resistance, on the order of 5-10 ohms. Make sure you meter scale is low enough to detect a few ohms. Did you check all of them?

Larry...

 

[Bird]

gyroman, I'll echo what LarryT said. I don't find here, or in your profile, what model Kubota you have, and I'm sure the proper reading is going to be different for some of the older models vs. the newer ones. My B2710 manual shows to check continuity between the glow plug terminal and the chassis and "If 0 ohm is indicated, the screw at the tip of the glow plug and the housing are short-circuited. If the factory specification is not indicated, the glow plug is faulty. Factory spec. Approx. 0.9 ohms"

Bird

 

[LarryT]

Thanks Bird. Even less resistance that I guessed. 0.9 ohms could easily be mistaken for a short. I'd guess that a glo plug failure mode could be either open or short. But I'd doubt all of them would fail at the same time. Look for differences.

Larry...

 

[TWINKLE_TOES]

gyroman,

I might be able to help if you can tell me what meter you are using. My manual (B21)says the same as Birds ~ 0.9 ohms. Most digital meters do a poor job of low resistance measurements.

Analog meters like the Simpson 260 (30,000 ohms/volt) can distinguish dead shorts from low resistances.

Either way, try this, short the meter leads togather and if it is an analog meter use the Rx1 scale and zero the meter and then measure the plug, if it is a digital meter, short the leads togather and remember the reading. Measure the plug and subtract the reading with the leads shorted.

 

[TomG]

Best check in a manual. My Ford 1710 manual gives resistance specs for the individual plugs and for the wiring. Best to be clear on whether a spec like .9 ohm refers to the parallel plug connections or to each individual plug. A parallel connection of three .9 ohm loads draws about 40A. A .9 ohm load draws about 14A. Ahh Uhm--it's early and my arithmetic may be suspect.

Glow plugs themselves are either good or bad. They don't get weak, but contacts or bases can become corroded, which slows them down. A poor connection on one plug would be reflected in a resistance measurement that is higher than spec. If the spec is given for the parallel connection, the reading would still be higher than spec. However, then you would be left with finding which particular connection is poor. It's not good to have one doggy plug, because the other cylinders have to be over-heated before the doggy one gets hot enough to fire.

Another way of checking plugs is to remove them, clean everything. Then, connect them to the wiring, hold the base against the cylinder head, turn on the pre-heater and see if they glow. If it glows, the plug is good, but connections in the wiring harness still may be bad. ‘Holding the plug’ involves the usual precautions when working with electricity. You don’t want to weld a wedding band to your finger.

 

[JATO_RaT]

Twinkle, I found your comment about digital meters interesting. I use a digital meter for the very purpose of low ohm resistance. It is so accurate. It is on the very high resistance loads, those in the meg ohms that digital gets a little quirky. What I observe with a high resistance is that a digital will continue reading many times per second a different resistance and refelect that on its screen. That being said, I actually find a test lamp being the easiest and sometimes the most accurate way to determine a glow plugs state. Glow plugs, like light bulbs tend to either work or not. Very rarely do they "short" but rather "open". I was also curious as to the posters reason for questioning his glow plugs. Is his machine starting hard? Here in California I have yet to use a glow plug on my Kubota, even once. I figure that since it starts in about 1/2 second everytime even after 10 years, it just doesn't need the assitance. Now my Ford diesel, its a different story... Rat.

 

[GlueGuy]

I guess I will echo what others have said here, with the added information that glow plugs, like light bulbs, change resistance when they warm up. So the 0.9 ohms will become much larger, very quickly after 12V is applied. That said, a DVM applies a relatively small voltage, so won't cause the glow plugs to warm up, or to change resistence (at least not enough to notice).

The bottom line is to use the lowest scale available to see if your glow plug is there. The difference between 0.9 ohms and 0 is not very much, and will look like the same (as in a short) if you're on a 2 Megohm scale.

GlueGuy

 

[Dub]

In my experience with checking resistance of glow plugs with a dvm; check the ohms in the lowest and the next lowest ohm position. I tried it in the lowest position and it ran down to zero. the 20k position read 2 ohms which is the correct reading for the L245. Unfortunately now i have three extra glow plugs. If a dealer is nearby get hte new plugs and test a new one for your model type. As stated earlier any variation of reading from plug to plug would be cause for concern.
See my earlier "L245 hard start "post under my unregistered callsign.

 

[Dub]

Further to my last. Make sure you disconect the leads from each glow plug when doing the test so no parallel readings occur. ie it has to be an individual test of each plug.
Am going up this fri to check the injectors on my L245. Any suggestions on "home checking tips". I've read the manual on having the required test equipment (which i don't have) so was just going to pull the injectors and fire each one into a clean parts washing can( to catch to fuel) and observe the spray pattern and if they start and stop the spray quickly and with no drip. Will also check the condition of them for obvious damage and cleaning required. Any other suggestions???

 

[Anonymous Poster]

If you have access to a DC clamp-on ammeter (i.e. F.W. Bell, or similiar), it can be a better means to verify glow plug functionality. Depending on the factory connections to the plugs, you may have to jury-rig a dedicated lead to each plug (energizing each, one at a time) to take the readings. In doing so, you can compare the actual current draw that each plug generates.

Good Luck.

 

[gyroman]

I got a lot a good info from you guys about my problem. Some updated info about my problem. My tractor is a L285 About 30 years old. I decided to check my glow plugs because its getting harder to start this winter here in Ohio. I am using a digitial ohm meter, and when I checked the terminal to the block the meter showed a zero on the screen. Thanks again guys.
Mike

 

[TWINKLE_TOES]

Out of curiosity I tested the glow plugs on my B21. The B21 has the two material plug type QGS (Quick Glow System) I used a current probe on the feed wire to the three plugs and a two channel oscilloscope, with the second channel monitering the voltage at the plugs (plugs are all in parallel) I left the main switch in preheat position for 30 seconds to see the resistance increase as the plug heated. Results were:

At time zero (preheat on) total current 27.2 Amps, Voltage 11.1 Volts.
At time =4 seconds the current began to decrease and at 30 seconds the current was 17.2 Amps. The voltage at 30 seconds was 11.4 volts. The time to reach 50% of the final value of 17.2 Amps was about 4 seconds (8 seconds from start)

At 30 seconds I started the tractor and the voltage and current dropped to Zero.

So... on the B21 the plugs cold are about 1 ohm and hot about 2 ohms.

I think the best way to test the plug is a flashlight battery and a light bulb. Touch the two wires togather look at the light, touch the two wires to the plug if its good the light will be quite dim, if its open the light will be really dim (out) if its shorted the light will look like it was when the lead are shorted togather. Use a blub thats draws about 1/2 to 1 Amp @ 1.5 volts.
Al

 

[TWINKLE_TOES]

Dub,

<font color=blue>"the 20k position read 2 ohms"</font color=blue>

That's an amazing instrument, who makes it and what is the model number?

 

[TomG]

I've got a Beckman DVM, and I'd expect that sort of performance from it.

 

[TomG]

My owner's manual indicated that injectors should be serviced at 600 hours. My dealer said not to bother until 2000 hours unless it was smoking. Bad spray patterns, wrong spill time etc. and it will smoke. At lot of smoke at start up, and the seals may be leaking down. I have neither, and I'm going to leave mine alone, but I might check the spill time. I believe a dial indicator and base are needed to check and adjust the spill time. I have old Starrett equipment, but an inexpensive button indicator and jig should be adequate.

 

[TWINKLE_TOES]

Tom,

I agree, Beckman is a fine company and has made instruments for a long time. What is the model number of your instrument?
Al

 

[Anonymous Poster]

I agree, Beckman is an excellent company.

We used Beckman's for years in our shop, but it got a little expensive sending them back to the factory for calibration & repair. The last invoices are in the early 90's about $110. then. The Beckman's were very sensitive to High Voltage RF and the guys would end up wacking them.

We switched over to Fluke and never had any more HV/RF glitch problems. As I'm writing this, I'm looking at one of the last Beckman holdouts in the shop, Beckman TECH 360...

P.S.- I've read the posts, maybe I missed something... What is the "original" reason he thinks the glowplugs are not working properly?

 

[TomG]

He says below 'harder to start this winter.' Perhaps the problem includes some missing and smoke at start up.

There are plenty of other reasons for hard starting, but the glow plugs are a candidate. I'd probably start by checking battery condition as well as the battery and starter cables. A starter that doesn't spin fast enough is going to give winter starting problems too.

Didn't know about Beckman and RF problems. I got mine when I was in the sound business, so RF wasn't much of a problem. I worked on aircraft NavAids while teching in the USAF. Some of the frequencies are near the radar range. We used mostly VTVM's or scopes back then. VTVM's probably don't exist today. RF sure is funny stuff. I was working on an omni-range while in school and got across some RF. I smelled something and realized that it was me burning. Never felt a thing.