L48 alternator/glow plug issue?

[Jason280]

I have an '03 Kubota L48 backhoe, with relatively low hours (728). For roughly the last year, I've had this intermittent dead battery/no crank issue. I pulled the alternator a few months ago, and had it tested at a starter/alternator shop. The shop said the alternator was fine, but the issue has continued. You can charge the battery, and everything will be fine. Crazy thing is, its completely unpredictable. Sometimes I can be outside running it for a couple hours, and it will crank fine...then suddenly, no crank (dead battery). Battery has been tested, and its not the issue. Coincidentally, I've noticed the glow plug "light" will some on intermittently as well, and sometimes stay on while the tractor is running.

Tractor runs like a top otherwise, and has never given us any other issues...its just this odd crank/battery issue. I've checked the terminals with the meter a couple times, and only getting 12.2-12.3v. It was doing this when I had it tested at the alternator shop, so I am curious if there is some sort of relay that "tells" the alternator to kick in/increase voltage to normal 13.7-14ish volts while turning. I did a little research on the glow plug light, and it seems like it is either the glow plug relay or controller....but I am not sure how its causing the no crank scenario (unless its simply killing the battery while running). That would sort of make sense, as I don't think there is any other 12v draw on this tractor (other than maybe lights, which are never used). Still doesn't explain, though, why I'm not getting 13+ volts with the tractor running.

The more I think about it, the more I am convinced the glow plugs are continuing to pull current with the tractor cranked, and it subsequently killing the battery...but I still can't figure out why I'm getting 12.2-12.3v with the alternator turning.

Suggestions?

 

[David_Kb7uns]

Check positive battery connector, some have a spade terminal that feeds some fuse holders by the battery for glow and other high current circuits. Sometimes holding the key on start and having someone move the connector helps. May also have a stuck glow relay if the light is on, and the alternator may need battery connection to excite if you have a bad connection.

 

[Roadworthy]

Check and clean all your connections really well as David suggested. Your system was not designed for continuous (or even intermittent) glow plug operation. They create more load than your alternator can supply. If they are coming on that problem needs to be addressed.

 

[Jason280]

I'm going to try troubleshooting it a bit in the morning, and will likely start by trying to disconnect the glow plug relay....see if that changes anything.

 

[moship]

Check and clean all your connections really well as David suggested. Your system was not designed for continuous (or even intermittent) glow plug operation. They create more load than your alternator can supply. If they are coming on that problem needs to be addressed.

Trying to learn here... Just how much current does each glow plug consume and how much does the alternator put out on the L48's?

If the GP's are on all the time, what are the chances they are still good?

I'd do a voltage drop test along the circuits in question. If uncertain how to perform, there are many youtube videos showing how.

 

[newbury]

I had a similar problem with m M4700.
Battery seemed to work fine most of the time, it would charge up and fire.... sometimes.
Took the battery to NAPA, they tested it 3 times, third time it failed. New battery, all has been fine for years and many many starts.

 

[Dave M7040]

Trying to learn here... Just how much current does each glow plug consume and how much does the alternator put out on the L48's?

If the GP's are on all the time, what are the chances they are still good?

I'd do a voltage drop test along the circuits in question. If uncertain how to perform, there are many youtube videos showing how.

A typical GP has a resistance of 1 ohm. Usual electrical formula of Current equals voltage divided by resistance.

Assume 12 volts + or - and a resistance of 1 ohm means each GP draws 10-12 amps.

If the glow plugs are staying on, you run the risk of the ceramic failing and ending up inside the cylinder where it will do serious damage.

Dave M7040

 

[Jason280]

Its all making more sense now. I believe the glow plugs are staying on, and overwhelming the alternator....which would explain the low voltage. First thing will be to disconnect the plugs, and try and rule out either the glow plug controller or the relay itself.

Should I go ahead and pull the glow plugs and check them, just to make sure there is no damage? I *think* they are likely fine, as the tractor has no trouble with cold starts (as long as the battery is charged).

 

[Dave M7040]

Its all making more sense now. I believe the glow plugs are staying on, and overwhelming the alternator....which would explain the low voltage. First thing will be to disconnect the plugs, and try and rule out either the glow plug controller or the relay itself.

Should I go ahead and pull the glow plugs and check them, just to make sure there is no damage? I *think* they are likely fine, as the tractor has no trouble with cold starts (as long as the battery is charged).

Remove the GP relay, charge the battery, measure the battery voltage while the engine is running.

If it is low then the GP's are not involved and you may need a battery and perhaps an alternator.

I am not convinced the GP's are staying on a draining the battery.

Dave M7040

 

[moship]

Dave7040,

Is the glow plug current draw constant or does it change as the GP heats up? I was under the impression it would pull 10-12 amps, but that it would drop off as the element heats up due to the resistance increasing. I've looked for graphs of the current over time, but haven't found any.

I'm with you in thinking GP remaining on is not the problem.