imbodie

Ok.. could be un-related but the last couple of weeks my truck has been harder to start than normal... and the Amp guage has been slow to kick up to the 14v range... Today I took it to a local autoparts store and after testing they said that batteries were good but alternator was only putting out 12.0 to 12.5 volts.... The guage and my Juice w Attitude both still show the voltage at 14ish?? The alternator on the truck has a warranty so I'm going to pull it and take it and exchange it, my question is why does the ECM voltage show to be correct, even while the alternator was being tested (and tested so low)??

Just curious,

Tim

SIXSLUG

You definitely need the higher output to keep the batts charged up so if the test showed 12.5 you aren't there...

The ECM should not be able to modify the output reading, or lie about it so I would r/r the alternator and consider that the ecm may be having an issue, not uncommon, they seem to wear out.

How many miles on the 240D? Great cars.

imbodie

I thought there might be two leads coming from the alternator or something of the sort... or maybe the ECM was reading correct voltage from some other source not directly from the alternator....

Not sure how they even checked the alternator, it was a multi-function test unit that also checked CCA and battery health while it was checking the alternator.... had to turn headlights and heater fan on, rev my engine and other sorted steps while the guy held the machine???

As far as the 240d, I'm not sure actually... the odometer shows 145k but I know the odometer has been changed or repaired...

-Tim

SIXSLUG

I don't think the juice would give a bad reading, and if the dash gauge is matching it that is 2 for 2.

Maybe go basic and clean up all the grounds you can find and check the leads coming off the alternator and see what you find..

The late 70's early 80 MB's diesels were great cars...

imbodie

Well, alternator is pulled and taking to the store for a bench test/exchange tommorrow... we'll see if it was a grounding issue or alternator issue...

imbodie

Ok took to parts store and let them bench test the alternator... it tested as good, was advised that bringing it back and having it tested again installed in the truck would not be a bad idea...

Re-installed this morning, drove to local (40 miles away) store, had it tested installed and it failed.... was only putting out 86 ams when its rated at 136 amps...

Removing it this weekend and taking back for a warranty exchange... I know it was a lot of trouble to remove/install/and now remove again but at least I know its the alternator... This also explains why I was getting the required voltage even after failing the first time....

Just thought I would update everyone.

-Tim

rickf

2+2 are adding up to 3 here? Why would it pass a bench test if it has a bad regulator or brushes? That would be the most likely cause of the problem but no matter, it should have failed on the test bench. 86 amps is more than enough once the initial draw is recharged so you should have been seeing 14.5 volts at every test point and no matter where it was tested if it was 12.5 at the battery then it is 12.5 at the ECM, period. Can,t be higher. This is why I do not trust high school kids with a piece of equipment that supposedly does everything for them and gives an answer. You can do these tests in your driveway with a 15.00 meter and get more accurate answers. Are BOTH batteries good? Were they tested individually disconnected from each other? When they tested it in the truck the second time did they use a full size AVR test setup? This is not some little handheld unit. There is no handheld that I know of that is going to be able to test a 136 amp alternator at full load. Think about it, that is just about the same amperage of most household service panels.

Rick

imbodie

Well... I basically agree with you, I really questioned the test meters 2 out of the 3 tests the old alternator had, but 2 out of 3 testing the alternator as bad was enough to get the alternator replaced... so now I'm moving on to other possible problems because with a new alternator installed, still having the same problem.

So where is the voltage regulator on a 2000 dodge diesel?? my worst fear is that it resides IN the ECM...

-Tim

patdaly

Your worst fears are true.

But the typical failure would be no charging at all............ For giggles, have you checked out your battery temp sensor and wiring? You don't have additional cardboard or rubber under the battery?

rickf

As Patdaly said the regulator is built into the ECM. I would look at all of the battery cables first though, both ends. Don't just look at them, take them off and clean them and put them back. Check the ECM and battery to body grounds also. Then check the voltages with a good volt meter at the battery with it running. If your external meter says 14.5 then go to your fuse box and just check the back exposed test tab of all the fuses and see what you get there. I am going to bet it is also 14.5. At that point the only thing I can think of is the connections at the ECM. Take the battery ground cables off of both batteries and then unplug all of the plugs on the ECM and see if any of the terminals are corroded. If not plug them in and out several times to clean the contacts and then hook up the batteries and check again. If that does not work the only solution is to find someone else with a same year and model truck and swap the ECM and see if that clears it up. If it does then you know what you need. Better to check all that other stuff first since it is free to do so.

Rick

imbodie

until earlier today reading another post I didn't know I had a battery temp sensor... is there one under each batter or just drivers side?? Whats the purpose?


This really isn't an issue yet.. I just want to catch what ever the problem is while it is still only annoying... and just to clarify The volt guage starts out at around 10volts and works its way up slowly to 13.8 to 14.0 volts and then stays solid at that level.... I'm just worried about the slowness to get up to voltage... its the same on dash guage and on my Edge monitor...

Tim

SIXSLUG

I think there is a temp sensor under each battery.

The purpose of the temp sensor is to keep it from overcharging/overheating and blowing up. It would need to get pretty warm to read underneath...

Mike Holmen

The PCM controls voltage not the ECM. The two wires on the alternator are the field contacts, there is no voltage control done by the alternator. Once the alternator gets weak, the PCM will terminate the field contacts on high loads and you'll get zero volts on the gauge in the dash. The air heater grid takes quite abit of power to cycle thru, thats what your seeing.

I beat that your having starter issues. The cummins starter are know for getting weak. Next issue is that the starter will only work at certain start positions. There is a neat starter mod, to improve the start contacts and replace the starter bushings.

My best way for determining battery condition is to disconnect one of the batteries and see what voltage you have during first heat grid start cycle. If you drop below 11 volts on a single battery, its probably nearly dead.

Blake West

I do have a question along the same lines, not to thread-jack, I ran into the same issue recently, my voltmeter in the dash would read down at 10 or 12v right after startup and then after about 20 minutes it'd go back up to 14v or better. I went and had the batteries tested individually and together, together they were putting out 750cca, when each battery was rated for 750cca a piece. After that they tested the alternator, and there was barely 12.1 coming to the batteries with a full electrical load. I replaced the batteries and the alternator in an hour or so.
Now at idle after startup, there will be a click sound, the dash will light up brighter, and then click and it will go duller, and this will repeat 3 or 4 times before coming on bright and staying on bright. Is this normal?

patdaly

Yep, grid heaters are cycling.