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Old 09-11-2014, 08:56 PM   #1
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Tach reads zero and alternator not charging

I have some electrical gremlin that I'm thinking might be related to my new chassis battery connections?
Today, while driving from Virginia to Morgantown NC my tach would bounce erratically. When going down hill with compression from the driveline on the engine (either by slowing or using the PAC brake) it would register rpms and the alternator would appear to be providing current. Conversely if I accelerated down a hill or was climbing a hill it would show zero rpms and the voltage meter would drop as if the alternator had kicked off.
If I used the battery boost while the alternator appeared off it would deflect the voltage on the dash and rc7 meter to a higher voltage but the tach would not engage.

Does this sound like a bad ground? I do have 5 direct connections to the chassis battery and I have not identified three of them. I'm thinking of redoing those ground connections tomorrow

I recently was getting a 268 code warning light and the cummins tech said that may be a bad ground to the ECM. He wiggled the wire harness in the ECM and the warning light went off. Maybe this issue is related?

I guess my alternator could be failing but would that cause zero rpms at highway speeds?

Help!!




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Old 09-11-2014, 09:26 PM   #2
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RPM, could be an ECM output , and alt output could be under the control of the ECM too.
I'd really get after those grounds .
Do you have a wiring schematic for the engine?

EDIT: According to the info I have on ISB & C's there are five battery fuses feeding the ECM, so it's important to check those too. Those may be in a separate fuse box in the engine bay, they are on the Spartan chassis.
Roadmaster may use something similar because Cummins would require it.
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Old 09-11-2014, 10:25 PM   #3
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Occam's Razor

Occam's Razor says the simplest solution is usually the best. If you haven't done so, you may want to unplug the harness on the back of the alternator, check for damage or corrosion and plug it again making sure you have a good connection. Both the volt meter and are powered through the harness.
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Old 09-12-2014, 07:38 AM   #4
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Quote:
Originally Posted by RandyS549 View Post
Occam's Razor says the simplest solution is usually the best. If you haven't done so, you may want to unplug the harness on the back of the alternator, check for damage or corrosion and plug it again making sure you have a good connection. Both the volt meter and are powered through the harness.

Are you saying the volt meter and tach are powered from the alternator harness?

I will do this today as well as redo the grounds that are wired directly to the battery.
I did spray corrosion block on the front run bay battery connections (the ones that go through the wall of the front run bay) but I don't think those would affect the alternator/tach.

I do have a coach wiring book I will also look through.



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Old 09-12-2014, 07:42 AM   #5
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Quote:
Originally Posted by Skip426 View Post
RPM, could be an ECM output , and alt output could be under the control of the ECM too.
I'd really get after those grounds .
Do you have a wiring schematic for the engine?

EDIT: According to the info I have on ISB & C's there are five battery fuses feeding the ECM, so it's important to check those too. Those may be in a separate fuse box in the engine bay, they are on the Spartan chassis.
Roadmaster may use something similar because Cummins would require it.

Skip
I have identified 2 of the 5 direct wires as solar panel charge (input) and Allison ECM. I have no idea what the other three are and have always wondered. Does your info say what the 5 are?


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Old 09-12-2014, 08:37 AM   #6
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The tach uses the alternator alternating current to sense/compute engine rpm. So the fact that you have a bad tach and an bad reading on the voltmeter would indicate that you have a failing alternator. Could have lost a diode or has a bad regulator or a bad/sticking brush. I would find a alternator rebuild place and take it and get it tested. You could also take it to Freightliner and have them check it.
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Old 09-12-2014, 06:37 PM   #7
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Tach reads zero and alternator not charging

Thanks Mike.
Upon closer look today I saw three smaller wires on the back of the alternator. Red, yellow and blue or black I think. The harness is about 90 degrees or more from the crimped rings putting stress on the bare wire where it enters the crimp.
This angle appears to have just about cut through the red wire which I think is labeled "remote sense". It's hard to see from the rear of the coach with a mirror.
That almost cut wire explains my mystery where it would work if I decelerated or activated the exhaust brake down a hill putting forward momentum on the motor and reconnecting the almost severed wire.

I will remove the three wires and put on new connections and support the harness at a better angle to the connections.
Getting up and in there will be a dirty challenge
I'll post some pictures.

According to my build sheet I have a Leece Neville A0014884-JB Alternator. If I ever did need to have another would you recommend getting it rebuilt or an alternative?

Thanks to all for steering me in the right direction

In looking at battery grounds I did also find where my Lambert LE-415 battery maintainer ground wire was not reconnected when Mastertech put in my new Lifelines at Perry:(. I had been wondering why the little green light did and why it wasn't on lately.
Now I know how the Lambert LE-415 Maintainer functions too!


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Old 09-12-2014, 07:31 PM   #8
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If required my recommendation would be to get your alternator rebuilt vice getting a new one. So many people seem to have problems in finding an exact replacement and it gives them trouble. If you have to take it off then be real careful not to turn the studs that the wires are connected to when trying to loosen the nuts. If the studs turn they will do damage inside the alternator.
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Old 09-12-2014, 08:05 PM   #9
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Is this risk also true with the 3 small wires or just the main positive and negative
I only need to redo one connector if that's a risk. I thought I would redo all three small wires while I'm at it
Should there be any current in the alternator if the motor is off? Maybe via the charge inverter or the maintainer?


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Old 09-12-2014, 08:24 PM   #10
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Check the wires with a voltmeter first before redoing the terminals. I think the DUVAC wire is always hot so disconnecting the chassis and house batteries would be prudent before you disconnect the leads. BTW the large BATT cable goes to the battery isolator center stud I believe.
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Old 09-12-2014, 08:31 PM   #11
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Check the wires with a voltmeter first before redoing the terminals. I think the DUVAC wire is always hot so disconnecting the chassis and house batteries would be prudent before you disconnect the leads. BTW the large BATT cable goes to the battery isolator center stud I believe.


Will do. I'll check them then switch the battery switches off and test again. I just don't like to have to remove the direct wired connectors such as the maintainer.
One day I'm going to install a switchable bus bar instead of 5 ring terminal sets (positive and negative) to the chassis bank and another direct wired set from the maintainer to the house bank.
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Old 09-12-2014, 09:32 PM   #12
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Here is what I have for the ISB/ISC wiring schematic.
It shows , tach as an ECM ' output.
Some minor differences between the B & C , but both show tach output, from the ECM.
I'll dig up the photo's and re-post.
Attached Files
File Type: pdf Cummins ISB ISC wiring.pdf (404.5 KB, 138 views)
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Old 09-12-2014, 09:47 PM   #13
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Ok , so here's the story. My 99 freightliner, wiring schematic, shows 5 fuses for the Cummins ECM, the member who sent me these photos has a newer Spartan chassis , with 5 fuses for his Cummins ECM, the schematic in the previous post shows 5 battery fuses for the Cummins ECM, so I'm sure the number of fuses is a requirement for Cummins engines. If you can't find them , contact Monaco , about their location.
First photo is of the fuse box, cover on, that he found. Second , cover off, shows fuse layout. His problem, an alternator failure had blown a 5 amp fuse , and his new alternator wouldn't work, due to no ignition feed to the alternator.

EDIT: Second photo is 90 degrees rotated from the first. Index the photos from the white connector. Top on photo 1, Left side on photo 2.
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Old 09-13-2014, 06:12 AM   #14
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I believe the ECM gets its tach signal from the alternator.
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