General Boards > Technical Support
RPM gauge
Scott Hinote:
We have a 2000 Beaver Patriot Ticonderoga with the 3126b 330 Caterpillar . Our ECM died and we had it replaced . But after getting it home I noticed that the RPM gauge wasn’t working . The company that did the replacement came back out to me and did more troubleshooting, they are saying that the gauge is bad . They also said when they were connected to the ECM with their laptop using Caterpillars software, that the gauge was getting the needed signal from the new ECM . Here’s my question if anyone might know, does the gauge operate off the ECM , or the alternator or the transmission ? I need to know because I’ve been told 3 different things, and before I move forward with buying a new gauge or just have the company that replaced my ECM , re calibrate the gauge so it operates correctly on the upper end higher rpm’s ? They have told me they can do that . Thanks everyone for helping out .
Eric Maclean:
Scott
These coaches could be set up with either an alternator drive or ECM signal drive .
But on page 26 of the 1996 patriot wiring diagrams it clearly shows the wiring path from alternator to tachometer.
( 1996 is as close as we have for wiring diagrams and is pretty relevant all the way to 2002.
Hope this helps
Eric
Scott Hinote:
Thanks Eric for replying, I don’t know why the Moblie Fleet service company that helped me with my ECM . Why they are telling me it gets the signal from the ECM . Everything I’ve been able to find out is it’s coming off the alternator . They were at my house for 9 hours and that’s what they came up with . I’m not going to jump and go buy a new gauge, if they did something to my alternator during the changing of the ECM . Sorry to bother you but I have a friend that’s in California, that I met in the Beaver forum in Facebook . I don’t know why but he had his alternator rebuilt . I’m just wondering if maybe I’m having a problem with that . I haven’t noticed anything, but I’m usually connected to shore power and my batteries are kept charged through the Inverter and the Echo charger . It’s going to be a pia but maybe I need to put my eyes on my alternator and take some voltage readings . Or I could just start the engine and see what my gauge is reading, there’s got to be a gauge that reads alternator output . Again thank you
Carl Boger:
Scott,
I would check the voltage out put from the alternator as it will be the most accurate. I know on my coach my alternator went out and it was still reading 14 volts on the gauge and the display, but only putting out about 12.2 at the alternator. Now the alternator puts out 14.6 or so and the gauge shows about 16.
Eric Maclean:
Scott
To diagnose your tach check the tach signal at the back of the tach itself.
Using a multimeter set on A/C voltage meter leads between the ground terminal and the signal terminal you should read a voltage in or around 6 to 8 volts or more , this signal comes from one of the stator leads of the alternator this signal is an A/C voltage as it is tapped from the one of the three phases before the rectifier
If your not getting a signal there check at the alternator ( the tach is driven off any one of the three A/C stator taps located in the recessed area on the back of the alternator just below the regulator .
If you have a signal at the alternator and not at the dash you will have to track the wiring as per the wiring diagram.
Also when you have the dash apart check all the wire connections as they have a bad habit of coming loose.
Hope this helps
Eric
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