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

[Steve Huber Co-Admin]

Gentlemen,
The 2002/03 Patriot wiring diagram (same chassis & engine selections as the 2000 Marquis) shows the tach signal comes from the ECM. See page 13 of the diagrams.
Suggest you not put a meter on the signal as the ECM outputs can be sensitive if not buffered.
Steve

[Eric Maclean]

Scott
It appears Steve is correct that the tach in the latter coaches were driven by the ECM.
So sometime between 1996 and 2000 beaver changed their system.
About the only way to verify if it has an alternator driven tach is to look at the back of the alternator for the presence of a stator tap wire connected to the alternator as that is the only thing a stator tap is used for.

Either way the signal to the tach weather it be alternator driven or ECM driven should be an A/C signal and can be read with an A/C voltmeter just be careful not to short the signal to ground.

Eric

[Scott Hinote]

Hey Eric thank you . And yes sir you are very correct . I’ve since found out that my tack gauge is the problem, it’s no good , I need to find a replacement, either a used one that’s working or a new one or send this one out to be repaired . But that was driving me crazy, I had to prove it was the gauge itself or I was going to go to the next part of the troubleshooting . If you know where I might get it fixed or a replacement one that would be great .

[Scott Hinote]

First I want to thanks Steve and Eric for helping me figure out the gauge was bad . Now I’m looking for either a used working gauge or maybe there’s somewhere I can send it to and have it repaired, or lastly a new one. Thanks everyone you’ve been very helpful .

[Eric Maclean]

Scott
Try Visone RV salvage they have some used original gauges just have to identify the one you need.
Most of the Magnum chassis used teleflex gauges branded with the Magnum logo.

https://rvcomponents.visonerv.com/cgi-bin/f/search.pl?

Good luck
Eric

[Richard Good]

My 98 Patriot Ticonderoga is driven from the ecm. When my ecm failed, the Caterpillar tech replaced it at my shop. He had to recreate the program as Cat had no record of a program for my engine. When he first fired up the engine, both tach and speedometer had no readings. After he added some more lines of code, both started working. My speedometer reads about 5mph. low, but interestingly, the computer reads right on.

[Eric Maclean]

Richard
The 1998 model year Magnum chassis used a teleflex speedo .
If you pull the dash out you will find dip switches on the back of the speedo , they are used to calibrate the gauge..
depending on the tire size and differential ratio ( gear ratio) .
These dip switches are set to relate with the number of pulses per mile
The pulse signal is produced by a speed sensor in the Allison automatic transmission via serial stream data shared with the engine ECM and other modules connected to the network back bone.

If you go to the coach assist area of the forum
Then go to brochures for almost all beavers then to Safari Motor Coaches (1994-2001)
Then to miscellaneous diagrams and fixes.
There you will find a page which has the teleflex calibrations for the 1997 model year.
Depending on your rear end ratio and tire size this might be what your looking for.

Eric

[Scott Hinote]

Okie dokie I’m going to have a close look at those manuals . Thanks, I saw them earlier but I haven’t looked into them yet, but it’s time I do .