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Topic: Tachometer Signal Source (Read 587 times) previous topic - next topic

Tachometer Signal Source

I have been without a working tachometer for some time. Since I have a VMSpc the non-working instrument on the panel is no big deal but I hate to have things onboard that do not work.  So I sent the tach to Ft Lauderdale for repair.  They just informed me that the instrument itself is working perfectly.  They suggested that it may be power/grounding or else the signal from the engine. 

When the tach was installed the needle would sweep full scale a time or two when I first turned on the ignition but would just sit at zero when I started the engine.  The LCD hour meter would come on but not advance.  Because of this I believe it has good power/ground. 

That leaves me with a signal problem or the wiring between the dash and engine room.  In a year old post about a different tach problem Barry (Barry & Cindy) mentioned that the signal comes from the upper flywheel area between the engine and transmission. I have looked in this area but have not seen any likely candidates for a signal generator.  In fact on my coach there is a heavy frame cross member that obscures this area. 

If anyone can help me locate the sensor I would appreciate it. 

Thanks
Jan & Richard Witt
1999 U-320  36ft WTFE
Build Number: 5478 Motorcade: 16599
2011 Jeep Wrangler Unlimited w/Air Force One
Jan: NO5U, Richard:KA5RIW
The selected media item is not currently available.

Re: Tachometer Signal Source

Reply #1 –
Believe it or not, it may run off the alternator.
Chris
Chris and Tammy White  CDA Idaho
Previous owners 1997 U295 36' 3126 Cat 300 HP Build # 4998
Former Foretravel tech & RVIA certified tech
Former owner Custom Satellite home/RV satellites 
Former owner Vans LTD  van conversions
Unemployed, panhandler, drag racer NHRA #6348

Re: Tachometer Signal Source

Reply #2 –
Most likely the alternator.
Peter and Frieda Morin
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: Tachometer Signal Source

Reply #3 –
Richard,

Your coach has an electronic M-11 so you can run the engine with the alternator disconnected and the tach will run just fine as I have done this before due to an alternator failure.

The engine position sensor monitors the engine position and the engine speed, then passes this information to the electronic control module (ECM) through the sensor harness. The engine position sensor is located above the accessory drive. This is where the tach should get its info from and would be a good starting place to start troubleshooting.

Measure the resistance from pin A to pin D of the engine position sensor.
Measure the resistance from pin B to pin C of the engine position sensor.
1000 to 2000 ohms is OK anything more or less replace sensor.
If the face is bubbled or cracked you will most likely need to replace the sensor.
If  there is oil in the wire connector you may get away with cleaning the connector with contact cleaner for a short term patch.
On very rare occasions you can have a sensor that checks good but have failed so the only way to confirm is to change out the sensor. They aren't very expensive (~$50 for the last one that I bought), you need to check your enigne number with Cummins Quick serve for the correct number for your engine but I think yours should be 432-6596.

One side of the sensor can fail causing the dash tach to fail and the other side will feed the Silverleaf. If both sides fail it will leave you setting on the side of the road. Hopefully this is clear as mud because I can't find the pics. as to what you are looking for.

Pamela & Mike

Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: Tachometer Signal Source

Reply #4 –
Mike if you can find Pics would be great, so far for me still hazy!!!
Chris
1999 U 320 DGFE
Build Number 5523
Chris & Elka Lang
In the field, Lonoke AR

Re: Tachometer Signal Source

Reply #5 –
Here is a couple of pics. from another post but not the ones that we were looking for. Seems like I posted some better pics some time ago but don't see them tonight. These are what the old style look like. The new style is built somewhat different and those are the pics. that I can't seem to find.
Mike

http://www.foreforums.com/index.php?action=dlattach;topic=22487.0;attach=26513;image
http://www.foreforums.com/index.php?action=dlattach;topic=22487.0;attach=26515;image
Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."

Re: Tachometer Signal Source

Reply #6 –
Jan, our engine does not have a computer, so the tach sensor is a stand alone unit that is only wired to the dash tach gauge, unlike your computerized engine with many sensors.

Re: Tachometer Signal Source

Reply #7 –
Mike,

Thanks for the write-up and pictures.  I found my Engine Position Sensor, it is in an impossible location.  I will have to find a female plug to be able to extend wires out far enough to check the resistances you describe.  I am attaching an image of my sensor but it looks identical to the one you posted. 

Thanks for your help, if I resolve this problem I will post the results. 

Richard
Jan & Richard Witt
1999 U-320  36ft WTFE
Build Number: 5478 Motorcade: 16599
2011 Jeep Wrangler Unlimited w/Air Force One
Jan: NO5U, Richard:KA5RIW
The selected media item is not currently available.

Re: Tachometer Signal Source

Reply #8 –
Quote from: Jan & Richard –
I found my Engine Position Sensor, it is in an impossible location. 

Richard,

That is a polite way to put it.  If the engine was in a class 8 truck the sensor would be a little easer to get to. 

That looks like the OEM installed one when the engine was built.  It don't appear to be leaking oil through the sensor out past the wires.  Once you unclip the plug I use some electrical alligator clip jumper wires to check the ohms.  Now if you find out that the sensor needs to be replaced I have no tricks up my sleeve that make the sensor simple to get to.

Mike
Pamela & Mike 97 U 320

"It's not what happens to you, but how you react to it that matters."