Dash tachometer quit

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Dash tachometer quit

August 14, 2020, 08:04:02 pm

My dash tachometer quit working. It will go back and forth when the key is turned on but stays on 0 when the engine is started.
The tach on my Silverleaf works fine. Do the get their signal from different places.

Re: Dash tachometer quit

Reply #1 – August 14, 2020, 08:18:10 pm

Quote from: oldguy – August 14, 2020, 08:04:02 pm

My dash tachometer quit working. It will go back and forth when the key is turned on but stays on 0 when the engine is started.
The tach on my Silverleaf works fine. Do the get their signal from different places.

Possibly the alternator

Re: Dash tachometer quit

Reply #2 – August 14, 2020, 08:39:34 pm

The '99 get the tach signal from the ecm same as silverleaf. Is the hour meter still working on the tach?

Re: Dash tachometer quit

Reply #3 – August 14, 2020, 08:41:38 pm

Don't know but will check.

Re: Dash tachometer quit

Reply #4 – August 15, 2020, 12:36:39 am

Same with ours... I haven't gotten around to fixing it yet but you are welcome to beat me to it, as long as you share the answer! If the ISC in our 99' U270 gets the tach signal from the ECM as Craneman (Chuck) says the ISM does, I would suspect the tach. But the fact that it does the full sweep when turning the key on makes think otherwise... it will be interesting to see what you find out.
Don

Quote from: oldguy – August 14, 2020, 08:04:02 pm

My dash tachometer quit working. It will go back and forth when the key is turned on but stays on 0 when the engine is started.
The tach on my Silverleaf works fine. Do the get their signal from different places.

Re: Dash tachometer quit

Reply #5 – August 15, 2020, 02:10:43 am

Several years ago the tach on my '99 u320, which is only slightly younger than yours, exhibited the symptoms you describe (the engine hours did not increase). After many hundred dollars worth of diagnostics at MoT and Allison (where MoT referred me) the gauge still did not work. I decided to purchase the Silverleaf VMSpc and ignore the gauge on the dash. I have gone that route for at least five or six years. Last fall, after several forum members had reported great results having gauges repaired at Lauderdale marine, I decided to ship the tach off to them in Florida. They checked it out and said that there was nothing wrong with the gauge itself (same thing MoT had said years earlier). I have since been told that the sensor for the tach on my coach is on the M-11 engine rather than the transmission or the alternator. I understand that it is hidden below the air conditioner compressor. I have yet to actually find or see the sensor but one of these days will get ambitious and find it and replace it, then my dash gauge may work again. Until then I am content to live with the VMSpc display. Quite frankly, a tach on an automatic transmission coach with engine and transmission computer controlled safeguards, is rather superfluous.

Richard

Re: Dash tachometer quit

Reply #6 – August 15, 2020, 07:23:40 am

Jan, I beg to disagree. You are right in the flatlands, but I find the tach critical for mountain driving.

Re: Dash tachometer quit

Reply #7 – August 15, 2020, 10:51:31 am

Would any of the schematics show the wire coming to the tach? Not my forte and I am missing some schematics. Sometime in the past I called FT and when they asked me to look at a drawing number, I didn't have it so they emailed it to me.

Re: Dash tachometer quit

Reply #8 – August 15, 2020, 11:45:42 am

I did some searching and the info I come up with is the tachometer sensor sends a signal to the ecm. Can't find any information about a sensor that goes directly to the front of the coach.

Re: Dash tachometer quit

Reply #9 – August 15, 2020, 12:27:01 pm

Quote from: craneman – August 15, 2020, 11:45:42 am

I did some searching and the info I come up with is the tachometer sensor sends a signal to the ecm. Can't find any information about a sensor that goes directly to the front of the coach.

Therein seems to lie the crux of the situation. Why does my (and other people's) VMSpc tach and engine hour meter work perfectly but not my dash gauge? The gauge has been checked twice and the wiring from the dash to the rear of the coach, according to MoT, is good.

The VMSpc can get info only from the ECM. So how does the tachometer gauge receive input that is different from the VMSpc?

I have no wiring diagrams which address this kind of detail.

Richard

Re: Dash tachometer quit

Reply #10 – August 15, 2020, 02:11:20 pm

The answer may lie in the fact that there are 2 sensors in the pickup and when both fail the light comes on, maybe the tach signal is coming from one and the other goes to the diagnostic plug. Just a guess but seems possible.

Re: Dash tachometer quit

Reply #11 – August 16, 2020, 02:57:10 am

Quote from: craneman – August 15, 2020, 02:11:20 pm

The answer may lie in the fact that there are 2 sensors in the pickup and when both fail the light comes on, maybe the tach signal is coming from one and the other goes to the diagnostic plug. Just a guess but seems possible.

Craneman, thank you. You say it is a fact that there are two sensors in the pickup. No one that I have talked with has mentioned that fact. That may very well explain why the tachometer gauge on the dash and the diagnostic plug which feeds the VMSpc are getting different info. Your information may spur me to investigate this further.

Thanks again.

Richard

Re: Dash tachometer quit

Reply #12 – August 16, 2020, 03:38:11 am

One of my sensors was oil soaked and the symptom was an erratic idle. My tach always worked. If the other side had failed would the tach not work but the motor idle perfectly?

Part was inexpensive and external. ISM I understand has a harder to fail newer design.

If you replace the sensor and your tach works that must have been it?

Re: Dash tachometer quit

Reply #13 – August 16, 2020, 10:34:13 am

Quote from: Jan & Richard – August 16, 2020, 02:57:10 am

Craneman, thank you. You say it is a fact that there are two sensors in the pickup. No one that I have talked with has mentioned that fact. That may very well explain why the tachometer gauge on the dash and the diagnostic plug which feeds the VMSpc are getting different info. Your information may spur me to investigate this further.

Thanks again.

Richard

I read about the two sensors in a previous post on the forum. I can see from pictures of the pickup, four wires.

Re: Dash tachometer quit

Reply #14 – August 16, 2020, 04:27:33 pm

Craneman I went out yesterday and found the sensor. I believe mine has four wires coming out of it which would be 2 senors.
I don't have time to do anymore trouble shooting right now as I'm getting ready to go away. As I have a tach working on the
Silverleaf I'm fine for now.

Re: Dash tachometer quit

Reply #15 – August 16, 2020, 04:33:02 pm

I stand corrected 4 wires. Changed the post with the wrong number

buy Position Sensor 2872362 for Cummins L10 M11 N14 Engine

Re: Dash tachometer quit

Reply #16 – August 16, 2020, 11:43:45 pm

Quote from: craneman – August 16, 2020, 04:33:02 pm

I stand corrected 4 wires. Changed the post with the wrong number

buy Position Sensor 2872362 for Cummins L10 M11 N14 Engine

Thanks for the link Chuck. I just ordered mine. I will figure out exactly where it goes once I have it and get back to my coach.

Richard

Re: Dash tachometer quit

Reply #17 – August 17, 2020, 06:53:52 am

Richard,

Here is a link to a post that has some pics. that may help you out on your search.
No start, nor CEL Please Advise

Mike

Re: Dash tachometer quit

Reply #18 – August 17, 2020, 01:53:22 pm

I pulled my sensor this morning, it takes less than 5 minutes and takes a 11/16th open end wrench. I checked the continuity in mine
and the 2 outer wires had continuity and the 2 middle ones had continuity, so I'm not sure that is the problem. As the Silverleaf
tach works I will leave it for now. Thanks for the advice Craneman it sure made it easier.

Re: Dash tachometer quit

Reply #19 – August 17, 2020, 02:36:46 pm

Wonder if that is 17MM instead of 11/16"

Re: Dash tachometer quit

Reply #20 – August 17, 2020, 03:08:45 pm

Quote from: wolfe10 – August 17, 2020, 02:36:46 pm

Wonder if that is 17MM instead of 11/16"

Metric on a twenty year old Cummins engine?

Re: Dash tachometer quit

Reply #21 – August 17, 2020, 03:22:14 pm

Quote from: Jan & Richard – August 17, 2020, 03:08:45 pm

Metric on a twenty year old Cummins engine?

Don't know, but 11/16" is NOT a common inch size.

Easy enough for someone to slip a 17MM wrench on it. 17MM is just a touch smaller than 11/16", but a very common metric size.

Inquiring minds want to know.

Re: Dash tachometer quit

Reply #22 – August 17, 2020, 04:20:49 pm

It probably could be as the engine is metric. Over the years I have used 11/16th a lot as 7/16th nuts use 11/16th wrench and the bolts
use a 5/8th wrench.

Re: Dash tachometer quit

Reply #23 – August 17, 2020, 08:05:22 pm

I went out and checked and it is 11/16. 17 mm won't go on and 18 is too loose.

Re: Dash tachometer quit

Reply #24 – August 17, 2020, 09:22:06 pm

Quote from: oldguy – August 17, 2020, 04:20:49 pm

It probably could be as the engine is metric. Over the years I have used 11/16th a lot as 7/16th nuts use 11/16th wrench and the bolts
use a 5/8th wrench.

Well after a mouthful like that witworth doesn't seem so bad upon reflection, haha
Never could figure out why you needed two different sized "spanners"

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