Dash tachometer quit

Topic: Dash tachometer quit (Read 3237 times) previous topic - next topic

Re: Dash tachometer quit

Reply #25 – October 29, 2020, 05:18:45 pm

Just a follow up, I replaced the sensor and the tach still doesn't work. I will keep looking for the problem when I have time.

Re: Dash tachometer quit

Reply #26 – October 29, 2020, 05:38:43 pm

Quote from: oldguy – October 29, 2020, 05:18:45 pm

Just a follow up, I replaced the sensor and the tach still doesn't work. I will keep looking for the problem when I have time.

I did the same thing a couple of weeks ago with the same results. Keep us posted as you try to sort this out. It might save me some effort when I get back to the rig.

Thanks,

Richard

Re: Dash tachometer quit

Reply #27 – October 29, 2020, 08:55:50 pm

SILVER LEAF LOL. Call Roger he can fix you up!
Chris

Re: Dash tachometer quit

Reply #28 – October 29, 2020, 09:02:26 pm

If you figure out what the signal is supposed to be at the tach, I can make up a tach generator crank trigger that will feed the OE tach.

Re: Dash tachometer quit

Reply #29 – October 29, 2020, 09:09:37 pm

Richard and I both have Silver leaf so that's why it's not a panic, I just like everything working

Re: Dash tachometer quit

Reply #30 – October 30, 2020, 12:37:49 pm

Still following. If the tach is hood and the sensor is good must be wiring? Mine doesn't work either.

Re: Dash tachometer quit

Reply #31 – November 09, 2020, 08:15:15 pm

I had time 2 days ago to do some checking. First the tach white wire 317 goes to the ECU C connector and 17 plug which is 3 rd. one
down and middle row. I have continuity to there. Yesterday when I checked it with a volt meter I have 4. something volts and
after I had the engine going it read 2. something volts. I don't know what that means. It still doesn't work. When I turn the key
the tach gauge does it's regular swing and then it stops at the high end of the scale.

Re: Dash tachometer quit

Reply #32 – December 21, 2020, 11:13:40 am

Did the sensor fix the problem?

Re: Dash tachometer quit

Reply #33 – December 21, 2020, 03:20:56 pm

No. Still trying to figger it out. The odometer in the speedometer is going. Some times its there and sometimes its not.

Re: Dash tachometer quit

Reply #34 – December 21, 2020, 03:48:48 pm

Same here. My Speedo goes out once in a great while. The tach is out like yours. In the above wire chase it said the whit one goes to ECU? Not sensor? Is there a signal from ECU that may be the causing issue? Speedo intermittent, related. Doesn't seem like this is rocket science?

Re: Dash tachometer quit

Reply #35 – December 21, 2020, 11:16:55 pm

Craneman had asked if the hour meter had quit too and it has. I checked the wiring to the ECU and it seems fine. Maybe next spring or summer I might seen both gauges out as Jan suggested. Right now I have a Silver Leaf which I use as it easier to see. I just like the
gauges to work as they are there. The Silver Leaf is keeping trace of mileage.

Re: Dash tachometer quit

Reply #36 – December 23, 2020, 09:40:47 pm

Those gauges fail frequently(see lots of posts) and this is the common failure mode.

Re: Dash tachometer quit

Reply #37 – December 23, 2020, 11:46:57 pm

What is the fix? Heard on another site the wire goes to alternator and a blown fuse

Re: Dash tachometer quit

Reply #38 – December 24, 2020, 12:02:32 am

The U320 doesn't get the tach signal from the alternator it gets the signal from a sensor on the front of the engine and then goes through ECU to the tach

Re: Dash tachometer quit

Reply #39 – December 24, 2020, 09:16:32 am

So if u change the sensor and the gauge, is it the ECU?
I hear of a TACHS quiting. I do not heat about a lot of fixes?

Re: Dash tachometer quit

Reply #40 – December 24, 2020, 09:49:27 am

Quote from: Ldillow – December 24, 2020, 09:16:32 am

, is it the ECU?

If it was the ECM you would be setting on the side of the road.
There is a couple of companies that will check/repair tach if it is the problem.

Mike

Re: Dash tachometer quit

Reply #41 – December 24, 2020, 10:26:42 am

Lots of speedometer shops deal with VDO so you might call one in your area and describe the symptoms, etc. The one I used in LA did a great job and had a fast turn around back in the '80's. Our U300 speedo only works part of the times so will be sending it in.

Pierce

Re: Dash tachometer quit

Reply #42 – December 24, 2020, 10:45:32 am

Ecus can fail on one component, but be fine for everything else. The ECU was bad on my 98 Cummins pickup. The prob!em was the ECU had a built in alternator regulator that fails. ECU is good for everything else, but the internal regulator goes out as a common issue. I just set up an external regulator. No reason to change ECU out.

So it seems that tach failure is a common issue.
What is the fix.
Haven't heard of any fix, except maybe the sensor or the tach. Seems like I have heard more of the tach being good, and the sensor being good. So what have been the fix?

Re: Dash tachometer quit

Reply #43 – December 24, 2020, 01:41:12 pm

Quote from: Ldillow – December 24, 2020, 10:45:32 am

So it seems that tach failure is a common issue.
What is the fix.

I have had my VDO gauge checked out by two different companies and both said that the gauge itself was just fine. I have replaced the sensor on the front (rear) of the engine. The gauge still does not work. My VMSpc gives flawless tach and engine hour information so the info from the sensor through the ECU apparently is working.

There is one more thing that I may investigate when I have the time and inclination to pursue it. The sensor has four wires with a short pig tail which plugs into a wiring harness. My understanding is that two wires go to the ECU and two wires likely go straight to the gauge, a redundant system. When I unplugged the old sensor, the plug had a good deal of oil intrusion. I cleaned up the plug with liberal amounts of spray contact cleaner and left it at that. When the gauge still did not work I just put this project on the back burner awaiting further inspiration.

I have since read a post here which made me think that maybe the oil had wicked up the wires inside the insulation and possibly found a weak spot in the insulation where the faint signal could short out between wires. My guess would be that this would not be too far up the wires. I may, at some point, investigate this further.

Unfortunately, I do not have an answer for you but this is where my story stands at this point.

Richard

Re: Dash tachometer quit

Reply #44 – December 24, 2020, 07:49:58 pm

The ECM has a "Digital Tach signal", at least that is what they call it on connector B pin 17 of the ECM and a "digital tachometer return" on pin 26 same connector. So if the sensor and tach is good, this would be the next place I would look. Still looking for ANY body that has fixed their VDO tach on near vintage 98, U320. Again, I hear a lot of broken tachs, but no fixes.

Re: Dash tachometer quit

Reply #45 – December 24, 2020, 07:51:51 pm

has anybody really verified where the tach wires go from the tach (other than power and ground, assuming they are good and not effecting signal from engine).
Thx!

Re: Dash tachometer quit

Reply #46 – January 01, 2021, 10:07:23 am

Has anyone changed the ECM?
Did it fix the problem?
The
Larry

Re: Dash tachometer quit

Reply #47 – January 01, 2021, 01:31:55 pm

All four wires from the sensor go into the ECM and one wire goes from the ECM to the tach. One day someone will find the
problem I hope.

Re: Dash tachometer quit

Reply #48 – January 01, 2021, 08:36:32 pm

Swap ECM with someone that their tach works?
I was thinking about disconnecting battery and then disconnecting all of the connectors on the ECM. Spray them with contact cleaner and reconnect them. Fixed a lot of problems that way. Don't want to open a can of worms though. Maybe I will just do the connectors with tach in and out signals.
Larry

Re: Dash tachometer quit

Reply #49 – January 01, 2021, 09:16:54 pm

That might be good idea. My tach quit after I had one of the plugs off to hook up my Jake brake.

Affiliate Notice