Erratic Tachometer

[teamchambers]

Greetings All,

I own a 2007 Diplomat 40sft with the Cummins ISL 400 engine.

Recently the tachometer has become erratic. At times it will fluctuate from 0 to 4,000. At other times it indicates normally. Their is no apparent change in engine RPM when this happens. I like to use the Aladdin Junior to monitor all engine systems while driving down the road. The engine RPM has a normal indication on this system.

I found the following two older threads about erratic tachometers ... The threads were rather old so the system would not let me reply ...

Erratic Tachometer

Eratic Tachometer

Any more input would be greatly appreciated.

Thanks

[86 Cavalcade]

Teamchambers, Search this forum for "instrument grounds" or "dash grounds". I have a 2001 Diplomat and was having trouble with my dash gages acting funny except for my tach and speedometer. I tightened up the existing grounds on the back of the gages and ran a new 12 AWG ground wire from the dash light grounds and the the voltmeter ground to a new ground point. This solved all of dash gage issues though. Other people have had trouble with the speedo and it was also a bad ground. One of the posts has the directions for changing the dip switch settings on the back of the speedo head. You may be able to go to an Allison service center and they may be able to change it thru the transmission controller. I would call an Allison service center first. George 2001 Diplomat

[Route 66]

Quote:

Originally Posted by teamchambers Greetings All, The threads were rather old so the system would not let me reply ... Thanks

You can reply to older threads by checking the box labeled "
I am aware that this Thread is rather old but I still want to make a reply." in the warning message.

[teamchambers]

86 Cavalcade ... Thanks for your response ... I will start with the grounds and see where that takes me.

Route 66 ... Thanks for the response ... I guess I was in to big of a hurry to READ the directions! :-)

Rick

[86 Cavalcade]

Rick, I would have an Allison Service Center scan the transmission controller before I pulled my dash panel loose. My 2001 dash has a lot of small light bulbs that were supposed to be plugged into the right holes and a lot of them had fallen out. About 1/3 of the dash lights were out and some of the warning lights were loose but had not fallen out of the correct holes. I was able to pull my dash forward about 4 or 5 inches, just enough so that I was able to add the ground wires and plug the lights all back in. The reason I did this on my coach was that when I turned my headlights on the dash voltmeter would go down to about 12 1/2 volts. Once I added the new ground wires I can turn on all of my lights, run the dash blower on high, and run the wipers and the dash volt meter will barely move. I also installed a new 200 amp, brushless, Delco alternator. I did this after I had worked on the dash because I think the regulator was going bad on this Leece Neville 160 amp alternator. George 2001 Diplomat

[teamchambers]

Quote:

Originally Posted by 86 Cavalcade Teamchambers, Search this forum for "instrument grounds" or "dash grounds". I have a 2001 Diplomat and was having trouble with my dash gages acting funny except for my tach and speedometer. I tightened up the existing grounds on the back of the gages and ran a new 12 AWG ground wire from the dash light grounds and the the voltmeter ground to a new ground point. This solved all of dash gage issues though. Other people have had trouble with the speedo and it was also a bad ground. One of the posts has the directions for changing the dip switch settings on the back of the speedo head. You may be able to go to an Allison service center and they may be able to change it thru the transmission controller. I would call an Allison service center first. George 2001 Diplomat

Quote:

Originally Posted by 86 Cavalcade Rick, I would have an Allison Service Center scan the transmission controller before I pulled my dash panel loose. My 2001 dash has a lot of small light bulbs that were supposed to be plugged into the right holes and a lot of them had fallen out. About 1/3 of the dash lights were out and some of the warning lights were loose but had not fallen out of the correct holes. I was able to pull my dash forward about 4 or 5 inches, just enough so that I was able to add the ground wires and plug the lights all back in. The reason I did this on my coach was that when I turned my headlights on the dash voltmeter would go down to about 12 1/2 volts. Once I added the new ground wires I can turn on all of my lights, run the dash blower on high, and run the wipers and the dash volt meter will barely move. I also installed a new 200 amp, brushless, Delco alternator. I did this after I had worked on the dash because I think the regulator was going bad on this Leece Neville 160 amp alternator. George 2001 Diplomat

George,

Thanks for the info ... I guess I still don't understand why you recommend to have the allison service center scan the transmission controller? It is not located on the dash (side panel near my left leg). It has been working fine.

Am I in jeopardy of loosing the programming while I am messing around with the wires?

Rick

[86 Cavalcade]

Rick, I believe the signal for your electronic speedometer is generated by the speed sensor in your transmission and it probably goes thru your transmission controller. Unless someone has changed the dip switchs on the speedometer head or thru a programming change that is why I would have the trans controller read. This will probably cost around $125.00 or so.I had a bad fuse holder in the battery compartment that is only a 5 amp fuse that goes to the transmission controller that had intermittent contact and when it would do this it was like shutting the ignition key off. It cost me $750.00 to find this at an Allison Service Center. It was found by running a scan of the controller. That gave them a clue to start looking for 12v power loss. You can call Allison and they will talk you thru some self tests that may help you isolate the problem if you have one associated with the transmission. It may turn out you just have a bad speedometer head. Good luck, George

[86 Cavalcade]

Rick, I miss-read your original post and saw that you said tachometer and not speedometer. My error!

The tach gets it's signal from the alternator. If it is a Leece Neville it has three field posts. You could have a bad connection back on the alternator. This is the same terminal that feeds the Hamser relay in your front run box. This is the relay that operates the alternator warning light.

I would look at the dash grounds also. I am sorry about my other posts. George

[teamchambers]

George,

Thanks for your inputs.

I ran a new ground from the dash to the frame ... no luck.

After talking with a repair shop and Monaco Tech support I am nearly convinced I have a bad gauge. I have one more test to run ... use my multimeter to test the signal to the tachometer ... If that signal is good ... then I am ready to order the new tach.

Thanks,

Rick

[wheato22]

Chambers,
You are on the right track now. The fact that rpm jumps all over the place points to the gauge itself. The tach in my '94 Monaco registers electrical pulses from the (Hehr Powerline) alternator. More rpm more pulses. My tach problem was different in that the rpm cycled from 750 to zero and then back to 750 every 2 seconds... only at idle. Hehr support recommended checking the wires connected to the regulator for bad connections and then if contacts look good replace the voltage regulator. New regulator fixed mine tach readout.

[teamchambers]

wheato22,

Thanks for the note ... I checked the signal to the tachometer ... the good news is I don't think I need to replace the Tachometer ... the bad news is the signal to the tachometer is all over the place.

The Monaco tech folks have encouraged me to check a 50 plug bundle of connections somewhere under the coach. Tachometer is pin number 10 :-).

I am going to check the alternator connection as well.

A keep wondering how much it would have cost to have someone else troubleshoot.

TC

[86 Cavalcade]

Rick, If this was my coach I would probably drive it to a Cummins service center and have them scan the ECM. They would be able to tell you if the output from the ECM was bad. I don't know where your ECM is located but if the output from it is OK then, your trouble is either the wiring between the ECM and the tach, the tach itself, or, the instrument grounds which you say you already checked. I have a chassis wiring diagram for my 2001 Diplomat and the pin # for my tach drive is #12 at the ECM. I can send you a chassis wiring print that may be the one for your coach if you want it. I think your coach has a mid coach connector and I think that is what Monaco is telling you. George

[Eaglesview]

Quote:

Originally Posted by 86 Cavalcade Rick, If this was my coach I would probably drive it to a Cummins service center and have them scan the ECM. They would be able to tell you if the output from the ECM was bad. I don't know where your ECM is located but if the output from it is OK then, your trouble is either the wiring between the ECM and the tach, the tach itself, or, the instrument grounds which you say you already checked. I have a chassis wiring diagram for my 2001 Diplomat and the pin # for my tach drive is #12 at the ECM. I can send you a chassis wiring print that may be the one for your coach if you want it. I think your coach has a mid coach connector and I think that is what Monaco is telling you. George

I had the same symptom on a new 05 Dynasty. Turned out to be poorly crimped connectors on wiring to the ECM. Cummins scanned and diagnosed as "loss of ignition".

Cummins had no interest in tracing the problem which was finally found and corrected by Tom at Massey's in Phoenix.

As symptoms got worse the engine would momentarily stop, restart, operate at limited power for about a minute and then come back to full power capability.

[teamchambers]

The piece of information that perplexes me most ...

Analog Tachometer ... jumps all over the place

Digital Tachometer as read on the Aladdin Jr system ... Rock solid

Do these two systems get input from two different locations?

That doesn't make much sense ... but who knows?