Tach swings left to right

[twobachs]

At times the tach will swing from left to right like from a 10 o'clock to about 2 o'clock positions. I have a Cummins ISL 350 with a Allision 3000. Also, when going up a slight grade the tranny OR engine jerks or bucks. Went to Cummins and they say they can't duplicate the problem and feels it might be the tranny. This problem has been going on and off for a couple years with two trips to Cummins with no solution. It's driving me crazy!!

Any suggestions??

[MaverickBBD]

What type of coach do you have? If it is a Freightliner Chassis you could call 1.800. FTL. HELP and they can walk you through how to zero and span your gauges. Leave a message if you don't get an answer right away. They are 100% on call back.

As to the jerking and bucking. Do you have the economy mode engaged with cruise control? Sometimes these two will "fight" each other over gear selection when climbing. What gear is it in and what gear is "requested" when this happens?

[Mike Canter]

Jerking and bucking going up hill can be caused by a blocked fuel filter. Have you changed BOTH of your fuel filters????

The tach these days run off the alternator because there is no ignition system on a diesel. The tach can be hooked up to any 12 volt wire powered by the alternator. It maybe a loose wire, a bad ground or an alternator starting to go bad.

[ajbjrvers]

can't have cruise control and jake/exhaust brake on at same time-- one wants to go-- the other slow down- shut off brake until it's needed

hope this info helps A. J.--Aime

[dsbike]

I have to agree with Mike Canter on the tach. I have seen this before on other vehicles, the tach jumps around & ends up being a bad 12v connection. On my 1999 Jeep Grand Cherokee it seemed to happen about once a year until I replaced the battery. Not because of this but it actually failed from age. It was always the battery terminals coming loose on the Jeep.

As for the shifting I don't have a clue. But it looks like the other replies may get you someplace.

[twobachs]

Our M0H0 is on a Freightliner. I changed the main fuel filter, but I don't know where the the other fuel filter is if there is one. I did find a loose battery post nut on the engine battery bank and as of now I haven't have the tach problem. As far as the bucking problem . . . I tried to run with and without the "economy mode" and with and without the engine brake. I tried with and without cruse control. In addition, during the bucking I manually down shifted to lower gears, but it bucked in 6th 5th and 4th. You can see why I'm so frustrated! I'm just not sure if it is engine or tranny. Please keep the ideas coming.

[Airtool]

There is a bad connection or defective ground somewhere.
The tachometer signal comes from the ECM and connects to the cab harness connector then to the instrument panel.
That is three possible areas for oxidation to form.
This can and will cause intermittent operation of the tach, speedo, curse control an other systems.
I have removed the ECM cable connection from the ECM and cleaned the connections. This cleared the problem.
This is not a job for the faint of hart or anyone with a lack of patience.
This link might help find something that will work.
caig.com - Home of DeoxIT® - CAIG Laboratories, Inc. or Product Literature

Dick.

[Mike Canter]

Most likely you have two fuel filters. I am not sure about your setup but most do so you might want to check. Normally you will have a primary fuel filter that has a water separator that is located off the motor and you will have a secondary filter that is usually mounted on the motor. Which one have you changed? If you have two filters and have only been changing one then that could be the problem. Do you have a Owners Manual because it should be shown in there.