Tach jumping

[domgbrl]

Crusing at 1800 rpm, the tach needle is bouncing/ jumping up to 2000 rpm. And when this happens the truck seems to be bucking and jerking slightly. Any ideas??

[Mopar1973Man]

Any error codes? 

 

Might fill out your signature so we know what year of truck and modifications you've got. Just of the top of my head sounds like a crank sensor but I don't know what year of truck your running.

[domgbrl]

99 2wd 3500, auto. Pretty much stock with exu and a air filter.  

[dripley]

More than likely the crank sensor like @Mopar1973Man says. Get the codes read to be sure. Hate to see you throw a part it.

[Mopar1973Man]

4 minutes ago, dripley said:

More than likely the crank sensor like @Mopar1973Man says. Get the codes read to be sure. Hate to see you throw a part it.

 

Exactly! 

[domgbrl]

I scanned it, no codes yet

[Marcus2000monster]

What did you scan with?

[Mopar1973Man]

Hmmm... Is this an automatic or manual transmission?

[domgbrl]

It is a auto truck. I scanned it with a OTC Encore scan tool. It happens most at a small part throttle condition, i can barely feel it driving on the highway, but when i tow my trailor it becomes more noticable. If i give a little more throttle it goes away

[Mopar1973Man]

Test for excessive AC noise issues. 

Then if you do find an issue, you'll need to replace your alternator then also consider doing this mod too.

 

 

[dripley]

I did the mod @Mopar1973Man mentions and my ac voltage dropped fron .035 to .010. I have only heard from one other that has done this, @IBMobile, and he did not see as much as I did but could not remember what his drop was. It will be interesting to see how this works out for others that chose to do it. 

[Mopar1973Man]

I'm going to aim for doing this mod soon myself and see what happens too. 

[Red Rambler]

I did the mod as well but put a new alternator on at the same time, so technically mine doesn’t count. I would check all of your wires as this could also be as simple as a wiring issue. 

Edited May 10, 2018 by Red Rambler