reklim Posted April 11, 2012 Share Posted April 11, 2012 I recently bought a 1998 ch613 tandem dump, and now busy trying to fix everything on it. Would anyone have an idea why the rpg gauge reads low. The engine runs fine and has power but the gauge only reads between 300 and 700 rpms ? Quote Link to comment https://www.bigmacktrucks.com/topic/24443-rpm-gauge/ Share on other sites More sharing options...
joes mack Posted April 11, 2012 Share Posted April 11, 2012 its prob out of calibration the tac should have a bunch of little switches on the back. if you have the old one set the switches on the new one to match the old one and all should be good. Quote Link to comment https://www.bigmacktrucks.com/topic/24443-rpm-gauge/#findComment-113756 Share on other sites More sharing options...
joes mack Posted April 11, 2012 Share Posted April 11, 2012 sorry about the earlier post i gave the wrong info. the info is for the speedo not the tach. i cant remember about the tach if it has a cable and the calibration switches or not on the 98. Quote Link to comment https://www.bigmacktrucks.com/topic/24443-rpm-gauge/#findComment-113767 Share on other sites More sharing options...
reklim Posted April 12, 2012 Author Share Posted April 12, 2012 Mine does have dip switches but i don't have an old tach to match. What could cause it to get out of calibration? Could the problem be a bad engine speed sensor( if that's what you call it ) ? Quote Link to comment https://www.bigmacktrucks.com/topic/24443-rpm-gauge/#findComment-113908 Share on other sites More sharing options...
joes mack Posted April 12, 2012 Share Posted April 12, 2012 if it has the switches thats how you calibrate it to the sensors to make it read right. i dont know if mack can tell you where to set the switches without puting it on a computer or not. but if the switches have been moved to where it should be then it might be a sensor. mabey mack pro68 or one of the other dealer mechanics can tell you more about it than i can. you might give barry at watts mack a call and give him the vin or something and get the info. Quote Link to comment https://www.bigmacktrucks.com/topic/24443-rpm-gauge/#findComment-113925 Share on other sites More sharing options...
reklim Posted April 14, 2012 Author Share Posted April 14, 2012 I put a new sensor on it today but it didn't fix the problem. Then checked power to the tach it was 12.9 v, the leads going to and from the sensor each read about 4.1 .After that i figured i had nothing to lose so i started changing the dip switches and with a certain combination the tach started working correctly. I put the tach back in place restarted the truck to make sure it still was working and it was ,but an hour later when i cranked it, it started reading low again exactly as it had before .Thanks for the advice Quote Link to comment https://www.bigmacktrucks.com/topic/24443-rpm-gauge/#findComment-114234 Share on other sites More sharing options...
joes mack Posted April 14, 2012 Share Posted April 14, 2012 youre welcome. i try to help if i have a little info about something but most of the time i dont know much and the way i do it is not the right way but it works sometimes.lol Quote Link to comment https://www.bigmacktrucks.com/topic/24443-rpm-gauge/#findComment-114260 Share on other sites More sharing options...
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