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Strange charging/tach issue

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Greetings! Just bought a 1997 Ram 2500 12v 4x4 auto. I was told the PCM was bad - turns out it was the wrong PCM (for a '99 and also bad). ACS kept my '99 PCM and sent me a refurbished '97 PCM for an auto. My speedometer now works and my tranny shifts as it should (although O/D is not kicking in - might be TPS?). My alternator is not charging, and my tachometer is not working. Below is a list of info I have collected and troubleshooting steps I have made:

  • PCM rebuilt by ACS (tranny would not shift out of 1st, speedometer, tach, alternator, a/c not working - now tranny shifts and speedometer works)
  • 7.5a fuse installed in W/BS wire from pin 25 connector C3 
  • Replaced alternator with AC Delco 120a unit from Summit Racing
  • Checked wires on back of alternator - 11.7v on white/blue stripe from PCM, ground on other wire
  • Hot lead from back of alternator shows battery voltage ~12v
  • Launch scanner shows TPS at 17% at idle (TPS is bad/needs recalibration?)
  • Launch scanner shows correct RPM (ESS is good? ESS is the only source of RPM, right?)
  • ASD relay replaced with known good relay
  • Checked all fuses and fusible links in engine compartment fuse box
  • Launch scanner shows P0753 and P1765 codes - both tranny focused, shouldn't be related to charging. 

 

I am assuming that since my scanner shows RPM while running that the ESS is good. Is there any way to check if it is causing the problem other than replacing it? 

If the alternator is new, turning while the engine is running, and has 11.7v and ground on the two connections on the rear, shouldn't it be outputting 13.5-14v?

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Fixed the charging - replaced the ESS with a new unit (did you know you can't get these from Chrysler/Dodge anymore?). I originally had the gap set at about .057" and the alternator was "kind of" working. I reached my oversized meathooks in there and adjusted to the required .050" and the alternator is now working like a  champ, but the tach is still not working. My PCM was just rebuilt by ACS. I assume that is not the problem. Any other hot spots to check? I read that fuse #12 in the dash fuse panel controls several gauges, but all of mine work... except the tach. If you've run into this before or even just read about it before please speak up. Thanks!

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Welcome To Mopar1973Man.Com LLC

We are privately owned, with access to a professional Diesel Mechanic, who can provide additional support for Dodge Ram Cummins Diesel vehicles. Many detailed information is FREE and available to read. However, in order to interact directly with our Diesel Mechanic, Michael, by phone, via zoom, or as the web-based option, Subscription Plans are offered that will enable these and other features.  Go to the Subscription Page and Select a desired plan. At any time you wish to cancel the Subscription, click Subscription Page, select the 'Cancel' button, and it will be canceled. For your convenience, all subscriptions are on auto-renewal.