Tach jumping and Overdrive not working - Dodge Cummins Diesel Forum
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post #1 of 12 (permalink) Old 03-30-2019, 10:24 PM Thread Starter
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Tach jumping and Overdrive not working

Hello all, I have a 97 2500 2wd 12v. The tach is jumping around and the trans wont shift into overdrive, the Gen light stays on. Ive searched on here everything I've found says if its crank speed sensor on harmonic balancer is bad the the alternator and a/c wont work either but mine work fine. The transmission was completely rebuilt new torque converter new valve body according to trans shop someone had been in trans painted the torture converter and it had peeled off going into everything and supposedly the valve body was trashed. When I picked up it today still no overdrive and tach jumping. (After they were gone of course.) I am wondering could the TPS cause these 2 issues or am I wrong. No flash codes and when I hook scanner up no codes. Any help would greatly be appreciated.

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post #2 of 12 (permalink) Old 03-31-2019, 01:27 PM
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Definitely sounds like the ESS. My tach would bounce around intermitently because one of the wires would periodically short out on the block where it had rubbed through due to vibration. I never lost AC and didn't notice the charging issue at first either but it would play havoc with the transmission.
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post #3 of 12 (permalink) Old 03-31-2019, 01:42 PM Thread Starter
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I found 2 of the 3 wires going to the low side of injection pump rubbed raw no insulation this morning, it plugs into the throttle plate down on the side, going to repair those and cross fingers. With a feeler gauge the ESS gap is .50 I believe I read thats about stock?

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post #4 of 12 (permalink) Old 03-31-2019, 11:30 PM
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Computer Controlled ground for Overdrive

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Originally Posted by zeke1 View Post
Hello all, I have a 97 2500 2wd 12v. The tach is jumping around and the trans wont shift into overdrive, the Gen light stays on. Ive searched on here everything I've found says if its crank speed sensor on harmonic balancer is bad the the alternator and a/c wont work either but mine work fine. The transmission was completely rebuilt new torque converter new valve body according to trans shop someone had been in trans painted the torture converter and it had peeled off going into everything and supposedly the valve body was trashed. When I picked up it today still no overdrive and tach jumping. (After they were gone of course.) I am wondering could the TPS cause these 2 issues or am I wrong. No flash codes and when I hook scanner up no codes. Any help would greatly be appreciated.


Many people make this mistake when overdrive goes out... The ground for Overdrive is controlled by the computer. Quick fix... check the ground off the computer or replace the computer.
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post #5 of 12 (permalink) Old 03-31-2019, 11:31 PM
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Tach will more than likely be the tach cable
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post #6 of 12 (permalink) Old 03-31-2019, 11:51 PM Thread Starter
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I repair wires overdrive started working and tach stopped jumping until I retaped the wires then back to jumping and no overdrive

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post #7 of 12 (permalink) Old 04-01-2019, 10:17 PM
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Quote:
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Tach will more than likely be the tach cable
Tach cable?? Have a part number for that?
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97 3500, 2 WD, G56, slightly bombed, 1.3 million miles. Started the second million on 8/24/13
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post #8 of 12 (permalink) Old 04-01-2019, 10:25 PM
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Tach cable?? Have a part number for that?
or a picture of one in place

98-4x4 5spd
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post #9 of 12 (permalink) Old 04-01-2019, 10:42 PM Thread Starter
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Yes picture/part number

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post #10 of 12 (permalink) Old 04-09-2019, 07:07 PM Thread Starter
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Ok so today after work I installed new VSS, truck shifts in and out of overdrive, tach still jumps a little until I turn A/C on then it doesn't jump but still no overdrive and no charging any help would be greatly appreciated

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post #11 of 12 (permalink) Old 04-09-2019, 07:20 PM
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All of those wires are depicted in the wire diagrams that are in the factory service manual. Have you done continuity checks and short to ground checks on them?

97 3500, 2 WD, G56, slightly bombed, 1.3 million miles. Started the second million on 8/24/13
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post #12 of 12 (permalink) Old 04-09-2019, 07:44 PM Thread Starter
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No I haven't, I ordered a factory service manual and I'm waiting on it to get here. I pulled the truck by vin on mitchell1 at work but NONE of wires matced. So I'm awaiting my service manual. After reading other threads, I'm going to get a can of electric parts cleaner from work and go through all connections with that. Very aggravating

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