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DeLvxe
Samba Member
Joined: January 08, 2019
Posts: 106
Location: Seattle
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 Posted: Wed Sep 22, 2021 12:11 pm Post subject: Tach and Subaru ECU don't agree on RPMs |
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Hi all, Hoping to resolve an annoyance I have with my van. I have a '91 with a 2000 EJ25. I recently (9 months ago?) had a new wiring harness put in from Autoventures to resolve an intermittent starting problem as well as a couple other gremlins. The van runs great, but the tach and the reading from my OBD2 port don't agree on the actual RPMs. My OBD reader consistently reads about 600+ RPMs higher than the tach.
1. Since my tach reports about 200 RPMs at idle and 3400 RPMs at 75 mph, am I safe assuming that the ECU is reporting the correct RPMs? - more like 800 RPMs at idle and 4,000 at 75 mph.
2. If my tach is reading low, what could be causing this and how to fix? It was reading correctly before the new wiring harness.
Thanks
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1991 manual camper with EJ25 |
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veloandy
Samba Member
Joined: December 04, 2010
Posts: 356
Location: Fort Collins, Colorado, USA
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| Posted: Wed Sep 22, 2021 2:03 pm Post subject: Re: Tach and Subaru ECU don't agree on RPMs |
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Does your tach get its signal from the tach pin from the Subaru ECU, or is it wired to the ignitor as described here?
Have you checked the tach signal wire for excessive resistance? |
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skills@eurocarsplus
Samba Peckerhead
Joined: January 01, 2007
Posts: 16852
Location: sticksville, ct.
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| Posted: Wed Sep 22, 2021 2:54 pm Post subject: Re: Tach and Subaru ECU don't agree on RPMs |
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talk to jeff
his newest signal converter box has provisions to adjust the tach output, i just forget how to do it
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| gprudenciop wrote: |
my reason for switching to subaru is my german car was turning chinese so i said fuck it and went japanese....... |
| Jake Raby wrote: |
| Thanks for the correction. I used to be a nice guy, then I ruined it by exposing myself to the public. |
| Brian wrote: |
| Also the fact that people are agreeing with Skills, it's a turn of events for samba history |
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wesitarz
Samba Member
Joined: August 20, 2012
Posts: 1486
Location: Victoria,B.C.Canada
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| Posted: Wed Sep 22, 2021 3:18 pm Post subject: Re: Tach and Subaru ECU don't agree on RPMs |
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Too funny I just adjusted mine.
02 2.5 Subaru, my tach was reading about 200 rpm higher than my TorquePro app. There is an adjustment on the back of the tach under a label. Peel it off and you can fit a small flat blade screwdiver in the hole to engage the potentiometer. You can see the slot with a light. Turn very slightly left (looking at the back of tach) to decrease, right to increase. Test at idle and higher say 2500-3000 rpm. I had the whole unit out and only attached at the 14 point connector. I found it easier to engage and turn it with it disconnected and trial & error to get it close. |
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skills@eurocarsplus
Samba Peckerhead
Joined: January 01, 2007
Posts: 16852
Location: sticksville, ct.
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| Posted: Wed Sep 22, 2021 4:28 pm Post subject: Re: Tach and Subaru ECU don't agree on RPMs |
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i have adjusted VDO tach's by your description in the past
jeff has made his interface box adjustable for various tach signals so there is no need to mess with the tach itself (unless there was a issue before)
jeff's box addresses this adjustment
_________________
| gprudenciop wrote: |
my reason for switching to subaru is my german car was turning chinese so i said fuck it and went japanese....... |
| Jake Raby wrote: |
| Thanks for the correction. I used to be a nice guy, then I ruined it by exposing myself to the public. |
| Brian wrote: |
| Also the fact that people are agreeing with Skills, it's a turn of events for samba history |
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