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Tom Powell
Samba Member
Joined: December 01, 2005
Posts: 4855
Location: Kaneohe
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 Posted: Sun Apr 27, 2014 11:58 pm Post subject: why does the tach hit 4000 RPM at start? |
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Sometimes when starting the engine the tach in my '87 Vanagon hits 4000 RPM
The engine start is normal except for the tach reading The idle settles at about 900RPM on the tach, but sometimes the tach fluctuates up to 1200 to 1400 RPM. The engine is not idling that fast, it remains at a smooth 900 RPM. I assume this indicates a bad signal from the ECU. I plan to swap in another ECU and observe the tach on startup with the replacement ECU. There are no tach fluctuations at highway speeds.
Aloha
tp |
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morymob
Samba Member
Joined: November 09, 2007
Posts: 4683
Location: east-tn
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| Posted: Mon Apr 28, 2014 4:15 am Post subject: |
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| If your idle stays at 900 and tac moves around u have a tac problem/wiring to it, it gets it's signal from a ign coil post not the ecu. |
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BikeJozz
Samba Member
Joined: March 19, 2010
Posts: 7
Location: Montreal, Qc
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| Posted: Mon Apr 28, 2014 4:20 am Post subject: |
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Mine does the same thing but on the higway. Try tapping the cluster when it fluctuate to see if the problem is in the cluster. When mine drops on the higway I gently tap the instrument cluster and it moves back to norml RPM.
Its on my to-do list of little quirks to fix...
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1990 Vanagon GL Westfalia 2WD |
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Tom Powell
Samba Member
Joined: December 01, 2005
Posts: 4855
Location: Kaneohe
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| Posted: Mon Apr 28, 2014 6:21 pm Post subject: |
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| morymob wrote: |
| If your idle stays at 900 and tac moves around u have a tac problem/wiring to it, it gets it's signal from a ign coil post not the ecu. |
If the tach gets its signal from the igniton coil post, where does the igniton coil post get its signal? Several years ago, 2008, I had a similar dying problem with another Vanagon. The common denominator in these two incidents was tach spikes. The first problem was solved by an ECU swap
http://www.thesamba.com/vw/forum/viewtopic.php?t=305163&highlight=tom+powell
An ECU swap is planned.
Aloha
tp |
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Tom Powell
Samba Member
Joined: December 01, 2005
Posts: 4855
Location: Kaneohe
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| Posted: Mon May 05, 2014 5:51 am Post subject: |
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ECU swap accomplished and the tach is a smooth 900 at idle without any spikes during start or at idle and it has not been dying at stops on the highway.
Aloha
tp |
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