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Old 03-22-2008, 09:03 PM   #1
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Variable Fixed gear ratio

Say what? Indeed.... I have a 5 speed manual Civic VX and most of the time at 60mph the tach is at 2000rpm. Someone once showed a pic of their VX at 65mph at 2000RPM. I found this very odd, as my RPM at 60mph was 2000RPM. Then, one day, while driving down the highway, I noticed that my tach was at 2000rpm at 65mph, and that it was at 80mph at 2500rpm when usually I'm at 75mph at 2500rpm. I found this very peculiar. But then about a week or less later it "reverted" back to it's old way of 2000rpm at 60mph and 2500rpm at 75mph. Any ideas what in the blue blazes might be going on??? Are my gear ratios actually randomly variable or is my odometer/speedometer misreading sometimes?
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Old 03-22-2008, 09:38 PM   #2
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honda tach's are famous for being way off. the best way is to buy a aftermarket one if you want a more accurate reading

and yes, the gears are fixed, not variable
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Old 03-22-2008, 09:41 PM   #3
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It's probably measuring error. Either the gauges themselves, or the pulses from the VSS and/or ignitor unit. It wouldn't hurt to check the various grounding points around the car.
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Old 03-23-2008, 04:06 AM   #4
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Is your clutch slipping?

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Old 03-23-2008, 07:30 AM   #5
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Clutch isn't slipping. I do remember now that the mechanic hooked up my ECU to his fancy $7000 computer and he said the tach was not reading at all on his computer. That was the reason I bought a new ECU... I thought maybe my current one was not working properly. But I still haven't installed the bloody thing. Thanks for the replies.
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Old 03-23-2008, 09:59 AM   #6
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The ECU has very little to do with the tach. The pulses for the tachometer are generated by the ignitor unit in the distributor. The ignitor controls power to the ignition coil, and thus when the spark plugs go off... One tach pulse is generated every time the ignition coil fires. The ECU is responsible for triggering the ignitor, but there's no direct electrical connection between the ECU and tach.
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Old 03-23-2008, 01:13 PM   #7
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clean and/or replace all the ground points. possibly upgrade the ground wires.
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Old 03-23-2008, 05:00 PM   #8
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Quote:
Originally Posted by bobski View Post
The ECU has very little to do with the tach. The pulses for the tachometer are generated by the ignitor unit in the distributor. The ignitor controls power to the ignition coil, and thus when the spark plugs go off... One tach pulse is generated every time the ignition coil fires. The ECU is responsible for triggering the ignitor, but there's no direct electrical connection between the ECU and tach.
In some cars that is true, but in some cars (newer) the tach is just a "dummy" gauge actuated by the computer.

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Old 03-23-2008, 06:52 PM   #9
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Quote:
Originally Posted by bobc455 View Post
In some cars that is true, but in some cars (newer) the tach is just a "dummy" gauge actuated by the computer.
I could see that, especially given the gauge "dance" that my mom's Subaru does when you switch the ignition on. But I'm talking about the specific case of the '92-95 Civic VX, which falls into a larger group which includes (at least) all '88-00 Civics, CRXs and DelSols.
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Old 03-25-2008, 10:03 PM   #10
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I would check the connections at the distributer and under the distributor cap. I've had that same problem with Hondas before, and often it was just a corroded connection at a plug or a loose connection under the distributor cap.
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