Tachometer question

[sigkadetm]

Ok I checked the brown/white wire from the coil to the tachometer and it checked out fine. Then I checked the white/black wire from the tachometer to the ground and all is well. Cleaned and checked ground wire from coil pack to engine. The wires from the magnetic pick up also checked out fine. I even tried a different tachometer. The tachometer still only reads if I rev up the engine then goes right down to zero when the engine is at idle. Has anyone experienced this problem? Any help would be greatly appreciated.

[spider2081]

Is the car Fuel injected??
Is the ignition switch a Sipea Switch??

[sigkadetm]

Yes it is fuel injected and it does have a sipea switch

[spider2081]

The alternator output terminal is connected to the battery all the time so be careful when making this test. Connect the red lead of your volt meter to the alternator output terminal and the black lead of the meter to the pink wire on the coil pack. Turn the key to the on position so the warning lights are lit in the dash. The voltmeter should read less than one volt. Let me know what reading your are getting

[sigkadetm]

Just took the reading and I got .07 volts

[spider2081]

That should mean the voltage connections through the ignition switch and connector are good. The voltage path is actually from the starter solenoid to the switch and then to the coil. The alternator output connects to the same place on the starter solenoid so you have basically checked the circuit.
There should be 2 brown/white wires on the D terminal of the coil one is for the tach and the other is for the Fuel injection computer. The one for the computer must be good as must the ignitions electronic control module or the car would not run correctly. THis pretty much leaves the brown/white wire from the coil terminal D to the tachometer, power to the tachometer and or ground connection as you issue.

Curious, have you measured the voltage at the alternator output post with the engine running? I would like to kknow what it is at idle ad then again at 2000 RPM. Measure both the Dc and the AC voltages.

[sigkadetm]

I assume I check for AC and DC voltage at the output terminal???

[sigkadetm]

I did do the upgrade to a 95amp alternator last year and the car ran fine. Let me check that voltage and I'll get back to you.

[sigkadetm]

Ok I checked the magnetic pick up and it was 705 ohms. Then I checked the coil and I got 10,090 and 1.2 ohms. Then I tested the alternator and got 14.75 volts at idle and 14.70 volts at 2000 rpm. Then I checked with AC and got 31.5 at idle and 31.3 at 2000 rpm.

[spider2081]

Ideally the Ac voltage measurements at the alternator output post should be less that 0.5 Volts AC. Are you sure the meter you are using was not displaying milli volts or 0.031.5 volts. It would be easy to miss the "m" in front of the V on the digital display. If you are actually measuring 31.5 volts AC from your alternator the diode assembly is probably defective. Your cars battery would still charge unless you required a lot of accessories to be operating at same time.

[sigkadetm]

I'll check again

[sigkadetm]

I just checked again and it read 31.3 volts at idle I used the 200 volt ac scale.

[sigkadetm]

I'll take the alternator down to Autozone in the morning.

[spider2081]

I'll take the alternator down to Autozone in the morning.

Hopefully they will know how to test it. When I brought my stock Bosch alternator to a local AutoZone the car wasn't in their computer so they didn't know what to do. So I went to Advanced Auto and the same thing happened. I was able to talk the kid through selecting the correct test adapter and checking the alternator.

The alternators high AC may not be your tachometer problem but often a lot of AC present on an alternators output is accompanied with a lot of noise spikes that can contribute to odd electrical issues. The 30 Volts AC is an issue in itself that should be repaired.

[sigkadetm]

Your right about autozone. They told me my alternator was fine so I took it to oriellys and they told be it was defective. I had another 95 amp alternator and hooked that one up and I still got 31volts ac. I'm going to get a rebuild kit with a new rectifier and try it again. I'm also going to do the ignition switch repair because when I push up on the wires in the back of the switch the tachometer starts to work normally. I'll let you know how it goes.....