AW: [DML] Wacky tach - major issue???

["Elvis Nocita" <elvisnocita@xxxxxx>]

Derek,

sounds like an electrical problem so don't worry too much,
the engine is not going to explode from that ;-)


Is there any other strange things happening in the dash ?
Dimm or flickering lights ?

The Tach has 3 wires. +12V, GND and Signal form the Ignition ECU.

If the ignition signal would be disturbed, the car would run like
crap or not at all. I think we can close this out for a second.

What I would suspect is the GND connection in the center console
close to the radio. There must be a capacitor near the A/C switch
and two more from the fan speed switch. The caps are there to filter
noises from the fan motor that could disturb other systems like...the tach ?

Also - wat does the volt meter show during this situation ?

May be there is a problem or with the +12V coming from fuse #5.
At least this is where I would start looking, especialy for loose
GND connections.

Do you have a schematic ? Can you read it ?

Elvis








So, I get in the car to head to work today, make it half way down the
block and decide that the window open is not going to be cool enough
heading to work, so I close it up and turn on the AC to MAX. Right
away the tach goes from aroudn 2k (in 3rd) to 7k. Now I immediately
saw it and slammed on the clutch and put it in neutral. As I had the
radio on and the AC blowing, I didn't hear the engine rev that much,
but I wasn't certain. So, turned off the AC (assuming that was the
issue, starting to troubleshoot) and get going again in first,
without problem. I make it around the corner and down the street with
no problem, so I put the AC back on and right away the tach starts
jumping wildly again. This time the radio is off and the engine
sounds completely normal, yet the tach is at 5.5k, 7k, 4k, all over
the place. I slow a bit and it lowers by 2k. So, I turn around, head
home, and park it.

Heading home I was in 3rd and the tach showed 4k, yet the engine
sounded fine. I thought it might be a belt as it seemed to happen
when I kicked on the AC, but I heard no belt squeeling, but still
checked the belts upon getting home and they were both there. Didnt
have time to mess with the car as I was then running late so I left
for work. Anyone have any idea what the issue could be? Tach going
bad? Clean the tach ground above the relay compartment? Something
worse???







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