bouncing tach

Padrino · 06-03-2004, 09:58 PM

Dwell's dead on 38 degree on my 2.2S. The tach has taken to bouncing of late. Will jump up to 8k when doing around 4k. All over the place. Any ideas? Car has permatune blue with 6 pins, running webers. Was fine forever and just in the last weeks taken a mind of its own.

Ken

D Hanson · 06-03-2004, 10:31 PM

I just like to think my ebgine revs so quickly that the tach has a hard time keeping up. It does seem this way in the sweet spot.

rotorhead · 06-04-2004, 12:28 AM

I had the same problem on my 88 930, check your voltage regulator by measuring the voltage across the battery terminals with the engine running. It should read read around 14v if it is higher than this then replace the regulator and it should fix the tacho bouncing.

Steve

Jim Sims · 06-04-2004, 05:28 AM

On the early cars this is sometimes traced to the points; check your timing and dwell. Jim

kach22i · kach22i's Garage

Ditto that, check/replace the points- I had a similar problem, but not the same.

I was told that the RPM's are taken off the points, not an actual reading of the engine. If the tack acts up it's sometimes the points.

Padrino · 06-04-2004, 07:47 AM

voltage is perfect at 14v. just had new gen/reg installed.

dwell is dead on at 38 degrees.

next????

Ken

Padrino · 06-04-2004, 07:47 AM

voltage is perfect at 14v. just had new gen/reg installed.

dwell is dead on at 38 degrees.

next????

Ken

RoninLB · 06-04-2004, 09:52 AM

Quote:

Originally posted by Padrino
next????

- change the good points to another good set.
- check 2 into 1 tach connector in harness, on left side of engine comp
- borrow a friend's good coil and CD to confirm yours is ok
- tachs have an internal spring that wears out.
- borrow a friend's tach to see if problem stays or leaves.

I assume the problem was there before you changed alternator. A presumably good alt and reg can cause a tach problem. Don't forget to report your success.. eventually.

markwemple · 06-04-2004, 10:05 AM

You would be surprised what a faulty ground strap can do. I would check all of them.

Randy Webb · 06-04-2004, 01:41 PM

sometimes caused by a CDI box
as well as the points, coil, V. reg., or ground straps...

braddb_82SC · 06-04-2004, 02:06 PM

Check your spark plug wires. Last time this happend to me I traced the problem to corrosion where a connector contacted a plug. I pulled the connector off the plug and cleaned it with some sand paper. The bouncing tach settled back down.

Another time it was due to a bad alternator or voltage regulator (integrated on my '82 SC). 24 hours after the onset of tach bounce the car stranded me on the side of the road due lack of electrical power. My battery was no longer charging. A new alternator solved the problem.

-Brad

kach22i · kach22i's Garage

Quote:

Originally posted by markwemple
You would be surprised what a faulty ground strap can do. I would check all of them.

Someone told me that there is a ceramic/porcelin ground connection that sometimes cracks causing many funny problems. It's located in front of the driver on the otherside of the firewall.

They said:
I had an electrical problem couldn't figure out what was causing it. There is a wiring harness on the fender wall directly in front of the driver. The ceramic posts had cracked and was causing a short.

Note: Seems like even good points aren't good enough for long on my car- going pointless by the end of summer.