If I downshift hard or let off the throttle at a high rpm the tachometer will appear to turn off for a breif second than jump back up to the actual rpm. This is on an S4 and it does not cause any problems it is just annoying.

It does not affect performance, anyone else have a similar problem or know of solutions?

 

Mis-firing trailing coil

Or

A loose or corroded screw on the back of the gauge cluster.

Or

If someone has cracked the tach open... it too could be bad or sticking.

 

it affected me when i had a broken airflow meter.

that ***** a pain in the *** when its broken and leaves you stranded.

 

Yea I have haltech e6x and run MAP so I know that a AFM is not the problem, I never opened the tach and rewired the trailing coils not to long ago and the problem still exsisted. I guess that leaves it to checking behind the cluster.

 

interesting problem.

 

Huh??

The trailing coils have a summed wire that feeds that Tach in the gauge cluster. If the coils are not firing correctly the tach in the gauge cluster will follow suit.

 

Yes I am aware of this, I was responding to the post above mine in which the guy said to check the AFM. I also was pointing out that recently I checked all the wiring on the coils and went though the voltages with a multimeter and it seemed okay.

 

The trailing coil grounds to the body, make sure it's clean and tightly attached. Or replace it! That fixed my tach bounce.

 

A somewhat odd way to see if it's the trail coil assy is to do the following. Find the black single wire bullet connector on the LEAD coil assy. Get a piece of wire that will reach from that bullet connector to the TRAIL bullet connector.

strip each end of the wire. Stuff one end in each bullet. Then go for a ride and try to duplicate the problem. IF it does not duplicate, I'd suspect the trail coil in some way.

In other words a person could unplug the connectors (two white connectors) and disable the trail coil and run the new wire as mentioned above. The tach will work normal that way without the trail coils being active. It's a trouble shooting aid so to speak. It eliminates one of the two items....tach or trail coil assy. It's just something I thought I'd throw in.