Tach On/Off Issue (s5)
Tach On/Off Issue (s5)
Hi everyone,
I'm trying to figure out why my tach drops to 0rpm. There are time when I start the car and it is working with no issues but after unmeasurable circumstances it just drops to zero and the CEL comes on. Here are few diagnostic notes.
*There are times when I turn the ignition and the car doesn't crank
*When the tach dies I do turn the ignition on again and it comes back to life. There will be times when it stays on and there are times when it just drops back to zero immediately
*I recently changed the CPU since I was having issues with my turn signal. I did notice that when I press the brakes the tach dims (granted the lights are on). I do want to note that the arrows do not lights up when I trigger a left or right turn signal (outside lights do flash)
*At first I thought there was a kinked wire. When the tach was running with no issue I drove over less than ideal road and it didn't drop to zero.
*Cleaned the ground on the trailing coil
From researching i am considering the following:
Alternator
Trailing coil
Starter? Battery?
Ignition wires (they are pretty old now)
Solders in the back of the tach? <- but if they are bad then the tach shouldn't work at all correct?
I'm trying to figure out why my tach drops to 0rpm. There are time when I start the car and it is working with no issues but after unmeasurable circumstances it just drops to zero and the CEL comes on. Here are few diagnostic notes.
*There are times when I turn the ignition and the car doesn't crank
*When the tach dies I do turn the ignition on again and it comes back to life. There will be times when it stays on and there are times when it just drops back to zero immediately
*I recently changed the CPU since I was having issues with my turn signal. I did notice that when I press the brakes the tach dims (granted the lights are on). I do want to note that the arrows do not lights up when I trigger a left or right turn signal (outside lights do flash)
*At first I thought there was a kinked wire. When the tach was running with no issue I drove over less than ideal road and it didn't drop to zero.
*Cleaned the ground on the trailing coil
From researching i am considering the following:
Alternator
Trailing coil
Starter? Battery?
Ignition wires (they are pretty old now)
Solders in the back of the tach? <- but if they are bad then the tach shouldn't work at all correct?
A similar issue has been seen before, but most people aren't on stock S5 ECUs with check engine lights...so I can't comment on that.
The tach dropping out has been linked to the trailing coil, which is where the signal originates. Usually swapping to a new trailing coil will fix this.
The tach dropping out has been linked to the trailing coil, which is where the signal originates. Usually swapping to a new trailing coil will fix this.
Joined: Sep 2005
Posts: 25,581
Likes: 136
From: Smiths Falls.(near Ottawa!.Mapquest IT!)
another thing is that if the tach is failing to get signal(but the trailing coil is working) there is a bullet connector at the LEADING coil that you can attach to the bullet connector at the Trailing coil..that should allow the tach to see signal.
Full Member
Joined: Apr 2013
Posts: 247
Likes: 7
From: Suffolk, Va
I had issues on my S4 with the tach dropping out sometimes as well. It would work at times and just drop out also. When I was having this issue I was running the RTEK with stock CPU then. I also had moved my secondary coils to a different location. I tried to make sure I had it grounded better as well. My issues went away after fixing the ground I believe.