Intermittent tach

[ksgrimsr]

Hi guys,

I debated posting this question under this category heading or under the electronics one, but since the source of the signal is the coilpacks, I thought I'd try here in the ignition group.

My tachometer works intermittently and there appears to be no rhyme or reason to when it decides to work and when it does not. When the tach is not working, hooking up ElanScan shows that the ECU is recording the engine RPM just fine.

I have re-seated the IHC connector pair in the engine compartment in case the connection was intermittent (the contacts looked pristine), but that made no difference.

I have a good digital oscilloscope but I'm new to the car and don't know where all the relevant wiring and connectors are to be able to efficiently back-trace to the source of the problem. If someone has some suggestions to help me root cause this or is aware of a common issue like this, I'd appreciate it.

Knut

[GeoffSmith]

Knut, the ECU gets the engine speed directly from the CAS whereas the tacho is derived from the coil pack. You should be able to pick up the brown lead from the coil pack or the White/Grey feed from pin B11 of the IPHC which goes up to the back of the tacho.

[ksgrimsr]

Knut, the ECU gets the engine speed directly from the CAS whereas the tacho is derived from the coil pack. You should be able to pick up the brown lead from the coil pack or the White/Grey feed from pin B11 of the IPHC which goes up to the back of the tacho.

Thanks for the help. Can you give me a tip on where/how to best access the IPHC connector so I might do a little signal tracing? Do I gain access to it through the top cover of the instrument cluster, from underneath the dash, or somewhere else? The electrical manual is not very clear on where all the listed connectors are (I asked a separate question on that a little while back under a different topic). I'm a new owner so I haven't discovered all the ins & outs yet. In case it matters, I have a US car.

Knut