Intermittant Tachometer

[EatsHondas]

All my gauges work perfectly 100% of the time except the tach. Sometimes it doesn't work for days, and then it will spring to life and work perfectly for a few days before dying again. I've noticed that when the tach starts working, it's usually pretty hot outside and the interior of the car is uncomfortably warm. When I realized this, I thought for sure that the solder joints needed to be reflowed because the outside heat was causing the solder to expand just enough to complete the circuit again.

I have:

- cleaned all the pins in c101 (the tach signal runs through here from the ECU)
- visually inspected and continuity-tested the circuit board connections that run from the SI board pinouts on the main cluster to the tach pickups (IIRC there are 8, and they all checked out fine when I was testing them in a ~72 degree room)
- visually inspected and continuity-tested the circuits that lead to the pinouts on the SI board.
- slapped the shit out of the dash to entertain the possibility of a loose wire. This method has never helped.

All my other gauges and cluster bits work without fail, so I'm willing to bet my SI batteries are okay unless you guys tell me otherwise.

I have read damn near every thread on the net about e30 cluster problems, and they're all full of the same suggestions. They almost never include what the problem was after it was finally fixed. Also, most people seem to have problems with multiple gauges at once, or the tach and econometer fail together.

Why only one malfunctioning gauge? And if the gauge itself was bad, why does it often work perfectly for days on end?

[Gregs///M]

If the SI board batteries have not been changed, if they are original. I would start by replacing them. If original, they are around 25 years old. No way are they any good anymore.

Dead batteries will cause intermittent operation of tach, temp, MPG gauges. Sometimes all at the same time, sometimes not.

Replacing fuses 10,12, and 21 is also a cheap easy way to rule out their involvement in the problem.

[EatsHondas]

Well it's been 2 years, but I've learned more about electronics and finally fixed my dead cluster components. Here's some cool things I've found out.

The SI batteries do NOT power the tachometer, speedometer, odometer, or the gas and coolant temp gauges. I have no SI batteries installed and all of the aforementioned items are working. The batteries are needed for the Service Indicator board (big surprise) only. I have a standalone ECU, so I have no way of testing the econometer anymore. I do know that it is pulse-width modulated and requires proper input from the factory DME as well as functioning speedometer and tachometer gauges.

If you're having cluster problems, take the cluster apart and inspect all the soldered joints and integrated circuits. A small magnifying glass helps. Resolder cracked joints and broken circuit pathways (a little solder goes a long way, be careful!). Don't forget the pins coming out of the small chip in the removable green plug thing (NOT one of the three plugs from the car's wiring harness) that connects to the bottom of the speedometer. My cluster had a loose, desoldered pin in there. Fixing that and a few other obviously broken solder spots got all my non-SI-related components working again.

[jake5]

I am dealing with a dead tach. I have now put in three different tachs. So I am pretty sure that is not the problem. I want to start checking power, But have no idea where to start. I have Bentley manual and they don't really show anything useful like pin outs for connectors. I am in the middle of a dash swap, and really just don't want to put the car back together. I also have a fuel sender out, so I am not sure if that is related.

[Gregs///M]

Well it's been 2 years, but I've learned more about electronics and finally fixed my dead cluster components. Here's some cool things I've found out.

The SI batteries do NOT power the tachometer, speedometer, odometer, or the gas and coolant temp gauges. I have no SI batteries installed and all of the aforementioned items are working. The batteries are needed for the Service Indicator board (big surprise) only. I have a standalone ECU, so I have no way of testing the econometer anymore. I do know that it is pulse-width modulated and requires proper input from the factory DME as well as functioning speedometer and tachometer gauges.

If you're having cluster problems, take the cluster apart and inspect all the soldered joints and integrated circuits. A small magnifying glass helps. Resolder cracked joints and broken circuit pathways (a little solder goes a long way, be careful!). Don't forget the pins coming out of the small chip in the removable green plug thing (NOT one of the three plugs from the car's wiring harness) that connects to the bottom of the speedometer. My cluster had a loose, desoldered pin in there. Fixing that and a few other obviously broken solder spots got all my non-SI-related components working again.

Let me elaborate on what the SI board does. With drained batteries still on the SI board, it can cause the SI board to intermittently fail. Symptoms such as non working or twitching temp, tach, MPG and OBC will occur. Speedometer and fuel gauge has nothing to do with the Si board.

Not all Si boards are the same. There are several generations and revisions, some of which require batteries to operate tach, temp, MPG and OBC so your blanket statement about the batteries NOT powering tach, speedometer, odometer, gas, or temp gauges is kinda wrong. Although the batteries do not directly power those gauges, using dead batteries WILL affect those gauges.

I have refurbished over 400 SI boards so I know this to be true.

[Cha Ching]

Gents, what would cause the speedometer to engage intermittently? Same issues? Cracked solder joints? Old (original) SI batteries?