[HELP] Tach not working? Facelift engine in Pre-Facelift car.

[damastah]

Hi guys,

I swapped a late model m20 into an 87 cabrio that also came with an m20.

Now the RPM on the tach doesn't work at all. The econo gauge doesn't work either, but I think it's only because the RPM gauge doesn't work properly.

I read up and tried to search, I only see information on how to fix it if it was a prefacelift motor into a newer car.

Can someone please help me? I'm stumped.

Thanks,
Josh

[EatsHondas]

My tach has been intermittant ever since I got my e30 about 2 years ago. Sometimes it comes to life and works fine, but most of the time it's either completely dead or reading about 2x the correct RPM. My best guess is either a loose pin or a fractured/corroded signal wire, but I have not been able to track down the problem. It seems to have the highest chance of working when it's very cold outside, and sometimes random bumps in the road will bring it to life for a short time. I have continuity tested all the pinouts and integrated circuit paths on the cluster and they all check out. I have inspected all three connectors running to the back of the cluster and the wires and pins seem properly seated.

I'm fairly certain you cannot check the signal from the ECU to the cluster with a conventional multimeter because it is a digital signal (on or off), not a voltage of varying amplitude. I also know that the cluster uses a removable and interchangeable "coding plug" to convert the signal from the ECU to the correct tach reading. ETA motors and "i" motors have different plugs, and the 4 cylinders may be unique as well but I'm not sure.

I have asked the forum for advice with my problems and the best suggestion I got was to replace the service indicator board inside the cluster. It's about an $100 part with no guarantees of it fixing my problem, so I'd rather live with no tach for now.

So the gauge was working properly before the swap and now it's completely dead? What M20 did you have and what M20 did you swap to? (B23, B25, B27, etc.) I'm asking because it might matter if you changed (or need to change) ECU's.

I wish I could be of more definitive help, but I have similar issues and have not been able to get to the bottom of them.

[damastah]

I had an m20b25, but the prefacelift motor.

I swapped in a facelift motor, I also swapped the ECU's as well to match the current motor in the car. I'm not sure why it's not working.

[RobDog]

The early E30's tach signal pin runs through the c104(3 wire plug in glovebox). Late E30's tach signal pin runs through the c101(main engine harness plug next to fusebox).You must splice and rewire these pins for the tach to work. Also there is a pin that has to be cut on the c101 because one side is hot while the other is ground and this will fry your engine harness. Have you rewired the tach already and its still not working?

[TobyB]

Pin 20 is the danger pin- and yes, I learned that with the smoke test.

As Rob says, the black wire in that 3- pin connector is the tach.

http://www.wedophones.com/BMWManualsLead.htm

All you need to know and so, so much more...

t

[downforce22]

http://www.strictlyeta.net/technical/328i_8.html

The very first split out of the wiring harness from the ECU is the C104 connector, which is supposed to run to the instrument cluster. Because the 325e and 325i connectors are different, you'll have to do some splicing or bridging. I wanted to bridge the wires since splicing can be messy and can cause some problems later on for someone else.

If you disconnect the harness from the ECU, you will see 55 pins with the sequence running from right to left, as follows:



Pins 1, 20, and 38 are adjacent to the wires and pins 19, 37, and 55 are on the free side of the connector face.

The two wires that must be bridged from the instrument cluster harness are #6 and #32: Pin #6 is the engine speed output and gives the instrument cluster the signal for the tachometer, while pin #32 is the fuel consumption output and gives the cluster the signal for the econogauge. If you have an OBC with the CODE feature active (and you still want to have it functional), then you'll also have to bridge the wire from pin #38, which is the input signal that enables the driveaway protection. So you'll have to bridge:

- black wire from instrument cluster harness to black wire on engine harness (runs to pin #6)

- yellow/white wire from instrument cluster harness to white/black wire on engiine harness (runs to pin #32).




Once you do that, voila! Everything should work nicely. The OBC, which receives its signal from the instrument cluster, will also function normally afterwards.

Thanks again to Mitch for all the help!

i had to this in my 86 325 (35 pin ecu) to get the motronic 1.3 (55 pin ecu) upgrade working

[3vilE30]

I have a 5k 84 eta tach in my 88 super eta works fine.
On the contrary when I bought the car it had a non working 7k tach don't know the year tho
I swapped in the 84 board and use the temp, fuel, speedo from the cluster I already had.

[nando]

The early E30's tach signal pin runs through the c104(3 wire plug in glovebox). Late E30's tach signal pin runs through the c101(main engine harness plug next to fusebox).You must splice and rewire these pins for the tach to work. Also there is a pin that has to be cut on the c101 because one side is hot while the other is ground and this will fry your engine harness. Have you rewired the tach already and its still not working?

it's only hot on airbag cars. on early cars, pin 20 is empty. the power comes from the car, not the engine harness. it powers the relay for the ABS pump.