Bmw e30 m50swap tach problems

[Eeken98]

My tach dont work but i have read online that it can be the coding plug but if its the coding plug thats wrong does the tach move at all or can it be dead because i have read that you need a new coding plug if the rpm dont read right but havent seen anything about the tach not move at all

[Brianmoooore]

Wrong coding plug gives wrong tacho. reading. It still works.
Do the SI leds in the instrument panel work?
What age is your car, and what model ?

[Eeken98]

Wrong coding plug gives wrong tacho. reading. It still works.
Do the SI leds in the instrument panel work?
What age is your car, and what model ?

okey whats the SI leds?
its an bmw e30 320 coupe 1986

[Brianmoooore]

SI leds = Service interval display - the 5 green LEDs + 1 amber + 1 red in the lower middle of the instrument cluster.
I think I probably know the answer to your problem from the second answer you gave.
An '86 E30 will probably have the tacho. signal (and fuel rate signal) going from the ECU to the instrument cluster by a three pin plug and socket (C104), rather than through the 20 pin C101 engine loom plug and socket.
This connector should have a green wire, a black wire, and a white/yellow or white/black wire, and will be found in the area behind the instrument cluster. The black wire and the white/black or white/yellow need to be connected to the black and the white/black in your M50 engine loom, which you have probably wired to the C101. The green is unused.

[Eeken98]

SI leds = Service interval display - the 5 green LEDs + 1 amber + 1 red in the lower middle of the instrument cluster.
I think I probably know the answer to your problem from the second answer you gave.
An '86 E30 will probably have the tacho. signal (and fuel rate signal) going from the ECU to the instrument cluster by a three pin plug and socket (C104), rather than through the 20 pin C101 engine loom plug and socket.
This connector should have a green wire, a black wire, and a white/yellow or white/black wire, and will be found in the area behind the instrument cluster. The black wire and the white/black or white/yellow need to be connected to the black and the white/black in your M50 engine loom, which you have probably wired to the C101. The green is unused.

Okey yes i have already tried that the black wire from the engine harness to the c104 black wire but nothing happened. And the w/b or w/y wire is for the fuel rate?
and the si leds dont work or i dont think there were any lamps in the cluster there. I have changed the batteries because i found out that i had only 1 battery in the cluster but it should have been two so i have replaced them.

[Eeken98]

SI leds = Service interval display - the 5 green LEDs + 1 amber + 1 red in the lower middle of the instrument cluster.
I think I probably know the answer to your problem from the second answer you gave.
An '86 E30 will probably have the tacho. signal (and fuel rate signal) going from the ECU to the instrument cluster by a three pin plug and socket (C104), rather than through the 20 pin C101 engine loom plug and socket.
This connector should have a green wire, a black wire, and a white/yellow or white/black wire, and will be found in the area behind the instrument cluster. The black wire and the white/black or white/yellow need to be connected to the black and the white/black in your M50 engine loom, which you have probably wired to the C101. The green is unused.

Now i have joined the black wire with the black in the c104 but no movment at all on the tach so what could be the problem?

[Eeken98]

SI leds = Service interval display - the 5 green LEDs + 1 amber + 1 red in the lower middle of the instrument cluster.
I think I probably know the answer to your problem from the second answer you gave.
An '86 E30 will probably have the tacho. signal (and fuel rate signal) going from the ECU to the instrument cluster by a three pin plug and socket (C104), rather than through the 20 pin C101 engine loom plug and socket.
This connector should have a green wire, a black wire, and a white/yellow or white/black wire, and will be found in the area behind the instrument cluster. The black wire and the white/black or white/yellow need to be connected to the black and the white/black in your M50 engine loom, which you have probably wired to the C101. The green is unused.

Now i have joined the black wire with the black in the c104 but no movment at all on the tach so what could be the problem?

[Brianmoooore]

One of the two versions of the SI circuit board (which also hosts the tacho. circuitry) has two NiCd batteries
on it, which provide memory power when the engine is off. These batteries have a limited lifespan, and when they fail, tend to go short circuit. The batteries may hang on for years in normal use, when they are constantly trickle charged from the main car battery, but presumably the main battery will have been disconnected for some time while the engine conversion was carried out, and may now have died, which is why I asked if the SI LEDs are working properly.
The short circuited batteries 'pull down' the power feed to the tacho. and this may cease to operate.
Open up the cluster, extract the SI board from the front half (remove coding plug first), place the board in a freezer for ten minutes, then measure the voltage across each battery. This should be either 1.2 volts or 3 volts, depending on whether you have the version with NiCd or Lithium batteries.

[Eeken98]

One of the two versions of the SI circuit board (which also hosts the tacho. circuitry) has two NiCd batteries
on it, which provide memory power when the engine is off. These batteries have a limited lifespan, and when they fail, tend to go short circuit. The batteries may hang on for years in normal use, when they are constantly trickle charged from the main car battery, but presumably the main battery will have been disconnected for some time while the engine conversion was carried out, and may now have died, which is why I asked if the SI LEDs are working properly.
The short circuited batteries 'pull down' the power feed to the tacho. and this may cease to operate.
Open up the cluster, extract the SI board from the front half (remove coding plug first), place the board in a freezer for ten minutes, then measure the voltage across each battery. This should be either 1.2 volts or 3 volts, depending on whether you have the version with NiCd or Lithium batteries.

I have changed the batteries already so they cant be bad already. I checked those si leds but i dont have them.

[Eeken98]

One of the two versions of the SI circuit board (which also hosts the tacho. circuitry) has two NiCd batteries
on it, which provide memory power when the engine is off. These batteries have a limited lifespan, and when they fail, tend to go short circuit. The batteries may hang on for years in normal use, when they are constantly trickle charged from the main car battery, but presumably the main battery will have been disconnected for some time while the engine conversion was carried out, and may now have died, which is why I asked if the SI LEDs are working properly.
The short circuited batteries 'pull down' the power feed to the tacho. and this may cease to operate.
Open up the cluster, extract the SI board from the front half (remove coding plug first), place the board in a freezer for ten minutes, then measure the voltage across each battery. This should be either 1.2 volts or 3 volts, depending on whether you have the version with NiCd or Lithium batteries.

I have changed the batteries already so they cant be bad already. I checked those si leds but i dont have them.

[Brianmoooore]

If you're sure that the black wire is continuous, all the way from pin 47 of the ECU to pin 7 of the blue plug of the instrument cluster, and is not shorted out to another wire somewhere along the way, then either the ECU or the instrument cluster must be faulty. If you have access to such a tool, an oscilloscope on the black wire should show if the ECU is producing pulses, or a volt meter should show some activity, varying with engine revs.
Next step would be to try a different instrument cluster. Are you using the coding chip that was fitted when the tacho. last worked, or have you changed it?

[Eeken98]

If you're sure that the black wire is continuous, all the way from pin 47 of the ECU to pin 7 of the blue plug of the instrument cluster, and is not shorted out to another wire somewhere along the way, then either the ECU or the instrument cluster must be faulty. If you have access to such a tool, an oscilloscope on the black wire should show if the ECU is producing pulses, or a volt meter should show some activity, varying with engine revs.
Next step would be to try a different instrument cluster. Are you using the coding chip that was fitted when the tacho. last worked, or have you changed it?

Yes i have tried to wire it so i had continous to the cluster but nothing i have tryed to measure voltage with a multimeter but not sure if i had it right it did read some small volts like 2-3 it did go up when i gave it gas. The car had no engine when i bought it so i dont know if the cluster worked before. But it should work if i buy a aftermarket rev counter and wire it to the black cabel and se if it moves then i know its the cluster? right?

[Brianmoooore]

Aftermarket tacho. should work, as long as it's the type that will work on 'low' voltage pulses, rather than the type that picks up high voltage pulses from the ignition EHT.
If you're measuring a varying voltage with engine revs on the black wire, then the ECU is probably OK.
Can'y you borrow or buy a cluster 'sale or return' from anywhere?
Bare in mind that any second hand cluster may well have batteries that have died, even if it was honestly described as working when it was removed.

[Eeken98]

Aftermarket tacho. should work, as long as it's the type that will work on 'low' voltage pulses, rather than the type that picks up high voltage pulses from the ignition EHT.
If you're measuring a varying voltage with engine revs on the black wire, then the ECU is probably OK.
Can'y you borrow or buy a cluster 'sale or return' from anywhere?
Bare in mind that any second hand cluster may well have batteries that have died, even if it was honestly described as working when it was removed.

I think im going to look for a aftermarket now cheaper than a cluster and i dont have any i can borrow so.