Tach signal help on fresh e30 m50 turbo

[scooter3k]

Hi!

So, first post here :)

Just wrapping up a fresh swap of an m50 from a 95 525 into my 88 e30 m3. And also adding a turbo. Here's my build thread on bimmerforums if you're interested...

http://forums.bimmerforums.com/forum/showthread.php?t=1533387

I asked this on bimmerforums.com too, but I thought this might be a better audience. One of the last issues I'm having trouble working out is getting my tach to work. Everything else in the cluster is working fine except the tach. The tach worked fine before the swap too.

So, the troubleshooting I've been doing...

I looked up the wiring diagram, for the 88 m3, the tach signal doesn't go through the c104, it goes through pin 9 of the c101 to the cluster from the DME. First, I pulled the cluster out to make sure the wires were going to the right place. The black wire at the back of the cluster has continuity to the c101 pin 9. c101 pin 9 has continuity to DME pin 47 (95 e34). I'm pretty confident the wires are going to the right place from the DME to the tach now.

That got me curious about the SI board batteries that sometimes go bad in the cluster. So I took the board out and it had already been replaced with a newer board & new batteries, dated 7-23-99. Used a multimeter, the batteries said 1.2 V on them, the multimeter read 1.28, so I don't think that they need to be replaced or that they are the cause of no tach signal.

Next I decided to check the resistance of the crank position sensor. For m50's it is supposed to read 1280 ohms +/-10%. Mine read consistently at 512.5 ohms. However, the car runs great (TRM rocks btw! very impressive for just the base tune) and doesn't show any symptoms of a bad crank position sensor. So now I'm just confused. Anyone have any ideas of what to try next or what my problem might be?

Another thing to add. My boost controller has a wire for the RPM signal, so I tapped into the black rpm signal wire right behind the tach. The EBC menu isn't showing an rpm signal either, so that supports the theory that the signal is not making it that far.

Thanks!

[Matt-B]

do you need a 325i coding plug?, you likely will, as most of us add one for our m50 swaps

and its an 8k tach in the e30 m3, you need to probably swap it to a 7k tach

[scooter3k]

do you need a 325i coding plug?, you likely will, as most of us add one for our m50 swaps

and its an 8k tach in the e30 m3, you need to probably swap it to a 7k tach

Nice, thanks for the advice there. That's a good idea, I'll start looking for one of those to use.

I still am not getting any signal to my tach when I start the car though...it just sits at 0 rpm. Any troubleshooting ideas for what to try there?

[Blackangusinc]

Bump for a good build!

[lennon]

take the m50 out and put the s14 back in. that'll solve more than one problem.

[scooter3k]

Lol...not the most popular apparently, but who really wants an old s14 anyway? =P

I took the cluster out and started her up and I was getting an rpm signal at my boost controller, which I wasnt before. Still looking for a 325i cluster I can try out to see if it works. Someone took every single BMW cluster @ the local u pull it.

[Lawson509]

I got a 325i cluster if you need

[scooter3k]

I got a 325i cluster if you need

Pm'd

[zenn0ne]

Nice, thanks for the advice there. That's a good idea, I'll start looking for one of those to use.

I still am not getting any signal to my tach when I start the car though...it just sits at 0 rpm. Any troubleshooting ideas for what to try there?

you can use the 8k cluster thats stock with the m3 as long as you it worked prior now I have to check on my build paperwork and I'll get back to you sir btw I've following yer build thread on bimmerforums I didn't know you went turbo good shit bro the e30m3 body handles the traction problems better then the regular e30 IMO and experience ;)

[scooter3k]

you can use the 8k cluster thats stock with the m3 as long as you it worked prior now I have to check on my build paperwork and I'll get back to you sir btw I've following yer build thread on bimmerforums I didn't know you went turbo good shit bro the e30m3 body handles the traction problems better then the regular e30 IMO and experience ;)

cool, thanks. let me know :)

i'm gonna play around with it a bit...it is possible an old connection just needs cleaning on my cluster or there's a bad ground or something...lol, just pulling out of my ass now.

i would like to use my original one since i welded a fitting in my oil pan for the oil temp gauge in the e30 m3 dash. and that mpg-ometer isn't going to be worth jack.

[zenn0ne]

ok buddy try this first pin 20 on the e36/34 side to the black wire at the c104 port, Its behind the glove box
that should get the tack working, while your at it if you run another wire from pin 24 on the e36/34 side or pin 8 on the e30 side, to the wight/yellow wire at the c104 port you can get the fuel consump gauge to work as well.

dont worry about the green wire its not need for the swap.

[zenn0ne]

So you sort out your problem...did you get the tach working

[scooter3k]

So, I figgered it out! I teed off the rpm signal wire to my boost controller. I wanted to test if that was causing issues so I clipped it. Low & behold my tach started working! Damn boost controller was eating too much of the signal I guess!