How can I figure out WHY my tach isn't working?

Why do I have to unlock my doors through my trunk?
User avatar
Yoshi
Site Admin
Posts: 9091
Joined: Thu Feb 26, 2009 7:47 pm
AntiSpam: No
Location: North VA
Contact:

How can I figure out WHY my tach isn't working?

Postby Yoshi » Sun Oct 19, 2014 12:52 am

I tried another cluster and it still didn't work but I'm not sure why or why not.
Image
Status: HG repair. 488wtq though!
pr0craztinazn
I <3 E30's
Posts: 490
Joined: Sun Aug 16, 2009 2:01 am
AntiSpam: No
Location: MD
Contact:

Re: How can I figure out WHY my tach isn't working?

Postby pr0craztinazn » Mon Oct 20, 2014 5:07 am

Can't sleep; advice might be shitty.

Pull the tach wire from the cluster harness and see what sort of signal it's getting. It's pin #9 on the C101 in the engine bay on a stock harness, which for some reason is just a black sheathed wire. The eta engined E30s also have a black tach signal wire. The signal frequency is variable, not the voltage, so be wary when probing with a multimeter. If memory serves, you have an oscilloscope, which would be far more useful for troubleshooting. Stock BMW input is a square wave. According to the following diagram, it's pin A7 going into the cluster. Fuck if I try and trace this any further or I am probably not going to sleep at all. I'll drive over and we can check this out if you're free later in the week.
Image

If you get nothing, you'll need to trace the wiring off the GTO ECU. I'm not exactlysure which wire that is off the top of my head, but if it's like a lot of other GM PCMs, it's a brown/red wire and probably pin 48 on the blue connector off the PCM/ECU.
User avatar
Yoshi
Site Admin
Posts: 9091
Joined: Thu Feb 26, 2009 7:47 pm
AntiSpam: No
Location: North VA
Contact:

Re: How can I figure out WHY my tach isn't working?

Postby Yoshi » Mon Oct 20, 2014 11:59 am

I do have variable voltage at A7 though. I should hook up my oscilloscope but I'm pretty sure that isn't the issue. I think it's somewhere in the cluster. I bet I could temp hook up an after market cluster and have it work. Too bad the spare cluster I tried didn't work either.
Image
Status: HG repair. 488wtq though!
User avatar
M20_fever
Größter Vorsitzender
Posts: 11026
Joined: Fri Feb 27, 2009 1:28 pm
AntiSpam: No
Location: Northern IL

Re: How can I figure out WHY my tach isn't working?

Postby M20_fever » Mon Oct 20, 2014 2:52 pm

I doubt both clusters have the same issue. My best guess is the GM tach signal isn't able to be translated by the coding plug on an e30 cluster.
Image
Midwestern Councel C Prepared class champion 2012
North Suburban Sports Car Club C Prepared class champion 2012
HSAX Instructor

GET YOUR E3P GEAR HERE: http://www.cafepress.com/e3pgearshop
User avatar
Yoshi
Site Admin
Posts: 9091
Joined: Thu Feb 26, 2009 7:47 pm
AntiSpam: No
Location: North VA
Contact:

Re: How can I figure out WHY my tach isn't working?

Postby Yoshi » Mon Oct 20, 2014 9:14 pm

The PCM was modified to work with 6 banger output. It's the same way they do the tach signal in E36s with LS swaps. Since the tachs work the same, it should work. I'm reasonably sure it's something with the cluster.
Image
Status: HG repair. 488wtq though!
User avatar
Yoshi
Site Admin
Posts: 9091
Joined: Thu Feb 26, 2009 7:47 pm
AntiSpam: No
Location: North VA
Contact:

Re: How can I figure out WHY my tach isn't working?

Postby Yoshi » Wed Oct 22, 2014 1:23 pm

Been reading around. Found this: http://www.bavrest.com/si-boards.html

The tell tale signs are:
CLT gauge not working
Mpg meter not working
Tach not working
OBC not working
Service interval meter not working.

Really, I figure the mpg meter doesn't work because the tach doesn't work. I have no OBC as well. On top of that, I don't have my coolant gauge installed so I can't verify if it works or not. My service indicator has been dead for a while. So that sounds likely.

The reason I think the SI board instead of the LS is because this stuff hasn't worked on my car since my first M50 swap. I do recall hooking in the factory coolant temp sensor and wiring it but not getting anything on my cluster. I figure the SI board batteries are pretty cheap and simple to replace.

Gonna yank my cluster soon and order the batteries. I think I need the nicd batteries but I would like to be sure.

Seems like the batteries are on their life span so I'm surprised I haven't seen more people bitching about their tachometers dying.
Image
Status: HG repair. 488wtq though!
User avatar
Yoshi
Site Admin
Posts: 9091
Joined: Thu Feb 26, 2009 7:47 pm
AntiSpam: No
Location: North VA
Contact:

Re: How can I figure out WHY my tach isn't working?

Postby Yoshi » Wed Oct 22, 2014 9:13 pm

For future self reference, these are the batteries I got.

http://www.radioshack.com/product/index ... ndSrc=cart

Sanyo CR14250SE 3V/ 850mAh Lithium 1/2"AA" Memory Backup
Image
Status: HG repair. 488wtq though!
User avatar
blasphemy101
I <3 E30's
Posts: 1041
Joined: Sat Apr 07, 2012 9:20 pm
AntiSpam: No

Re: How can I figure out WHY my tach isn't working?

Postby blasphemy101 » Thu Oct 23, 2014 4:21 pm

I ran into a similar problem on my car. Everything BUT the tach worked. 2 junkyard clusters (they were broken too) and a new SI board later, my cluster works fine.

I guess my point to add is that a dead/dying SI board doesn't necessarily present all the common issues. If all the issues are present, though, you can be almost guaranteed that's the problem.

** There's also a wire that runs by the shifter (I think it might be for the reverse switch) it also killed my tach by grounding out on the chassis when it got pinched by the shifter. Since you have a different trans, I doubt that wire is there any more.
User avatar
Yoshi
Site Admin
Posts: 9091
Joined: Thu Feb 26, 2009 7:47 pm
AntiSpam: No
Location: North VA
Contact:

Re: How can I figure out WHY my tach isn't working?

Postby Yoshi » Thu Oct 23, 2014 5:37 pm

I actually run the factory reverse wiring since the T56 has the same reverse switch type. What wire are you talking about? Why the hell would something tach related be near the shifter?!
Image
Status: HG repair. 488wtq though!
User avatar
87e30
I <3 E30's
Posts: 2014
Joined: Wed Oct 27, 2010 5:25 pm
AntiSpam: No
Location: New Jersey

Re: How can I figure out WHY my tach isn't working?

Postby 87e30 » Thu Oct 23, 2014 5:55 pm

Yeah I'm pretty sure nicad batteries are not required. My batteries have been dead longer than I've owned the car and all of my gauges work fine so don't get your hopes up too much just yet.
Schwarz 5-speed 87 325is (newest project)
Arktisblau 5-speed 86 325e (current DD)
Schwarz 5-speed 87 325e (parts car/LS1 swap?)
Gazellenbeige automatic 85 318i (70,000 miles)
Alpine white 5-speed 87 325is (my first e30, possibly for sale)
99 Suburban
User avatar
blasphemy101
I <3 E30's
Posts: 1041
Joined: Sat Apr 07, 2012 9:20 pm
AntiSpam: No

Re: How can I figure out WHY my tach isn't working?

Postby blasphemy101 » Thu Oct 23, 2014 8:36 pm

87e30 wrote:Yeah I'm pretty sure nicad batteries are not required. My batteries have been dead longer than I've owned the car and all of my gauges work fine so don't get your hopes up too much just yet.


Are you sure yours are dead? Conventional information from the rest of the community says the batteries are the problem. That said, I replaced the entire board, so I don't know for sure.

Yoshi wrote:I actually run the factory reverse wiring since the T56 has the same reverse switch type. What wire are you talking about? Why the hell would something tach related be near the shifter?!


I have no idea, but that was definitely the problem. I was able to reproduce it by grounding out the cut part of the wire. I wonder if that's were the speed sensor from the diff runs..?

There's also a good procedure for testing the cluster in the Bentley manual.
User avatar
87e30
I <3 E30's
Posts: 2014
Joined: Wed Oct 27, 2010 5:25 pm
AntiSpam: No
Location: New Jersey

Re: How can I figure out WHY my tach isn't working?

Postby 87e30 » Thu Oct 23, 2014 11:46 pm

blasphemy101 wrote:
87e30 wrote:Yeah I'm pretty sure nicad batteries are not required. My batteries have been dead longer than I've owned the car and all of my gauges work fine so don't get your hopes up too much just yet.


Are you sure yours are dead? Conventional information from the rest of the community says the batteries are the problem. That said, I replaced the entire board, so I don't know for sure.


Well my SI lights have never worked. I assume because the batteries are dead. I've never actually taken the cluster out and tested them. I'll try to remember to do that if I ever install the ODO gears I bought like a year ago.
Schwarz 5-speed 87 325is (newest project)
Arktisblau 5-speed 86 325e (current DD)
Schwarz 5-speed 87 325e (parts car/LS1 swap?)
Gazellenbeige automatic 85 318i (70,000 miles)
Alpine white 5-speed 87 325is (my first e30, possibly for sale)
99 Suburban
User avatar
Yoshi
Site Admin
Posts: 9091
Joined: Thu Feb 26, 2009 7:47 pm
AntiSpam: No
Location: North VA
Contact:

Re: How can I figure out WHY my tach isn't working?

Postby Yoshi » Sun Oct 26, 2014 2:00 pm

viewtopic.php?f=25&t=2277

Well... That sucked. I got my inspection lights working. What fucking use is that to me? Also, the dead LEDs actually do more to infuriate me than the whole thing not working.

I need to find a way to test the tach itself. Might just say fuck it and get an after market tach :-/
Image
Status: HG repair. 488wtq though!
User avatar
blasphemy101
I <3 E30's
Posts: 1041
Joined: Sat Apr 07, 2012 9:20 pm
AntiSpam: No

Re: How can I figure out WHY my tach isn't working?

Postby blasphemy101 » Tue Oct 28, 2014 6:38 pm

I may have an extra tach laying around. If I do and it matches yours (there are a couple different ones) I'll send it to you for the price of shipping.
User avatar
Yoshi
Site Admin
Posts: 9091
Joined: Thu Feb 26, 2009 7:47 pm
AntiSpam: No
Location: North VA
Contact:

Re: How can I figure out WHY my tach isn't working?

Postby Yoshi » Tue Oct 28, 2014 8:37 pm

Got the tach working. Fuse 21 wasn't even there... Problem is now that the tach is reading incorrectly. The tuners fiddled with settings to try to get my tach to work but I guess the final settings they left it with aren't right. Near redline it reads 1k rpms lol.
Image
Status: HG repair. 488wtq though!

Return to “Electrical”

Who is online

Users browsing this forum: No registered users and 1 guest