Tachometer is not working.

#19

Fred42 wrote:

[quote]FWIW, I believe the tach signal comes out of the ECU through a three-prong connector (C101?). If memory serves the wire colors are black, green, & blue (I’m not sure about that but I think the tach signal was the black or blue/black wire). But you might want to check that connector.
–Fred[/quote]
The routing of the tach signal is a function of the production date of the car. Early cars (up to 8/87) take the tach (and econometer) signals off a three pin connector pigtailed off the engine harness near the DME connector. Later cars route the signal through C101 (the round connector next to the fuse box). So it matters that the engine harness and car have to match up.

#20

[scratching my head]

Does this diagram state which wire(s) are for the tachometer?

This image shows the gauge cluster connectors.

#21

On my 89 i tach is c101 pin 7 black.

#22

The tachometer signal comes from pin 6 of the DME connector to pin 7 of C1. C1 is the blue connector.

#23

jlevie wrote:

Thanks Turbo and Levie. I confirmed that the black wire has continuity from the DME to the cluster. I need to figure out the next test.

#24

The best next test would be to look at the signal on the tach wire with a scope.
If the pulse train is present the problem has to lie in the instrument cluster. Otherwise
the problem will be with the output stage in the DME.

One might be tempted to swap in a different DME to eliminate that as the cause,
But when dealing with a similar problem and being in a hurry I wasted two DME’s
going that route. It turned out that the fault was in the cluster and it blew the
output stage in the orginal DME and the test unit. Replacing the SI board in the cluster
and using a fresh DME was the fix.

#25

Some additional info.

The cluster I’m trying was freshly taken out of another car from Al, and it is in working condition.

I have an external shift light/tach attached to the DME (black wire) and it works with no issue.

I have tried a total of 3 DMEs.

#26

If the shift light works, the tach signal from the DME sounds to be valid. The problem then will be the cluster.

#27

Guys, does this wire need to go anywhere?

#28

All I can tell you is that mine goes through the firewall with the rest of the harness.

That is rd/bu right?

#29

turbo329is wrote:

[quote]All I can tell you is that mine goes through the firewall with the rest of the harness.

That is rd/bu right?[/quote]

This is coming out of the DME connector.

#30

jlevie wrote:

Al Taylor said this cluster was working. Hmmm. Maybe a bad ground? I checked those this morning.

#31

Rob in VA wrote:

No

#32

Al Taylor is mailing another cluster to help diagnose. Fingers crossed!

#33

Al was nice enough to send another cluster. Still no tach, so the problem isn’t within the cluster. I’d really like to get this figured out.

#34

Any resolution on this?

Being the idiot that I am, I snipped the cluster of wires that goes to the OBC. I figured, since the OBC has not been hooked up why not just cut the harness and save a lbs or so.

Now my tach is not working…

My car is an 89… Who would have thought that the OBC is tied into the Tach…

Now I’m at a loss…Any thoughts on an easy fix for this?

Thanks

#35

I’m in the same boat. I clipped some wires in the stereo area and now no tach. That is the only thing that I’ve done since it was working that I can think would cause it.

Subscribing…

#36

If we could ID the wire going into the cluster than maybe we could just run a wire from the coil or from the correct wire from the ECU?

#37

Sorry guys. I haven’t had a chance to further review, but to be honest I don’t know what else to look for so I’m kinda giving up.

#38

For those of you that have cut the wires to your OBC: If you check your Bently manual you will find that many of these wires are hot. If you did this with the battery connected you most likely have blown a fuse. I think 10 is the one for the tach. Good luck.