Tachometer is not working.

#12

Whelp - getting the stock tach working is still on my list of things to get done over the ‘winter.’ I just got a gauge cluster from Al and he confirmed it was a working unit. I swapped it out today and still no tach function. I’ll verify the black wire that was mentioned before, but are there any other things I should look for?

#13

I hope you figure this out. My Dad has the same problem and I haven’t had time to troubleshoot…

#14

i know this is basic, but have you checked fuses rob?

#15

kishg wrote:

I have.

#16

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

#17

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]

Fred,

That’s a good point. The tack signal must be in the C101 as it’s the only interface between the engine harness and the car electrical system except for the battery power. There are slight pinout differences between the early and late C101 connectors. The pinout diffences could explain the problem. Rob, has your tachometer ever worked with this engine harness?

#18

I recall the previous owner saying that the tach was intermittent and just stopped working. It never worked for me. He installed a shift light which gets the signal from the ecu connection. The shift light also tells the rpm and it has always been 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