I have a tachometer that doesn't work ('78 280z) . Does anyone have any suggestions on how to troubleshoot it?

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'78 280Z

I'm not the guy to ask about that.

I have a bench full of them and can't make them work in my car, since I swapped over to electronic ignition.

Frank

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1970 240Z

I checked the wiring diagram and there seemed to be too many places where a broken wire could be the culprit. Finding where the break is - that's something I'm not ready to take on. I was hoping someone might have some tips, or maybe a working tach that I can swap out. I might be lucky and the wiring will be fine (but I'm not betting on it).

Paco

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'78 280Z

What kind of ignition do you have, points or electronic?

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1970 240Z

Electronic. No points.

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'78 280Z

Q: did your present tach EVER work with the electronic ignition?

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1970 240Z

It never worked. I've had the car 5 years now.

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'78 280Z

Do you know for sure if your distributor is stock for 1978? Might it have been upgraded to 1979 or later unit?

Tachs seem to have been dependent upon the same-year distributors. If the prior owner installed a later-year distributor, the tach might not be getting a signal anymore. Can you determine what model year your current distributor is? If, for example, you determine the distributor is a 1980 model, you would want to buy a 1980 tach.

Our member Bryan Little's DATSUN Z GARAGE has some very good info on this:
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"SEVENTH- Ignition

There is more to the Zcar ignition system than any other part of the car, so this is a long section below.

POINTS vs ELECTRONIC IGNITION

Points distributors are an obsolete technology when it comes to high performance engines. The reason is that Dwell (the amount of time the points stay open) changes if there is any play in the distributor shaft. Dwell directly affects ignition timing, so any slight rocking back and forth of the shaft varies your ignition timing. Point float and bounce can also cause the spark timing to scatter at high revs. Datsun competition makes a solid advance plate breaker to address this. Mallory also makes an interesting dual point distributor for Datsuns which I have never tested.

Electronic distributors are usually rock-solid when it comes to timing. Shaft play can still cause slop in the distributor but generally doesn't cause the timing to fluctuate the same way. An electronic distributor can give you full coil saturation with a strong, accurate spark past redline.
.

Nissan made three electronic ZCAR distributors
from 1975-'83
Style 1 came on '75-78 cars. It came with 1 or 2 internal fat magnetic pickups inside.
This distributor uses a magnetic reluctor and pickup to send a strong pulse to the FI brain underdash which fires the coil. This is considered a "Magnetic Trigger" distributor.
Style 2 came on '79-83 cars. It came with a built-in ignition module on the side
This uses a magnetic reluctor wheel and small pickup coil to send a pulse to the ignition module on the side of the distributor which fires the coil. A simple, self-contained ignition system. Pre-1981 models used the E12-80 module, '81-83 models used the E12-92.
Style 3 came on '81-83 turbos. It uses the FI brain and a crank-firing system.
These require the turbo FI brain and several sensors, I doubt if it could be wired into an older Z without a lot of trouble.
WIRING A E12-80 and 280ZX DISTRIBUTOR INTO A 240Z


This mod converts a 240Z to an ZX electronic distributor. It's not needed on a 280Z or ZX which already have electronic ignitions.

- Find a 1979-'83 280ZX distributor. If its '81-83 it will have the E12-92 module which needs to be changed to a E12-80.
- Remove and clean the metal rear of the IC module so it can ground itself to the side of the distributor.
- Remove the triangular hold-down plate on the base of the distributor. Burnish it, as well as the spot where it contacts the distributor and replace...this helps everything ground well to the block. Note that this plate rotates, you may need to play with the position to get the proper timing mark range you want.
- Use quality spade lugs and wire with TIGHT crimps and solder the wire to the spade connections. Don't solder or crimp onto the E12-80, just make sure the spades fit on tight.
- You will need to buy a longer L28 distributor base for the front cover if this is a 240Z. Motorsport Auto used to carry them them.

A 240 tach will not work with this setup because its inductive pickup isn't compatible with the signal from the E12-80. There are two solutions: Replace it with a 1975-78 280Z tach and connect the tach sensor lug to the negative terminal on the E12-80 module. If the tach jumps around, solder a 7500-10,000 ohm resistor inline with the sensor wire to reduce the signal voltage. If it still won't work simply buy a Autometer #3990 black face tach.

WARNING: if you have a MSD type igniton DON'T hookup the E12-80 or tach directly to the coil. The 450 volts can fry it. Follow the ignition's hookup guide".
* * * * * * * * * * * * * *

All very good stuff. Thanks, Bryan.

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1970 240Z

Thanks. This is great information. I'm pretty certain that its the stock distributor, but I'll have to look closer.

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'78 280Z

Whatever became of this? Did you get it working?

It turns out I *AM* the guy to ask about this!! I read on another Z site that some owner installed the stock ballast resistor back into his car, after he had replaced his breaker point ignition with an electronic (Pertronix) ignition system, and his tach began working again.

On Thursday I took my Z to Vinny's for a list of things and asked him to replace the resistor (which we had taken out 5 yrs ago, when I switched to Pertronix).

LO! and BEHOLD! My tach works again after 5 years of silence!

The Pertronix system tells you to remove the ballast resistor because the new electronic ignition doesn't need it. But the tach does! The ignition works just as well with or without the ballast resistor, but the tach will not work without it. I could always tell my tach was not broken, because during a long drive it would slowly creep up to 8,000 and peg itself there until I shut the car off. So it was getting a signal from SOME where. It just needed the resistor to work right.

I don't know if the same approach might help you or not? What do you think?

Frank

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1970 240Z

Thanks Frank. I've put off working on it for the next few weeks. Too much work and too much heat in the garage to work comfortably. I'll come back to it and this thread to see how I can trouble shoot it. I may ask you to take a looksie at the next meeting if I can make it. I guess I first need to make sure the distributor is stock. If it is, then find a stock tachometer and swap it out to test it.

Paco

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'78 280Z

Did you make any progress on this? I found I have a late-260/early 280 tach. If you know which modular system your ignition uses, this might work for your car.
I wouldn't expect you to buy it until you knew if it worked on your car. If it did, we'd talk cost. I could loan it to you at the next meeting, then get it back or settle up at the following meeting, depending on what results you had. That gives you a month to try it out.
It's still possible your own tach might work if you re-install an inline ballast resistor.

BTW, I found NONE of my gauges worked unless they were well grounded in the dashboard. Just letting them hang free and hooking them up to the wires didn't work for me. In order to tell whether a new tach would work, you should expect to mount it into the dashboard. AND, if you happen to have a dash-cap, you can expect a real challenge to replace the tach or speedo gauges. Most caps have a small lip which extends into the gauge nacels, and it's *JUST* big enough to prevent the gauge from sliding out forward.

Just wanted to make your day happy.

Frank

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1970 240Z

Thank you! I'll take you up on trying your tach, but as you mentioned I'll check the inline ballast resistor first. Unfortunately my dash is indeed a dash cap, so I'll simply have a few more screws to remove.

I've been wondering what was under the cap anyway. I found a great video on how to restore a severely damaged dash to show room condition and I've been thinking about it as a winter project.

I'll be sure to make it to the next monthly meeting, but if the re-install of the inline ballast resistor works, I'll let you know.

Paco

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'78 280Z

Paco ~ next meeting coming up. What progress have you made on this? Did you determine which distributor system you have, or have you tried the in-line resistor yet? Will you be at the Old Saybrook meeting this month?

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1970 240Z

Frank,

I have an electronic ignition system but I have no idea which of the 3 versions it is. If it is stock then it would be the version that came with S30's from '75-'78. I picked up a ballast resister this afternoon from Derek. I figured I would try it out to see if it makes any difference. I'll be in Old Saybrook, but probably will not have made any more progress on this. If you can help take a look and help narrow down which distributor I'm dealing with then I can at least purchase a tach from the same model year and try that approach.

I'll see you Wednesday.
Paco

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'78 280Z