Voltage regulators, and tachometer fluctuations

[Inf]

Can anyone tell me if this voltage regulator is original in my 3/72 240z?

I bought a replacement at Napa thinking it might solve my bouncing tach problem, but it didn't. So i'm guessing this one still works fine. The replacement has the exact same housing and same style of plug.

The one that was there to begin with also had an inline fuse on one of the wires. This Napa/Echlin replacement didn't.

I replaced my 240z tach (which was shot anyway) with a 280z tach and I keep getting an erratic tach. It sits steady at idle, but if I really put my foot into the gas while driving, the tach will spike then slam back down to zero and start moving around erratically for a sec, then if i am cruising it will level off probably around the rpm I am running at.

My theory was that the voltage being delivered to the + terminal on the coil was changing as a function of the acceleration of the alternator innards, which made the amplitude of the pulse on the - terminal that this 3 wire tach reads change as well.

A new voltage regulator later, and it seems this theory has been shot down.

Other things I investigated were

-poor wiring on the signal line, ran new 14g wire, no change

-poor ground connection, ran a new one, no change

-'2.2k ohm' figure for signal line inline resistor being wrong? bought a rheostat for 0-10kohm and fiddled with it, 2.2k seemed the best since it kept the needle steady at a certain rpm, but no setting managed to get rid of the spike on acceleration.

Well, this post started out just asking what the original voltage regulator looked like, and who made it, but it ended up taking a whole different

direction.

If anyone has any other ideas on what the deal with this tachometer are, I would be GLAD to hear it! I am running pertronix ignitor with a pertronix flamethrower coil with the ballast resistor in place. I tried the original coil, and it still did the same thing.

I'm getting pretty close to giving up and just buying an autometer tach, but I want to keep an original looking set of gauges

[Bambikiller240]

Andrew:

The OEM VR on a 72 240Z would not have that inline fuze.

A replacement VR that I bought on eBay (pic attached) has a similar label to the one in your picture, but no fuze. It is an OEM style VR that can be adjusted.

If you want, I can take a pic of my original VR. I'm not sure there are any identifying marks/printing still visible after 32 years. Let me know.

[gundee]

Andrew

You will have to go back to a 240 tach. The 280 tach is not interchangable.

They work differenty and are wired differently. The 240 connects to coil + and the 280 connects to coil -.

[Inf]

I Connected it as it would have been connected in a 280z, as per brian little's instructions.

Signal wire goes to - post on coil with inline 2200ohm resistor

positive post to ignition 'on' +12

ground post to ground

and made sure to leave the plug with the original inductive loop in the dash so that the coil would receive the +12 it needed since it goes through the loop that was formerly part of the 240 tach. As a side note, the 240z tach did the same thing as this one is doing, so now that i think about it, i should probably look for another problem. maybe a faulty pertronix unit? hrmmmmmm

That will have to wait a while though since I am about to move to another city tomorrow.

[gundee]

Which site is Brians? I would like to read that. Sometimes I have to draw it out on a piece of paper before I get it. Thats interesting.

Thanks.

[Inf]

His site is here : http://geocities.com/zgarage2001/

It seems like he has changed his content though. He is no longer recommending replacing the 240z tach with the 280z, but rather with an autometer. Maybe others had some similar problems? I know of one guy on zcar.com who had the exact same problem as I am a few years back. I emailed him and actually got a reply, he eventually sold the car having never solved the problem. :disappoin

I am thinking of switching to the autometer. There are some other things i'll investigate first, but it seems like when you're dealing with an old tach like this, there could be any number of things wrong with it that I dont even know enough to figure out.