The fun never ends: bouncy tach, car dies, alternator ID?

[mikesarge]

So I took the wife out today to show off how great the car is running now that I’ve spent a fortune on an engine and transmission rebuild.

Great timing. Got the car warmed up, then the tach starts bouncing around intermittently, then dying when I put in the clutch. Takes 20-30 seconds of sitting to restart. Happened on one of the busier roads in town, middle lane, that sucked.

I did get it home, wasn’t much fun with it dying every few blocks, but we did it. I let it sit for a couple of hours to cool down, then measured voltages. Everything looked fine at idle, but the engine wasn't as hot anymore. Searching reveals that the earlier symptoms are consistent with a dying regulator, where voltage spikes cause the CDI to go haywire with high voltage spikes, but the dying and inability to start seems like it could be something more, open to thoughts.

Anyone familiar with this alternator? The only info I can find on it was a single post on this forum about shops in Australia. Should I just replace this regulator and put it back together? The windings look essentially new, everything feels tight, so my best guess is the regulator has crapped out, based on the bouncy tach.

[93nav]

I assume you don't have a voltmeter installed in the car since you did not mention it. There are cheap voltmeters you can buy that go in the cigarette lighter socket. Real cheap on e-bay, less cheap at your local autoparts store.

Go to have anyway, not just when there is a problem.

There are several threads on the topic on Pelican.

[DaytonaCoupe66]

You likely eliminated this already if you have the alternator out but on my 930 with similar symptoms I found the ground wire from the alternator to the engine case has corroded at the bolt on the case. I had the alternator tested and all OK so went back in and found the bad ground disguised to look like it was fine. When wiggled it broke free.

[MichaelSJackson]

First let me qualify everything I'm about to post. I'm terrible at electronics. I can figure out the plumbing of wiring, but that's it.

When I had the "bouncy tach" problem, it ended up being diodes in the built in regulator. My tach was more than bouncy; it would also run backwards (jump to ~6000 and then go down as the rpms went up). I managed to limp the two miles home.

Anyway, that's what I was told by the shop I found. I had to find one that knew about the older electronics. Was directed to it buy an older, established air-cooled Porsche shop.

I do think it resulted in damaging the tach itself. Afterwards, one of the dampeners in the tach was fubar and it would bounce when I came off the accelerator. Sent that in to a speedo shop to fix.

[mikesarge]

Originally Posted by DaytonaCoupe66

You likely eliminated this already if you have the alternator out but on my 930 with similar symptoms I found the ground wire from the alternator to the engine case has corroded at the bolt on the case. I had the alternator tested and all OK so went back in and found the bad ground disguised to look like it was fine. When wiggled it broke free.

The ground to the engine case is split wide open, and I planned to address that as well, but didn't consider that as a possible primary and/or concurrent cause of these symptoms. Good to know.

I haven't been able to find anyone in town who can test this alternator. The only shops in the Portland area that have testing equipment are the FLAPS folks, and their equipment is not compatible with this kind of alternator.

The regulator was only $30 for this alternator, based on the bosch part number, so I've ordered one and hopefully I'll be able to test both soon.

[Ok here we go]

If you're looking for a reputable alternator repair place and don't mind shipping or driving north to the Seattle area, Romaine Electric is where I had mine repaired a few years back.

I had a bouncy tach, and replacing the VR along with making sure the grounds are clean made the difference. I used a unit made by Valeo (OEM but made in China if you can believe it). Although, it did take about a month to get because it was dropped ship straight from Germany by way of Florida. Didn't want to chance a unit made by HuCo

[pkabush]

There absolutely has to be a shop in Portland that can test your alternator. I’m sure someone will chime in with a name shortly.

[mikesarge]

Originally Posted by pkabush

There absolutely has to be a shop in Portland that can test your alternator. I’m sure someone will chime in with a name shortly.

I hope so! I spent quite a bit of time between the google machine and the telephone and couldn’t find a single business that is both 1)still in existence and 2) capable of spinning an alternator without a pulley on it.

[spoke]

Originally Posted by mikesarge

...then the tach starts bouncing around intermittently, then dying when I put in the clutch.

I had a similar bouncy tach and then dying engine but nothing having to do with the clutch. Turns out the green wire of death to the distributor was shorting out.

When this is happening and you put your voltmeter on a 12V wire (maybe the cigarette lighter) did the reading jump around?

[mikesarge]

Originally Posted by spoke

I had a similar bouncy tach and then dying engine but nothing having to do with the clutch. Turns out the green wire of death to the distributor was shorting out.

When this is happening and you put your voltmeter on a 12V wire (maybe the cigarette lighter) did the reading jump around?

I didn't ever get a solid test with the bumpy tach, because I got it home, died as it rolled into the spot, and I let it cool down for a bit before I got back to testing. At that point the issue had disappeared. I also wasn't about to drive it anymore, given the highly stressful experience I had driving it with it dying every couple of blocks.

Based on my research it looked fairly conclusive that it was the voltage regulator. Now I know that it could just as well be the green wire I guess.

My green wire is the one-piece type, as opposed to the kind with the connector that our host sells. If my problem persists or returns once I get the new VR installed, I'll next go to the green wire. bleh. I hate throwing parts at a problem.

[spuggy]

Originally Posted by MichaelSJackson

I do think it resulted in damaging the tach itself

There's 15V capacitors in both the tach and the speedo, IIRC. They don't much appreciate being fed more voltage than that on a continuous basis. Like when the regulator goes screwy.

They also just get old and eventually die; probably more likely to do that if they see voltages higher than they're rated for. Replacing with 35V caps isn't a bad idea.

[JSV798]

Originally Posted by 93nav

I assume you don't have a voltmeter installed in the car since you did not mention it. There are cheap voltmeters you can buy that go in the cigarette lighter socket. Real cheap on e-bay, less cheap at your local autoparts store.

Go to have anyway, not just when there is a problem.

There are several threads on the topic on Pelican.

My 78SC had a bouncy tach for years until I read on this forum that I should get a voltmeter and plug it in the lighter socket. Sure enough it read 18+ volts while the tach was swinging; new regulator fixed it. Without this forum I'd probably still be driving around with a bouncy tach as it would go away after a couple of miles from cold.

[spoke]

Originally Posted by mikesarge

My green wire is the one-piece type, as opposed to the kind with the connector that our host sells.

The green wire on my 930 was also a one piece wire. The weak point of these wires is at the connector to the distributor. The wire takes an almost 180 degree turn out the distributor in a very tight and hot area. Over time the insulation hardened and broke off.

The test for this is very simple. Pull the connector off of the spark unit and find the 2 wires going to the distributor. Put your ohm meter across these wires and measure resistance. It should be in the 40-80 ohm I think. I would read 50 ohm then zero when I jiggled the wire near the distributor. You'll need to clip the wires on the connector so you can measure resistance as you jiggle the wire. An assistant also helps so they can hold the DMM leads on the connector while you mess with the wires.

[mikesarge]

That’s excellent- thanks!