OK, now what? (charging system question)

gjp1960 · 05-20-2004, 06:14 PM

I have a 1973.5 911T, and a few weeks back the generator light came on. I checked alternator and it was fine. Suspected the external voltage regulator failed and picked up a similar model from a donor car. The original one was a Marchal SEV 14v, and the replacement was a Motorola SEV 14v.

I installed the VR this evening and started the car. It functioned perfectly, and I was pleased to see that the gen light was no longer on. I drove it around town a bit to warm it up, about 10 minutes or so. Then I turned onto a county road for a nice evening spin at highway speed. As soon as it hit about 3500 rpm, the engine sputtered significantly and the tachometer gauge jerked over to about 7000. It had never missed a beat in the past so I found that very strange. I tried it again, and same thing happened. I drove slowly back home and parked it. Batteries seem normal, no excessive heat.

I have no idea what could have happened. Was I wrong to replace the voltage regulator with anything other than new? Could this have done any damage?

Any insight would be appreciated greatly!

Greg

Early_S_Man · 05-20-2004, 06:58 PM

Greg,

Without system Voltage measurements ... it is impossible to discern what happened.

The tach could have gone crazy from either high or low Voltage ... battery OR regulator problems ...

No, I don't think there is aproblem with trying a used regulator, since SEV = Motorla, same product, markings vary!

Just what exactly did you do when ...

Quote:

I checked alternator and it was fine.

Did you pull the alternator and have it checked at a shop?

Check the battery Voltage before starting, system Voltage at idle, above 2000 rpm, and during a test run ... and give us more data to work with!!!

stlrj · 05-20-2004, 07:05 PM

It's possible your alternator brushes are worn down to where you have erratic charging issues like not charging one moment and over charging the next which could effect the sensitive electronics in your CD ignition.

Joe

RoninLB · 05-20-2004, 07:30 PM

If you have a problem finding fault with routine testing you may have a noise supperssor going kaput. They came w/ external regulators. If so just remove it and install the plug directly into the regulator.

gjp1960 · 05-20-2004, 08:41 PM

Thanks for the replies. I removed the alternator and had it checked at a shop. I had new brushes put in as the old ones were getting worn.

I will get some readings and post again later.

gjp1960 · 05-23-2004, 05:41 PM

I took some voltage readings on this.

The voltage at the battery is 12.5v with the car off, and 14.5v idling. When I slowly increase rpm, the voltage at the battery increases as well. At about 3500 rpm, the engine starts to sputter and tach goes berserk as before, and the meter is nearly up to 16v. I should not be getting that high of a reading, should I?

At any rate, I put the old voltage regulator back in and it runs fine. No sputtering and no wacky tach movement. I think the wise move at this point is to get a brand new replacement voltage regulator and not mess around trying to find another 30 year old one.

If anyone can point out something I am missing on this, I would appreciate it.

Thanks Early S Man, stlrj, and RoninLB for your help.

Greg

Randy Webb · 05-23-2004, 07:11 PM

definitely not - that voltage reg. would have cooked your battery.

RoninLB · 05-23-2004, 07:25 PM

Quote:

Originally posted by gjp1960
I tach goes berserk as before, and the meter is nearly up to 16v.

wisdom in the explain.
I love these tachs for many elec. reasons they can go berserk.

It gets my attention faster than the dull red light.