Don, in response to your email.

"They" said my voltage regulator was toast because I was complaining about the bulb replacement light going on and off and the car running rough and sometimes stalling. I originally asked them to check the alternator and the battery and this is what they found. Maybe I should keep my mouth shut next time...

I think I've been had again!

What are the symptoms of a faulty v.r.?

BTW, this was a Volvo dealer and I am going to see them again about the above problem which has not gone away! Oh, the stress!

Thanks for writing.

L.

Oh, I get it. Your last post said "voltage meter," and that threw me for a loop, but you meant regulator. So my long answer about volt meters is meaningless (like so much else I say). I was confabulated.

I like Larry's analogy to a magnetic brake. The alternator converts engine power to electric power, and the regulator controls that conversion. If the regulator is cutting in 'n out, then the alternator will impose a highly variable mechanical load on your motor. One instant it'll be bogging the engine down, the next instant it'll allow the engine to speed way up. The engine control will be unable to maintain a stable engine idle speed.

The regulator assembly usually includes brushes, and you can expect them to be worn to a nub somewhere around 150,000 to 200,000 miles, more or less.

"...complaining about the bulb replacement light going on and off and the car running rough and sometimes stalling..."

I don't understand their logic of the bulb-out indicator and the VR, but I do agree with Larry's assessment about the unstable idle and the VR.

"I think I've been had again!"

Well, maybe not.

Frankly, a bad volt meter woulda been easier.

/// There are posts in FAQ's (for repair shops that keep web sites) that the brushes wearing out or failing to advance with wear can cause the light to be out when it should be on. I found this listed as a "Volvo tip" in a recent web search.

In other words the voltage regulator fails but because the brushes are not in touch with the slip rings the light does not come on. If the brushes slip forward with normal engine vibration the light would then come on until brush wear again broke the light circuit.

I don't know about you particular problem but since I read your post I wanted to give you this information.

It is possible for the alternator to act as a magnetic brake and disrupt engine idle. This particular situation might well cause that rough idle. Normally the alternator is on or off. Having it switch in/out because of a circuit fault would load and unload the engine.

Lias -

I didn't see the first post on your problem so this may be redundant or off-line. However, having no love of dealers myself, here goes.

1) ALWAYS remember that the service writer gets a commission so the incentive is other than a minimum-cost job.

2) There are two voltage regulators on board, one is in the dash and controls voltage for the gauges, to other handles the charging system. It's the latter that is in question since you referenced the alternator.

3) Don may correct me but I can't see a way that failing alternator regulator would cause rough running unless the battery was close to dead.

4) On the alternator the voltage regulator and brushes are available as a single unit, can be purchased over the parts counter, and can be replaced with very simple tools and skills. The unit should be around USD $65.

5) There is no ethical problem with getting a second opinion from an independent Volvo shop. I hope there is one near you.

Good Luck, post with your questions/results.

Bob

/// The new computer controlled alternator/voltage regulators and the simi-digital voltage regulators were developed to cure the problem of rough idle caused by the alternator/regulator.

Think of the alternator as a magnetic brake. A circuit problem in the VR or a bad cable can switch the alternator on and off. It is possible to stop an engine at idle by controlling the alternator demand.

OK. My newest is a 1988 240GL, and I was "Off my turf". I'd looked into my WorldPac catalog and saw that the voltage regulator p/n 3523710 shows OK for B21, B23 and B230 from 1982 to 1993, but it's an old book. The logic holds once one realizes the relative size of the load that can be put on the alternator while at idle. While it feels like a rough idle (problem with engine) it is acutally a fluctuating load, right? Thanks for the update.

Regards,

Bob