Hi guys,

Started up my rebuilt engine and will be breaking in the engine during the coming days, but found that voltage fluctates alot when cold.
between 12,5V and 13,5V at roughly 1 Hz frequency.
After a few minutes of idling the voltage stabilizes at 14V.

What do you guys think - time for a new voltage regulator?
Actually last year, last drive before taking engine out, my water pump died, causing coolant to be all over the alternator.. So not unlikely that the alternator and/or regulator has been damaged by beeing soaked in coolant?
Or anything else could be causing these voltage fluctations?

 

Ordered a new Bosch Alternator (including regulator).
Hopefully changing these parts will fix the issue.
Just strange why this only happens when Cold / for the first minutes of running.

 

Are engine RPMs stable when this voltage fluctuation occurs?

If so it is odd. What I have observed almost all the time when cold starting my Turbo is the voltage level climbs to very near "14V" (using the dash gage) and stays there steady as the engine idles (and provided I add no electrical load like turning on the headlights or the A/C).

When I take off and drive the car the voltage level starts to drop some after some miles and on a mild day after say 10 or 15 miles the voltage level is down a fraction of a volt which tells me the battery has been topped up to replace what it lost from the start.

The only times the Turbo voltage level has not risen to "14V" right away is if the car has been out in the rain or has just been washed. In this case often (almost always) the voltage level stays at "10V" until the serpentine belt and accessory drives shed the water. The belt can emit a "chirp" once in a while as it kind of grips then doesn't grip but I know from experience patience is key and after a bit the voltage level climbs right up to where it should be and all is well.

If you tell me the engine is dry then it reads like a voltage regulator though possibly a marginal belt or tensioner could account for the variation in the voltage level until the belt warms up and grips better. Long shot I think though.

 

that'll do it i bet. i've always noticed a minor variation from startup to steadily maintained gauge numbers. the new one will ride at 14 for awhile when new until it too "settles in" at the *proper* 13.8 ( closer to 13.5 w full elec load ).

 

With the new alternator I see 14V and no fluctation.
So that did the trick :-)

 

^ absolutely works most all the time after a cpl months ( or less ) it'll probably only "stay" at 14 at startup, ( mine still does after 3 yrs..) and the sweet spot seems to be 13.8.

 

The issue is the voltage regulator. They have a heat sinc in the rear that adjusts voltage based on the engine temp. If your voltage is moving around it's definitely that.

Also the gauge is totally in accurate. Immune was showing 13.8 on the gauge but was closer to 13.3

Lastly, I'm now using and IB227 regulator from a GM Saturn. It has a setpoint of 14.7, which is much better for modern batteries, especially the lithium battery I'm running. I see 14.2 all the time now.

 

^ funny you mention that, as i dont trust many of the gauges either, but have never tested for accuracy. as long as i rarely see red, I'm good.

 

What's involved in swapping to a GM regulator?

 

To swap the regulator you have to take the alternator out as it's on the rear. Takes about 5mins to swap once the regulator is out.

The only different betweent the GM and Porsche regulator is the GM version uses a post and nut, so you need to cut the Porsche plug off and install a ring terminal. Very simple.

the regulator in the 996 has a setpoint of 14.2V where the GM Saturn has a setpoint of 14.7V. Basically it lifts the voltage .5v higher.

 

If you bought that from GM I'd be interested in a part number, seems to be a pretty common part with knockoffs everywhere! A GM part should st least have decent testing heh