New Finding: Pulsing Voltmeter while driving
Thread Starter
Drifting
Joined: Jun 2014
Posts: 3,129
Likes: 236
New Finding: Pulsing Voltmeter while driving
Recent changes by me:
CE Panel refresh, refresh of grounding points.
New observation,
When in motion, my voltmeter needle "pulses" , but not when motionless.
In motion, at 2000 rpm, the pulse rate is 90 beats/ min, will slightly increase and decrease with rpm variation, from 80-110 or so....
The needle on my gauge deflects from 12.5-13.5 volts.
Doesn't happen at all sitting motionless, regardless of rpm.
Starting and charging great...
Is my car starting to come alive like Frankenstein lol ??
Dan
CE Panel refresh, refresh of grounding points.
New observation,
When in motion, my voltmeter needle "pulses" , but not when motionless.
In motion, at 2000 rpm, the pulse rate is 90 beats/ min, will slightly increase and decrease with rpm variation, from 80-110 or so....
The needle on my gauge deflects from 12.5-13.5 volts.
Doesn't happen at all sitting motionless, regardless of rpm.
Starting and charging great...
Is my car starting to come alive like Frankenstein lol ??
Dan
Rennlist Member
Joined: Jun 2008
Posts: 4,715
Likes: 89
From: Tasmania, Australia
Here's my guess ... Sounds like you might be getting a cross feed of the speedo pulse from the cluster, which would mean that the cluster has a compromised/resistive ground, and that pulse of voltage at the ground point is modulating the voltage at the voltmeter, by backfeeding the voltmeter ground connection.
Double check/do again the grounds that relate to the cluster. Use Deoxit or similar to ensure a good connection.
Double check/do again the grounds that relate to the cluster. Use Deoxit or similar to ensure a good connection.
Thread Starter
Drifting
Joined: Jun 2014
Posts: 3,129
Likes: 236
Great place to start.... thanks....
by the way, it was pretty rewarding to see so many little gremlins that I "hadn't noticed" resolve themselves after the CE refresh, I now have dash lights, door lights, etc which I had not yet addressed separately that are now just fine.
by the way, it was pretty rewarding to see so many little gremlins that I "hadn't noticed" resolve themselves after the CE refresh, I now have dash lights, door lights, etc which I had not yet addressed separately that are now just fine.
Rennlist Member
Joined: Aug 2011
Posts: 906
Likes: 69
From: Wayne, PA, USA
Had a very similar problem, although my issue did occur when sitting still when I raised my RPMs passed 3000. It took months to figure it out, but Captain Earl helped to figure it out.
What voltage regulator do you have in your alternator? I had a KAE one, and one of the brushes didn't sit perfectly on the commutator. You could tell as the brush was clean except for a champfered edge.
When the car would run at low RPM the one brush was taking the power work easily. However as the RPMs built up, power would jump from the commutator to try brush at a frequency, blowing out the voltage well above what the voltmeter in the dash would spec.
We found it was a fault of the KAE design as several KAE VRs had the same issue. changed it to another type and the issue was gone.
Best of luck finding the gremlin!
What voltage regulator do you have in your alternator? I had a KAE one, and one of the brushes didn't sit perfectly on the commutator. You could tell as the brush was clean except for a champfered edge.
When the car would run at low RPM the one brush was taking the power work easily. However as the RPMs built up, power would jump from the commutator to try brush at a frequency, blowing out the voltage well above what the voltmeter in the dash would spec.
We found it was a fault of the KAE design as several KAE VRs had the same issue. changed it to another type and the issue was gone.
Best of luck finding the gremlin!
Team Owner
Joined: May 2004
Posts: 31,164
Likes: 4,161
From: Philly PA
FWIW as Jason points out using non standard replacement Bosch parts cans cause other issues to surface.
When fitting new electrical parts to your 928,
always use Bosch parts.
yes its usually more expensive to buy Bosch ,
but it greatly reduces the diagnostic time spent trying to figure out WTF is going on,
after.......... I just installed a new alternator or some other such event.
When fitting new electrical parts to your 928,
always use Bosch parts.
yes its usually more expensive to buy Bosch ,
but it greatly reduces the diagnostic time spent trying to figure out WTF is going on,
after.......... I just installed a new alternator or some other such event.
Rennlist Member
Joined: Mar 2007
Posts: 3,669
Likes: 76
From: Central Virginia
Dan, I'm resurrecting this thread because this issue began for me right before my 2 hour drive up to Frenzy. Were you able to resolve it? I have determined it is not the charging circuit by attaching an analog voltmeter to the hot post and an engine ground and observing while driving that that voltmeter read steadily, and at correct voltage, while the voltmeter in the instrument cluster did its little dance. I am going to take Dave's suggestion and clean the grounds again - his analysis makes a lot of sense, but would like to know what you found, if anything.
Thread Starter
Drifting
Joined: Jun 2014
Posts: 3,129
Likes: 236
Dan, I'm resurrecting this thread because this issue began for me right before my 2 hour drive up to Frenzy. Were you able to resolve it? I have determined it is not the charging circuit by attaching an analog voltmeter to the hot post and an engine ground and observing while driving that that voltmeter read steadily, and at correct voltage, while the voltmeter in the instrument cluster did its little dance. I am going to take Dave's suggestion and clean the grounds again - his analysis makes a lot of sense, but would like to know what you found, if anything.