85fortheDrive

About once every 10-12 starts, the voltage meter on our 84 5-spd will go goofy on start up. The typical goofy is that no voltage will show. Sometimes the voltage runs all the way up to 16V. I have confirmed that this is not just a gauge issue; bulbs and headlights dim and brigthen correspondingly to the fluctuations. The problem usually goes away after a few minutes.

I'm wondering if this is due to a problematic ground. If so, do I have all the ground points listed here?

1. Back hatch - strap from battery
2. Above central electric panel
3. Under dashboard on driver's side
4. Engine to chassis under car on passenger's side

Any others to check?
Suggestions to make sure the conductivity is good?

Or am I off base with this investigation?

Alan, if you reply, can you also send a can of heat?

Peace,
Tim

Bill Ball

The 84 wiring diagrams don't include a map for the ground locations. However, on each page they list grounds...

-Valve cover (I and II)
-Steering console
-CE console
-Body front left
-Body front right
-Firewall
-Body (rear tailights)

Probably worthwhile just to do Wally's annual electrical maintenance.
http://www.nichols.nu/tip725.htm

Also, pulling the pod to have look at the electrical board and clean up the contacts might fix this.

Alan

Tim - OK - we have heat again in Phoenix (came back last weekend) so I'll send some off to you...

If you can confirm you are seeing voltages really surging up to 16v its almost certainly a regulation issue. For the alternator to generate 16v for any appreciable period of time it really has to be a problem with the alternators regulator - this can be related to a poor battery connection - since the regulator relies on a good battery - but the only connections that count here are the battery ground, the alternator ground (via case) and the battery positive connections from the battery to the starter to the alternator.

The most likely culprit is the battery ground strap in my opinion (since presumably the car still starts OK). I would get a replacement strap or monitor the voltage from the battery negative post to the ground point directly when the lights appear to dim or get very bright - you may need to be on a 2v or 200mV range but if you see this spiking to more than milivolts you have a problem with the strap.

Alternatively just get a new strap and see how it goes - or flex the ground strap by hand and see if it makes any difference...

If the voltage is not really getting to 16v and only appears to fall below ~13.5v occasionally that could be a grounding issue elsewhere - say the pod grounds...

I assume when the lights dim & get bright this is all of them - not just the headlights?

BTW 16v is very bad for the electronics and will reduce lifetimes substantially...

Alan

Bill Ball

I was going to say the same, but he noted he gets ZERO readings as well at times.

j.kenzie@sbcglobal.net

Hi Tim,
My little knowledge agrees with Alan's (duh!). It sounds like the voltage regulator. Depending on the alternator, it may be an external item or an integral component.
BTW how are you doing?
How is house hunting?
Best of luck. I keep driving through the snow. I plan to install the Porken tensioner this summer so maybe we can set up a get together.
Good luck

Garth S

If there are a lot of miles on the alternator, a well worn carbon brush/slip ring set can cause erratic charging issues - as they skip along the rotor.

I had a true 16v spiking issue last fall that became a hair puller: while that was a most unusual case, it could happen twice: short story version is that one of the three stator coil windings was contacting a case through bolt: eventually, the wires insulation erroded, creating an intermittant short to ground before the negative diode plate**. This drove the regulator nuts ....

** to make the long story version, the alternator is a 3-phase device, wound in a WYE configuration in our case. Each phase winding, located staggered in the stator, feeds two diodes, + and - ..... for a total of 6 in two plates of 3.
With one shorting to ground, there was an AC leakage that was creating havoc in a regulated 14V DC world.

Alan

Of course if the voltmeter reads zero and the car is still running it is for sure lying to you. Below about 8v its very unlikely the car will run properly. The problem is that a connection issue to the gauge can't cause the voltmeter to see more voltage than the alternator generates - only less... Now it may be inaccurate so you need a secondary independant (DMM) measurement...

So you may possibly have 2 issues going on - verify the high voltage issue first - its potentially the most damaging... and zero volts is not really feasible while running

Alan

928FIXER

Tell me...are we using that highly accurate lab grade instrumnet that is located in the dash for these observations????

85fortheDrive

Thank you. Experience tells me that in order for it to arrive still fresh, you should pack the the can of heat in dry ice...

I will order a new battery ground strap. Simple enough and a legitimate first step. All the bulbs brighten and dim with this fluctuation, from headlights to instrument lights. The alternator is new, as some of you know. I purchased a new one from Rog a few months ago. I have a new battery as well, since the previous one had a bad cell. The battery is an identical replacement to its defective predecessor. Wonder if I should switch to a better brand of battery. Bought it at Murray's Discount Auto Parts, but I can't remember the brand name.

FWIW, this problem RARELY occurs on a cold start. It's most likely to happen when I'm starting the car after it's been off for 15 minutes or less.

Thanks as always, Alan and Bill.

JHowell37

FWIW, you can get a generic ground strap at just about any auto parts store that will work fine for diagnosing your problem. Those flat factory straps take up minimal space but the wires inside tend to corrode and break up over time causing shorts. It may not be the solution to your particular problem, but it's probably better to spend $10 to eliminate that suspect rather then $60.

I believe there's another ground point inside the car in the rear passenger-side corner. At least there is one there on the '85.