Alternator D- ????

[patkeefe]

Why do some of the CIS devices ground through D- on the alternator (or the voltage regulator)? I'm just curious as to the principle beind this.

I just rewired the engine compartment, and I get some odd things at start up...gen light will stay on for a few seconds, and the tach will act erratically for maybe 10 seconds, but then it settles out. I can't figure out why this would happen. There are still some bad circuits from PO wiring some stuff, like 85 circuit at the airflow sensor not working. This tach thing is annoying.

Pat

[304065]

Pat,

The WUR relay is energized by D- and D+/61. Those are the alternator negative and excitation circuit, respectively, and CIS uses them so the WUR can heat up before the car is started. When you turn the ignition on, current flows from the battery through the ignition switch and into the warning lamp bulb, through the "blue wire" to D+/61, where the voltage regulator senses that the voltage it's seeing on that terminal is less than the 14V "set-point" of the regulator, so the VR sends that voltage to the DF wire, through the brushes to the rotor and to ground. This energizes the field, inducing a current in the stator which gets rectified by the main diodes and fed back into D+/61. If the voltage present at D+/61 is equal to what's flowing into the circuit through the blue wire, the bulb goes out because no current is flowing in the circuit. Likewise, the WUR relay would de-energize at that point.

The reason for the ground there is to make sure you have a very precise voltage-- if you grounded somewhere else, say up by the battery, the distance and conductivity of the chassis would give you a different potential difference. It's also convenient because it's in the engine compartment.

[boyt911sc]

Originally Posted by john_cramer

Pat,

The WUR relay is energized by D- and D+/61. Those are the alternator negative and excitation circuit, respectively, and CIS uses them so the WUR can heat up before the car is started.

John,

Are you sure? In Pat's case, the WUR/ AAR/TV (if any) and FP will be energized when the motor starts to turn. There is NO power to enrgize these CIS components when the motor is not running. FYI.

Tony

[patkeefe]

John:
Thank you. My current configuration is that the FP relay (#1 above) is out of the picture, as the 85 circuit doesn't break when I lift the airflow plate. I have a kill switch jumped from 87a to 30, so 85 and 86 are out of the picture. Kill switch brings on the FP, and energiges all of the CIS functions as needed.

My tach issue may be a result of the MSD device added as part of the RPM Solenoid Switch, which delays boost until whatever plug in module is in the MSD tells it. Otherwise, I have 6 pin Bosch ignition, fully functional.

So, adding a supplemental ground in the engine compartment at D- should harm nothing? My "new" Valeo alternator had this terminal stripped in the body of the alternator, which I drilled a tapped to 6mm a while back, but have had a distrust in this connection ever since.

Pat

[304065]

Tony,

Look at the circuit diagram above, the relay coil for the WUR is energized by D- (battery negative) and D+/61 (excitation circuit). Power flows in D+/61 when the engine is not running with the ignition turned on.

The fact that Pat says the gen light stays on proves it, the relay coil might be pulling the voltage down so the light stays on even though the voltage has come up-- a simple voltmeter test through a start would verify. Also, the tach bounce is a voltage fluctuation.

[304065]

Hmm. . . so for a later 'SC (using th '82 diagram from the main page) it's different-- the fuel pump relay is wired up opposite what you would typically find in DIN 72552--

30- power supply to the fuel pump, gets its power through the relay wiper from

87- normally open contact, when the relay is energized, this is fed with power from the starter terminal 50

87a- normally closed contact-- when the relay is NOT energized, this gets power from the ignition switch terminal 15 through fuse 16-25A

Terminal 30 also feeds the warm-up regulator and supplementary air valve.

Have to do more research as to why the two different power feeds. . .

Anyway, my answer doesn't change, they still all ground to D- as you can see below, but the function changes from the 73.5- to the later car somewhere along the line.

[equality72521]

Originally Posted by john_cramer

Power flows in D+/61 when the engine is not running with the ignition turned on.

That's the key.

[boyt911sc]

Originally Posted by john_cramer

Pat,

The WUR relay is energized by D- and D+/61. Those are the alternator negative and excitation circuit, respectively, and CIS uses them so the WUR can heat up before the car is started.

John,

Let's say your above statement is correct, that the WUR and AAR are energized before the start-up. If this was the case, then the fuel pump will be also running before the motor starts. Why? Both FP and WUR are commonly connected at terminal #30 of the fuel pump relay. If one gets power, then the other component is energized too. Follow my logic?

That's why I said that's not the case. Let's analyze and review the wiring diagrams of CIS motors from '77 to '83. Have you actually checked the WUR for power when you set the ignition switch to 'ON' position? There is no power to both FP and WUR when the key is at ON position. How could the WUR get heated when there is no power supply?

Lastly, if you're correct, then going back and re-visiting my CIS 101 is my next option. And be thankful for this discussion. Thanks for the feedback.

Tony

[patkeefe]

Tony
I've had a long day and not given this much thought. However, you are correct. Power to the FP and WUR will come in at 87 of the relay in START (50), and switch to 87a (15)when he car is verified to be running through the 85 and 86 terminals. Tony, as you know, my car is jumpered, as though it were for a FP test procedure. As long as it is jumped from 30 to 87a, I will get power to all the devices. Downside is overrev protection, which I have never muched worried about.

John, these diagrams are very helpful, much better than the Bentley diagrams. I appreciate your explanations. I have to go out of town for the next couple of weeks, so I'll have time to think these gremlins over.

Pat

[911quest]

Originally Posted by patkeefe

Why do some of the CIS devices ground through D- on the alternator (or the voltage regulator)? I'm just curious as to the principle beind this.

I just rewired the engine compartment, and I get some odd things at start up...gen light will stay on for a few seconds, and the tach will act erratically for maybe 10 seconds, but then it settles out. I can't figure out why this would happen. There are still some bad circuits from PO wiring some stuff, like 85 circuit at the airflow sensor not working. This tach thing is annoying.

Pat

The theory is the D- is the ground field created by the Alt. The fuel pump relay must maintain a ground for 87 to stay closed and if the car died the alternator would stop spinning and would no longer be creating the negative field and the relay would lose its ground and 87 would then become open and the car would no longer run do to no fuel being pumped.....

[patkeefe]

Thanks Tony P. From the wiring diagrams above, it seems that only the airflow switch would drop out the 87a circuit by pulling in the 85/86 contact, which would then kill off the ground to D- as you describe. So, that seems to be the answer.

Now, to figure out why my airflow switch stays closed, even if I pick up the plate. It used to work normally, before I put in the stainless steel airbox...

[rick-l]

Originally Posted by john_cramer

The WUR relay is energized by D- and D+/61. Those are the alternator negative and excitation circuit, respectively, and CIS uses them so the WUR can heat up before the car is started.

Let's review the voltage levels on the D+ and D- terminals.

D- is a hard connection to ground

D+ is the output of the diode trio that goes into the regulator and also to the light on the dash.

• With the alternator not turning
  • the diode trio in the alternator is back biased and essentially not there.
  • the regulator is calling for charge and has the field control turned on
    • This provides a low impedance path to ground through the regulator.
      • This is why the dash light is on
      • This puts about 0 volts on both sides (term 85 and 86) of the relay coil in the picture, and the relay is off
• When the alternator turns the diode trio rectifies the alternator output and the D+ terminal will have battery voltage on it.
  • The dash light goes off.
  • This puts about battery voltage on term 85 and ground on term 86 of the relay coil and it turns on
    

So the WUR is only heated when the engine is turning and adding heat to the block, not when you are cranking and trying to get it started. Very clever.

Originally Posted by john_cramer

[patkeefe]

One other annoying problem...which has been recurring for a year or so...
I checked on some stuff today. I noticed with the car idling in the garage, that the wires to the WUR will tend to get very very hot. Physically smoking hot. It has fused these wires together before, which is one reason I rewired the engine. Battery voltage with the car not running is 12.54V. Voltage across the D-/30 feed to the WUR and AAR is 11.57V. In the past, I have run with the AAR disconnected, which solved that problem, but then I have no AAR functionality. When the engine was out this past month, I checked out the AAR, as I figured I may have to rebuild it (Good post by Mysterytrain, BTW). However, the AAR functioned well on bench test, resistance was per specs, and it opened and closed as it should, so I said it's OK.

So, I would assume I am getting a large current in the WUR/AAR circuit to cause the wiring heating problem. Is the voltage drop the cause of the current increase, according to V=IR? I wouldn't imagine a 10% drop in voltage would be indicative of such a seemingly large increase in current.

I hate electrical problems. After I shovel some snow, I'll go back and get some more readings.
Pat

[Mysterytrain]

Pat, Check the resistance of the heating elements in the AAR and the WUR. If they are low, like single digits, they are starting to look like a short..and the wires will get hot.

[patkeefe]

Ron:
I read your AAR thread, and I have the resistance you have in the AAR, which was about 32 ohms, IIRC. My WUR is assumed OK, as it is a new special 930 model from Brian Leask. My old WUR exhibited the same tendencies.
Will the resistance in the heating elements change during use? I would think not, but I do have something weird going on.
Pat

[Lorenfb]

"This puts about 0 volts on both sides (term 85 and 86) of the relay coil in the picture, and the relay is off"

Not totally correct! The relay is in parallel with the field winding and as such
does draw some current which in many cases causes the alternator to not
start charging. This requires adding a resistor in parallel with the alternator
light which also solves the typical alternator non-start situation at idle,
i.e. the engine must rev to 1500-2000 RPMs on some older 911s.

The better approach, as used on the 911SC, is to run the WUR and AAR
off the same voltage as the fuel pump regulator, i.e. controlled by the
sensor plate switch.

[patkeefe]

My car is an SC, a 78 MY. I think my biggest problem at the moment is that I just now pulled my WUR apart, and found the internal wiring, and male Amp Jr connector totally fried in the WUR. It will be hard to tell from the attached pictures, but the WUR electrics are toast. That explains the weird reading I alluded to earlier.

The better approach, as used on the 911SC, is to run the WUR and AAR off the same voltage as the fuel pump regulator, i.e. controlled by the sensor plate switch.

That is exactly how mine is wired. Currently, the airflow plate switch doesn't break. It used to, until last year when I had the engine removed and replaced. It still worked up until a few months ago, when I still had the plastic airbox, and not the current stainless steel airbox. At that time I had full function of the FP relay, and it all worked as Loren describes above. I will note that I never had rev limiter function, which seems to be a simple circuit to energize 85/86 coil, and kill off the fuel pump temporarily. Then, the FP relay function quit working, and new FP relay didn't fix the problem. I shook out just about all of the 30/D-/85/86/87/87a circuits, which seemed intact, but still had no FP relay function. So I put in a kill switch, essentially a jumper. I can put a FP relay, stripped of its cover, into the socket, and watch the action: key on, the coil is energized, won't de-energize when key is in start position, run position, or by lifting the plate.

I think I am overlooking something simple here; maybe a bad wire, or an intermittent ground loss or short in the trunk/fusebox area.

[patkeefe]

Returning to this for a minute...
My WUR has been rewired with a new heating element, and is on the way back to the Garden State. Are the heating elements polarity sensitive? I have tested the AAR on either polarity, and it worked the same on both. I am assuming that these heating elements cannot be wired backwards; after all, it is just a fancy resistor.

The factory wiring on the Amp JR to the AAR has two brown wires, although my girlfriend says one has a very faint red stripe on it (I will assume this to be positive).

Thanks!
Pat

[patkeefe]

So, after two years of my car apart, I am here in the garage putting it back together. I was just looking to finish my wiring, and said to myself "is the WUR polarity sensitive?". So I did a search, and I found this. I am evidently still as dumb now as I was in 2007!

[boyt911sc]

Pat,

What's your problem now with the WUR? I'll be more than happy to assist you in your troubleshooting. First, check the resistance (Ohms) of the WUR before you install it. Second, establish ground to terminal #85 (FP relay socket). This will be a simple plug and drive project. It's been a while since I last saw you.

Tony