I thought the car was an S4? Did you change the CPU on the car as well?

 

Gah... my fault this time.

Honestly, don't know yet (about the CPU, this is a franken-car)... guess I'll have to find out tomorrow. Yes, the car is an S4, with multiple S5 and other harnesses thrown around. I'm weeding them out one by one. AGreen knows what my engine bay used to look like I have good notes here, certainly enough to keep me busy. Thanks for your help (once again). Much appreciated.

 

I should say that the charging system has never really worked correctly since I bought the car... this will make me pretty happy when its corrected!

 

Is there any reason these 2 wires would be causing the 15 volts issue?

 

Not sure, but the alternator can self excite itself if the rpm is high enough so it will then create voltage output even if the wire to excite it were disconnected. The voltage regulator might be the cause for the above average reading.

 

Thought so. Jeez, I want to hurry up and get home so I can start messing with this. Hope I'm not getting my hopes up for nothing...

 

CPU is marked FB05, and wiring is as you said (W/B above L)... so safe to say its an s4 CPU.

I'll go test the voltage on the W/B wire in a sec.

 

W/B wire at the CPU shows 11.3V with key to on... 14+V with engine running. does this mean that the relay is bad? Its just going across a RL circuit, and a diode...

EDIT:

So the voltage is supposed to be 12V at the CPU.

So really... the only thing left to do is essentially hook up the alternator wires to the known correct/good ones.

 

Done!

W/L has 12V constant... W/B has... some low number of volts.

Will have it load tested again tomorrow!

 

So the W/B wire is backfed by the relay. And the Meter fuse receives voltage from the charging system so w/the car running the voltage increases.

 

And this is w/the key to on I suppose?

 

Like a half of a volt... strange. But without the alternator's load on the CPU, that wire had about 11.5

Yes, with the key to "on."

 

When the W/B wire is connected to the alternator w/key to on the alternator then drops the voltage close to a ground level which then causes the idiot lights to go on if you had them. So if the alternator was dropping the voltage from 12 volts unconnected to low voltage when connected then it is working properly as it relates to this specific wire.

 

Then with the car running, the voltage should return to around 12 volts to (in theory) shut the charge light off... Right?

 

Correctomundo!

 

Well that sucks. Voltage remains low (.5V) while running, so I guess something inside the alternator is jacked.

At least the wiring is fixed so I wont destroy another alt... but hey, lets see what the load test says tomorrow...

 

No update... Weather was too crappy. Still have low voltage on w/b

 

I assume you've already gone through with the alternator diagnostics outlined in the FSM?

http://www.rotaryheads.com/PDF/2nd_g...cal_System.pdf

(starts around page 8)

 

If you measured the terminal at the alternator w/the W/B wire not connected but the other two wires connected then it might tell you if the low level voltage seen on the W/B wire is actually coming from the alternator or the wire is accidentally grounded thus causing the low voltage.

 

New load test results:

Charging system:
Good

No load - 14.04V 7.6A
Loaded - 13.78V 6.7A

Ripple: 31mV

Drain test: 3.46A

The drain test before correcting the two wires was at .5A (with car off). Just hooking those 2 wires up added 3A? Which of the two might be the culprit? Could there be a short inside the alternator maybe?

 

Checking whether the W/B is ground accidentally or not would probably be a good start.

 

Something is up... I started going through the FSM tests...

For the first time ever, the "fan" LED and "shift up" light in the instrument cluster came on.

Maybe the wrong W/B wire at the CPU... I'm all screwed up again. FML.

When I disconnect the harness from the alternator, the lights go out... reconnected, they come back on.

And Satch, to give you an answer, W/B had no ground. I'm going down the "wrong wire" road right now.

 

I need to mention that I ran a wire from W/B at the CPU to alternator's W/B wire. There is nothing else connected to this. When I disconnect this specific wire from the alternator, the shift light and fan light go out.

 

In post #34 you said it had a low number of volts. I then asked how much. You replied .5 volts. In this car anything close to zero volts qualifies as a ground signal. The low voltage that is supposed to be on the W/B wire w/key to on and engine off is considered a ground. The W/B wire has a ground as stated above or it has a ground w/the engine running if there is a malfunction in the alternator otherwise it is supposed to be 12 volts or so. You state that the W/B wire had a low voltage reading w/key to on and engine running thus the problem is from one of two sources, either the alternator is problematic or the wire is accidentally grounded.

 

Then the alternator is problematic. There is no possible way the wire is accidently grounded - I can see the entire wire.

I've had a lot of RX7s... this deal with the shift up and fan light coming on, they come on in about the same amount of time after I turn the key as the idiot lights would go out after turning the key on any normal RX7. Too strange.

I'll borrow an alternator from someone and see if I can rule that out.