Here's One For The Books!

Maintenance/Repairs
1

Vehicle: 1996 Acura TL, 2.5L, 5 cylinder.

Complaint: Vehicle loses electrical power depending on how long it’s driven and the electrical load on the alternator.

The vehicle was towed to the shop with a totally failed electrical system. Meaning no power at all.

Found 100 amp battery fuse blown.

Replace the fuse and vehicle starts.

Test charging system: No output from the alternator.

The alternator output is controlled by the ECU and the Electrical Load Detector. Here’s the wiring diagram. http://www.justanswer.com/uploads/Themaxview/2008-08-05_151314_acc.PNG

Remove the alternator and bench test it. Voltage regulator no good. Replace the alternator. Alternator now puts out 14.5 volts at idle but as the electrical demand becomes greater voltage from the alternator drops to battery voltage.

Hook a scanner up to monitor voltage control and output. Scanner cannot communicate with vehicle. Bad ECU.

Replace the ECU and now scanner can communicate with vehicle.

Check charging system with scanner and all works properly except for output from alternator.

Check for a failed ELD. Here’s that procedure. http://www.rywire.com/catalog/images/troubleshooting/code20-eld-test.jpg

ELD checks good.

If you disconnect the white/green wire from the back of the alternator it removes the ECU and the ELD from the circuit and the charging system operates as a conventional charging system. Remove the wire, still the same.

Now after doing all this diagnostics and repair, what is preventing the alternator from keeping up with the demands of the electrical system?

And when I tell you, you won’t believe it. The son didn’t when I showed him.

Tester

2

Come on, I hate waiting.

3

I’d want to see some voltage drop testing before I hazard a guess, but maybe a poor cable connection somewhere or a battery problem? You don’t say anything about battery testing here.

Also with the 100A fuse blown and a fried Honda ecm (pretty rare for me) I’m thinking someone may have tried to jump start backwards?

4

The battery was tested three times and showed good. And for yucks and giggles a known good battery was installed. Still no joy.

Tester

5

Hmm, no battery problem, no voltage drops, how about some aftermarket accessories overloading the system?

When I guess this one right I’ll tell you about the underdash fire that was caused by the air filter.

6

The vehicle had an aftermarket amp connected to the battery. That was the first thing that was disconnected before proceeding on to the problem.

Tester

7

I guess the clue was “son”.

8

The only clue with “son” is, he’s an auto technician. And he’s never seen this before.

Tester

9

Anything To Do With Spiders ? Am I On The Right Track ?
CSA

10

Hah! Has nothing to do with spiders.

I wish!

Tester

11

This kind of stuff is fun (not for the person wrestling it though) and I’m going in several different directions as to the cause. I’ll think on it some more rather than shotgun an answer. It’s got to be something so simple …

Don’t provide the answer too quickly as that spoils the challenge. :slight_smile:

12

I’ll give up. The red/white wire keeps coming to mind as a potential cause but I keep thinking it’s something much simpler or goofier than that.
Inoperative headlight, or lights, as a cause? Just a wild guess.

13

Here is an off the wall guess: There may be a clue in that a 100 amp fuse was open (blown). A lot of amps are going somewhere. Could it be a wire that is flexing in the underhood wind or due to engine movement, a wire that is rubbing against a sharp, grounded metal edge to wear through the insulation to make an intermittent short circuit or overload?

14

Sorry, I assumed that the mention of son meant that this was his car, not his customers car and that the chain reaction started with the aftermarket amp or the big capacitor that is often used with them. That could blow the 100 amp fuse, but a declining voltage from the alternator indicates a very heavy load or a low, unregulated field voltage.

The removal of the green white wire leads be to believe that the ground wire between the engine and the block was broken or disconnected, but there should be several of these. It could also be a bad ground from the ELD but that is checked on test 3c.

The last guess would be that there is still a very heavy draw on the electrical system, but then I would think that pulling the green white wire would not solve this.

15

An after market sound system installed by a moron would be my guess. My daughter’s first boyfriend blew out all the inside the car. I opened up the center console after asking him where he ran the wire and found all the wires just twisted together and laying together in a heap. Of course they shorted to each other and blew out everything. Luckily it was an older Honda and did not have all the computers to fry.

16

OK, I assume none of the info you provided is a red herring, that the blown 100A fuse and the dead ECM are related to the weak charging system. I also assume you tested and verified proper voltage through the entire control system, and also for less than 50mv drop across all grounds. If the alternator output is fine at the beginning but tapers off as load increases I’m assuming the alternator is not the fault. If removing ELD from the circuit also doesn’t help, must be a basic problem, but I’m not sure what.

Is the crankshaft pulley separating not spinning the belts fast enough, and the blown fuse and ECM the result of reverse-polarity jump starting?

17

Blown big fuse and multiple blown electrical parts (ecm, v regulator) suggests a honking big surge.
Any nuclear devices detonated nearby?

Does it have something to do with the alternator’s ground connection?

18
" Alternator now puts out 14.5 volts at idle but as the electrical demand becomes greater voltage from the alternator drops to battery voltage."

Just to be clear you do mean that things are turned on, not that the rpm’s are increased? As load is added and the voltage drops, does increasing the engine speed bring the voltage back up?

"If you disconnect the white/green wire from the back of the alternator it removes the ECU and the ELD from the circuit and the charging system operates as a conventional charging system. Remove the wire, still the same."

I don’t understand the significance or the last sentence.

19

The significance of the last sentence is, the ECU and ELD are no longer controlling the alternator output. So they’re not the problem.

Different electrical loads were applied to the alternator. Headlights on, vent system on, rear defogger on, etc… Engine RPM’s had no effect on the alternator output.

Tester

20

Slipping glazed belt?