mklein9

There are bunches of threads on this topic but none that I found that exactly matched my symptoms, so I thought I'd start a thread so search engines might find some hits.

My symptoms:

* Jerky on acceleration, getting rapidly worse the longer I drove
* Eventually, CEL is on (solid); "Drive to Garage" notice on dash
* Occasionally "Brake distribution" and a variety of other warning messages on dash
* Trickle charging the battery overnight solved all issues, for a few minutes of driving
* Voltmeter on dash starts at 13.5 or a bit higher when battery charged, and slowly drops while driving. Major problems show up when voltage drops to around 12.5V. Voltage does not ever rise while driving
* When battery fully charged, starting is no problem -- strong starter motor, fast cranking

Based on these symptoms, it seems clear that the battery itself is fine but is not getting charged, or is getting charged too slowly to compensate for the car's use of electrical power while driving.

My initial theory was the voltage regulator had failed based on numerous similar reports on various fora. Getting that alternator out was a bear. Replaced the regulator, did not change anything. $37 part, 5+ hours labor.

Second theory: the cable connecting the alternator, starter, and tying in to the B+ terminal on the right side of the engine compartment which then goes to the battery and other electrical connections throughout the car. $38 part (Sunset Porsche). The old cable did not look corroded, just a little less shiny than the new cable. No outward signs of failure.

Cable replacement fixed the problem. Voltage is now 13.8 - 14.0 at all times when RPM is above 2k.

Notably, I was able to replace this cable without removing or loosening either the alternator or AC compressor. I had to remove the air filter housing and the throttle body and the air intake plenum it is connected to, but that's all. With those removed, it is possible to access both the bolts on the starter and the rear of the alternator without much trouble. The starter bolt needs a long extension (I used about 14") including a wobble extension to allow a little bit of an angle.

After undoing the three cable connector bolts and the two nuts holding the B+ terminal in place, feed the smaller and shorter section of the cable that used to be connected to the alternator into the same gap between AC compressor, AC lines, and intake manifold that the longer and thicker section of the cable going to the B+ terminal is in. Pull the whole cable out by pulling the B+ terminal and wiggling and twisting as the L-shaped terminal foot (starter connector) comes through. I had very little trouble getting the cable out this way. Installation is the reverse; the only problem I had was I pushed too hard getting the cable in and disconnected an electrical connector going to the AC compressor that took a little time reconnecting. Watch for this wire and move it out of the way before pushing the cable in.

Attached is a photo of old and new connector at the starter. Not obvious at all that there is a problem. The new connector is shinier. The old connector shows a little bit of oxidation of the copper strands.

Ahsai

Great work. That sounds like a very good and easy way to replace that cable. Should be much faster than removing the alternator and loosening the a/c compressor.

CDLVancouver

This is my next task...i have the cable already.
If you had more pics of how you went in the back thatd help.
Glad it worked to fix your problem. Mine is hesitant starting/turn over when engine is fully warm... Hoping this fixes it. Ive already replaced the clutch ignition lock switch to no avail.

sjg1138

I had a similar experience. The cable I took out did not show visible signs of deterioration but my electrical problems were solved with its replacement. I also took the engine ground wire off and cleaned up the connections and put it back on. I also used a liberal amount of dielectric grease on all the connections.

mklein9

Sorry, I didn't take any pics during the process. It wasn't all that difficult. I don't know why all the DIYs have you remove the alternator and loosen the AC compressor. Maybe mine is different somehow (my engine was recently rebuilt and completely torn down, so it may be slightly differently assembled). I had also replaced the voltage regulator the week previously (which didn't improve the symptoms) so I knew how the cable was connected to the alternator. Otherwise I would think it might be tough figuring out where the bolt is on the back of the alternator and an inspection mirror helps locate that easily along with the channel for the cable when reassembling. It's a little tight behind the alternator, but I had no trouble getting a 3/8" ratchet and socket in to loosen the nut and I removed it by hand.

The most trouble of all was putting the intake manifold plenum back on, until I completely removed the two inner hose clamps. The rubber sleeves need to deform a lot to get the plenum back on and no matter how loose the clamps were they always got in the way. I found it's much easier to use a 7 mm socket and 1/4" ratchet with 6" extension instead of a screwdriver to loosen or tighten the hose clamps. Also, when removing the plenum definitely follow the directions at Pelican Parts for breaking the seal that forms between sleeve and plenum two at a time (here).

mklein9

Well, I was mistaken. The original problem as described at the top of the thread is still there. Maybe some of the components were marginal because it appears to be a little better, but is definitely not fixed. It occurs only after 15-20 minutes of driving and getting hot, particularly stop-and-go. Actually, I am not sure if heat or time is the primary culprit, or a combination of both. I have not driven the car 30+ minutes on the freeway at speed since this problem started.

Thinking it is some part of the charging system I have now replaced the full alternator, the starter/alternator cable, and the battery (it was 6 years old). No change.

I measured voltage drop between B+ terminal in engine compartment and + terminal of battery under moderate load (2k RPM, AC on, radiator and engine fans on): 0.05V. Same measurement done between engine block and - terminal of battery: also 0.05V.

When the misfiring occurs I get a P0336 fault code in Durametric. That's the crankshaft position sensor. If the charging circuit is somehow not working correctly then who knows what faults might show up, so it would seem to make sense to solve the charging issue first (also from a well respected mechanic who heard some of the symptoms second-hand).

Ahsai

I take that your voltmeter gauge reading stays at 12.5v after 15min. You need a full diagnosis like here to figure out where you lost the voltage.

http://www.renntech.org/forums/topic...tage/?p=240055

To access the B+ termnal at the back of the alternator, see this post http://www.renntech.org/forums/topic...cess/?p=241245

mklein9

Ahsai, thanks for the pointers. I measured the voltages in your post and got:

Test #1, Alternator casing to B-: -25 mV
Test #2, Alternator + to B+: 150 mV
Test #3, Alternator + to jump terminal: +50 mV
Test #4, Jump terminal to B+: 100 mV
Test #5, Alternator + to alternator casing: 12.5 V

This is with car idling, low beams and AC on, dash voltmeter showing 12.5 V. This is after a drive of about 20 minutes where higher RPM voltage started right at 14 V and by the end of the drive was 13.5 V.

This is with alternator, alt/starter cable, and battery replaced in the last week. It would seem to point to the alternator, but the old alternator and this one (a rebuilt Bosch) behave the same.

Ahsai

Hi Mike, basically Test #5 fails because your alternator is only generating 12.5v measured at it's B+ terminal at the back of the alternator. It should generate 13.5v - 14.5v even with load.

I don't know what to tell you but I think you need to try another alternator. It's not uncommon for a Bosch rebuilt unit to fail out of the box. And it's very common for an alternator to behave normal when cold but drop its output once warmed up.

Ahsai

BTW, when you said at the end of the drive the voltage is 13.5v. Where was that measured and how that relates to the 12.5v dash voltmeter reading?

mklein9

Ahsai, 13.5V is at the dash voltmeter and is at higher RPMs (2k+). At idle the dash voltmeter shows about 12.5 and that matches the DVM reading.

Ahsai

Got it. Lots of cases I saw even if you bring the alternator to a shop to bench test, it will pass when being tested cold. Once warmed up and in the car, it will fail. Can you shoot a video of the measurement to show the alternator is outputting only 12.5v and send it to the seller to get a replacement?

mklein9

Ahsai, I am going to be able to get a replacement alternator, but the shop that sold it to me (Parts Heaven) doesn't think the alternator is the problem, but they'll do it anyway.

I'm still not entirely convinced either. What bothers me is that the symptoms are *exactly* the same with old and new alternator. Same length of time until the symptoms appear, same manner in which they appear. That seems awfully unlikely for two alternators, no?

CDLVancouver

given that your symptoms that persist, i think your "new" alternator is a bad one...
i had the exact same symptoms last year and it was 100% alternator. i replaced it with a brand new alternator (not a reman or a diy reman based on a thread here)
good the shop is exchanging it for you.

Ahsai

Ok, I can only think of three more (less likely) possibilities:

1) When you measured 12.5v, are you sure you were touching the probe on the stud that comes out of the back of the alternator, and not on the nut or the wire terminal on it? Suppose the alternator generates 13.5v on the stud and there's corrosion between the stud and the nut/wire terminal, you could lose voltage there and falsely conclude the alternator is bad. This you can re-check.

2) Your belt is slipping somehow. Are the belt and the belt tensioner tight and in good condition? As the load of the alternator increases, the drag on it also increases so if your belt is slipping, the alternator won't be able spin fast enough to provide the adequate power. I don't know of a device that could test the rotational speed of the alternator (maybe make a mark on the alternator pulley and shine a stroboscope on it???). Speed of the alternator = engine rpm x crank pulley radius / alternator pulley radius.

3) There's a single wire that energizes the alternator with some small current controlled by the instrument cluster. So in theory it's possible that the instrument cluster circuit is bad. I don't even know how to test this and how complicated or simple this circuit is.

Personally I have not heard of 2 and 3 above but anything is possible I guess.