Alternator / VR issues
 

I recently installed a new bosh remad alternator in a 3.2 Carrera. All went fine including the installation of the cowling on the rear of the alternator which is a challenge. Went for a test drive and the system was charging at 14.1 but after about 20 minutes the voltage dropped to around 11.5 jumping to 12 and back down to 11.5. After another 10 minutes or so it went back up to the 14 level. The warning light for the battery and alternator cigerate lighter volt meter were lit when the voltage was at the 11 level. When I stopped and turned off the ignition then back on, the dash battery light was off. If I waited 10 minutes or so, the dash light would eluminate and the engine would start and charge at 14.1. This on off charging continued so assume there is a bad connection somewhere or the VR is faulty.

Today I pulled the alternator again and checked all the connections and all is okay. Wires r in good shape too along with the ground wire and the connections on the rear of the sending unit gauge. Reassembled and went for a test drive and the same issue occurred.

My next step is to check the connectivity of the blue wire which powers the idiot light and also check the electrical connection from the engine to the wireing harness at the rear fuse pannel in the engine bay.

Appreciate any advice you all might have on the issue. It would seem if I had a grounding problem I would loose all power.

Bob

Make sure your blue wire is not broken or corroded. Change the connector to be sure, solder.

In a normally operating system once the low startup resistance of the indicator light/bulb provides the initial rotor magnetic excitation it is no longer needed/required again until the ignition is next switched.

Most likely a problem with the VR since the battery charge light did not come on with the ignition switched on.

Intermittent slip rings another possibility.

Reman often means just bearing replacement, test for VR & slip rings, intermittents are often missed.

slip rings? as part of the Alternator? It was my understanding that the alt was rewound along with the VR. It was purchased through my mechanic from a national supplier. The OE new one is not available anywhere incl our host. Not sure what that is all about as I would have gone new.

Further update, I tested the conductivity of the blue wire back to the alternator light on the dash and this is fine. Checked the power plug in the engine compartment and cleaned the contacts, rechecked the battery terminals and they look good too, 12.6 v and 14.1 charging. Ground straps also check out fine.

To recap, when I go for a test drive, the charging system works fine at a steady 14.1 but after 15 minutes or so and after the engine has warmed up, the voltage drops down to the low 12.s. It will however go back up at times so sure looks to be an intermittent issue.

Could this be a battery issue that may have been damaged from the original voltage spikes before I replaced the Alt with this unit, or a faulty diode that is faulting after the engine has heated up. There was a comment in one of the trouble shooting articles that with Bosch alternators, you have to be sure the alternator light is a minimum of 2w, mine is 4w which seems to be the standard.

I'm almost ready to bring this to my mechanic for some more advanced testing but would sure like to find out on my own, less costly too.

Bob

Does the 87 still have the 14 pin connector in the engine compartment? If so, check that for corrosion. I had similar problem with erratic charging which turned out to be a loose 14 pin connector, in particular pin 11, the dreaded blue wire.

yes I checked that and cleaned both the female and male connections. I had read that this was a potential cause in another thread. Maybe I'll check this one more time.

Bob

Assume you charged battery before applying system charging with new alt. If the battery is old you might replace it anyways.

What are you using (in-car, presumably) to monitor voltage in use, on the road?

Your mechanic should be able to tell you:

Voltage engine off
Voltage engine idling
And most importantly, voltage under load using a suitable load testing device at around 2K rpm.

I'd consider another guy if he cannot get to the source of the problem using above data. Anything else is just guessing.

I'm using a cigerate lighter VM to monitor plus double checking with a DVM at the battery.

Voltage engine off is 12.5
At idle it is 13.4 now but has been up to 14.1
At load with all lights on and radio it shows 13.4.

13.4 seems a bit low doesn't it? Earlier when I went on a test drive it held at 14.1 for 15 minutes or so then dropped.

If the blue wire had a fault/short, wouldn't the Alt light come on if I understand the process correctly? The light does not come on when the voltage dropped.

I'm going to clean the 14 pin connector again just to be sure.

Very strange

All electrical components being turned on is not enough load to expose intermittent issues. Need to get a real load tester hooked up.

Also, maybe your meter is inaccurate. Has the car been dead at all since alt replacement?

Sure sounds like the voltage regulator doesn't like to work when it gets warm.

Battery has never been dead and read as fully charged. The Bosch alt had a tag warning to be sure the battery was fully charged. I'm thinking it's the VR again but sure seems like there is something else going on as this make no 3, original last summer, rebuilt that one which started spiking last week and now the remad Bosch.

I'll clean the 14 pin socket again and if that does not work I'll bring it to a specialist, ugh.

Somewhat depending on OAT but otherwise 13.4 is virtually perfect for a fully charged battery.

If you have access to a spare car battery might be worth a try.

Possibly an intermittently shorted battery cell as the battery heats.

All fixed now, the rebuilt Bosch alternator was faulty. Replaced with a new Valeo which is the oem.