Alternator Voltage Regulator

nickbartleet · 03-06-2021, 01:15 PM

I replaced the voltage regulator on my 944 as it was worn out and since then I've been getting this strange thing.. when I go to start the car it will regularly just cut all the power... Everything dies. I have to disconnect and reconnect the battery to get another go of starting it. As soon as the battery is disconnected and reconnected voltage is restored and I can start it. After a few attempts it invariably starts.

The voltage regulator was a good quality one and it did fix the problem I was having with voltage fluctuation from the old worn out one.

Now, today, she won't start... no spark. DME seems to be fine as getting 12v pulse to the injectors and the coil on turnover. Fuel pump all good.. DME relay ruled out. When you turnover there is a discernable voltage drop on the cockpit voltmeter to 8v. Battery fully charged and brand new a few weeks ago.

Removed the new voltage regulator and there is uneven wear like the prongs are not riding smoothly on the rotating contacts inside the alternator, are they notoriously difficult to install or is it just me or a worn alternator?

I checked the resistance across positive and negative on the ignition coil and it was reading about 1ohm, not .6 as suggested elsewhere but feels like this could be a red herring.

Anyone had issues with replacing the voltage regulator as it was a real pain when I first installed it with having to reseat it in the alternator a number of times before the car would start.

Jfrahm · 03-07-2021, 04:19 AM

Losing all power when you try to start is a sign of a bad or loose battery cable.

Uneven wear on the alternator brushes is not uncommon with a new regulator/brush assembly and a worn slip rings. Not a big deal typically. It won't affect getting the car to start. You don't need an alternator to start at all. Just a decent battery charge.

nickbartleet · 03-11-2021, 11:58 AM

Thanks for that, that's helpful to know, i shall start checking all the battery cables

It needed some fresh ignition components, so has a new ignition coil, distributer cap and rotor arm, and i also took the alternator to the alternator shop and had it overhauled with new bearings and the slip rings shaved down.

Of course the car is still not running haha, but it all needed doing anyway.

My problem is that i am getting no spark, but seem to have 12v at the positive on the Ignition coil with ignition on, and and led bulb on the negative is illuminated when the ignition is on and then pulses when I crank so i think the DME is still doing as it should.

The alternator guy suggested that maybe when the old voltage regulator broke and the voltage shot up, the cable between the alternator and the starter motor solenoid could have been fried and may have excessive resistance, or perhaps the solenoid was damaged.

As there is no spark, but seemingly there is power to the ignition coil and seemingly it is dropping to earth, what should i check next make? I wonder if there is 12v but not enough current to power the coil maybe?

I'm not sure what to check next really... a fresh 12v power lead to the + on the ignition coil? manually dropping the - to ground to try and get spark? any thoughts would be great.

nickbartleet · 03-11-2021, 01:24 PM

I forgot to add, that now it seems to be cranking nicely, and there is injector pulse, and fuel pressure is all good, so just no spark.

TibetanT · TibetanT's Garage

Hello Nick:

Dumb question here, but when you were working on replacing the Alternator's Voltage regulator, did you have the negative cable off of the battery post?

Whenever you work on the Electrical system on these P-cars, you should always make sure that the negative cable is taken off.

If you do NOT have any bounce on the Tach now, this may point to problems with the reference sensors or worse, the ECU/DME brain is non-functional.
I do hope that is not the case. Try putting the lights on and then crank the car to see if they go dim>>>if lights go dim>>bad battery. OR, a bad connection as mentioned above.

Try some starting fluid in the intake to see if the car fires up.

Let us know how it goes, and "Good Luck!"

nickbartleet · 03-12-2021, 01:37 AM

Thats a very good question. Yes i did, and always do disconnect the battery, as have had to have my ECU refurbished before because a garage jumped the car so i know how careful you have to be.

I do have tach bounce yes, and seem to ge getting pulse detected with a flashing node light to the injectors and the ignition coil but no spark.

Its strange. I suppose it makes a sensor or dme fault less likely but without knowing if the DME is sending good signal or swapping the dme with a known good one it's hard to say for sure the voltage regulator spike didn't fry something.

Does anyone know if it is ok to put 12v straight from the battery to the + on the ignition coil just to rule our a resistance issue in feed to the coil?

Jfrahm · 03-12-2021, 06:34 AM

I think you should see OK voltage there just with a DMM and if it's set to AC or Hz you should see the negative pulses from the DME. I think it'd be OK to hotwire the + and/or intermittently ground the - to check for spark on the coil wire but I have not tried it.

It might not be OK to leave the + wired directly to the battery for more than a few minutes.
Ignition System Troubleshooting

Some systems do not run full voltage to the coil during normal operation.
-Joel.

nickbartleet · 03-14-2021, 08:35 AM

I just tried the ignition coil test which revealed no spark. Then i wired the ignition coil positive directly to the battery +, and tapped the ignition coil negative on the battery coil negative and still no spark.

The ignition coil was the first thing i replaced when i realised there was no spark, so i can only presume the HT lead from the coil must be bad?

Or i'm unlucky and both my original bosch coil and the brand new bosch coil are bad which feels unlikely.

nickbartleet · 03-14-2021, 08:52 AM

any now i test the cable and am only getting .7 ohm resistance. Very confused.

i connected the spark plug thread to the battery neg -, the coil pos + to the batter pos + and the coil neg - was being tapped on the batter neg and no spark, but the ht lead has less than 1 ohm resistance and the coil is brand new (bought it to fix the problem).

And the battery is new and fully charged and happily turns over the starter with the new starter solenoid i just fitted.

Scratching my head now.

Jfrahm · 03-14-2021, 12:02 PM

The coil sparks when you break the power connection. Put the coil wire (or any wire) into the coil and the other end a few mm from ground. Power the coil and it should spark when you disconnect the ground. You can do this as fast as you like, the coil can produce several sparks per second.

A good spark will jump 10mm or so in free air. It's harder to jump the gap under compression so to test in free air you need to see it jump a wider gap.

-Joel.

nickbartleet · 03-14-2021, 02:03 PM

OK, great, so i'll try this rather than testing it with the spark plug like i have been doing. Cheers!

Jfrahm · 03-15-2021, 03:42 AM

A spark plug will tell you if you have spark yes/no but not if it's a strong enough spark. A spark plug is a good 1st test, maybe less fiddly if you are trying to restore a missing spark.