Mike D'Silva Posted 29January, 2018 Report Share Posted 29January, 2018 DC242, I like your diagnostic train of thought.. and to me, it sounds like a faulty alternator... Link to comment Share on other sites More sharing options...
Redracn Posted 29January, 2018 Report Share Posted 29January, 2018 While the alternator may have an issue cars can run just fine on the battery and should be able to do so well bellow 12V. They need to do this to start as the voltage when cranking can easily go below 10V. While voltage fluctations may be showing there is an issue it is very unlikely the main issue is the alternator. Charge up the battery and disconnect the alternator the car should run fine until the battery goes flat. There is also no better time to locate the issue than while it is happening. A inductive pickup timing light would be a great start as would a spark gap tester available from most auto shops for a few bucks. The spark of an electronic ign should easily jump 2cm at cranking. If not then you have a coil or lead or ignitor or button or cap or suppy issue. Based on the description something in the car is marginal and possibly voltage dependant and has only surfaced due to a possible issue with the alternator. Fixing the alternator will only cover over the actual problem which will surface again sometime into the future. One other possibility is the rectifier in the alternator is shot. But this is always permeant and results in a large reduction in alternator output. It also generates a lot more noise/possible interference on the 12V which can affect the electronics. Most Alternators also suck their cooling air in from the rear so the cover with tube is simply to ensure a cool air supply to prevent overheating/life shortening temperatures with the alternator working hard when driven in hot conditions. Link to comment Share on other sites More sharing options...
Redracn Posted 29January, 2018 Report Share Posted 29January, 2018 I should also add the the voltage is not that meaningful unless you also have the alternator current and rpm. Voltage fluctuation can also be caused by battery issues and problems with other loads that cause varying current consumption. Link to comment Share on other sites More sharing options...
DC242 Posted 30January, 2018 Author Report Share Posted 30January, 2018 Redracn, I agree about the power fluctuations and the issues they cause. My difficulty is when the undefined fault occurs, the car won't idle so jumping out to investigate is difficult, and given the intermittent occurrence, assistance is not always possible. Oh the joys of older cars. The alternator has been dropped off for testing so we'll see what that shows. Link to comment Share on other sites More sharing options...
Redracn Posted 30January, 2018 Report Share Posted 30January, 2018 While a modern car would probably give a diag code the older ones were a bit weak at self diagnostics but they do have the advantage of simplicity. You can get a remote starter switch that clips to the starter and crank/start it while holding the throttle from under the bonnet. Clipping on a timing light is also quick and easy at this point. A trained ear would be able to tell what sort of missfire you have but a simple test is to see how hot each exhaust pipe is by spitting on it. But unless you are an expert at how far spit jumps when it lands on a hot exhaust an infra red pyrometer is a better bet to see if it is a particular cylinder(s) or is it random between al cylinders. The age old question that is near the top of the diag decision tree. Fuel or Ignition? Link to comment Share on other sites More sharing options...
DC242 Posted 30January, 2018 Author Report Share Posted 30January, 2018 Forgot about the old remote starter. I think there's one hidden away in the back of the tool box. Last used 1982 I think. As for your spit testing, I'll go with the heat reader. Will be easier to use that trying to start car, hand juggle the throttle, spit and measure how far the splatter go. Still, would make a great youtube video. Have ordered an ignition spark tester today, so when alternator gets re-installed I'll be good to go with my check list. Link to comment Share on other sites More sharing options...
DC242 Posted 10February, 2018 Author Report Share Posted 10February, 2018 Here is an update , and hopefully a close to this topic, for anyone who's interested. I deposited the alternator to the auto electrician, who dismantled the unit and found the regulator to be buggered, the diodes (I think thats right) to be ok, and the front support bearing to be siezed on the the shaft and worn out. Thankfully the regulator was easy to source locally but the bearing was a special order because it was a heavy duty unit not normally seen in a Bosche alternator. Oh, and also there was a clip somewhere inside that had broken and a new one had to be machined. So, all back up and running. Cost worked out to be similar to sourcing a new one from overseas. What was interesting was that when the electrician ran the unit up on his test bench, he was surprised at how much effort it took to run the alternator when it was load tested. I saw it in operation and the driving motor noticeably struggled when a load was put on the alternator. A comparison with a newer alternator showed nowhere near the same effort for the same output. Prior to re-installing the alternator, I ran the car without it. Starting with a standing charge of 12.7v, turning over saw this reduce to 9.6v and when running it returned to 12.04v and was as happy as anything. No coughing, spitting, stalling. Nothing. So the motor can run happily with low voltage, just not with the mechanical strain of the alternator. When re-installed (with cooling duct connected), everything works as it should and the output of the alternator keeps things above 13.0v, even with the a/c on. Only question now is how many additional kilowatts would be available with a newer type alternator. Link to comment Share on other sites More sharing options...
Dreamr Posted 10February, 2018 Report Share Posted 10February, 2018 1 hour ago, DC242 said: Only question now is how many additional kilowatts would be available with a newer type alternator. How about you put your foot down and let us know .... Good to see you got this sorted without too much drama .... Link to comment Share on other sites More sharing options...
ANF Posted 10February, 2018 Report Share Posted 10February, 2018 Unusual that their test bench struggled? Alternators are pretty simple things and it's hard to advance how they function. I imagine your alternator to be similar, if not a lower output, to my 928 one, I had this tested when I was going through alternator issues and it did not tax the test machine at all. Most test benches will only have a motor that is about 5hp ± ... Typically a 75 amp odd alternator will need only say 3 odd hp to run it ( that is at peak load too, which rarely happens), so no gain will be made by changing a fully functioning alternator.... Link to comment Share on other sites More sharing options...
DC242 Posted 10February, 2018 Author Report Share Posted 10February, 2018 I hear what you say. I've never encountered this before either. Both the auto elec and I were surprised, but I couldn't argue with what I saw. If it was the alternator before it was reconditioned, I would've just put it done to it being stuffed, but this was afterwards. Still, its running and that's the main thing. Link to comment Share on other sites More sharing options...
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