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Discussion Starter · #1 ·
Hello everyone!

I have a problem with my idle speed when I have a few electrics on.

The problem is this. When I turn on one electric "device" (for example headlights), my idle drops a bit (~30rpm), but is ok. If I turn on something more (e.g. headlights + heater fan) the idle drops a bit more (say another ~30rpm) and again seems OK, but after about 10 seconds, it drops even more, to a total of ~100rpm drop. This means that if I set my idle to about 850-900rpm, I have problems because my idle drops to 750rpms and the alternator cannot keep up , so I have to keep my foot an the pedal to idle it about 900rpm to avoid the voltage droping to battery level . The cure I use is to set the idle to about 1050rpms, so with accessories on I get an idle-speed of 850-900, to keep my voltage up, but during daytime driving such a high idle is a bit iritating.

I had this problem with the stock 45A alternator, so about a year ago I changed to a 90A alternator from a late '80s BMW (identical mounting and pulley) and a 74Ah battery, but still the same...

Any ideas or reccomendations to try?

Thank you in advance!
 

· Old Opeler
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5,564 Posts
Maybe a look at an idle speed increasing solenoid like the ones used to up the idle speed when the air conditioning unit is turned on would help. Wire it up so when the headlights are turned on it is activated. Have a look at some of the later model cars with air conditioning to see how this works - the solenoid is usually located in the fuel injection accelerator linkage area on the motor.
 

· boomerang opeler
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i have found this to be a normal thing for any car with a carb
the only cars that don't do it are the ones with fuel injection they have an idle control valve to deal with the rev drop as the load on the engine increases as more power is pulled from the alternator(even though it just spins in a magnetic field it still pulls power from the engine)
as jim says you can fit an idle solenoid to up the revs or just turn up the idle 50-75rpm it is more stable (more revs make more power so it looses less revs as it has more power)
 

· Member
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239 Posts
Seems your'e not charging right?

Seems like your not charging right for some reason to me? You can have the alternator and voltage regulator checked out on a bench somewhere, that only leaves the battery and accosiated wiring. Sounds like a generator, not an alternator, I'd check these out beofore trying to add anything.

Regards,
Rick
 

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Discussion Starter · #6 · (Edited)
It is surely an alternator, and bench test shows good. As for the voltage regulator I have tried two different, and they both react the same...

I saw that the 45A unit's pulley although identical to the eye, it has a different curve towards the diameter, so the belt sits more "inwards" (about 2,5mm) thus giving a smaller radius and smaller overal pulley perimeter to the belt, so the alternator will spin a little faster with it. I installed this pulley today in my 90A unit and took it to a alternator repair shop for bench-test, to make sure it will not get overloaded by the faster rotation, and the man said it is ok to 9000rpms, well I rarely go over 4000, and the car limits to 7000...
I will check tomorrow night (today iI am staying in), because the problem is evident at night, and post any news (hopefully good)!
 

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gr_diver said:
Hello everyone!

I have a problem with my idle speed when I have a few electrics on.

The problem is this. When I turn on one electric "device" (for example headlights), my idle drops a bit (~30rpm), but is ok. If I turn on something more (e.g. headlights + heater fan) the idle drops a bit more (say another ~30rpm) and again seems OK, but after about 10 seconds, it drops even more, to a total of ~100rpm drop. This means that if I set my idle to about 850-900rpm, I have problems because my idle drops to 750rpms and the alternator cannot keep up , so I have to keep my foot an the pedal to idle it about 900rpm to avoid the voltage droping to battery level . The cure I use is to set the idle to about 1050rpms, so with accessories on I get an idle-speed of 850-900, to keep my voltage up, but during daytime driving such a high idle is a bit iritating.

I had this problem with the stock 45A alternator, so about a year ago I changed to a 90A alternator from a late '80s BMW (identical mounting and pulley) and a 74Ah battery, but still the same...
Any ideas or reccomendations to try?

Thank you in advance!
Well if the alternator seems to check out on the bench and your sure that the voltage regulator is working and you had the same problem with the 45 amp alternator, it seems your telling me that there is something wrong with the associated wirng in the charging system??? Everything I've read here on this forum has been an increase in Alt. size 50-70 Amp. and everyone exclaims how bright all thier dash lighting is! :confused:

At least this is where I think you are in your troubleshooting process, or am I (you) missing something here? Sometimes the simplest approach is the fix and often the last approach as it seems too easy! Double check wiring to battery, power & ground as well to the alternator as maybe you've overlooked something. A lot of talk about ground wires here on the forum.

KISS METHOD!

Keep
It
Simple
Stupid

Not that you are stupid, that's just what the KISS Method Approach stands for!!! OK

Regards from accross the Big Pond to you! Only been to Thailand, would love to visit Greece someday!

Rick
 

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Discussion Starter · #8 ·
Today I was thinking, that the 45A unit was also a replacement about 10 years ago when my dad used to drive the car. My father is the type of guy that takes his car to a "friend's" repair-shop, states his problem, leaves and picks it up later without even opening the hood to see what has been done. So I believe that the 45A alternator was also not a correct unit for my car, as I don't know from what car it came from (yes, it was used...), and propably is relatively worn by now (this means last year when I took it out)... Tommorow I will go to an Opel dealer and ask for a correct alternator pulley for my engine, I will have both olds with me to compare, and if see any differences I will buy a new one...
As for the wiring, it is good, as I changed it together with the alternator last year, using thicker wire which has MANY more and much thinner small copper fibres, to increase the conductive surface, used gold plated connectors, and replaced battery to starter, starter to alternator, and alternator's ground cables. In addition, my battery post cables are clean and in very good condition, so wiring is propably out of the question, and it has to do something with the alternator(s)...
I'll see what I can do the following days...

P.S. Thanks rangerrick, every recommendations are useful! And don't worry, I know that you didin't mean to insult by the K.I.S.S. method. Cheers!
 

· boomerang opeler
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5,661 Posts
gr_diver said:
The cure I use is to set the idle to about 1050rpms, so with accessories on I get an idle-speed of 850-900, to keep my voltage up, but during daytime driving such a high idle is a bit iritating.
another thought is to put an over speed pully set on (the pully ratios are changed so the alternator runs faster at idle) this will give you more power at lower revs in the altenator but may give you problems at constant high running but will keep the output up at idle so you can be at normal revs
 

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Discussion Starter · #10 ·
Well, the smaller pulley from the old 45A unit did the miracle! I installed it and today I took the car out. It worked wonders! My idle is set to 900rpm, and with electrics on (headlights, fan, rear window defroster, stereo+amplifier) it didn't fall under about 830! And thus my voltage was good and steady over 13.4V, to a max 14.2V, depending on the accessories that were on at various times... Maybe it was that little extra speed, that was enough for the alternator to keep up with the demand.
Propably the old unit was so worn, that it could not keep up with demand, and the new needed a smaller pulley. Cars are so frustrating sometimes, as symptoms might be the same, but causes totally different!

BUT WE STILL LOVE THEM AND KEEP OUR HANDS DIRTY TRYING TO FIX THEM!

Thank god, this sh!t was annoying me every winter for the past 3 years!!!

Thank you ALL, you have been very kind by helping me with all those ideas and recommendations!
 
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