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Discussion Starter #1
1989 Grad

I’m sure more testing is needed but wanted to run by group for any initial thoughts.

when I start car and give it no gas, so starts and holds idle rpms, idiot lights come on and then go out and at same time, voltmeter drops to around 10.5 volts. Then when I rev the engine, idiot lights flash on and then cut off and volt meters rises to a little over 12. When I then drop down to idle, hovers at.12 volts. Almost like there is initial need to rev up alternator to over come resistance then when current flowing is reading 12 volts at idle.

Next....as I drive down the road,as the rpms increase, the volt meter drops to 11.5 or less and when I come to a stop, voltmeter returns to 12.

voltmeter never reads much above 12
Battery 3 years old
Battery test at 12.68 volts with key off
At idle reads 13.46
Readings using multi tester ar battery
Cleaned up grounds last summer including engine strap and neg battery connection at trunk.
Not sure age of alternator
Haven’t run multimeter at higher rpms yet as need to find someone to help.

thank you for any suggestions
 

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1989 Grad

Battery test at 12.68 volts with key off
At idle reads 13.46
they are all decent readings.

Is it only the battery warning light that comes on when you rev the engine?
Have you perhaps renewed the bulb at some stage in the monopod, and used the wrong wattage?

The green wire in/out of the electrical junction block (left fender) is for the battery warning light...is that secured tightly, clean, no slight breaks in wirestrands etc?
 

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Discussion Starter #3
they are all decent readings.

Is it only the battery warning light that comes on when you rev the engine?
Have you perhaps renewed the bulb at some stage in the monopod, and used the wrong wattage?

The green wire in/out of the electrical junction block (left fender) is for the battery warning light...is that secured tightly, clean, no slight breaks in wirestrands etc?
Thanks, will check junction box. When I initially rev engine all lights come on briefly then go out. Battery light never comes on after that when running. Have not changed any lights
 

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Battery now drains dead. Recharged and put multimeter tester in series( key off of course) and when set at 10 amp reading multimeter goes to 1 and I don’t think 1 amp but is an out of range reading as is 1 at all settings
Maybe voltmeter was trying to tell me something when showing volts dropping as revs increased.
Will start pulling fuses to see which circuit.
Any thoughts appreciated
 

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when I start car and give it no gas, so starts and holds idle rpms, idiot lights come on and then go out and at same time, voltmeter drops to around 10.5 volts. Then when I rev the engine, idiot lights flash on and then cut off and volt meters rises to a little over 12. When I then drop down to idle, hovers at.12 volts. Almost like there is initial need to rev up alternator to over come resistance then when current flowing is reading 12 volts at idle.

Next....as I drive down the road,as the rpms increase, the volt meter drops to 11.5 or less and when I come to a stop, voltmeter returns to 12.
A dying alternator can show strange symptoms, you may wish to call it suspect. It is certainly possible there is some small wiring issue and definitely follow advice on cleaning wiring and connections, but before you spend a lot of time on it, consider replacing the alternator. If the symptoms stop, it was the alternator. If symptoms persist, put the original alternator back in - you now have a spare. Then put in the time to trace the wiring issue.

These are very normal readings. Your Volt gauge could be going south after many decade of life.
Unlikely for the test instrument to be the problem but not impossible. An easy test is to check against a few known standards such as some new AA batteries stacked in series.
 

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A dying alternator can show strange symptoms, you may wish to call it suspect. It is certainly possible there is some small wiring issue and definitely follow advice on cleaning wiring and connections, but before you spend a lot of time on it, consider replacing the alternator. If the symptoms stop, it was the alternator. If symptoms persist, put the original alternator back in - you now have a spare.
I agree with stevespiderguy - the alternator is your most likely culprit. But instead of buying a new one, I would have the old one tested. If it's bad, it may only need a new brush-regulator assembly (though there would be some logic in doing a total rebuild while it's on the bench).
 

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Battery now drains dead. Recharged and put multimeter tester in series( key off of course) and when set at 10 amp reading multimeter goes to 1 and I don’t think 1 amp but is an out of range reading as is 1 at all settings
not sure I follow that...
...anyway if battery drains dead (after what? a day, a week?), either you have a massive parasitic drain or your 3 year old battery has given up the ghost....if you're lucky it has a 4 year guarentee! ;)

Doc here shows how to do a simple test for a parasitic drain (a drain can also be caused by a bad diode in the ALT)
 

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Just quick thank you for responses. Replaced alternator with new one. Seems fine now. Live in small town and work full time so was easier than running around finding repair shop.
Old alternator showed output so maybe something minor like diode.

if anyone wants old alternator just let me know and I will ship. No cost
 
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