Flickering lights

[dguy]

I'm at a loss to explain this one; any help would be appreciated. 

'86 Iron Duke, with the alternator from a '84, rebuilt about 4,000km ago.  There was no indication of any problems with the charging system when the alternator was attached to the '84 drivetrain.

At any RPM and any electrical load, there is a noticable flicker in any lighting system in the car.  It increases slightly with RPM, but not by much.  It appears (by eyeball) to have a 10-20Hz frequency at idle (what I'd give for an oscilloscope sometimes).

All electrical connections are clean & tight.  Battery cables are good (new).  A DVM across the battery shows a rock-steady 14.8 VDC when running, but I'm guessing that an analog voltmeter will show a slight up/down swing.  No measurable AC ripple in the system which one would expect with a regularly fluctuating voltage.  No power-hungry accessories have been added to the car.

[aaron88]

Sounds like a shaky alternator.  Add a capacitor to the circuit to filter out a bit of the giggle.  Use the oscilloscope you don’t have to test for the right size filter.

Aaron

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[GoFast88]

I always have a hard time with adequate grounds

[2ML67]

Agree with Aaron sounds like the alt. Would quickly check all grounds then if not better replace the alt, after all its so much fun to do so on factory engines. Unlike my 3800SC Fiero the alt is easy to change as well as the starter unlike some peoples cars. Dan

[dguy]

Sounds like a shaky alternator.  Add a capacitor to the circuit to filter out a bit of the giggle.  Use the oscilloscope you don’t have to test for the right size filter.

I've thought about that, but unfortunately I don't have access to a 'scope.  I'm slightly tempted to splice in one of the big capacitors that audio nuts & their thumper cars like to use, but most of them are a heck of an investment "just to try".

I may also try replacing the diode pack in the alternator even though it really isn't all that "old" at this point.  I wouldn't expect a new diode set to start to fail so quickly, but sometimes shit happens.

I always have a hard time with adequate grounds

I'm going to try adding another engine-to-chassis ground & observe what happens, but I have my doubts that it will be effective.  All of the major grounds were replaced with new cables when I installed the motor, and the connections were cleaned, dried, and goobered up with dielectric grease.  I even replaced that flimsy 14 gauge ground at the transmission case with a 4 gauge cable.

[dguy]

Agree with Aaron sounds like the alt. Would quickly check all grounds then if not better replace the alt, after all its so much fun to do so on factory engines. Unlike my 3800SC Fiero the alt is easy to change as well as the starter unlike some peoples cars.

  That's probably where I'm going to end up going if adding a supplementary ground doesn't stop it.  The famed CS-130 upgrade sounds like a good idea for a number of reasons.

[aaron88]

I may also try replacing the diode pack in the alternator even though it really isn't all that "old" at this point.  I wouldn't expect a new diode set to start to fail so quickly, but sometimes shit happens.

If you aren't showing AC current then the diodes are working, the capasitors arent properly filtering though.

Aaron

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[dguy]

Someone forgot to check the basics first.   

Loose belt.

Tight enough not to squeal, but loose enough for the span between the alt. to the water pump to "flap" slightly when running.  The "flap", was as the same frequency as the flicker in the lights.

[aaron88]

Glad we could help.

[dguy]

I take that back.  My eyes must've been playing tricks on me yesterday.   

Oh well...  I've been wanting to play with a CS-130 for a while now anyway.

Does anyone know whether or not the alternator bracketry on the 87-8 L4 is identical to that of the 86?

[fiero308]

Don
Darth just posted some info on PFF:
check
http://www.fiero.nl/forum/Forum2/HTML/057419.html

should help

gp

[dguy]

Darth just posted some info on PFF:
check
http://www.fiero.nl/forum/Forum2/HTML/057419.html

I missed that on my PFF "run" yesterday.  Thanks!