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Idle RPM sensitivity to signalling?



 
 
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  #11  
Old April 18th 06, 09:17 PM posted to rec.autos.tech
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Default Idle RPM sensitivity to signalling?

Either your idle speed is too low or the alternator is not capable of
meeting the electrical demand at idle. This could be due to defective
internal alternartor parts such as the diodes or stator neutral
connection. It could also be due to excessive resistance due to bad
connections somewhere in the charging circuit. The proper diagnosis
would begin with an accurate battery condition test such as a load test
and capacitance test. If the battey proves to be acceptable then the
charging system could be tested for excessive voltage drops and a
graphing multimeter or oscilloscope could be used to observe the
voltage ripple in order to determine if the diodes are in good shape.
Beacuse there are so many possible causes for the symptoms you
described, I would recomend diagnosis by a competant technician.
Otherwise you may wind up replacing lots of expensive components for no
good reason.

Kevin

Ads
  #12  
Old April 18th 06, 09:21 PM posted to rec.autos.tech
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Default Idle RPM sensitivity to signalling?

I'm liking this explanation, based on the OP's clarification of the
problem. I would also check all connections between the alternator and
battery.

nate

Mike Romain wrote:
> I have seen that when the body loses it's ground.
>
> The GM's usually have a mesh strap from the bell housing to the body
> with a small black wire from the battery post to the body. When the
> mesh strap goes, the small wire will be severely overloaded and will
> usually start to melt the insulation before it burns up and the vehicle
> dies.
>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 88 Cherokee 235 BFG AT's
> Canadian Off Road Trips Photos: Non members can still view!
> Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
> (More Off Road album links at bottom of the view page)
>
> Aaron407 wrote:
> >
> > I have a 95 Grand Prix GTP, and if I'm signalling at idle (in gear, my
> > foot on the brakeat a dead stop) my RPM decreases by about 50 RPM when
> > the signal light is lit and cycles back up when it turns off and
> > continues during the periodicity of the signalling. My dash lights also
> > slightly dim with the same trend. My question is, is this normal?
> > Should the engine idle and interior accessory lights really be this
> > sensitive to such a small electrical draw? I have checked my battery at
> > idle and it's charging at 13.8V, and I haven't had any other electrical
> > problems. However, I do have some other erratic idling when not
> > signalling, so if this could all be attributed to the same electrical
> > problem I'd love to figure it out. Thanks.
> >
> > 407


  #13  
Old April 19th 06, 12:56 AM posted to rec.autos.tech
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Default Idle RPM sensitivity to signalling?

Aaron407 wrote:
>
> I have a 95 Grand Prix GTP, and if I'm signalling at idle (in gear, my
> foot on the brakeat a dead stop) my RPM decreases by about 50 RPM when
> the signal light is lit and cycles back up when it turns off and
> continues during the periodicity of the signalling. My dash lights also
> slightly dim with the same trend. My question is, is this normal?
> Should the engine idle and interior accessory lights really be this
> sensitive to such a small electrical draw? I have checked my battery at
> idle and it's charging at 13.8V, and I haven't had any other electrical
> problems. However, I do have some other erratic idling when not
> signalling, so if this could all be attributed to the same electrical
> problem I'd love to figure it out. Thanks.
>
> 407


YOur battery is shot. Buy a new one.
  #14  
Old April 19th 06, 08:22 PM posted to rec.autos.tech
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Default Idle RPM sensitivity to signalling?

Aaron407 wrote:
>
> I have a 95 Grand Prix GTP, and if I'm signalling at idle (in gear, my
> foot on the brakeat a dead stop) my RPM decreases by about 50 RPM when
> the signal light is lit and cycles back up when it turns off and
> continues during the periodicity of the signalling. My dash lights also
> slightly dim with the same trend. My question is, is this normal?
> Should the engine idle and interior accessory lights really be this
> sensitive to such a small electrical draw? I have checked my battery at
> idle and it's charging at 13.8V, and I haven't had any other electrical
> problems. However, I do have some other erratic idling when not
> signalling, so if this could all be attributed to the same electrical
> problem I'd love to figure it out. Thanks.
>
> 407


Is the actual engine RPM as indicated by a tachometer independent of the
cars electrical system dropping, or is it just the electronic tachometer
that is fluctuating? If it's just the electronic tach, it could be a
high resistance somewhere in the electrical system like a ground strap
or battery terminal.

Pete C.
  #15  
Old April 20th 06, 11:40 PM posted to rec.autos.tech
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Default Idle RPM sensitivity to signalling?

The tachometer fluctuating corresponds to the dimming of the rest of
the system, but the actual engine RPM variance is so small (~25-50RPM)
that it's too hard to tell if it is actually changing just by sound (I
might have to check with an OBD-1 scanner). I've just been assuming
that the tachometer wouldn't be susceptable to electrical loading in
the rest of the system and was quite accurate, but I may be wrong.
Also, I checked my ground, it's definitely solid. Since everything is
still running ok, I'm not too overly concerned, but would the battery's
ability to hold charge and the voltage regulation be the next things to
verify?

407

  #16  
Old April 21st 06, 12:06 AM posted to rec.autos.tech
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Default Idle RPM sensitivity to signalling?

Mine also can get swingy when my fan belt gets polished up. I test that
by taking a cold off engine and seeing if I can hand slip the alternator
pulley. If I can it will slip under load because the alternator takes a
few HP to spin up under load.

I would look at the battery cable ends next and clean them just because
it helps. When I get corroded cable contacts my volt gauge gets swingy
at idle and the battery doesn't get a deep charge.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Aaron407 wrote:
>
> The tachometer fluctuating corresponds to the dimming of the rest of
> the system, but the actual engine RPM variance is so small (~25-50RPM)
> that it's too hard to tell if it is actually changing just by sound (I
> might have to check with an OBD-1 scanner). I've just been assuming
> that the tachometer wouldn't be susceptable to electrical loading in
> the rest of the system and was quite accurate, but I may be wrong.
> Also, I checked my ground, it's definitely solid. Since everything is
> still running ok, I'm not too overly concerned, but would the battery's
> ability to hold charge and the voltage regulation be the next things to
> verify?
>
> 407

  #17  
Old April 21st 06, 02:54 AM posted to rec.autos.tech
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Posts: n/a
Default Idle RPM sensitivity to signalling?

Aaron407 wrote:
>
> The tachometer fluctuating corresponds to the dimming of the rest of
> the system, but the actual engine RPM variance is so small (~25-50RPM)
> that it's too hard to tell if it is actually changing just by sound (I
> might have to check with an OBD-1 scanner). I've just been assuming
> that the tachometer wouldn't be susceptable to electrical loading in
> the rest of the system and was quite accurate, but I may be wrong.
> Also, I checked my ground, it's definitely solid. Since everything is
> still running ok, I'm not too overly concerned, but would the battery's
> ability to hold charge and the voltage regulation be the next things to
> verify?
>
> 407


Weren't you were talking about low rpm - idle speed???
An alternator puts out few amps at idle. Enough to run the car but perhaps not
enough to run the car, accessories, lights, etc. At low rpm there may be a draw
on the battery. Rev the engine to 1000-2000 rpm and see if the dimming still
occurs.
If not, the battery is shot. If it does, then both the alternator and battery are
shot.
Or a bad connection.
 




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