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Discussion Starter #1
When the AC is turned on there is an increased engine vibration that is annoying.

I measured the voltage using vcds.

On highway, the AC on, the headlights/ fog lights on it is 13.0-13.1 V

At idle with above things turned on the voltage reads 12.4-12.5V

With everything TURNED OFF, it reads 13.9-14.0V, and vibration dies down a bit-but still is present.

The battery light is Not on. I always keep the battery maintained with trickle charger. It’s 2 yrs old.

Do I have a dying alternator? Bad AC? Or these figures are normal?


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Seems a bit weak to me, it should be well over 13 on the highway and closer to 13 at idle. Do you have a larger stereo drawing down the power?
 
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When the AC is turned on there is an increased engine vibration that is annoying.
I measured the voltage using vcds.
On highway, the AC on, the headlights/ fog lights on it is 13.0-13.1 V
At idle with above things turned on the voltage reads 12.4-12.5V
With everything TURNED OFF, it reads 13.9-14.0V, and vibration dies down a bit-but still is present.

Do I have a dying alternator? Bad AC? Or these figures are normal?
That does seem a bit low, but I wouldn't be too concerned.
The regulator is working fine.
There could be a faulty diode or bad connection in the alternator, this would cause the output to be reduced by 1/3, and could cause vibration.

The vibration could be caused by an engine fault, such as a vac leak.
 

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You would hear a load on the engine when everything is switched on, but vibration is not normal. Remove the belt and spin the alternator. Listen for any crunchy sounds. Sending you a PM.
 
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Discussion Starter #7
It does appear that the alternator is faulty.
You could get it tested, or replace it.
Thank you Tom. I will get it tested.
What makes you think it is faulty? The irregular voltage drop?


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The low voltage under conditions that it should handle, and the vibration.

A faulty field coil, bad connection, or failed diode, will cause it to run on only 2 of the 3 phases.
This causes low output, and vibration due to the imbalance.
 

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Discussion Starter #9
My 1.8t 2003 has 90amp alternator.

Would 120amp work?


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Yes. It’s the reason I have a 90a for sale. I upgraded to 120a because of my sound system and auxiliary electronics.


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Discussion Starter #12
I have read about Overrunning Alternator Pulley(OAP) being more efficient and quieter. I think the 90a alternator in 1.8ts have solid pulley.

Can the solid pulley be replaced with OAP?


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I have read about Overrunning Alternator Pulley(OAP) being more efficient and quieter. I think the 90a alternator in 1.8ts have solid pulley.

Can the solid pulley be replaced with OAP?
Replacing the pulley certainly won't help your current issue, and I wouldn't be using a different pulley anyway,
 

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Discussion Starter #14
Replacing the pulley certainly won't help your current issue, and I wouldn't be using a different pulley anyway,
Thanks Tom.
I was referring to installing the upgraded pulley on the new(refurbished) alternator. But it seems to be the best to stick to the original.


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Discussion Starter #15 (Edited)
I went to auto part stores to get the alternator tested. Half of them said it’s good the other half said the voltage regulator is bad.

VCDS shows I am getting 12.0-12.1V at idle with AC, headlights and the radio on. It goes up to 13.0-13.1 as I cruise.

Also, out of the blue today I got the
(P0507-Idle control system RPM higher than expected) code. The idle is fine but I am getting a lot of engine vibration under load.

I cleaned the TB and did alignment using vcds. There is no vacuum leak.

No dim headlights, no flickering dash or dome lights and no battery light.

Should I definitively assume the alternator is dead?


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I believe that the alternator is almost certainly faulty.
The regulator is almost certainly NOT faulty.
I can't be certain from here!
 

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Discussion Starter #19
Update:
I stumbled upon a new looking alternator in the junkyard. (Not bad for $24)
Installed it. The numbers improved considerably.

At idle: 14.6 V
All accessories on(AC, high beams, radio, defrost): 13.4-13.5 as opposed to 12.0 before.

BUT:
-The reading at the battery terminals is different from what VCDS reads. (14.6 vs. 14.0)
-Also, I did voltage drop test. All accessories on, it came 0.12v. Is it acceptable? I checked grounds as much as I could. Cleaned them.
-I still feel vibration when Alternator is on load.
Thoughts?




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