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I am having an issue with a 2002 TDI that I just bought. After a long test drive and lots of checking of systems, I bought this car last week. I drove for 30 minutes checking the manual trans, engine, a/c, and electronics. Then performed some tests while it was parked. Everything checked out fine. I drove it about 45 miles back to my house and saw that the generator light was intermittently coming on. I took my girlfriend to a parking lot to have her practice driving a stick then went to the store. In all I drove about 65 miles before noticing any issues.

On the way back from the store later that night the ABS light came on with the generator light and a few others lights, then the car died a few blocks from home. I brought my truck to jump it, but the bug died about 30 seconds after taking off the jumper cables while I was still in the parking lot. I jumped it again and let the battery recharge a little more. I made it to the school parking lot next to my house before it died again. We jumped it, let the battery charge, them finally made it home after driving very fast the last 1/4 mile.

After checking all the wiring I found that the battery top fuse bot was melted. I fixed that by removing the generator to battery wire with the 150amp fuse and bypassing the fuse holder with an external 150amp fuse holder. That didn't fix it. When checking the alternator "exciter" wire, the blue wire that is running in the harness from the dash lights, with the engine off and key to the on position I found that it is reading ~12v. No problem there, but the alternator was still not turning. When I got the engine running I wanted to check the blue "exciter" wire so I removed it from the alternator. Amazingly, the alternator started turning and the dash light was not on anymore. After messing with the plug I found that the wires must have been loose and that was keeping the alternator from working. The bad news is that the alternator looks to be turning too slowly and intermittently changes speed (I guess it might be the pulley clutch adjusting) and is not producing enough voltage to charge the battery and the car dies after running for a bit. I suspect that the wiring harness is at fault, but don't want to replace it if it is an alternator voltage regulator issue, and not a wiring issue.

So, my question is: should I first change the wiring harness and see if that fixes it all? Or is there a way to test if the regulator is faulty?

I've been reading several posts about similar issues, but none that discuss the alternator working after the 2 wire plug is removed from the alternator.
 

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Well, I just found out what a pain the TDI is to work on. My hands are cut, bruised and filthy.

I removed the alternator to battery wire and replaced it with a 2ga wire and 150amp strip fuse in it's own plastic case, separate from the battery top fuses. I also reused the old 6ga alternator to battery wire as an additional ground and ran it to a bolt that secured the air cleaner box. I reused the alternator harness and added some plastic conduit to protect it from heat and rerouted it to make it more accessible if I need to change it later.

The good news is that the wiring is looking better than ever and will be easy to remove if need be. My car starts, the engine runs and puts out around 13v. The bad news is that the alternator only works when I disconnect the 2 wire plug from the alternator. When I plug it in, the dash generator light comes on and the alternator stops spinning. When it is unplugged the light is off, the alternator starts moving and everything seems normal.

What is going on with this set up? I thought the blue "Exciter" wire would make the alternator voltage regulator tell the alternator to run. But it seems to be the opposite. Why would it only work with the plug unplugged? My Haynes manual says that the other wire in the plug is the "Diesel Direct Fuel Injection Engine Control Module". What the heck does that have do with the alternator? Is it safe to drive my car around with this plug undone?
 

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\ The bad news is that the alternator only works when I disconnect the 2 wire plug from the alternator. When I plug it in, the dash generator light comes on and the alternator stops spinning. When it is unplugged the light is off, the alternator starts moving and everything seems normal.
The alternator stops spinning??

Explain or take a video and post it on YouTube with a link here.

Do you know if the alternator pulley is an over run clutch type of alternator?>

Is the belt maybe slipping because it is not wrapped around the pulley enough or the tensioner is bad?

Take a picture of your belt/pulley and post for comment.
 

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Discussion Starter #5
The first time I took the car to Autozone, the alternator wasn't turning at all so the test showed 0v/dead alternator. Luckily the store is close so I made it there and back just on battery power. That was before I found that unplugging the 2 wire plug would actually get the alternator to turn.

I got the battery charged today and got the car back to Autozone. The battery showed 25cca and I wasn't able to start the car after I parked it at the store. The jumper box they brought out didn't get it started either. It got busy at the store, so they couldn't do a check on the alternator. I jumped the bug with my friend's BMW and got it back home after a 2nd jump just down the road. We let the battery charge more the 2nd time to assure we could return home.

I'm pretty sure of 2 things: 1: The alternator will turn when the plug is undone, but it doesn't seem to produce ~14v like it should. 2: My wiring has passed all tests so I has to be a problem with the regulator, the pulley, the tensioner or the alternator itself. I shall perform some more tests tomorrow.

I am still perplexed about the alternator running with the plug undone. Does anyone have an explanation for this?
 

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What I mean by the alternator spinning is that the cooling fan which I believe is part of the rotor assembly moves when I remove the plug, but nothing happens when the plug is plugged in. I can see the fan moving through the vent slits on the case on the rear of the alternator. So, I believe that this would rule out the pulley being totally inop since it is obviously turning something. However I know that means it could still not be working correctly.
 

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I'm having a hard time; understanding what you are describing about the alternator. However, if you think you are having problems with the alternator; pull the alternator and have it bench tested, at a auto parts store. When you do that; you can get a "pass" or "fail" answer and can go from there. IF you can make a video with a portable device; maybe, we can see and you can show us, what you are talking about. :confused:
 

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There is clearly a mechanical problem with this alternator. Likely it has an one way clutched pulley that is slipping.

What happens is without the 2 wire connector hooked up, there is no load on the alternator, but when the 2 wire cable is re-connected, the alternator is loaded and something is slipping.

If you look at this post and my pictures, you will see up close what the one way clutched pulley looks like. There is a plastic dust cover on the pulley which is a dead give away. If your alternator has a dust cover, it has the one way clutched pulley which is likely bad.

See this thread and the pictures - http://newbeetle.org/forums/1-8-liter-turbo/50839-alternator-pully-failure-what-best-brand-replacement-buy.html
 

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I'll second that you likely have a bad alternator pulley. It can be changed in the car, but is not easy and requires special tools.

I would suggest you just replace the alternator. I will also suggest only to use a Bosch reman or new Valeo. They typically come with a ratchet pulley, return it if it doesn't.

You will soon find there are few jobs harder than replacing the alternator on a TDI Beetle. There is no easy way, just several methods that are equally difficult and/or time consuming.
 

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Discussion Starter #10
I will perform a few more tests today to see if there is anything with the wiring that is at fault. If not, I will remove the alternator to have it tested. Thanks for the input. I will update with my results
.
 

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Thanks JFOJ! This sounds exactly like what is going on. I'm testing 12v at both wires in the harness. The dash light goes out when the plug is disconnected. The alternator fan on the rear side spins when I disconnect the plug, then stops when reconnected.

I put a screw driver in the alternator case and was able to spin the fan in both directions, which I believe would only be possible if the clutched pulley was faulty. Is this correct?

If my pulley was good the fan would only spin freely in the counterclockwise direction (as viewed from the rear of the alternator), but since it's busted the fan will move clockwise also?

I'm almost ready to undertake an alternator replacement if this is the case. The alternator was replaced by the previous owner 25k ago, but I think it is a cheap replacement and not a Bosch or Valeo.
 

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Discussion Starter #12
Yep, bad pulley. I put a screw driver in the rear fan and after removing the serpentine belt, I was able to spin the pulley in both directions freely.

I just picked up a reman Bosch and am starting the switcheroo.

-Unplug the 2 wire plug
-Unscrew the Alternator to Battery cable
-Remove the big plastic skid plate and the small splash plate
-Use 16mm wrench to loosen tensioner, them remove serp belt
-Use a star bit to remove the fan and let it hang from it's wire to the ground out of the way.

I'm now getting ready to remove the 3 bolts on the tensioner and unbolt the A/C conmpressor.
 

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You can get the pulley for about $50 and replace it with the alternator still in the engine bay. If you are lucky you can replace it with the alternator in place.

I could not get the pulley to "break free" so I have to actually use and impact on the pulley, but the impact knocked the pulley loose without too much issue.

I would be VERY hesitant to use a pulley that comes with a reman Alternator, I would still install a new pulley regardless of your decision.
 

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These pulleys vary a lot in price and depending on where you purchase them they can cost up to or over $80!

This part pricing software site is not for VW parts, YET, however, Audi is live and there are a lot of Audi parts that cross to VW.

So you can look up the part number and load it into this tool and see where the best prices are.

Audi Part Number Price Comparison

Hopefully the Author will add a VW parts price comparison soon.

$28.32 shipped on ebay seems to be the lowest price.

"022903119C" | eBay

RMEuropean has the pulley for $27.20, but they have a $65 free shipping mininum.

FCPEuro has the pulley for $29.99 but free shipping starts at $49.00 BUT NOTE - ALL PARTS purchased from FCPEuro have a LIFETIME Warranty regardless of the Manufacturers Warranty!!!! So depending on the part and the risk, sometimes a slightly more expensive part from FCPEuro is wise for the LIFETIME Warranty.
 

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I finished the alternator swap in about 4 hours. I have to use the car for work this wknd and couldn't wait for online parts to get shipped. I feel this job will go much faster if I have to do it again in the future. Hopefully with the new (reman) alternator that will be several years away.

If I had the leisure of time and option of getting better parts right away, I would have pulled the alt, then tested each component individually to determine what needed to be fixed.

My bug drives great with the new parts. I took it to the store to return the old alt for a core refund, and also took some oil from a recent change in my truck. The battery tested fine on their machine, and the alternator was putting out 14.2v. I also had them give me the codes that are giving me a CEL. None are alternator related, and I will start digging into those fixes later. I gave my girlfriend some more driving lessons and after 45 mins of slow creeping and parking practice, the bug was still humming along with no signs of charging issues.

Life is now a little less stressful with a Brand New (To Me) working New Beetle TDI. I hope to get a lot of MPG and satisfaction with my first VW.
 

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