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TDI Conversions Discussions on converting non TDIs into TDIS. More general items can be answered better in other sections. This is ideal for issues that don't have an overlap and are very special to swaping engines.

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Old November 26th, 2017, 12:14   #586
Hasenwerk
 
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Do you have the correct "exciter" circuit in there? Normally, in a Volkswagen, when you turn the key ON, but the engine isn't running the alternator light comes on. This is part of the exciter circuit. One side of this light goes to the 12V switched circuit and the other side goes to the D+ terminal on the alternator. The light goes on because the alternator isn't making energy and it is essentially a ground circuit at that point. When the engine is on, the alternator makes energy and D+ goes high and turns the light off. D+ is looking for a reference voltage - so if this isn't connected in your Ranger then it leads to a confused state on the alternator and charging issues. To make the circuit is easy, just a small light bulb or 1K 'ish' resistor between 12V switched and the D+ terminal.
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Old November 26th, 2017, 21:35   #587
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Thanks for the input guys. Very good ideas.

I'll do a couple checks to rule things out:
1) Verify my exciter circuit is sending 12v to D+ (it was when I checked duing the swap)
2) Very easy to swap batteries
3) Will try and load the alternator as much as possible and measure voltage as A-man described. I've often thought this would be a good way to determine if your starter lead and ground are providing resistance to high current flows. Guess I'll need to upgrade my multimeter to one that has a MAX function.
4) above test will indicate if connections are needing to be cleaned.

Thanks again.
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Old November 27th, 2017, 17:05   #588
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Quote:
Originally Posted by greengeeker View Post
I've often thought this would be a good way to determine if your starter lead and ground are providing resistance to high current flows. Guess I'll need to upgrade my multimeter to one that has a MAX function.
100% correct and yes min/max is a necessity when flying solo! This method is far and away the most practical and accurate way to check any automotive circuit for unwanted/excessive resistance. Again, good luck!

Last edited by A-man930; November 27th, 2017 at 19:10.
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Old November 28th, 2017, 10:20   #589
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Quote:
Originally Posted by A-man930 View Post
100% correct and yes min/max is a necessity when flying solo! This method is far and away the most practical and accurate way to check any automotive circuit for unwanted/excessive resistance. Again, good luck!
What should one see for max voltage drop for either the starter circuit or the alternator circuit? <<1V?
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Old November 28th, 2017, 11:01   #590
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Depends on who you ask but ideally under 500 or 600mV. Considering the problem you're having I would expect it to be quite obvious if there's a problem here (over a volt maybe?)
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Old November 28th, 2017, 21:10   #591
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Apologies I seem to be having some issues with the picture server tonight...I'm not consistently seeing the icon which allows me to copy the medium-sized image.

Well I might have stumbled onto something tonight.

I did a quick test at idle turning a couple loads ON. You'll notice that the duty cycle goes DOWN with each subsequent load APPLIED.



Here is the same graph but I'm showing the inverse of what VCDS is showing....seems to make more sense.



The last thing I did was rev the truck with no loads applied. You'll notice that the duty cycle INCREASES as the alternator speed increases...opposite of what you would expect.



So given the behavior I'm seeing I wanted to compare the original logs but the inverse of the Ranger's:



Looks a lot more reasonable. 35% duty cycle compared to the 25% of the Jetta.

At this point I'm assuming that I have the two wires to the alternator swapped. Will need to double check those tomorrow.
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Old November 28th, 2017, 21:19   #592
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the field wire is just a sense wire for the computer,
meaning if they're hooked up backwards then the alt isn't getting excited by the 'battery lamp' as I doubt they'd add provision to put current to the alternator field directly from the computer.

if the alt isn't getting an excitation signal it probably won't self excite until you rev the motor a good bit above idle, dunno about these specific alternators but I know a ford 3g alt (pretty modern) with a '97 explorer accy drive (from memory a pretty close ratio match to the ALH stuff) needs about 2700 RPM before it'll self excite.

also, the 'battery lamp' will have increasing voltage across it with decreasing load on the alternator (battery light on the dash turns off when you turn on the headlights or what have you)

this is all for if the two small wires are reversed
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Old November 28th, 2017, 21:26   #593
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Fair enough. I will say that the new alternator immediately jumps to >14V when I start the truck. I'll have to double check that the battery light functions properly which I think it does : turns off as soon the truck starts and illuminates when the voltage dips below a certain threshold. Had the pleasure of eyeing that evil little gauge recently. Fun fact. Did you know a TDI will run on at least 7V? I don't know how low it really will go because that's where a scangauge shuts down.
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Old March 4th, 2018, 13:05   #594
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Thank you for posting your experiences during this project, greengeeker. I intend to perform a similar swap and this thread has already proven very informative.
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Old March 5th, 2018, 12:09   #595
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Quote:
Originally Posted by DoesItDiesel View Post
Thank you for posting your experiences during this project, greengeeker. I intend to perform a similar swap and this thread has already proven very informative.
Thanks D.I.D. That's exactly the reason I tried to capture as much detail in this thread as possible.
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