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91 Vanagon -cranks, won't start- Dash RPM feed wiring fault
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VicVan
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PostPosted: Wed Aug 05, 2015 11:41 am    Post subject: 91 Vanagon -cranks, won't start- Dash RPM feed wiring fault Reply with quote

Hi everyone,

I have a 91 Vanagon, Automatic, US non-Californian.

(edit : Go here, page 2, for a more up-to-date explanation of the problem : http://www.thesamba.com/vw/forum/viewtopic.php?p=7781037#7781037. I edited the title as well).

The problem : It cranks, but won't start. After troubleshooting, I found that terminal 15 on power supply relay box was grounded. On the other end, at the ignition switch harness, terminal 15 is grounded too. It shouldn't be, because that's what brings power to the Power supply relay in the engine compartment.
Question : Any ideas ? Why and where would it be grounded ?
I can't understand from the diagrams where this wire goes (what is its route between the ignition switch and the engine compartment).



More details :

1 What happened : driving fine, then engine stopped working just like that. Roadside diag : fuel pump OK, no spark. Got towed back home.

2 Further inspection : The next day, still no start but in addition fuel pump wouldn't work no more.

3 What has been tested and works :
Fuse box under dashboard : all fuses OK.
Spark plugs : changed (was on my list anyway).
Ignition coil (green label) : Primary and secondary resistances OK.
Distributor : looks pretty recent, visual OK.
Fuel pump : direct power supply by linking terminals 30 and 87 of the fuel pump relay : works. OK.
Ignition switch : tested (thanks to this guide http://cabby-info.com/OldBlue/files/Vanagon-ReplacingIgnitionSwitch.pdf) OK

4 What has been tested and doesn't work :
Primary ignition wire : Resistance is approx 2,2 kOhms. Needs to be changed.
Spark plugs ignition wires. Resistances range from 6 kOhms to 6,4 kOhms. need to be changed.
Power supply relay socket : continuity between terminals 85 (brown, to ground) and 86 (red circle on my photo, black wire, to ignition switch via coil). Raised my eyebrows, because that is the command part of the relay. Of course, I measure 0 Volts on switching the key to ignition.

Image may have been reduced in size. Click image to view fullscreen.


I then found out that the terminal 86 (red) was grounded. It is line 15 on the diagrams.
then here is grounded too (the red connector goes to fuse box above coil, the yellow connector goes to main harness)
Image may have been reduced in size. Click image to view fullscreen.


then here on the ignition switch socket : terminal 15 has continuity with ground
Image may have been reduced in size. Click image to view fullscreen.


Thanks a lot to all the topics and info that helped me make it so far in my troubleshooting, I just need a bit more help !
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'90 Westiti, 2.1 auto


Last edited by VicVan on Tue Aug 11, 2015 9:47 am; edited 2 times in total
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crazyvwvanman
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PostPosted: Wed Aug 05, 2015 11:56 am    Post subject: Reply with quote

I'd guess that it isn't really ground but rather it has low measured resistance to ground. That might be expected since there are a lot of things connected to 15 that also use ground. You are probably just reading all those parallel resistances.

The real question is when the key is on do you see 12 volts on 15 at the switch on the black wire and at the coil terminal 15 black wires.

Have you heard about the Pin D15 failure on the back of the main fuse/relay panel? Search here for info on that if you have 12 volts at the key switch black wire but not at the coil black wires.

Mark
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VicVan
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PostPosted: Wed Aug 05, 2015 12:07 pm    Post subject: Reply with quote

Hi Mark,

Thanks for your answer. I don't have 12V at the coil terminal 15 when I turn the key. Bu I do have it at the key.
I'll look into the Pin D15 failure !
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VicVan
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PostPosted: Thu Aug 06, 2015 9:25 am    Post subject: Reply with quote

Good news : pin D15 is nice and shiny, as good as new.
Bad news : pin D15 is not the error I was looking for.

I checked, I have continuity between d15 on the white connector behind fuse box, and the ignition switch connector (picture just above, red circle).
So problem would be between fuse box and engine compartment ? How do I troubleshoot that part ?
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Merian
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PostPosted: Thu Aug 06, 2015 11:39 am    Post subject: Reply with quote

you said the fuel pump works when directly wired, right?

did the injectors spray ok then?

IIRC, the Bentley has a diagram of some cable runs
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VicVan
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PostPosted: Thu Aug 06, 2015 12:21 pm    Post subject: Reply with quote

Hi Merian,

Merian wrote:
you said the fuel pump works when directly wired, right?

Yes it does.

Merian wrote:
did the injectors spray ok then?

Not checked (yet)


Merian wrote:
IIRC, the Bentley has a diagram of some cable runs

I'm deep into them, but the part between ignition switch and ignition coil is not very clear to me (yet ?)

I just bought new ignition wires, I'll try starting the engine with these on and while bypassing the power supply relay.
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crazyvwvanman
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PostPosted: Thu Aug 06, 2015 2:08 pm    Post subject: Reply with quote

The ignition coil gets 12v power to its terminal 15 on a black wire from the key switch via pin D15 of the fuse/relay panel. Then that power passes on via a smaller black wire to the engine relay box to turn on the ECU power relay. Jumpering the power relay WON'T also power the ignition coil.

I made a "wiring bypass tool" to do what you need done. Search for me and that term.

Mark

VicVan wrote:
......
I just bought new ignition wires, I'll try starting the engine with these on and while bypassing the power supply relay.
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VicVan
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PostPosted: Fri Aug 07, 2015 8:06 am    Post subject: Reply with quote

Yesterday I checked all the wires, cleaned some grounds, checked every connection... Got both relays to work properly again (fuel pump, etc). But :
- still no spark at the plugs,
- only 9,5 V at the coil when I turn the key to ON (battery is charged, 12,5 V). Enough to click the relay, but is it enough for the coil to work properly ?

Mark I am going to build your bypassing tool this morning and start over from there.

One question though : Could the ignition coil be faulty, although the measurements of primary and secondary resistances are OK?
Primary (should be between 0,5 and 0,8 ) : 0,8 Ohms
Secondary (2,4 to 3,5 kOhms) : 3,1 kOhms
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Merian
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PostPosted: Fri Aug 07, 2015 10:42 am    Post subject: Reply with quote

yes, possible - I don't know a different test tho

I'd move to something else (for a while) unless the coil has 100k miles on it - then I'd try to think where I could buy a quality coil (not Chinese or Mexican manf.)
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VicVan
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PostPosted: Fri Aug 07, 2015 11:26 am    Post subject: Reply with quote

Well that's the thing, I just bought the van with 270k miles on it. the motor was supposedly rebuilt 50k ago (and it runs really nice (when it starts)). I don't know how old the coil is... The green label is all worn out and stripped.

I did another test, found here http://www.clarks-garage.com/shop-manual/ign-04.htm

Ignition Coil Test

Disconnect the ignition coil output wire at the distributor cap.
Connect a spark plug to the end of the ignition coil output wire which you just disconnected.
Connect a ground wire to the threaded portion of the spark plug.
Disconnect the ignition coil ground wire from the negative terminal on the coil (Green Wire).
Connect one end of a ground wire to the ignition coil negative terminal.
Turn the ignition switch to the ON position.
Tap the other end of the ignition coil ground wire jumper on an good grounding point (for example the battery negative terminal) and look for sparks at the spark plug that correspond to the frequency of your tapping of the ground wire.
If you have a good spark at the spark plug, the ignition coil is good.
If you don't get a good spark, check for approximately 12 VDC from the coil positive terminal (black wire) to ground with the ignition switch in the ON position. You should also get approximately 12 VDC from the coil negative terminal (Green wire) to ground


Turns out I had no spark, barely a weak blue one every 10 or 20 contacts.

Voltage at the coil, with ignition ON, is
-terminal 15 (+) to ground : 9,6 V
-terminal 4 (-) to ground : -11,9 V
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PostPosted: Fri Aug 07, 2015 11:36 am    Post subject: Reply with quote

To make that coil test more valid you need to give it a 12v power feed that doesn't rely on the long black wire feed from the key switch. You could have a weak or unreliable power feed to the coil preventing it from making good spark.

Mark
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VicVan
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PostPosted: Fri Aug 07, 2015 11:37 am    Post subject: Reply with quote

I agree with that ! I'm on my way buying the parts in order to build your bypassing kit. I'l give you an update in a couple of hours !
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VicVan
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PostPosted: Fri Aug 07, 2015 4:11 pm    Post subject: Reply with quote

So, Mark I have built my own bypassing tool. thanks again for your tutorial about this, it will be handy to have it in the Vanagon.

With the tool in place, the engine cranked but didn't start.

I grounded the negative terminal of the coil, put a spark plug on the outlet of the coil, no spark whatsoever.

So should I change this coil or not ? It seems it's not 100% sure it's the faulty piece, but what else could it be ? Confused
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Merian
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PostPosted: Fri Aug 07, 2015 4:15 pm    Post subject: Reply with quote

go for it - the problem is what brand of new coil will not be a POS

or swap in a known good borrowed one

or build your own spark test bench
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VicVan
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PostPosted: Fri Aug 07, 2015 4:24 pm    Post subject: Reply with quote

A store nearby carries the Becker brand, German import. 89 Dollars (CAD). I think I'll go with that.
I've thought about borrowing one, but I've got no one to ask...
And how do you build a spark test bench ?
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PostPosted: Fri Aug 07, 2015 4:55 pm    Post subject: Reply with quote

it's not the simplest thing in the world, but here is a link I found for you:

http://www.diagnosticnews.com/tips-using-oscilloscope-ignition-coils/


a local auto electrical shop might be able to test it also but they'll charge $$...
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Wildthings
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PostPosted: Fri Aug 07, 2015 6:19 pm    Post subject: Reply with quote

Put a meter on the #1 (-) terminal on the coil and see if you get a voltage fluctuation when you crank the engine. A digital meters may be kind of useless here, so if you can't figure out what is going on maybe use a test light which should flicker.
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VicVan
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PostPosted: Fri Aug 07, 2015 6:39 pm    Post subject: Reply with quote

Merian, interesting link. However I don't have an oscilloscope or means to access one...

Wildthings, I'll try that tomorrow. But would the fluctuation be a good sign or a bad ? I would say bad, meaning the coil couldn't get to deliver enough amps after a few cycles...
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Wildthings
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PostPosted: Fri Aug 07, 2015 9:03 pm    Post subject: Reply with quote

VicVan wrote:
Merian, interesting link. However I don't have an oscilloscope or means to access one...

Wildthings, I'll try that tomorrow. But would the fluctuation be a good sign or a bad ? I would say bad, meaning the coil couldn't get to deliver enough amps after a few cycles...


It is the fluctuation that makes the coil fire. The system lets amperage flow through the coil to store electro-magnetic energy and then when the current flow stops the energy is released in the way of a high voltage spark.
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VicVan
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PostPosted: Sat Aug 08, 2015 7:16 pm    Post subject: Reply with quote

So, test performed using a 12V LED,, with Mark's bypassing tool (meaning clean current arriving to the coil directly from the batttery).
Intensity of light varies. I should have filmed it, but if I had to describe it, it's like the voltage signal feeding the LED was a wave with peaks around 10 or 12V, and valleys around 5V.

So I reopened the Digifant Training manual. Page 119 states that no spark and light flashing indicates a defective coil.
If I get it right, the flickering light measures that the coil has all conditions to perform, but still produces no spark, so it needs to be changed.

Out of curiosity, what is physically wrong in the coil itself ? If it is only made of 2 wires, and the resistance measurements are correct, what has "broken" inside ?

Image may have been reduced in size. Click image to view fullscreen.


Thank you very much for your help.
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