91 Vanagon -cranks, won't start- Dash RPM feed wiring fault

[Merian]

take a look at this:

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/igcoil.html

[VicVan]

Thanks Merian. This brings me back to university...

So I bought a new coil, and... nothing. Same problem, won't start.
I don't have an assistant right now, so I can't check for sparks. I'll check that out tonight.

I'm a bit lost here...
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'90 Little Blue Truck, 2WD auto, FAS GenV 2.0 NA (AVH)

[Merian]

likely can rule out the coil - that's something

why not summarize what you've tested so far

[VicVan]

Well, good idea, let's start over.

Problem : Engine cranks, but doesn't start. No spark at the plug. No spark at the ignition coil.

Changed parts :

Spark plugs (Bosch),
ignition wires (five of them, Bosch),
Ignition coil (Beck Arnley)

Checks performed succesfully :

Ignition switch OK
All fuses in fuse box OK
Pin D15 in fuse box OK
Both relays in engine compartment (fuel pump and ECU supply) OK
Fuel pump runs, idle valve thing runs (vibrates)
Hall Sender check (Bentley 28.43) V=10,9 V , OK
Hall Sender check (Digifant Training manual, 119 and 120)

Checks performed unsuccesfully :

Tension at the + (terminal 15) of coil with ignition on : 9,6 V only. However, using bypassing tool (connecting terminal 15 directly to the battery) doesn't make the engine run (although it does bring the tension at the coil to 12,1 V)
Ignition switching function from control unit (Bentely 28.44, see here, left column http://www.thesamba.com/vw/forum/album_page.php?pic_id=1390039) : Voltage between 1 and 15 is 5,5 V with ignition on, and when Hall sender center wire is grounded, briefly increases to 7,0 V (it should "increase briefly to approx 4,5V" says Bentley)

By looking at it, I only see two things that could be wrong :

The ECU
The way I look for sparks

The ECU looks pretty new, the label is very clean. And for the spark plug, I just put a spark plug ignition wire directly into the coil output, lay the threaded part of the plug on the engine (to ground it), have the assistant crank the engine, and look for sparks.

Any ideas ?
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'90 Little Blue Truck, 2WD auto, FAS GenV 2.0 NA (AVH)

[rockthebus]

My Hall sensor tested ok, but when I wiggled it with the engine running it cuts out. In the UK brickwerks.co.uk sell one for £30.

[Navy_Flyer]

[crazyvwvanman]

One more quick check. At the coil is a connector with 2 green wires. These plug onto spades of terminal 1 of the coil. The thicker green wire is from the ECU to trigger the coil to spark. Unplug the connector and plug it back on with ONLY the thicker wire making a connection to a spade on the coil.

The other thinner green wire connects to the dash area to feed an rpm signal to the oil warning board and the tach. The test above disconnects this dash rpm feed. While it is very rare there have been cases where a failure in the oil warning circuit board or the tach have kept the ignition coil from sparking. The test above eliminates that possibility

Mark

[VicVan]

Rockthebus, Navyflyer, I looked at the Hall Sender connector, and as the rotor it is in very good shape. Good to know though.

Then I went on with Mark's idea, coneecting the coil (-) only to the ECU, and not the dash :

And...
IT STARTED ! At last ! It started right away, running pretty smoothly, I revved it a bit by hand, let it run for about a minute, went fine. Needs to be test driven.

Thank you so much Mark for this tip. Thanks to all of you for your precious help, this really helps me know my van better.

Now, I am going to look into the wiring diagram, see where this wire goes, and most importantly : can I drive around without it ? (It would be on a temporary basis, I want to fix it of course)
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'90 Little Blue Truck, 2WD auto, FAS GenV 2.0 NA (AVH)

[VicVan]

I checked continuity from the connector that goes from the coil (in the picture above) to the relay panel under the dashboard, and there is continuity.

Is the RPM gauge faulty ? Or should I check something in the oil warning circuit board ?
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'90 Little Blue Truck, 2WD auto, FAS GenV 2.0 NA (AVH)

[Merian]

dunno, but....

1. congrats!

2. This should be in the FAQ as the list you made above will help others

3. if a failure in the oil warning circuit board or the tach can keep the ignition coil from sparking, you should hunt down the design engineers and kill them

[crazyvwvanman]

You need to get to the instrument cluster to see what the problem is. The green wire from the coil goes to the 14 pin connector of the cluster, below the back of the tach. A quick check is to unplug that connector and see if the problem goes away. If it goes away then you need to figure out which is the cause, most likely either the oil pressure circuit board or the tach.

On the back of the speedo there is a small branch of the blue foil that plugs in there. Inside the case of the speedo is where the little oil pressure board is. It has nothing to do with the speedo, VW just stuck it in there so when the oil warning buzzer goes off it does so right in your face. The connector has 6 pins used but it is a little larger than that.

On the back of the tach an even smaller branch of the blue foil plugs in to feed the tach. That tach connector has 3 pins used.

So to figure out which is causing the problem you unplug the small branch of the blue foil from each of those 2 places and see which one is related to the problem.

Mark

[VicVan]

Thanks Mark, I'm printing your post and heading back to the van !

[VicVan]

Well well well... I removed the instrument cluster, to have a look at this T14 connector, and here is what I found

(Fortunately, the fingers in the picture are mine, I didn't find them in there. Could have been worse I guess...)

thank you, previous owners !

The thing is, I'm afraid to dismount the tacho and speed back plates, it could rip the whole thing apart. So I can't perform Mark's trouble shooting for now.
I would need to redo the harness connector wiring I suppose ? Is the blue foil still good ?

Can I drive the van without the small green wire attached, Mark ?
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'90 Little Blue Truck, 2WD auto, FAS GenV 2.0 NA (AVH)

[fraggle00]

That is horrible..

I would get the gowesty foil replacement and clean up the mess that's there. I will bet that something else is going to go wrong whe you try to stuff all that back behind the cluster!
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'91 Vanagon Carat
'87 Porsche 928S4 DOWN
'12 Fiat 500 Abarth

[VicVan]

The thing is, the kit GoWesty sells is 290 USD...
But that's the idea. I think I'll go with this : http://www.kpcnsk.com/?p=138. It'll require some wires, a lot of patience. I'll also have to rewire the connector from the inside of the vehicle.
I would like to postpone this project and drive the van as is, with the small wire disconnected, I hope that's all right.
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'90 Little Blue Truck, 2WD auto, FAS GenV 2.0 NA (AVH)

[fxr]

Plenty of vans don't have a tach anyway - so why not.
_________________
Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300

[VicVan]

Sure, but not having the oil low pressure alarm concerns me a bit though.
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'90 Little Blue Truck, 2WD auto, FAS GenV 2.0 NA (AVH)

[jmranger]

Congrats for all the progress made.

I understand your concern about disassembling any more. But reading crazyvwvanman post, and looking at the image above, I believe he recommends keeping the top right 14-pin connector plugged, and either disconnecting the bottom left 9-pin (6 used) connector (that feeds the oil pressure monitor, hidden in the speedo) or the center-right 3-pins one (on the bump) that goes to the tach. No disassembly needed. This would allow you, maybe, to have one of the two system working by only disabling the faulty one.
Be careful unplugging these connectors, it's easy to do damage. Ask me how I know. If it was me, I'd only disconnect the small one and hope the van still starts.
And then, I'd run the procedure in the topic below to test whether the oil pressure monitor actually works.
http://www.thesamba.com/vw/forum/viewtopic.php?t=571725

[VicVan]

Hi JM, thanks for your answer. I don't have concerns about disassembling, don't worry ! As a matter of fact, I just did what Mark and you explained. I plugged both green wires on ignition coil (like it should be), and tried :
- both connectors plugged : doesn't start. But we already knew that.
- tacho connector unplugged, oil board plugged : doesn't start.
- tacho connector plugged, oil board unplugged : doesn't start.
- both connectors unplugged : doesn't start
- without small green wire on ignition coil : starts.

Some short-circuit in the blue foil ?
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'90 Little Blue Truck, 2WD auto, FAS GenV 2.0 NA (AVH)

[crazyvwvanman]

You skipped the first step in my suggestion. I said to unplug the 14 pin and see if the problem goes away. That would tell you if the problem was in the cluster or somewhere before it. Then if so, figure out which part of the cluster. Clearly with your disaster you can't simply unplug the 14 pin but you could cut the green wire near where it is soldered to the cluster and see if that solves the issue. That would disable the tach and part of the oil warning circuit but would still allow the basic oil warning light to work.

EDIT: I can't tell for sure from the photo but the wires may have been extended with other colors of wire. If so you may need to trace back to the splices and verify which color is which. There may be duplicates since most people wouldn't have enough different colors to extend all the wires with a unique one.

Mark