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Stalling and highway hesitation in nowhere Argentina
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nassau98
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PostPosted: Tue Dec 23, 2014 8:44 am    Post subject: Stalling and highway hesitation in nowhere Argentina Reply with quote

We're enjoying our '87 2.1 driving south on a massive trip and now in southern Argentina. Now, deep in the south and literally hundreds of miles between gas stations, much less towns, we developed Vanagon syndrome / highway hiccups a few days ago. We changed the fuel filter and oxygen sensor. The spark plugs, the plug wires, and distributor and cap all look fine. I'll order a Gowesty harness and have it expedited here as this has been unnerving in such desolate countryside. I'm not comfortable dismantling the mass air flow sensor here with limited tools and the local mechanics have never seen a Vanagon.

I thought I'd try one more thing this morning though, and that would be to clean some terminals with electrical plug cleaner. I disconnected the O2 sensor wires (the expensive Bosch kind), and the mass air relays and cleaned them. A local mechanic also cleaned inside the distributor cap a bit (looked good). Now the Vanagon starts fine but after a minute can't hold idle and stalls. If I drive, the first minute is fine but then putting in the clutch stalls the engine. Needless to say that's unnerving so far from civilization and so close to the holidays with things closing.

Any ideas? Was I wrong to clean the terminals with spray cleaner? (It's an Argentinian cleaner and I didn't use a brush, just a bit of the spray). With such simple procedures how could I have mucked things up even more?

Any advice greatly appreciated! Happy holidays.


Last edited by nassau98 on Fri Dec 26, 2014 6:45 am; edited 1 time in total
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914 mike
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PostPosted: Tue Dec 23, 2014 9:12 am    Post subject: Reply with quote

Bad gas is a common problem down there....has it been happening with more than one fill up? ......try and find some octane boost?

Good luck
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Bluwesty
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PostPosted: Tue Dec 23, 2014 9:18 am    Post subject: Pressure regulator? Reply with quote

I had a difficult to diagnose similar prob in a 84 Westy. Eventually diagnosed as fuel pressure regulator cheap and easy to replace, but not easy to get where you are.
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Jake de Villiers
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PostPosted: Tue Dec 23, 2014 9:27 am    Post subject: Reply with quote

Could be water in the gas. Put half a litre of methyl hydrate in the tank and see.
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Wildthings
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PostPosted: Tue Dec 23, 2014 10:20 am    Post subject: Reply with quote

I am going to guess that the shielding braid of the coax going to the O2 sensor has shorted out to the core wire. With the engine off use your meter set to ohms to see what the resistance is between the core wire of the coax and the ground. It should be very high.
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tschroeder0
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PostPosted: Tue Dec 23, 2014 1:57 pm    Post subject: Reply with quote

yeah as above that seems like a fuel issue, have you pulled the outlet line from the gas tank to check flow? maybe some junk in the tank.
give us more info, any smoke upon start or when running, does it die quicker under load?
also try bypassing the idle control (plug the two wires together)
Is you cat falling apart and clogging the exhaust outlet?
take a good look at all the engine/trans grounds are they all connected and clean?
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nassau98
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PostPosted: Tue Dec 23, 2014 3:29 pm    Post subject: Reply with quote

Thanks folks for the tips. I'll see about testing the O2 sensor with an ohm meter.

As for the gas here, it surely is sketchy, but this vanagon syndrome has been going on for a few fill-ups already.

The plot thickened now. I believe some sensor is on the fritz because again the first minute is fine and then the van wants to die. It's now blowing out black smoke (a first for the van). We pulled the plugs and they were as black as night. We cleaned the plugs, started the car, and within a minute the car died again. Again the plugs were very black. We pulled the injectors and one was already clogged. The injectors were in great shape recently, so I want to believe whatever electrical sensor is now not functioning properly is keeping the mixture of fuel and air from setting properly and quickly plugging the injectors and blackening the plugs.

If I now kill the ignition and and then restart the van, I have another minute or so of relatively smooth driving (functioning idle) before the same drill starts again. The van gets hesitant while driving and as soon as the clutch goes in the motor dies.

Yes, on the last tank of gas I did put in some 108 octane from a bottle just to be sure. No noticeable difference. We've also run some fuel injector cleaner as I thought too it could be water in the gas or bad gas. No noticeable difference there either. While the gas is surely not the greatest and that's contributing to the problem, I don't think that's the only cause. This morning the van ran and idled as always and my only issue was the highway hiccups. Now I seem to have complicated the issues.

Any more tips and suggestions appreciated! Thanks!
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Wildthings
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PostPosted: Tue Dec 23, 2014 4:50 pm    Post subject: Reply with quote

nassau98 wrote:
Thanks folks for the tips. I'll see about testing the O2 sensor with an ohm meter.


It is the wiring from the ECU to where the harness for the sensor plugs in that you want to check the resistance of, not the sensor itself.
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yellowjacket
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PostPosted: Tue Dec 23, 2014 6:37 pm    Post subject: Reply with quote

Agree with Wildthings on checking wiring. Check exposed (unsheathed) wiring at plugs into sensors. I'd start with the Hall Sensor wiring, alot of heat off the engine at that location, mine fell apart in my hand.
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nassau98
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PostPosted: Tue Dec 23, 2014 7:26 pm    Post subject: Reply with quote

Thanks for the clarification, wildthings. I'd actually indeed first measured the O2 system and was going to report that all looked good there Smile. In remeasuring the wiring that the O2 sensor plugs in to, I got a much lower resistance reading than I would have thought on the dual plugs when connected to the ground set of wires going in to the firewall on that drivers side. (The green single wire of the O2 sensor wiring showed continuity). I would have thought this would register infinity, right? I will check first thing in the morning how the wires look further on, but a first glance didn't show any sign of fraying or shielding in bad shape.

I'm not too familiar with where that wiring goes. I'm also not familiar with the ECU. Will read up on that what I can find. Any tips on potential next steps?

On another note... from a PM I received on this topic I also checked the wiring going to the temp II sensor. When connecting one side of the ohm meter each to the two terminals in that connector, I got a reading of 8.33 when set at 20k resistance. There too I would have thought I would get infinite resistance. Is it possible the O2 wiring and temp ii wiring issues are correlated? Or I am barking up the wrong tree with the temp ii check because I didn't test that against a ground? I'll try that too first thing in the morning to compare apples to apples.

Thanks again for all the help so far. Any further tips greatly appreciated as my fiance isn't too keen to spend the holidays not just isolated, but also without knowing what the next move is.
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Wildthings
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PostPosted: Tue Dec 23, 2014 7:48 pm    Post subject: Reply with quote

If you have a shop manual redo your resistance test exactly as it says to do in the manual. If you still have something other than infinite or at least very high ohms then you will have hopefully found your problem. Here is a picture from the gallery of the coax with the end cut off, you can easily see the sheathing braid and not so well see the center core.

http://www.thesamba.com/vw/forum/album_page.php?pic_id=1190953
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tschroeder0
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PostPosted: Tue Dec 23, 2014 7:54 pm    Post subject: Reply with quote

I think wildthings has the right answer on this.
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Wildthings
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PostPosted: Tue Dec 23, 2014 8:09 pm    Post subject: Reply with quote

The TSII sensor has a temperature depended resistance that is shown on charts in the manual. It should always be checked by removing the plug from the ECU and reading the resistance through the harness. Problems with the resistance reading for the O2 sensor and the TSII sensor are probably not related.
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Howesight
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PostPosted: Tue Dec 23, 2014 8:26 pm    Post subject: Reply with quote

Your problem is a grounded oxygen sensor signal wire. The dead giveaway is the black smoke (indicates an over-rich fueling condition) and the fact that you can shut off and re-start and run for a minute.

Here's why I believe this is your problem:

The oxygen sensor creates a low voltage signal (with very small current) based on the difference in oxygen in the exhaust gases and the oxygen in the ambient air. The ECU has a "lambda system" which uses the oxygen reading to add or subtract fuel to constantly adjust the fuel mixture so as to hover around 14.7 lbs of air for every pound of fuel. When functioning normally, the lambda system adds fuel, which reduces the amount of oxygen sensed, which then causes the lambda system to reduce fueling, and so on and so on, so that by hovering around the 14.7 Air Flow Ratio (AFR), an average of 14.7:1 AFR is maintained.

Since both the voltage and current generated by the oxygen sensor are very small, the wire that conducts this small signal is SHIELDED by a co-axial outer layer of wire that is connected to ground. The only purpose of that outer wire is to shield - - it does not convey any current as designed.

BUT, the ground wire has a nasty habit of making inadvertent contact with the sensor wire that is in the centre of this shielded cable. This reduces the voltage in the signal wire to zero. The lambda system interprets the zero voltage as an abundance of unburned oxygen and adds fuel to correct this condition. Unlike modern vehicles that will only correct up to a certain point and then throw a check engine light, the VW digifant system keeps adding fuel until there is so much over fueling that the engine quits. When you shut off and re-start, the whole process of iterations of sensing too much oxygen (this is not, of course really happening, but the lambda system interprets the grounded signal wire in this way) and the process of adding fuel repeats and repeats. Each time you switch off the ignition, the iterative process starts again from zero. This is why you can re-start briefly.

Wildthings has posted the photo showing where to look for the most likely spot where the continuity may have begun between the signal wire and the grounding shield.

In this thread you will find a couple more photos with a bit more detail:

http://www.thesamba.com/vw/forum/viewtopic.php?p=7283309
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PostPosted: Tue Dec 23, 2014 10:37 pm    Post subject: Reply with quote

Sounds like you have the "bucking vanagon syndrome ". There is simple fix for this, but you need the small harness that plugs into the Mass Air sensor .
See http://www.telusplanet.net/public/gary2a/rack/afmharness/afmharness.htm
I would do this before you go spending lots of cash on other parts.

I had the same symptoms as you and obtained the harness which took about one minute to install.
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Mellow Yellow 74
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PostPosted: Tue Dec 23, 2014 10:49 pm    Post subject: Reply with quote

To check whether it is the O2 sensor, couldn't you just disconnect it and the ECU will run in open loop mode? This is the mode it is running in when you first start it and then it goes into O2 closed loop control once the T2 sensor tells the ECU is warmed up.

If it is the O2 sensor you should be able to drive it no problems, but if it is not the O2 sensor the T2 sensor is probably the next likely thing.
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morymob
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PostPosted: Tue Dec 23, 2014 11:49 pm    Post subject: Reply with quote

If oxy sensor wire is shorted to shield unplugging wont change the problem. Reading this i dont see you actually , correctly testing 4 a short. Where u unplug wire from sensor, ATthis plug conn going to ecu inspect shield to be frayed, loose strand (s ) that could touch center wire. Remember shield is grounded at ECU ONLY. Measure between shield & center wire, u will ger a resistznce from ecu cktry bur NEVER a shory, unplug ecu connector then reading between shield & center wire is open, no resistance.T he delay after u start eng before starts to smoke is norm, , u can test by shorting a good one & it wont smoke immediatly. My 11st one was intermittent , found by checking plug as mentioned above & trimmed shield back.I f u want a fpres tester find the round dial tire guage, one that the tube part screws off, clamp a sect of fuel hose to the 'metal T'' where fuel hoses connect, remove the screw 1st. I keep 1 in my tool kit, cheap.In a real pinch & if u can locate a 800 ohm resistor u can conn across temp 2 terms to fake ecu to think eng is at norm temp (or close enuf).could fudge some eithrr way depending what u can find ,even a variable pot type, set resistance with meter, my 2cts.Grounds, around , under, coil r a group of them, also on cyl head, under ac comp, CLEAN all, check terms 4 corroded ends, dont lose any, the elect ckts r all referenced to ground, why they can cause u troublr.
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Wildthings
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PostPosted: Wed Dec 24, 2014 6:19 am    Post subject: Reply with quote

Bazzer485 wrote:
Sounds like you have the "bucking vanagon syndrome ". There is simple fix for this, but you need the small harness that plugs into the Mass Air sensor .
See http://www.telusplanet.net/public/gary2a/rack/afmharness/afmharness.htm
I would do this before you go spending lots of cash on other parts.

I had the same symptoms as you and obtained the harness which took about one minute to install.


Lets not confuse the issue. What you posted applies only to the later Digifant units while he has the earlier Digijet unit.

Mellow Yellow 74 wrote:
If it is the O2 sensor you should be able to drive it no problems, but if it is not the O2 sensor the T2 sensor is probably the next likely thing.


As morymob says you can't fix a grounded coaxial wire to the O2 sensor by disconnecting the O2 sensor from the harness, the ECU will continue to get a zero voltage signal indicating the mixture is very lean and try to compensate by making the mixture grossly rich.
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wecm31
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PostPosted: Wed Dec 24, 2014 7:06 am    Post subject: Reply with quote

Wildthings wrote:

Lets not confuse the issue. What you posted applies only to the later Digifant units while he has the earlier Digijet unit.



But isn't an 87 2.1 Digifant??

Still sounds like a problem with the O2 circuit, as you guys have explained quite well Laughing
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nassau98
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PostPosted: Wed Dec 24, 2014 8:56 am    Post subject: Reply with quote

Well, progress continues and I really appreciate all the feedback. Upon reading your posts this morning I excitedly went out and checked the green O2 wire. Indeed I was not aware that it is a coax and saw that perhaps some of the grounding outer shielding was touching the inner wire at the connector to the O2 sensor wiring. I started the van and took it for a test drive and ALAS, after a couple minutes the problem reappeared.

I then did as you guys suggested and retested the wiring to the O2 sensor with the ohm meter per Bentley page 24.62 at the ECU. Unfortunately the tests came back as the book said they should: 1) with the O2 sensor disconnected and the green wire connected to negative, I received continuity. 2) After reconnecting the O2 sensor wiring I received infinite resistance. I'm dismayed, as I really hoped the wiring was the issue.

I then disconnected the O2 sensor (green wire only) and started the van. The van seems to idle decently fine for many minutes. This seems then another indicator that it's not the wiring, as there's not a zero voltage signal per morymob. I did not take it for a spin, as I was curious to see what the O2 sensor looks like. I've removed it and it's charred and black as night. That's unfortunate, as 2 days ago it was the brand new more expensive Bosch variety.

Can I clean this O2 sensor, as it's the only spare one I brought with me? The nearest town to sell any kind of auto parts whatsoever is at least a few hundred mile drive. How far can I drive with the O2 sensor inserted but with it disconnected before exacerbating other issues? I don't see how the O2 sensor could have gotten so charred unless it was indeed an O2 wiring short causing the van to run so rich for the last few short minutes. Any other ideas as to what could cause that?

On another note, regarding the temp ii sensor, I tested that too while I was at the ECU both before and after letting the van run for a few minutes and got decreasing resistance with increased temperature, so that wiring also seems fine to me.

As always, feedback greatly appreciated.
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