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90 Vanagon suddenly running rough - coil?
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pfewesty
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PostPosted: Wed Jan 13, 2021 4:46 pm    Post subject: 90 Vanagon suddenly running rough - coil? Reply with quote

I'm new here - 1st post is a ramble. Until recently my relatively new to me 1990 Westy with 165k miles has been running beautifully since I got it about 2 months ago. I've put 3.5k miles on it. I was returning from a 100mi. trip and driving up an incline on a bridge when the engine started to miss and it felt like a cylinder was dropping out. When the road flattened out it ran better, but would miss every now and then for the remainder of the drive. This problem has gotten progressively worse over the last 2 weeks with the engine missing under acceleration/load. Van always starts instantly. Pulled plugs. 1&2 looked good. 3&4 somewhat fouled but not too bad. While running I pulled wires off the distributor. #3 seemed to be the problem. Swapped plug wires between 3 and 4. Problem seemed to follow the wire. Installed new plug wires. Engine started right up as usual and ran well until warm -- 2-3 minutes -- then started to miss. I pulled plug wires again and now I can't reliably find the problem cylinder. It seems to move. Injectors are good. Could this be a coil issue? In my 35 yrs. of wrenching on cars I've only replaced a coil once or twice.
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djkeev
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PostPosted: Wed Jan 13, 2021 4:58 pm    Post subject: Re: 90 Vanagon suddenly running rough - coil? Reply with quote

We have another member on here chasing symptoms similar to yours.

He has tracked it down to what seems like an exhaust valve.

He has AMC heads running the stock AMC valves which are known to be troublesome.
He has stopped driving it and plans to pull the head before catastrophe occurs.

My AMC headed engine lost an intake valve when the valve retaining portion of the valve stem broke off.

Check to see what heads you are running, VW heads are clearly identified on top by the nice smooth castingVW numbers and a date stamp molded in.

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


The AMC head has AMC but the castings is rough overall.

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


The AMC head is good, their valve quality is known to be poor.

Easy thing to check...... and cheap!

Just thinking out loud.
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pfewesty
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PostPosted: Wed Jan 13, 2021 5:21 pm    Post subject: Re: 90 Vanagon suddenly running rough - coil? Reply with quote

Thank you for the quick reply. Yes -- AMC heads installed by PO in 2018. I have the paperwork somewhere so I can see which shop in Seattle did the work which might inform the quality of valve work. I forgot to mention that I put more oil into this engine than anything I've ever owned. Maybe a 1/2 qt. to qt. per visit to the gas pump. Not a visible leak anywhere. Westy friends tell me "not to worry -- oil is cheap".
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DanHoug
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PostPosted: Wed Jan 13, 2021 5:47 pm    Post subject: Re: 90 Vanagon suddenly running rough - coil? Reply with quote

not to bash AMC but i lost an exhaust valve guide within 10k miles on super duper modified GoWesty head. point being, it happens, not bashing GW nor AMC but somewhere along the line setup or materials were wrong.

i think tight factory valve guide clearance was my failure foil... it was interesting to set up my own head and establish valve guide clearance by the spec... it felt sorta loose to me but allows the all important oil-of-life to get to the rubby bits.

or your coil could be bad. or the O2 sensor. or the TempII sensor. or the fool pump. or the regulator. or your Blummenvasen is empty.
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PostPosted: Wed Jan 13, 2021 6:19 pm    Post subject: Re: 90 Vanagon suddenly running rough - coil? Reply with quote

VW felt a qt of oil in 1000 miles was acceptable. Maybe pull the sparkplugs again and do a compression test. Easy to install new plugs at the same time. Then see how it does.
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PostPosted: Wed Jan 13, 2021 6:48 pm    Post subject: Re: 90 Vanagon suddenly running rough - coil? Reply with quote

pfewesty wrote:

...
Engine started right up as usual and ran well until warm -- 2-3 minutes -- then started to miss.
...


Try unplugging O2 sensor and see if that has any effect
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pfewesty
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PostPosted: Thu Jan 14, 2021 8:01 am    Post subject: Re: 90 Vanagon suddenly running rough - coil? Reply with quote

This AM --Started right up and drove nice for 5mins. or so. Just as the temp mark was moving out of the white it started missing. Disconnected o2 sensor from green wire and it smoothed out within a couple of seconds. Runs and drives good (maybe not great) with wire disconnected. Green wire (all wires for that matter) to ECU is as from factory and unmolested. Service records from PO indicate new o2 sensor installed in 2018. Failed sensor or ground/short in wire?
Thank you all. Happy to have eliminated head problems for now!
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Ahwahnee
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PostPosted: Thu Jan 14, 2021 8:17 am    Post subject: Re: 90 Vanagon suddenly running rough - coil? Reply with quote

pfewesty wrote:
...I put more oil into this engine than anything I've ever owned. Maybe a 1/2 qt. to qt. per visit to the gas pump. Not a visible leak anywhere. Westy friends tell me "not to worry -- oil is cheap".


How full are you filling the oil?

Many (e.g. me) find things do better if the oil level is about 1/3 of the way up from the bottom mark.

It is easy to overfill -- because of the angle of the stick there is not a huge difference between the two marks.
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PostPosted: Thu Jan 14, 2021 8:30 am    Post subject: Re: 90 Vanagon suddenly running rough - coil? Reply with quote

The oxygen sensor is polling all 4 cylinders and to a point will adjust for any straying of the stock mixture. This works great when all 4 cylinders are running equally.

When the sensor can create a problem is when one or two cylinders are not running to spec. Say you have one lean cylinder. The average mixture to the sensor is lean. It sends a message to the ECU to richen the mixture. The ECU can only adjust pulse width for all 4 equally. So, its adding fuel to all the cylinders when only one is really needing more fuel.

When you disconnect the oxygen sensor, this tug of war ends. The engine is actually running in open loop off of it's preprogrammed fuel map.

So, yes your sensor could be bad, but it could also be that the engine is out of spec for what the sensor is wanting, and that's why the engine runs better with the sensor disconnected.

In theory, a proper running in tune engine should not need the oxygen sensor at all and mpg performance etc would be equal to running in closed loop.
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pfewesty
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PostPosted: Thu Jan 14, 2021 8:55 am    Post subject: Re: 90 Vanagon suddenly running rough - coil? Reply with quote

I try to keep the oil level just above the bottom mark.
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hdenter
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PostPosted: Thu Jan 14, 2021 9:39 am    Post subject: Re: 90 Vanagon suddenly running rough - coil? Reply with quote

Have you checked for any exhaust leaks? Even a minor leak upstream from the O2 will draw in air and fool the O2 sensor into thinking you are running lean...

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PostPosted: Thu Jan 14, 2021 10:44 am    Post subject: Re: 90 Vanagon suddenly running rough - coil? Reply with quote

Mine had the same issue, turned out to be a bad Vacuum line coming form the intake to the Power brake line. You could nit really see it until you removed it and then it was painfully obvious. The metal support wires were rusting and it just ate through the line.
I chased this for a while and changed out a few parts along the way. It now runs better than it has for years.

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Wildthings
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PostPosted: Thu Jan 14, 2021 1:50 pm    Post subject: Re: 90 Vanagon suddenly running rough - coil? Reply with quote

Dump a bottle of FI into the fuel tank and see if that clears things up.
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pfewesty
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PostPosted: Thu Jan 14, 2021 6:08 pm    Post subject: Re: 90 Vanagon suddenly running rough - coil? Reply with quote

I'll check/do and report back. Thank you.
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PostPosted: Thu Jan 14, 2021 7:42 pm    Post subject: Re: 90 Vanagon suddenly running rough - coil? Reply with quote

Stop driving it.

New plugs, cap , rotor, wires. Check all grounds fir the engine fir bright and shiny connections. Careful inspection of the Hallsensor wiring on the distributor

A new to you car needs evaluation of fuel tank quality, fuel line replacement, clamp replacement.
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pfewesty
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PostPosted: Tue Jan 19, 2021 6:06 pm    Post subject: Re: 90 Vanagon suddenly running rough - coil? Reply with quote

I put in new plugs, wires, checked and cleaned cap and rotor, grounds, wiring and reset the timing. I pulled the o2 sensor, found it to be very sooty and replaced it with a new one. everything seems to be back to normal and it is running well again. so between running rich and likely some oil blow through it seems the o2 sensor was contaminated --
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