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Help Troubleshooting/ Diagnosing intermittent poor running issue
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the_benjamin_effect
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Joined: May 31, 2010
Posts: 192
Location: Gateway to the North Cascades, Washington State
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PostPosted: Thu Sep 16, 2021 6:46 pm    Post subject: Help Troubleshooting/ Diagnosing intermittent poor running issue Reply with quote

Help Troubleshooting/ Diagnosing poor running issue.

1987 Syncro Vanagon. GW 2400cc installed new in 2008 and 40k miles now on the engine without issue until now.

Long synopsis:
Returning from Descend On Bend Labor day weekend to North West Washington. Drive down was easy, no issues. However, on the return about 3.5 hours from Bend Oregon, driving North on a steep incline (Maintaining 4th gear, 3000 RPM WOT) the van started to suddenly lose power, then return to normal. Sometimes this would happen several times in a row. Pulled over to inspect any leaks or anything out of the ordinary- everything looks good. Started right up, drove for about 20 minutes and it started again. We made it to our destination for the night which included about 30 minutes of light offroading to a dispersed campsite we know of. Van is now running like a dream again on this light-flat offroad trail using Low gear and first gear only. Next day we depart and drive another 3.0 hours north with no issues at all until the last 15 minutes of the trip until we arrive home (same power loss, but now during normal town driving). Turned off the engine in the garage and I instantly recognize the smell of the exhaust is different than normal. I’ve driven around town the last few days- no issues, but exhaust is still smelling funny.

Some other things of note:
-New plugs, cap, rotor, wires last October 2020. New MANN air filter in July 2021.

-Ambient Air temp wasn’t hot, maybe low-mid 80’s *F

-Water temp on the stock instrument panel was good throughout the whole trip (never climbed much above the LED)

-Always maintain 65-70 MPH on the highway, shift down when necessary, I don’t lug the engine.

-I use 92 octane as per GW engine spec.

-The thought of bad gas crossed my mind… but then it happened on the following tank as well.

-We were traveling with another Syncro that was behind us. They said they saw a puff of black smoke from the tailpipe every once and awhile. (I assume this to be in conjunction with the power loss effect I explained above).

-I have a driving log that I maintain very well. I calculate my avg. MPG at every fill and document it. My usual hwy MPG is 17.0. The last two fills after the power loss effect were 13.0, and 13.1 respectively. The 13.1 was all flat Interstate driving at 65 MPH (15 gallons to go 197 Miles).

-I did feel very minor power losses on the flats an hour before the major ones on the steep inclines, but at the time I thought it was just crosswinds/passing traffic/semi-trucks, etc.

I do have a few ideas of what this issue could be but wanted to shoot it out to the community to get some feedback.



Cheers!
Benjamin
LOCAL 8251
_________________
-1967 Sundial Camper 1914cc "Sunny"
-1978 Deluxe Westfalia Jake Raby built PowerStroke 2109cc "Westy"
-1987 SYNCRO Westfalia GoWesty 2400cc "Ruby"
-2000 Subaru Impreza Sport EJ22 ¼ million miles "Trusty"

International Association of Machinists and Aerospace Workers. I.A.M. 751
International Brotherhood of Naval Flight Engineers. I.B.N.F.E. LOCAL 8251
My other ride has 18,400 horsepower!
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Wildthings
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PostPosted: Thu Sep 16, 2021 8:42 pm    Post subject: Re: Help Troubleshooting/ Diagnosing intermittent poor running issue Reply with quote

Unplug the O2 sensor and see what effect that has.

Your symptoms sound similar to Vanagon syndrome, but that diagnosis is always iffy.
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the_benjamin_effect
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Posts: 192
Location: Gateway to the North Cascades, Washington State
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PostPosted: Fri Sep 17, 2021 3:57 pm    Post subject: Re: Help Troubleshooting/ Diagnosing intermittent poor running issue Reply with quote

Ok, Reporting back…

I unplugged the O2 sensor and went for a long drive today. I wanted to include all types of driving situations to see if I could replicate the power loss, I drove on some twisty back roads, I climbed Mt. Baker to the ski resort (5100 ft) with a couple of long hard pulls, down the mountain and back roads to the interstate. Glad to say the power loss never came back with the O2 sensor unplugged. This journey was 154.5 miles with an average MPG of 14.0. Not ideal, but looking at my fuel logs it matches other similar trips I have made when climbing steep inclines and back roads. I’ll take it.

Now, I wanted to test my hwy fuel economy. Topped off my fuel tank at an interstate gas station and headed South 40 miles to turn around and head North back to the same gas station (even used the same pump and nozzle to eliminate any variable I could control). 17.6 MPG! My hwy fuel economy is back with the O2 sensor unplugged. Also, never even a single power loss.

…And the exhaust doesn’t stink anymore.

Does this mean my O2 sensor is malfunctioning?

I’ve dug around TheSamba for more info on the O2 sensor, and I understand that it is a single point to monitor all cylinders exhaust gas mixture, and adjust the air/fuel ratio to correct for any deviations. But… if only one cylinder is running lean the sensor will sense this and adjust for more fuel to be delivered to the entire system, leaving 3 cylinders running rich- which is what I think was happening to me with the puffs of black smoke, power loss and stinky rich exhaust smell. Or the O2 sensor is malfunctioning and sending erroneous information to the ECU for an issue that doesn’t exist.

I’m leaning toward changing the O2 sensor and see where that leads me.

What is the next step if it comes back after changing the sensor, or should I just cross that bridge when/if I ever get to it.

Thanks all!

Benjamin
LOCAL 8251
_________________
-1967 Sundial Camper 1914cc "Sunny"
-1978 Deluxe Westfalia Jake Raby built PowerStroke 2109cc "Westy"
-1987 SYNCRO Westfalia GoWesty 2400cc "Ruby"
-2000 Subaru Impreza Sport EJ22 ¼ million miles "Trusty"

International Association of Machinists and Aerospace Workers. I.A.M. 751
International Brotherhood of Naval Flight Engineers. I.B.N.F.E. LOCAL 8251
My other ride has 18,400 horsepower!
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DanHoug
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Joined: December 05, 2016
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Location: Bemidji, MN
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PostPosted: Fri Sep 17, 2021 4:09 pm    Post subject: Re: Help Troubleshooting/ Diagnosing intermittent poor running issue Reply with quote

the Bosch O2 sensor models used in our vans are considered 'tune up' items that become suspect around 60k miles. sure lots of people go longer. a bit of silicone RTV from either an engine gasket, exhaust leak repair attempt, or in the intake system and the zirconium sensor becomes contaminated forever more.

easy to check out... with the sensor PLUGGED IN, back probe the connector and the voltage reading should bounce above and below 0.5v about 1/second or more frequently.
_________________
-dan
60% of what you find on the internet is wrong, including this post.

'87 Westy & '89 Westy both 2.1 4spd

Past projects can be found at--
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hardway
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PostPosted: Sun Sep 19, 2021 1:11 pm    Post subject: Re: Help Troubleshooting/ Diagnosing intermittent poor running issue Reply with quote

Hello Benjamin.

The oxygen sensor or lambda probe is a simple device. It is a battery. It generates a voltage due to the difference in Oxygen content between the gas in the exhaust system and outside air. The sensing element has to be in contact with both samples of gas. If there is outside air in the exhaust system the output is inaccurate. Exhaust leaks can draw outside air into the exhaust through the effects of the Bernoulli principle. The old style Zirconia sensor is only precise and accurate at a stoichiometric ratio. That is to say when the air/fuel ratio leads to complete combustion or a balanced equation where all of the reactants are consumed and none are left over in the output.

The ECU reacts to this input. You can force the mixture rich by grounding the input wire. Or you can apply voltage and drive the mixture lean. Your symptoms indicate a short to ground inside the sensor. By disconnecting the sensor as Wildthings suggested you caused the ECU to ignore the lamda probe input.

The lambda probe can get lazy and conflict with the timing of the fuel mixture changes of the ECU. Or go to ground as yours seems to have. They can skew the output voltage but that happens much more rarely. They can be fouled by foreign substances or fooled by outside air in the exhaust.

If you have no exhaust leaks then just change the sensor. Do you still have the clip-on shield for the sensor? Rotate it to protect the sensor from road debris and water.

Charles Probst wrote a very good book that was published by Bentley Publishers. The title is Bosch fuel injection and engine management. It is an old book now but still a good one. The book also deals with modifications and high performance. I recommend it. You can learn a lot about your engine through understanding this and checking the output voltage of the lambda probe.
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Socratic Dog
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Joined: September 14, 2018
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PostPosted: Mon Nov 01, 2021 3:45 pm    Post subject: Re: Help Troubleshooting/ Diagnosing intermittent poor running issue Reply with quote

Check the shielded green coax wire the O2 sensor ground wire connects to. Its insulation can fracture over time, leading to shielding touching core>>short. Happens erratically. Can take 10 years of trying to figure out a slowly worsening running problem to figure it out. Ask me how I know.
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the_benjamin_effect
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Location: Gateway to the North Cascades, Washington State
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PostPosted: Sat Oct 01, 2022 4:49 pm    Post subject: Re: Help Troubleshooting/ Diagnosing intermittent poor running issue Reply with quote

**SOLVED**

Update 1 year later to my poor running issue topic for others searching the forum with similar problems in the future.

hardway wrote:
If there is outside air in the exhaust system the output is inaccurate. Exhaust leaks can draw outside air into the exhaust through the effects of the Bernoulli principle.


^^hardway^^ was correct in his keyboard diagnoses. For about 6 months after my trip in September 2021 I just ran with the o2 sensor disconnected, as I don't drive the syncro much in the winter months. It ran strong, climbed strong, exhaust smell was normal, and MPGs were normal with the o2 sensor still disconnected. Spring time rolled around and I decided to investigate more now that the concrete in my garage is a tad warmer. I found an exhaust leak in one of the collectors upstream of the o2 sensor and catalytic converter. Replaced the exhaust collector gasket and plugged the o2 sensor back in. I've now run all Spring and Summer long camping in the Cascades and surrounding mountains with ZERO issues as stated before in my post. In summary... I never changed the o2 sensor, as I wanted to eliminate each variable one at a time...

Ended up as simple as an exhaust leak.

My lesson learned:
Poor running issues = check upstream exhaust leaks, don't jump to immediate o2 sensor change.

Cheers!
Benjamin
_________________
-1967 Sundial Camper 1914cc "Sunny"
-1978 Deluxe Westfalia Jake Raby built PowerStroke 2109cc "Westy"
-1987 SYNCRO Westfalia GoWesty 2400cc "Ruby"
-2000 Subaru Impreza Sport EJ22 ¼ million miles "Trusty"

International Association of Machinists and Aerospace Workers. I.A.M. 751
International Brotherhood of Naval Flight Engineers. I.B.N.F.E. LOCAL 8251
My other ride has 18,400 horsepower!
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