intermittent O2 Waring light + Hard Start/Stumble - Mercedes-Benz Forum
 
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post #1 of 9 (permalink) Old 04-10-2019, 09:21 AM Thread Starter
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Date registered: Apr 2019
Vehicle: 1987 190e 2.3
Location: Houston, TX
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intermittent O2 Waring light + Hard Start/Stumble

Hello. New Member here.

A little about myself and my car:
I've recently acquired a 1987 190e 2.3 with ~ 73k on the odometer and in what I generally consider very well maintained condition.
I should also maybe add that this is my first non-diesel Mercedes, but that I've owned and cared for six Volvo 240 daily drivers, several of which were K-Jet equipped and that I'm at least fairly knowledgeable about the mechanical side of the systems operation.

The electrical side of things - the "E" in KE-Jet, as it were - I'm still getting caught up to speed on. And that's why I've come here looking for some possible guidance.


The problem:
The car generally runs, drives and idles well enough. However, its started having a hard cold start and stumbling stalling issue.
Any time the issue crops up the 02 warning light with come on. Light on = Problem. No Light = No Problem.

The O2 sensor has been replaced (it appears) fairly recently with a universal splice-in type. I've also replaced by the OVP and fuel pump relay. And I've checked the wiring between the ECU/Lamba control unit and the O2 sensor.

When the car is warmed up and running well and I try to take a reading between pins #2 and #3 on the diagnostic socket I get a steady 2.7 volts. No fluctuation. When I take a reading directly from the O2 sensor plug under the passenger-side carpet I get a variable reading that bounces between about ~118-122 mV.

Are there any other sensors tied directly into this circuit that could be causing an issue/interrupt? Otherwise I'm wondering if my ECU isn't just slowing starting to fail.

Thanks in advance,
BC
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post #2 of 9 (permalink) Old 04-10-2019, 12:38 PM
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Date registered: Dec 2012
Vehicle: 89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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Welcome to the forum.

The ECU's in these cars are rather robust if they are left alone. Things like hot plugging-unplugging them is highly advised against.

I would suspect your O2 sensor/connection the most since someone tried to save $40 to splice in a universal one. Might have also damaged things in the process if they were not skilled in the art.

The oxygen sensor is supposed to be bouncing around/sweeping a lot larger voltage (do not quote me but something like 0.5V +/- 0.4V.
Again do not quote me on this but check into it.

If you are to replace it, I would stay away form the universal and just get one that plugs in. That's what I've done (always).

I think you are reading a steady 80% duty cycle which might be just the oxygen sensor fault (please check that)
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post #3 of 9 (permalink) Old 04-10-2019, 03:01 PM
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Date registered: Oct 2007
Vehicle: 89 190E 2.6 x2
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I would agree that most likely it's a bad split on the 02 sensor connection as well. With a bad 02 sensor, you won't have any fluctuation in voltage.
As dolucasi said, best to replace w/ a plug in sensor.

Since you're familiar w/ Volvo k-jet, troubleshooting, I can tell you that everything is generally the same. My neighbor who used to own a Volvo shop, helped me test my 02 sensor and tune my duty cycle a couple months ago. I also wrote up a post about how we used an 02 sensor tester which provided a visual representation of whether the sensor was working.

https://www.benzworld.org/forums/w20...en-sensor.html

#1.1989 190E 2.6 355 Diamond Blue Metallic, lots of euro goodies, Borbet wheels, Koni shocks, Brabus W124 springs

#2.1989 190E 2.6 877 Blue Green metallic, Euro headlights w/ HID projector retrofit, 15" AMG monoblock wheels, AMG replica body kit, rear lip spoiler

#3 1992 190E 2.6 888 Teal Blue Metallic, donor car parted out.
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post #4 of 9 (permalink) Old 04-12-2019, 08:08 PM Thread Starter
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Thank you both for the quick response. Apologies for not being able to return the favor--it was on of those weeks at work.

The problem seems to have disappeared just as quickly as it appeared. Which is nice since it makes the car much more driveable, but does complicate troubleshooting the root cause. I went ahead and ordered a new Bosch direct-fit O2 sensor and am contemplating dealing with the cat while I'm at it. The rear half of the exhaust looks newer but, based on it's appearance, I wouldn't be surprised if the cat itself were original.

I initially suspected a bad splice too. Seemed the most obvious culprit. But no amount of wire tugging seems to be able to trigger the symptom. Based on the info I've managed to dig up so far however the numbers I'm getting directly from the sensor are definitely out of wack. So the sensor itself may just simply be dead. It does have me scratching my head a little bit though since I've never known a failing O2 sensor to cause only intermittent issues like this. Maybe I just need to keep reading up on it though.

Which also reminds me--thanks for posting that link to the O2 tester post. That ought to come in handy when I get around to checking and adjusting my air/fuel mix. It's also nice to know that at least some of my Volvo knowledge should carry over.

Could either of you guys possibly recommend a good post/link on using the X11(?) diagnostic port and/or schematics for building a blink code reader for it? I'm not too shabby with a soldering iron, but most of the links I've seen so far on the subject are either dead, or lacking in technical details.
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post #5 of 9 (permalink) Old 04-12-2019, 09:22 PM
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The new 02 sensor will gave you a good baseline to start from before you start mixture adjustments.
Here's a good post about how to build an X11 code reader
https://www.benzworld.org/forums/w12...de-reader.html
I forget that Federal cards don't have the diagnostic LED (Dolucasi and I have both CA cars)

#1.1989 190E 2.6 355 Diamond Blue Metallic, lots of euro goodies, Borbet wheels, Koni shocks, Brabus W124 springs

#2.1989 190E 2.6 877 Blue Green metallic, Euro headlights w/ HID projector retrofit, 15" AMG monoblock wheels, AMG replica body kit, rear lip spoiler

#3 1992 190E 2.6 888 Teal Blue Metallic, donor car parted out.
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post #6 of 9 (permalink) Old 04-12-2019, 10:33 PM
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Date registered: Dec 2012
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Just to add to 355's comments, and touch on your Cat question. If the car is not burning any considerable amount of oil your CAT has many years of service left in it.
My original got replaced at 190K miles and my car was burning significant amount of oil for the last 50-60K miles.

The CAT's are NLA so your only choice is aftermarket and the quality of them even brand new will not be anywhere near your 80K mile old CAT.

Do you have the pre-cats like our 89's? These are close to the exhaust manifolds and they do serve a function but those are generally not replaced anyway.

So your CAT's will not be effecting your O2 sensor issues anyway.

Let's see if you can get back to 450mV +/- 400mV O2 sensor swing that is needed after you replace the sensor.

- Cheers!
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post #7 of 9 (permalink) Old Yesterday, 06:29 PM Thread Starter
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Well, I installed a new O2 sensor tonight. Factory style Bosch. No dice. The warning light has been on continuously the past few days and right now the car just idles like crap for a few seconds before dying. It was driving great last weekend though. Spent an entire day running around taking care of errands without so much as a stumble. I'm really scratching my head at it. I was under the impression k-jet cars with Lamdba just went into full mechanical mode new the emissions system failed. But so far I haven't seen anything besides the sensor, the ecu, and the wiring between them that should trigger the warning light. Or more importantly why that light being on should make the care so impossible to drive.

It looks like the '87 does have pre-cats installed. Small bulges where the header pipes meet the exhaust manifold?
Thanks for the link to X11 tester build. Looks very straight forward. I'll probably cobble one together this coming weekend. I also noticed that the emissions label under the hood says the car conforms to U.S and State of California regulations. But as far as I can tell I only have the 9-pin X11 port with no built-in LEDs. Not sure what to make of all that either.
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post #8 of 9 (permalink) Old Yesterday, 10:15 PM
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Now that you replaced the oxygen sensor, you should repeat the voltage testing and report and that.
You are correct these cars go into limp mode when the OVP malfunctions (and the ECU voltage is completely cut-off)
However your condition is different (O2 sensor/connection issues) so I'm not sure if the car goes to limp mode (mechanical only control) in that case. You can check this with EHA current.

Measure your EHA current. If it is zero, it must be in limp mode, meaning the EHA is no longer regulating your lambda ratio.

Measuring this current will also tell you a bit about what is happening. If it is railed in one direction or the other (+20mA or -20mA), you know something is terribly wrong.

- Cheers!
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post #9 of 9 (permalink) Old Yesterday, 11:03 PM
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I should add one more comment:

I have owned my car for the first 13 years and the last 3 years. It has only thrown a check engine light once during these years at 60K miles under regular driving conditions. And that was when I took the car on a skiing trip to tahoe (high altitude). At that time the dealer molested the lambda tower and adjusted my lambda (upon my return to sea level)

Just making a point that it is not that common to have the check engine light trip. Oxygen sensor can do it, EHA being railed will also probably do it (I believe). OVP malfunction does not do it. Ignition malfunctions will also not trip the check engine light.

So it should not be too difficult to diagnose your problem, may take some patience though.

- Cheers!
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