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    Thread: Suspected Oxygen Sensor Controller Problem...

    1. Semi-n00b
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      06-02-2013 09:30 PM #1
      Long and short of it is a friend of mine fabricated a new exhaust system for my stock 1989 Cabriolet (CIS K-Jetronic) and now the O2 system doesn't appear to be working. I replaced with a brand new O2 sensor... still running mega rich with no control. I bought a meter to measure the duty cycle on the test port... measuring 4.5% (or 95.5% if I reverse the leads) all the time, no matter what I do, what I connect or disconnect, how rich or lean I adjust the air fuel mixture, etc. I'm thinking it's the O2 controller... has anyone ever heard of having one damaged from MIG welding on an exhaust while the O2 sensor is connected? (Not that I know for a fact this happened... just a theory.) I've tried some of the diagnostics from the cabby-info.com page but I can't really get anywhere because of the perpetually constant duty cycle reading. Any way to test the O2 controller itself? Can I check an output that leads to the frequency valve side of things? I'm kinda stuck. Thanks for any input...

    2. Member briano1234's Avatar
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      06-02-2013 10:06 PM #2
      Quote Originally Posted by onephatcabby View Post
      Long and short of it is a friend of mine fabricated a new exhaust system for my stock 1989 Cabriolet (CIS K-Jetronic) and now the O2 system doesn't appear to be working. I replaced with a brand new O2 sensor... still running mega rich with no control. I bought a meter to measure the duty cycle on the test port... measuring 4.5% (or 95.5% if I reverse the leads) all the time, no matter what I do, what I connect or disconnect, how rich or lean I adjust the air fuel mixture, etc. I'm thinking it's the O2 controller... has anyone ever heard of having one damaged from MIG welding on an exhaust while the O2 sensor is connected? (Not that I know for a fact this happened... just a theory.) I've tried some of the diagnostics from the cabby-info.com page but I can't really get anywhere because of the perpetually constant duty cycle reading. Any way to test the O2 controller itself? Can I check an output that leads to the frequency valve side of things? I'm kinda stuck. Thanks for any input...
      Yes that is a possibility. Even tho you are grounding the pipe, the fact that you are putting HIGH current near it is enough to make me always either disconnect the negative battery cable, or unplug the sensor. The Electronic Gremlins are a wily sort they are always looking for new ways to ZAP you.

      Have you tested the sensor?

    3. Member kamzcab86's Avatar
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      06-02-2013 11:48 PM #3
      Quote Originally Posted by onephatcabby View Post
      has anyone ever heard of having one damaged from MIG welding on an exhaust while the O2 sensor is connected? (Not that I know for a fact this happened... just a theory.)
      I have. A Vanagon guy recently fried his Subaru (conversion) ECU (genuine ECU; one that does a lot more than our Jetronic controllers) when having a piece of the engine welded back together for a temporary fix... and failed to disconnect the battery properly.

      Quote Originally Posted by onephatcabby View Post
      I've tried some of the diagnostics from the cabby-info.com page but I can't really get anywhere because of the perpetually constant duty cycle reading. Any way to test the O2 controller itself? Can I check an output that leads to the frequency valve side of things? I'm kinda stuck. Thanks for any input...
      Have you done the tests in this guide: http://cabby-info.com/Files/LambaTesting.pdf ? If not, do them and report back. Also, what's not in that guide but is in the linked table (http://www.cabby-info.com/images/Fue...OXSTable.png): Actuating the full-throttle switch. If you're seeing no response from the ECU, I'd start with the grounds and checking for power at the ECU.
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    4. Junior Member Mo''s Avatar
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      06-03-2013 07:08 AM #4
      Quote Originally Posted by onephatcabby View Post
      .......... has anyone ever heard of having one damaged from MIG welding on an exhaust .......
      Possibility is 100%, probability is completely random.
      ---
      Maybe too late for this bit at this point, but best practice while welding on computer controlled cars is to first disconnect both battery cables and connect them together.
      The welding ground clamp should be connected directly to the component being welded and as close to the weld area as possible.
      While not often practical, disconnecting all ECUs is preferable.
      ---
      Moving on, you need to know if your car's lambda control ECU is still good or not.

      Start by bypassing the fuel pump relay with either a jumper from 30 to 87 or swap in the horn or load reduction relay (whichever fits) and switch on the key. Fuel pumps should now be running, lambda ECU should be powered up.

      Go to the frequency valve on the fuel distributor, measure voltage on the red/yellow wire, expect approximately battery voltage.

      Disconnect the oxygen sensor, measure voltage on the green wire from the ECU, expect 0.45 VDC to 0.5 VDC.

      While the oxygen sensor is disconnected, also disconnect the throttle switch and thermo switch (not the thermo-time switch, that one is not connected to the ECU at all), check duty cycle at the test port expecting 50%.
      ---
      Given the symptoms you've posted, I'd be hoping for a simpler issue than a fried ECU.
      I'd be suspecting (read that as "hoping for") a failed lambda supply relay, an open lambda ECU ground at the cold start valve, possibly a short to ground in the oxygen sensor's signal lead back to the ECU.
      The oxygen sensor's green lead wire is actually a coaxial, shielded cable, the signal wire runs inside of and insulated from an outer braided and grounded noise shielding sleeve. If the signal shorts to the shield the ECU will read that as a lean condition and compensate rich.
      ---
      What we're doing here is powering up the lambda ECU and frequency valve, verifying power and ground, then disconnecting all inputs so the ECU will run in open loop.
      ---
      What duty cycle meter did you get and can you post a link to it? Perhaps a photo of the meter's display while it's in duty cycle mode?






      .
      Keep a Straight Face.
      Sincerely,
      Mo'

      .

    5. Semi-n00b
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      06-03-2013 08:33 AM #5
      Thank you for all of the feedback. I will try the new suggestions this evening and get back to you all. Here is a link to the meter I picked up, it was the only one I could find stocked locally. http://www.harborfreight.com/lcd-aut...kit-95670.html

    6. Member kamzcab86's Avatar
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      06-03-2013 12:41 PM #6
      Quote Originally Posted by onephatcabby View Post
      Here is a link to the meter I picked up, it was the only one I could find stocked locally. http://www.harborfreight.com/lcd-aut...kit-95670.html
      That meter does not have a duty cycle setting. It has dwell instead. So, just to be sure (since you mentioned measuring duty cycle), were you using the dwell setting (at 4 cyl.), or the Hz setting (which, on that meter, does not measure %)? If it was the latter, next go 'round use the dwell setting at 4 cylinder (it will read in degrees), with the red lead connected to the blue/white wire, and the black lead connected to ground.
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    7. Semi-n00b
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      06-03-2013 01:10 PM #7
      Crap... I'm sorry... in my haste this morning, I accidentally linked the wrong meter. It's this one... with Frequency / Duty Cycle functions. (I kinda wish I had one for dwell instead though.) http://www.harborfreight.com/5-in-1-...ter-98674.html The reviews on the meter were good, I'm actually a manufacturing engineer in the microelectronics industry and for being a cheapo Chinese Harbor Freight meter it seems to be as accurate as my $300 Fluke meters, my Flukes don't have a duty cycle or dwell setting unfortunately. I'm not sure I trust my duty cycle reading though... I have the positive lead on the blue and white wire in the test port, negative lead to ground... and I get 4.5% duty cycle all the time... even when I close the wide open throttle switch. Once I establish confidence in my duty cycle measurement, I'll probably be fine tracing out the issue, I'm just not certain if a 4.5% duty cycle is even feasible. Additionally, the O2 sensor is brand new, I bought and installed it as part of the troubleshooting process. It's a genuine Bosch replacement. I'll try the fuel pump relay trick tonight (done it before when setting up my warm-up regulator pressures) and check measurements suggested. Thanks again for all of the help...

    8. Junior Member Mo''s Avatar
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      06-03-2013 01:27 PM #8
      Quote Originally Posted by onephatcabby View Post
      Thank you for all of the feedback. I will try the new suggestions this evening and get back to you all. Here is a link to the meter I picked up, it was the only one I could find stocked locally. http://www.harborfreight.com/lcd-aut...kit-95670.html
      Um, this one star review on the HF page linked above might be a clue........

      _________
      "disappointing

      This meter may be an OK DMM, but with its inductive pickup will NOT work reliably on wasted-spark ignition systems (used on Fords and other makes), nor does the dwell feature when used ...Read complete review

      This meter may be an OK DMM, but with its inductive pickup will NOT work reliably on wasted-spark ignition systems (used on Fords and other makes), nor does the dwell feature when used to set the duty cycle on computer-feedback carbs. My experience of trying it on other cars has been uniformly disappointing; the tachometer is awkward, readings using the inductive pickup erratic, as is the dwell. Overall one of the biggest disappointments I've bought from HF."

      _________

      Duty cycle on feedback carbs is very similar to the duty cycle on CIS' frequency valves, both are mixture control solenoids.

      Test that tester on two circuits on the car.
      Connect to Terminal 1 on the ignition coil, expect dwell to increase drastically with RPM. Best I recall, somewhere around 18 to 20 degrees (on the 4 cyl scale) at idle, much higher at higher RPM, like 60 to 75 degrees.

      Then test on the green/white Hall generator signal wire at the base of the ignition distributor.
      Best I recall on this one is around 40 degrees, this one should be rock steady no mater what RPM.

      No help from the HF page either, the link to the meter's manual doesn't work, at least not here with all three browsers I tried.
      ---
      Oh yeah, OP has posted conflicting info, clarification can help us help you.
      First post you posted;
      "......measuring 4.5% (or 95.5% if I reverse the leads) all the time...."
      As already noted, the meter you linked to doesn't read directly in duty cycle. Therefore, it cannot display as a percentage. Further, 90 degrees is the maximum a dwell meter can read on a 4 cylinder scale.
      The three cylinder scale should max out at 120 degrees, go there only if you like converting readings.
      All CIS troubleshooting materials I've ever seen list values in percent of duty cycle, 4 cyl dwell or both.

      Even further, dwell meters generally (I say generally, I know there are exceptions, I have one, gives me a headache when I get it switched around, especially when I fail to notice) can only display negative slope values, reversal of the leads should not be necessary nor desirable.
      Keep a Straight Face.
      Sincerely,
      Mo'

      .

    9. Junior Member Mo''s Avatar
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      06-03-2013 01:40 PM #9
      Quote Originally Posted by onephatcabby View Post
      ..... I accidentally linked the wrong meter. ......
      Sorry too, cross posted.
      Page for that meter does have a working manual download.
      Looked briefly through the manual, used search for 'slope' too, found nothing.
      While in the duty cycle range, look close at the display for a + or - symbol, indicating slope.
      It's negative slope we want, or at least prefer, more headaches in positive slope.
      While in duty cycle mode, try toggling the 'range' or 'select' buttons, try short and long press combinations, any you care to guess at, watch the display closely for the appearance of + or -.
      Keep a Straight Face.
      Sincerely,
      Mo'

      .

    10. Member kamzcab86's Avatar
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      06-03-2013 01:42 PM #10
      Ah; wrong meter explains things!

      Quote Originally Posted by onephatcabby View Post
      I have the positive lead on the blue and white wire in the test port, negative lead to ground... and I get 4.5% duty cycle all the time... even when I close the wide open throttle switch.
      A) Cabs produce negative slope; most meters read positive slope. Therefore, reverse the leads: negative lead on blue/white wire.
      B) Be sure the meter is in the "duty" mode when measuring (% should appear on the screen). I have to press "range" on my meter after selecting "Hz/%".

      If you're certain the meter is functioning properly, the measurement remaining the same with the full-throttle switch actuated indicates something is amiss that you'll need to track down (as previously stated: power, grounds, relay, etc.).

      Ron: My Craftsman does not display slope, nor does the manual stipulate what it reads. I had to figure that out by actuating the full-throttle switch.
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    11. Semi-n00b
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      06-03-2013 11:13 PM #11


      Thank you everyone for the time you put in to this thread. Just the few responses you all gave had quite a bit of typing and thought involved, and it's very much appreciated. I got home from work tonight to an empty house, which was the perfect time for me to dive in uninterrupted into trouble shooting. I started by connecting the meter to the test port with the leads reversed (negative on the blu/wht wire). I then installed my jumper wire in the fuel pump relay socket... turn the ignition to on and walked around to check the duty cycle. Low and behold it was reading right there at about 50%. I started the car (it was cold) ... the vibration from the car starting jostled the test leads and they fell to the side of the shock tower... right at that moment the duty cycle instantly climbed to 95%. I reached down to grab the test leads and as I lifted them back up the duty cycle fell down to 50%. After fiddling with the wiring a bit, the duty cycle again was pegged at 95% (because I reversed the leads polarity this time... otherwise it would still be reading 4.5% like earlier noted) and didn't respond to anything I did. I turned off the car, unplugged the O2 sensor black wire from the green coax. I measured the VDC at the green wire... .021mV (basically noise). I checked the continuity from the green coax to ground... BINGO! Dead ringer short to ground. 'Mo nailed it... shorted coaxial shielding to the center conductor. So it ends up my friend welding didn't cause this after all. (which made me relieved... I felt bad for him, he was really worried .) I have had some really bizarre intermittent idle and running issues from time to time leading up to this... I bet that thing was bouncing around randomly shorting here and there for years. I spliced together a new coax cable, attached a new spade connector, put everything back together and was finally able to tune the air/fuel mixture on this car. It has never sounded this good, I'm finally happy with it. Thank you again everyone. (And I highly recommend this meter... great value for $40, lots of functions.)


    12. Member gunnarpaul's Avatar
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      06-04-2013 10:45 AM #12
      Car looks awesome!
      If you're heading to the grave, you don't blame the hearse.

    13. Semi-n00b
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      06-04-2013 03:36 PM #13
      Thanks Gunnarpaul!

    14. Member rabbitnothopper's Avatar
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      06-04-2013 06:50 PM #14
      can you explain the coax cable idea?

      i know the green wire is the shielded wire which surrounds the interior wire

      but...how did you manage to fix it?

    15. Semi-n00b
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      06-05-2013 12:19 AM #15
      rabbitnothopper~ The shielding was shorting to the center conductor at the very end of the cable where the phenolic spade connector is. The shielding terminates to nothing essentially, it just ends at the connector. I cut the connector off leaving about an inch of wire intact. I then removed the shielding from that piece so that all was left was the center conductor sticking out of the connector. I then crimped an environmental splice (a.k.a. a butt splice) onto the wire sticking out of the connector. I then took a fresh 6 inch length of insulated 18 gauge wire and inserted and crimped it into the other end of the butt splice. The original "green wire" I then stripped back the shielding about an inch and stripped the center conductor to which I used another butt splice to attach it to the freshly lengthened piece. The shielding is really only necessary where the O2 sensor cable becomes bundled with other cables to go through the firewall, the shielding prevents noise from being induced into the sensor wire from adjacent wires. (You'll notice that the wire coming from the O2 sensor itself is just a simple non-shielded wire.) That's about all there is to it. I added 6 inches of wire just so I could reach the connector from the top side of the car for future potential diagnostics purposes... it wasn't necessary, I could have just stripped fresh wire on the center conductor of the green wire and used a butt splice to reattach the original connector. Below is a picture of a butt splice... just in case folks are unaware. I'll take a picture of the actual repair tomorrow, to hopefully clarify my above ramblings.


    16. Member rabbitnothopper's Avatar
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      06-05-2013 09:32 PM #16
      thanks i know EMI effects all kinds of electronics
      good explaination which makes sense

      i was just curious how you fixed it
      why didnt you use a small coax cable with twisted wire in the center?
      there are wires adequate to this application
      that wire would have also helped shield the o2 reading

      and yes according to diagrams and looking closely at the ends of the wire

      the interior wire is the only important wire

    17. Member Vwspen3310's Avatar
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      06-18-2013 07:48 PM #17
      on the exact same subject:

      I have been trying to figure out the performance issues of my 81 1.7l cabby, and it turns out me as well as the previous owner (maybe 5 or more years) have been driving the thing with the oxygen sensor casing grounding to the signal wire. I saw this thread and you had the EXACT same issue I was having. 96% on my duty cycle reading. Popped off the connector and sure enough, the retarded PO had the casing and the signal wire clamped together.

      Its now fixed and adjusted perfectly thanks to you posting your issues!
      Do it once, do it right.

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