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Corsa C both fuel trims too high

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  • [Corsa C 2000-2006] Corsa C both fuel trims too high

  • #2
    Welcome to the Forum.
    You should know by now, that is what daughters do

    My first suspicion is the new Lambda sensors - If they were NOT genuine GM (Vauxhall) or Bosch, there is a good chance that they have let you down.
    After-market sensors are notoriously unreliable.



    • #3
      yeh dont I know it

      thanks for the welcome and reply

      I fitted one Bosch and one another known make but I cant recall the name - it came from lambadapower, I dont think it was NGK and the bosch one went on the front. If I put the scanner on, I can get the 02 sensor readings live - presume that will tell me? or using a multimeter across the pins?

      EDIT the rear one was delphi


      • #4
        ok, thats interesting - have just read the live data on the 02 sensors...

        Engine warming up
        S1 is reading between 0.10 and 0.150 ie going up and down with STFT showing 25%
        S2 is reading static at 0.460 with STFT showing 99.2%

        Engine hot
        S1 reading 0.00 at idle 25% STFT. 0.00 to 0.100 when revved 0.00 STFT
        S2 0.665 to 0.705 STFT 92%

        PS have edited the above
        'LS' Member
        Last edited by SXIcorsa; 03-09-2016, 05:24 PM.


        • #5
          I'd try putting a new coolant temperature sensor on it. They're cheap and easy to fit. They go weak before they fail and can cause problems with fuelling.

          Delphi are usually OEM spec by the way
          1972 Viva restoration thread -


          • #6
            done this, no difference. have connected a fuel pressure gauge to it. With key turned and pump on its showing 1.5 BAR. haynes says it should be 3.8 BAR but doesnt say whether engine should be running or not.

            Is my fuel pressure too low?


            • #7
              changed the fuel filter, now got nil fuel pressure showing on gauge! No squirt of fuel when valve pressed down after running for 10mins, if just slowly comes out. Engine still starts ok and idles for 5 mins ok then idles rough.

              edit - getting confused now. shows 3 bar when idling but brand new tester has a slight leak at coupling....
              'LS' Member
              Last edited by SXIcorsa; 04-09-2016, 07:33 PM.


              • #8
                A long shot question here . . .

                Have you checked the oil pressure sensor? Is it leaking? You might have to unplug the cable to check.

                Or has it been leaking before and replaced?



                • #9
                  Hi there, and yes! (read on lol) it is leaking quite badly and will put a new one on wednesday. But I do have some good news - the issue seems fixed. The bad news is I'm not sure how! Heres what I did in the end, over last few days

                  1. read codes p0170 and latterly p0313
                  2. unplugged MAF - engine ran the same (rough)
                  3. swapped MAF for 2 others from running cars - made no difference so reackoned not the MAF
                  4. measured fuel pressure, gauge was faulty but managed to get 3 bar with engine idling - changed fuel filter. because of the 3bar thought the pressure was ok.
                  5. checked intake hoses for leaks - none
                  6. took off purge valve and checked for leaks with Mityvac (none) also put power to it and made sure it clicked.
                  7. checked spark plugs - all same colour very sooty
                  8. changed temp coolant sensor

                  still running rough and STFT climbing to 25% straight after codes cleared.

                  by now, I was stumped and on verge of taking to garage. One thing that was bothering me was lots of oil in front 02 plug - dripping in oil when you took it apart but no oil on any of the wires feeding it. Googled that and found issue with oil wicking along wiring loom often as a result of the oil sensor. Cleaned the plug as much as possible and put it back in - no difference, still running rough. So I went to garage as tank approaching red and put in half a tank, then went for a 40 miles drive and ranted it. When accelerating it was ok, when feathering throttle and cruising it was jumpy BUT after about 10 miles I suddenly noticed it was running smoothly. Drove another 25 miles, all good then parked up. Checked STFT and it was 0%, also LTFT as well. Car now running ok! One other thing I did prior to the 40m trip was wrap tape around the front 02 sensor as I could not see how it was getting oil in it except maybe from perhaps a mist from the leaking oil sensor?

                  What fixed it??!!


                  • #10
                    Great that all is OK. But i think that it may be short lived.

                    Oil gets into the wiring and tracks along the cables from the leaky oil pressure sensor.

                    I had the same issue starting back in May (lots of posts on this forum). It took till a few weeks ago to finally find the issue.

                    In my case the oil found its way to the O2 sensor underneath the car (downstream of the CAT). I cleaned the connector out with brake cleaner and all is good so far. I had checked all other connections including the upstream O2 sensor and no oil was present.

                    I would suggest

                    1. change the oil sensor ASAP (which you are doing)
                    2. check the connector of the O2 sensor downstream of the CAT. It's under the car so you need to lift it on a hoist. You probably have oil there as well. Clean out both the make and female connectors
                    3. Clean the O2 sensor upstream of the CAT. Get rid of the oil you have found.
                    4. Check the connector that goes to the top of the throttle body for oil as well. Clean it if any oil found

                    You may need to check the connectors where you find every week until you see no further signs. I use a cotton bud to swab the connectors to see if any oil is there.

                    The oil can kill the O2 sensors but if they are recently new cleaning the connectors regularly might save them

                    What fixed it? I think the cleaning of the connectors on the upstream O2. But the problem will come back if you don't get rid of all the oil in the connectors.

                    Hope this helps


                    • #11
                      yes it does help alot. It wasnt until I googled "oil in 02 sensor plug" that i realised there was even this issue and some Mercs have it alot as well apparently. I do recall taking plug out of MAF a while ago and thinking that was oily also. Just couldnt work out how oil was in there when I'd sprayed it with contact cleaner. Only this afternoon I was blaming my daughters boyfriend for spraying the plugs with oil!

                      Just one question re. the what fixed it - I did clean out the front 02 plug many times with tissue as much as I could but it still ran rough for 10 miles before clearing - why wouldnt the improvement be noticed straight away if it was this that was causing the issue?


                      • #12
                        Honestly i am not sure why the fix didn't happen immediately. I can only suggest an intermittent short caused by the oil. Perhaps ECU also trying to make sense of the messages it is receiving????

                        My own car had some good days and not so good days as i tracked the problem down.


                        • #13
                          I would guess you've had more than one cause for this problem and by what you've done you've resolved them. The theory says that the ECU will work on current information and not be adversely affected by historic codes - but - I know from experience that this isn't always the case. The ECU can struggle when old codes are present and it can sometimes take a while for things to stabilise.

                          As said, replacing the oil pressure sensor is a must as oil in the wiring gets into the ECU connection (as well as everywhere else mentioned) and then you've got real problems.
                          1972 Viva restoration thread -


                          • #14
                            well, the lights on again. Daughter used the car today to do four 3 miles trips ie to work back home for lunch then to work then home at 5.30pm. Lights on, engine juddering. I cleared the codes, went for a drive, STFT 0% from the off but engine juddering a bit the cleared after 3 miles and STFT still 0% and no light. Reading live data whilst driving, front 02 sensor was showing mostly 0.00 unless I floored it then it started showing readings and at end of the drive the front 02 readings were showing whenever foot was on throttle whatever the speed.

                            Does the oil travel along the loom inside the wire casing ie along the copper wires itself. The front 02 sensor feed wires are bone dry, yet still wet with oil inside the plug and thats the only way I can see the oil would travel?

                            things are starting to fall into place now. I could never work out why both 02 sensors were playing up 6 mths ago when cars only done 80K. Replacing them both fixed things...until the oil is running in to the 02 sensors and knocking them out??? What about I take them off and upend them for a week (to let oil traces run out) and leave the sensor plugs hanging or is the damage already done?
                            'LS' Member
                            Last edited by SXIcorsa; 06-09-2016, 10:20 PM.


                            • #15
                              To the best of my knowledge the oil tracks on the copper wire and get into the inside of the plug. Capillary action apparently. My downstream O2 sensor was bone dry on the outside of the connector and cables. The oil was inside the plug. Here is a picture of the old sensor connector. The connector under neath the car was also quite wet. I dont have a pic of that.

                              Replacing the sensors will work for a while since the terminals are dry. But after a while, (maybe 500kms) the faults will return.
                              The sensors may be OK. The connector might stop some of the oil from getting into the workings of the sensor. But the oil is causing false readings to the ECU

                              You need to get rid of the oil in the harness. Only way that worked for me was to check and clean out the all the connectors, one by one, eliminating each as a cause until no more oil showed up. (I was lucky. Oil only was in the downstream sensor)

                              Unfortunately you seem to have a lot of oil in the works. (MAF plug, spark plugs as you mention)
                              'LS' Member
                              Last edited by grwalker; 07-09-2016, 06:40 PM.