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  1. mr_s

    '97 Vortec 5.7 K2500 Suburban 'Open Loop' issue

    Here's the other thread where I documented everything I tried: https://www.gmt400.com/threads/check-engine-light-query.47659/
  2. mr_s

    '97 Vortec 5.7 K2500 Suburban 'Open Loop' issue

    Yeah, I finally got it sorted a little while ago (think I had another thread and forgot to update this one!). I replaced the ECU with one from eBay (with the same part numbers). Seems that either a previous owner had the EGR and O2 tuned out of it - after testing everything else, it was the...
  3. mr_s

    Check Engine Light query

    Well, the new ECU went in this evening and..... it's sorted - went into closed loop mode as soon as it got up to temperature. Happy days! The only trouble now is that the EGR has been blanked off (and I can't see any connectors for it in the area...) and it sometimes throws a check engine...
  4. mr_s

    Check Engine Light query

    Ordered a replacement 'stock' ECU from a '97 K2500, so I'll report back when it arrives and is fitted...
  5. mr_s

    Check Engine Light query

    Thanks for explaining @Schurkey that makes sense. The o2 sensors do indeed report sensible numbers (0.7-0.8v at idle and if I blip the throttle they go to 0.1 or so). I keep leaning towards the PCM being the issue, do you happen to know if I can use a PCM from any 1997 Vortec 5.7, or if it...
  6. mr_s

    Check Engine Light query

    @Schurkey 'Grasping at straws' is the main focus for the battery disconnect... And predictably it made no difference whatsoever. The scan tools - 2 different OBD2 bluetooth 'ELM327' type adapters, 2 different apps on my phone (the main one I use is Torque Pro) shows no codes unless I provoke it...
  7. mr_s

    Check Engine Light query

    Just a quick update on this (having finally found a few minutes to work on it!), I removed pin 23 from the red connector on the ECU, and as predicted it had the same effect as unplugging the ECT sensor. I've now disconnected the battery and will leave it a couple of days, see if it helps. If...
  8. mr_s

    Check Engine Light query

    @AK49BWL Yep, I figured that would be the case, but I'm running out of ideas...! Not had much chance to work on her over Christmas, but I may get a few hours this weekend. I'm definitely checking the right sensor - I removed the connector to the other one (in the block) and the dash gauge...
  9. mr_s

    Check Engine Light query

    @Schurkey The scan tool reports no fault codes, all it says is 'Open Loop due to insufficient temperature'. The scan tool reports coolant temp as being read correctly (replaced the thermostat and ECT sensor just in case, as I have no idea how old they are), o2 sensors are brand new and reporting...
  10. mr_s

    Check Engine Light query

    Thanks @df2x4 and @b454rat, but it turns out it's just me being a dumbass... The Check Engine Light comes on and goes out as it should. However, if you turn the engine off and turn the key back to 'on' then the light doesn't reappear. If you take the key fully out, leave it a few seconds then...
  11. mr_s

    Check Engine Light query

    I have a 1997 K2500 Suburban, and when I go to start it all of the lights in the cluster light up momentarily and then all go out. The 'Check Engine' light doesn't come on at this point (the bulb is good, I can trigger it by unplugging various sensors, so I know the light itself is good). Just...
  12. mr_s

    '97 Vortec 5.7 K2500 Suburban 'Open Loop' issue

    Quick update: New ECT sensor and thermostat now installed. No change, the old ones were OK. That said, it does get up to 194F now, as I wanted it to - so it's not all bad! Could the 'insufficient temperature' be related to anything else that I'm missing?
  13. mr_s

    '97 Vortec 5.7 K2500 Suburban 'Open Loop' issue

    Ok, so the wire on pin23 on the blue connector to the ECU is a 'known' (just not by me until now...) mod that can be done, as documented here: https://chevroletforum.com/forum/silverado-fullsize-pick-ups-21/diy-walkthrough-vcm-ecu-ground-wire-update-39893/ Out of curiousity, I pulled the ECT...
  14. mr_s

    '97 Vortec 5.7 K2500 Suburban 'Open Loop' issue

    Another thing I noticed, is that on pin 23 of the blue connector I have a blk/wht wire connected. I've looked at all the schematics and they all say that pin isn't used. I'll trace it back later to see where it goes, but does anyone have any ideas what it might be for?
  15. mr_s

    '97 Vortec 5.7 K2500 Suburban 'Open Loop' issue

    Well I've driven it around a bit, and been back to the garage (to check that my app was reporting correctly) - it's still not going into closed loop and the emissions are high. Not sure what to try next, any ideas? Are there different parts of the ECM that require signal from the ECT sensor? My...
  16. mr_s

    '97 Vortec 5.7 K2500 Suburban 'Open Loop' issue

    I haven't cleared any codes, but I did disconnect the battery for a few days while I was doing some recent work... I'll run it a few times, see if that helps. Thanks!
  17. mr_s

    '97 Vortec 5.7 K2500 Suburban 'Open Loop' issue

    Yup, that's why it's got me stumped...
  18. mr_s

    '97 Vortec 5.7 K2500 Suburban 'Open Loop' issue

    Looking for some assistance with a problem I have... I've got a 1997 K2500 Suburban with a 5.7 Vortec and it won't go into closed loop mode, I have the 'Torque Pro' app on my phone, and a Bluetooth OBDII dongle plugged into the car. The o2 sensors seem to be sending the correct signals back...
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