87MJTIM Posted April 18, 2018 Share Posted April 18, 2018 As my signature states: 87 4.0 Laredo. I have Nick's REM to give me readings from the ECU. Lately, the engine is running stuck in open loop (OL). I have the REM set to display engine temp., Open/Close status, O2 volts and (something else). I start the truck up in the morning and let it run for a few minutes - 2 to 3. The REM shows it switched to CL. I start to drive away and it switches to OL. It will remain in OL. It does not switch back to CL. The ECU came out of a 90 XJ with a 5 spd. The O2 sensor was replaced last fall with the NKG, or whatever # Cruiser states. The O2 volts at start up are 4.+ volts. I can watch the volts drop to ~ +/- 2.5v when it switches to CL. I will drive only a short distance when it switches back to OL. The O2 will stay at or below 2.5. The O2 usually reads below 2.5 most of the time. The engine temp per the REM is at 185* and below while moving. At idle, it will rise up in to the 190s. Once I start to move, the temp drops back down. Before I pull out a parts cannon, does anyone have a suggestion on where to start my testing? The Renix fuel injection manual only describes how the system works in a perfect world. It does not give a detailed trouble shooting guide. I am going to replace the t-stat to address the temp issues. What about a CTS? (Part # for a CTS?) Link to comment Share on other sites More sharing options...
Ωhm Posted April 18, 2018 Share Posted April 18, 2018 Using REM, find your Fuel Trim values. This will determine if you're running Rich or Lean. Link to comment Share on other sites More sharing options...
87MJTIM Posted April 18, 2018 Author Share Posted April 18, 2018 When in OL, FT is 128 short term. REM show lean. Link to comment Share on other sites More sharing options...
Strokermjcomanche Posted April 18, 2018 Share Posted April 18, 2018 The O2 sensor should constantly and quickly be moving back and forth between 1and 5 .Had the same issue and had to replace my brand new NTK sensor because my voltage was standing still , after that it ran beautifully and moved to closed loop within the 1st minute of running . I have the R.E.M. Too .. Link to comment Share on other sites More sharing options...
87MJTIM Posted April 18, 2018 Author Share Posted April 18, 2018 the O2 does change, but will read <2.5v most of the time while cruising. While idling, it will bounce around +/- 2.5v. Before I swapped the O2, the signal was 4.98v - flatline. Link to comment Share on other sites More sharing options...
cruiser54 Posted April 18, 2018 Share Posted April 18, 2018 02 sensor is reliant on the heat from it's internal heater, not engine temp. Yours should be switching about once a second. See if you have 12 volts or so at the red wire at the sensor and that the black wire has no resistance to ground. Link to comment Share on other sites More sharing options...
dvitha Posted April 18, 2018 Share Posted April 18, 2018 Clean the terminals on relay for o2 sensor heater, also on the connector to the o2 sensor its self. Like all above said the readings should be bouncing around every second or two from lower to higher and back. make sure it is NKG sensor and no burned wires. Renix's years wiring and connectors are mot of the time are the issue . every 75k to 80k replace that o2 sensor. Link to comment Share on other sites More sharing options...
87MJTIM Posted April 19, 2018 Author Share Posted April 19, 2018 Gonna get the DVOM to it this weekend. I will post the results. Link to comment Share on other sites More sharing options...
87MJTIM Posted April 21, 2018 Author Share Posted April 21, 2018 Follow up: With a DVOM, KO/EO - Tested the orange wire (pin A) from the heater relay - got 11.8v Tested the gray wire (pin C) from ECU - got 5.01v Ohm tested the ground (pin B) to engine block - 0.000 I found this on NAXJA for a reference. http://www.naxja.org/forum/showthread.php?t=1012701 I'm open to suggestions. Link to comment Share on other sites More sharing options...
Ωhm Posted April 21, 2018 Share Posted April 21, 2018 Vehicle harness pinned out good for A,B&C. One more check is needed at the component side. Pin A to B for continuity (O2 heater). 88electrical manual shows 6Ω's. If this shows good, suspect O2 sensor, the component. O2 voltage needs to swing rapidly between Rich and Lean, as stated above. If new O2 doesn't solve your problem, we need to go back to REM and FT values. Link to comment Share on other sites More sharing options...
cruiser54 Posted April 22, 2018 Share Posted April 22, 2018 There seems to be some mix-up lately with the NTK sensors. I don't know if they are mis-boxed or what. Link to comment Share on other sites More sharing options...
carnuck Posted April 22, 2018 Share Posted April 22, 2018 There seems to be some mix-up lately with the NTK sensors. I don't know if they are mis-boxed or what. Bosch had a round of mis-boxed ones some time ago. The wires in the plug weren’t done right. Check the stamped number on the sensor itself and if your old sensor is around, Check the wiring at the plug matches on both. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
87MJTIM Posted April 22, 2018 Author Share Posted April 22, 2018 2 hours ago, cruiser54 said: There seems to be some mix-up lately with the NTK sensors. I don't know if they are mis-boxed or what. An internet search keeps coming up with NGK and NTK as the same parts. Are these the same? Link to comment Share on other sites More sharing options...
HOrnbrod Posted April 22, 2018 Share Posted April 22, 2018 Samo-samo Link to comment Share on other sites More sharing options...
87MJTIM Posted April 22, 2018 Author Share Posted April 22, 2018 1 hour ago, HOrnbrod said: Samo-samo Thx Link to comment Share on other sites More sharing options...
87MJTIM Posted April 22, 2018 Author Share Posted April 22, 2018 Sensor ohm test pin A-B - 4.5 ohm bad sensor? Link to comment Share on other sites More sharing options...
Ωhm Posted April 22, 2018 Share Posted April 22, 2018 I would call that good. Without having to ask everyone to measure their O2 sensor heater resistance, to see if this is in the ballpark. Faulty O2 heater circuit component side would be open circuit or zero ohms between those two pins. Link to comment Share on other sites More sharing options...
cruiser54 Posted April 23, 2018 Share Posted April 23, 2018 I think 6 to 8 is standard IIRC. And, if they're bad, it's usually no resistance. I used to take my DVOM to the junkyard with me. Link to comment Share on other sites More sharing options...
carnuck Posted April 23, 2018 Share Posted April 23, 2018 I recall someone not in the know spraying old school silicone lube on O2 sensors before installing. Poisoned it right out of the box! Link to comment Share on other sites More sharing options...
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