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SoCalManche

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  1. Do you have a REM? If not, this is the O2 sensor test per Cruiser54: O2 sensor testing 1987-1990 Renix For the Renix years, 87-90, the O2 sensor has 3 wires, 2 black and 1 orange. The orange wire (largest gauge of the 3) is the 12-14 volt power that comes from the O2 sensor heater relay on the passenger side firewall, and that powers the internal heater in the sensor so that the sensor can work at idle, and almost immedietly after start up. Loss of that power will hurt gas mileage even with a good O2 sensor. One of the black wires is a common ground for the heater power and O2 signal to the ECU, so a poor ground will give a voltage feedback from the heater power input, to the ECU causing poor mileage even with a good O2 sensor. The third wire, also black is a voltage feed wire, 5 volts, from the ECU to the O2 sensor. The O2 sensor is an O2 concentration sensitive variable resistor. At optimal O2 concentration the 5 volt input feed to the O2 sensor drops to 2.45 volts due to losses across the O2 sensor to ground. That same wire if disconnected from the O2 sensor will read 5 volts constant to ground. At idle that voltage should read 1-4 volts oscillating quickly back and forth roughly once every second. At 2000 rpm it should run between 2 and 3 volts max, and is optimally running between 2.3 and 2.6 volts at 2000 rpm (in park). A digital meter can NOT be used for reading the O2 sensor voltage, but it can be used to test the ground and the 12-14 volts to the heater and the 5 volt feed from the ECU with power on and engine off. You must use an old style analog meter with the needle gauge on the display to see the voltage swing back and forth with the engine runing. If the O2 sensor readings are not right, say they read 4 volts or 1 volt steady, you have a problem. BUT before you blame the O2 sensor make sure it has good wiring, and make sure the proper voltage is feeding it, by turning power on, engine off to read the engine off voltage feeds (12-14 volts on the orange wire, and 5 volts on one of the two black wires), and ensure the ground wire (power off) reads less than 1 ohm to the battery negative post. A leaky exhaust system or leaky fuel injector(s), or bad compression, bad rings or leaky valves, bad plugs, wires, cap, rotor, HV coil, and so on, or combination of these, can also cause a lean or rich condition that gives you high or low O2 sensor readings that are not the O2 sensors fault, so try and verify those other items also before buying parts like an O2 sensor to fix your problem.
  2. Went to swap in an injector I had that I knew was functioning last I used it; Before swap: Started truck up again to see how it would start; she retained LEAN/OPEN LOOP condition. After swap: Started truck up and same occurrence; retained LEAN/OPEN LOOP condition. I then swapped the injector around to see if orientation mattered (been told in the past orientation does NOT matter); as soon as truck started, cycled to CLOSED LOOP and O2 sensor immediately starting pinging back and forth between RICH/LEAN. Can we verify that orientation matters? I've always just thrown injectors in without looking at orientation and it didn't seem to matter - that was always luck? Also, what are ST values supposed to be in idle? She was in the 160-180 range.
  3. When prior IAT was pulled, it was coated in fuel. Raw fuel can't really come from anywhere besides the injector, no? Considering that fuel regulator vent was already monitored as being dry during operation.
  4. Second start-up was normal. Switched to RICH and ST immediately dwindled to 0 within seconds. Of course, once 0, the "CEL" came up and then REM showed shift back to OPEN LOOP. Injector?
  5. No seepage from that vent. Just started her up, and she wouldn't even go into RICH this time; she retained LEAN and OPEN LOOP, and sounded like a damn lawnmower while running, also smelled like one honestly. Not the first time to have that happen either. I'm gonna do a couple start ups and see how they differ, if at all.
  6. They don't deviate. Both are showing 128. That may provide insight.
  7. So back at the grind; Threw in a "new" IAT and all sensors now running normally as far as what REM is telling me. I've tried three different O2 sensors: 1st O2 sensor wouldn't pull truck out of LEAN and stayed OPEN LOOP. 2nd O2 sensor shifted into RICH, and briefly pulled into CLOSED LOOP, but then shifted back to OPEN LOOP. 3rd O2 sensor same as 2nd. Maybe the exhaust manifold has a hairline crack? REM isn't able to tell me how O2 sensor is operating beyond the scope of RICH/LEAN because it's a 2.5. I've tried backprobing, but I don't get the ~5V readout that's supposed to occur? Terminal A (yellow wire): Battery voltage Terminal B (black wire): Ground Terminal C (orange wire): 0.97V with truck running.
  8. Just saw that post. My IAT had all year to give break, and instead it happens most likely a hair too late. Ha.
  9. If you have a spare, just throw one my way and the invoice too. Haha
  10. Update: Finally put everything back together after compression test, started her up, and IAT finally bit the dust. Wires are fraying and causing REM not to read properly. A while back, this issue would happen, but even with the misread, she would still run closed loop and O2 still did its job. At at stand still until I can find another IAT. On same note, when I pulled the IAT, she was somewhat pretty wet with fuel; is that due to lean condition on cold start? As for the potential intake leak, all good; all bolts seated properly and the TB vacuum points you showed that are notorious for leaks, yes, I've always had a very minor hiss right at that point; it's never hindered running condition however. I will get O2 voltage reading once "new" IAT is installed.
  11. Wires are new, I'll have to check the cap but I think I threw a new one on a while back. Shouldn't have a leak at the intake since it hasn't been touched, but maybe a crack randomly developed.
  12. Forgot to add this photo. Is there a reason why 2 and 3 are fouled even though they have best compression? These are the new plugs put in after alternator swap by the way.
  13. Dry Compression Test: 1 - 145 / 2 - 145 / 3 - 147/8 / 4 - 140 Wet Compression Test: 1 - 152 / 2 - 162/3 / 3 - 160 / 4 - 151/2 Cylinder 1 is a PITA to properly test dry, let alone wet, so that number could be off a bit for the wet test. Tested cylinder 4 twice with somewhat same result (first test was at 149/150).
  14. Yes, all grounds are squeaky clean. Yessir, I've done those as well as most of the other tips as well (if they are applicable to '86 2.5L)
  15. The odds of a sensor going bad right when I swap the plugs? Damn, I need to play the lottery!
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