I have a stubborn "LEAN MIS-FIRE" problem with my 1996 MY 4.0L AJ16.

Even after replacing too many parts:
All O2 sensors and harness connectors (O2 sensor orientation test completed with IDS/WDS)
Throttle Position Switch (TPS reset using IDS/WDS)
MAF (I have 2 new aftermarket and 2 used)
coils, and harness connectors with shrink wrap over all failing insulationPlugs (Champion RC12YC)
Fuel filter, and fuel pressure regulator (pressure is good), Air filter
Rebuilt fuel injectors (that looked different, so I rebuilt the original injectors, flushed them and reinstalled the originals)
Exhaust manifolds (they were cracked), and front catalytic converters
(I'm sure there were more)

I still have not been able to fix this, and could really use some expert help.

Symptom 1: repeated MIL codes
P0171, ADAPTIVE FUEL, Combustion too LEAN, Bank 1
P1138, HO2 sense circuit lack of “swing”, Bank 1, Sensor 2 Sense circuit indicates lean combustion (No HO2S response)
P1315, Persistent misfire (one cylinder identified and injector switched off)
P1314, Misfire Rate catalyst damage, Bank 2
P0300, Random misfire detected

Symptom 2: Champion Spark plugs look VERY LEAN (bright white)

Symptom 3: Low voltage on O2 sensor "C" (B1S1)
Here are the O2 sensor voltage traces (using IDS 118.5/WDS with a genuine VCM).
Sensor A= Bank 1, Sensor 2 (downstream)
Sensor B= Bank 2, Sensor 2 (downstream)
Sensor C= Bank 1, Sensor 1 (upstream)
Sensor D= Bank 2, Sensor 1 (upstream)


I have changed all 4 O2 sensors, and the Bank 1 Sensor 1 O2 sensor (sensor "C") twice, and still get the same results.

I have checked ALL the O2 sensor wiring and it is OK.

When I turn the engine OFF, key ON, I can watch the voltage rise back to 5v.

I believe this O2 sensor problem is causing my AMFR and FMFR to drift out of spec.

I found a way to "hack" reset the AMFR using IDS/WDS: Vehicle Configuration - Set-up and configuration - Engine and transmission - Fuel trim set up. I don't actually have a smog machine, but if I lie and say the "measured" carbon monoxide level is 05.% or 1% or 1.5%, WDS updates the ECU at least a little (engine runs rough during change)...keep repeating the process until you get the PASSED screen and the level is right. I was able to change my AMFR from -12.5kg/hr all the way to 531 g/hr. Spec according to Bulletin Number 18-53 and 05-1-31 is AMFR -4.2 to +2.8 kg/hr. The problem is, even after I get the AMFR adjusted to spec, it drifts right out again.

Is the O2 sensor telling the truth? Is that really is the O2 level? what is going on here?

Symptom 4

I also wanted to re-set the FMFR per Bulletin Number 18-53 and 05-1-31 (apparently, fixing the initial AMFR problem WONT be enough; you must also re-establish the proper AMFR and FMFR for the ECU...it can't do it without your invention)

After setting up the 4 traces, per the bulletins, the signal for the Calculated engine Load Value "CLV" reading keeps dropping out (error messages that I can't look up). The transmission had started shifting very badly, so I replaced the VSS. Shifts are better, but the CLV signal is still dropping out. When I check ONLY the CLV, it seems fine.

My smog is past due by 1 1/2 years, and the great state of California could tow my car away to 'save the world' if they catch me driving it (so I don't drive it).

 

hi this is my first post...got a 96 in august...did everything you did,,,and still the same codes you had...ended up being one or both of these..hole in egr hose and when i did the coils i reversed 5 and 6 (the 2 closest to the dash) when i swapped the hose and swapped the wires it was perfect and had been perfect since..

 

Since I only have a problem on bank 1,I switched the upstream O2 sensors, and the problem stayed on bank 1.

I switched the O2 wiring to see if the problem would switch to bank 2, but it stayed on bank 1.

Then I switched the coils and plugs from bank 1 to 2 (1 to 4, 2 to 5, 3 to 6), and the problem stayed on bank 1.

What do you think about the knock sensor for bank 1? WHY IN THE WORLD are the knock sensors not included in the PIDs or in the MIL codes?

 

Knock sensors so rarely fail on these cars, so I have no idea if a failed knock sensor can wreak the havoc you are experiencing. I wouldn't think it would be able to flatline your 02 sensor though.

I do suspect an ECU issue. The engine is definitely detecting something going wrong in Bank 1 only. Perhaps switch the knock sensors, or at least extend the harnesses so that you can connect the second bank to the first one, and vice versa?

Bad knock sensors should produce a code. P0326-P0332

Can you perform a compression test on the cylinders? I believe auto parts stores can loan that tool out?

 

Hi Sromkee,
I'm interested by your technique of "hacking" the fuel trim adaptation. Did you manage to do it with IDS? Could you develop the method? When do you know where to stop?!
Any inputs is welcome!
Thanks,

 

Basically, I used IDS 117.5 that defaults to WDS for the 1996, and followed the promts.
When it ask if I wanted to adjust as PPM or %, I chose %. Since I don't have a smog machine, I can't actually read my CO level, but I guessed... Really high (10%) then checked the results, then really low (0.5%)...I could see the fuel/ air mass changing; I don't remember off hand which way I went.

I will find some time and write up a procedure with pictures

 

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