97 Montero Sport Monitors Not Setting

I have a 97 Mitsubishi Montero Sport where three of the monitors (CAT, EVAP & EGR) are not setting. I have put a couple thousand miles on it and still will not complete drive cycle. A couple of Mitsubishi mechanics have both told me they believe it is the ECU, but I want to be sure before I replace it. I recently replaced the ECU a few months ago for another issue. That problem has been fixed but I had these three same monitors not setting before replacing the ECU so it seems unlikely to have a bad ECU if the same three monitors were not setting both before and after ECU swap. There are no DTC codes - permanent or pending, which is why the mechanics believe it is the ECU. Can anyone help shed some light on this?

Here is the Live Data I pulled on the vehicle (at operating temperature) if it helps:
DTC_CNT 0
FUELSYS1 CL
FUELSYS1 - -
LOAD_PCT(%) 20.0-20.4
ECT(deg F) 183
SHRTFT1(%) 2.3-4.7
LONGTFT 12.5
RPM 695-710
VSS(mph) 0
SPARK ADV 14.0-17.0
IAT(deg F) 87
MAF(lb/s) 0.01
TP (%) 0.0
O2B1S1(v) 0.080-0.840
SHRTFTB1S1 1.6-3.9
O2B1S2(v) .060-.100
SHRTFTB1S2 1.6-3.9

O2S Rich-Lean Threshd(V) Test Value 0.460
O2S High for Switch Test Value 0.560

this is all I could find.

The catalyst efficiency monitor works by comparing the output of the upstream oxygen sensor with the sensor downstream of the catylist.
The first check for P0420 or related code is to use live data from a scantool to compare the signal voltage upstream sensor with the sensor downstream of the catylist.

Thank you Shayne for the information but yes I do have that already. I have the Mitsubishi Service Bulletin that lists all of the specific procedures for readying the monitors and have followed it on several occasions with no luck. I even tried placing the vehicle rear on jackstands (two sets for added security) and ran the drive cycle that way too but still nothing. The first Mitsubishi mechanic I talked to said it was the PCM. I told him I did think it was PCM because I recently (5 months ago) replaced the PCM for another problem I was having and I had the same three monitors not set both before the PCM was replaced and after. Logic tells me it is unlikely to have the same problem with two different PCMs. He asks a couple of additional questions - I answered - and then he said "Again, replaced the PCM". I told him that I was not confident in his answer and he just said, "Good luck to you!"

I then sought out a second opinion from a second Mitsubishi mechanic and he told me that the first mechanic is correct. Without a DTC code, there is nothing else it could be other than the PCM. So what did I do (after I made my initial enquiry here)? I went ahead and bought another PCM, installed it, ran the drive cycles and...SAME THING, none of the three monitors are setting. This is exactly why I have been reaching out for help - I don't want to be a parts changer - there are enough of them around. The car runs fine - no trouble codes, just can't get the monitors to set. There has got to be some kind of problem that is preventing them from setting and yet not serious enough to throw a code. And yes the check engine light is functioning properly. The light comes on in KOEO, and they goes out a second or two after the engine is started, plus the scan tool is registering as No Codes.

I would think maybe the next step would be to check the devices related to those monitors. Maybe?

Thank you Andy for the video. I will watch it when I get home. I replaced the O2 sensors about 7-8 months ago when I thought I had a problem with them when in reality they weren't functioning because the fuel system was in Open Loop, so changing the O2s did not change the outcome. Once I fixed the issue creating the OL, the O2s started dancing again. I may try to put the originals back in and see what happens (considering they are OEM and the new ones are aftermarket) - see if anything changes with that.

Thanks again!

Look for anything that isn't right on the scantool. Sensors not fluctuating when the should be. I remember reading a case study on a taurus that wouldn't run the monitors, it ended up being the fuel tank pressure sensor stuck at 5 volts. They unplugged the sensor and the monitors ran and set a code for the fuel tank pressure sensor. But didn't set a code before because it hadn't run the monitors

Only other example I can think of was on Pine hollow diagnostics YouTube channel. He had a Sebring that wouldn't complete monitors and ended up being a bad downstream O2 sensor.

We’ve had a few different occasions at our shop with cars not setting a monitor, usually Cat. I don't remember a time that a Cat monitor didn't run after a new Denso o2 sensor. Sometimes you can go in mode 6 data and see one of the tests have failed.

Thanks Bruce, all the data I have available on my scan tool is posted on the initial post. Data that was fluctuating I posted as a range and data that was constant, I posted as a single value. I'm just not really sure what the data is telling me. I know a limited amount about O2 and fuel trims but very little other, such as MAP or MAF readings.

Thanks Dennis, I believe the new O2s I put in about 8 months ago were Denso O2 sensors. I may try putting the OEMs back in and see if the data remains the same. I did have someone earlier today mention Mode 6 but not something i can do with my scan tool. I will see if there is someone I can get to view that for me. The person that told me about Mode 6 told me to talk to the guy running the auto shop at the local community college - that's he likes to look at things like this and Mode 6 views to teach his students. I guess very similar to what ScannerDanner did at Rosedale. So sounds like a good option for me at this point. But the same guy also told me that he has had struggles with setting monitors on Mitsubishi's. They require a very specific drive cycle, you have to run it in a specific order, and sometimes you have to run it multiple times. He also told me the CAT will not set until AFTER the EGR sets.

Thanks!

On your PID list the O2 b1s2 doesn't look right but you are missing EGR and evap data, so you might not be seeing whatever is wrong with all that missing data. May need a different scantool to see it.