I wonder what would happen if you insullated the t'stat housing and sensor...
I would also log the voltage to the ohtwo sensor heaters. I fouund the following:
"P0125 set if after the engine is warmed up, A/F Sensor Output* does not change when
conditions (a), (b), (c), and (d) continue for at least 1.5 min.:
a. Engine speed: 1,500 rpm or more
b. Vehicle speed: 25 û 62 mph (40 û100 km/h)
c. Throttle valve is not fully closed
d. 140 sec. or more after starting engine
*Output values changes inside ECM only
After checking around further, those are the conditions that factor into the fault. So the code haas nothing to do with the coolant temperature sensor gating out the closed loop operation, but instead is related to the O2 sensor readings..
I'll check into the O2 sensor next."
Yep, that's what the techs have been telling me for years.
Not sure, but I don't think that would do anything. This also happens after the vehicle has been on the road for hours in 80-90 degree temps. As you pointed out, coolant temp has nothing to actually do with this - at least in this case.
The techs did log the voltages, etc. on the sensor heaters and sensors themselves. They brought that up a few months ago - at the same time as the short issue on the Sports - and nothing came up. Everything was well within spec and they drove it around for quite a while. Of course, the code wouldn't trigger.
That defines an O2 sensor - specifically the forward sensor on the '90s FED Sports - issue. I've been through that from the service manuals. It meets the a-d criteria, but I'm certain the sensor output changes. I can log the output from both sensors and they're definitely constantly changing when it triggers. I've even got logs of everything through a trigger.
The other thing that doesn't sit right is the timing of the happening. It takes me about 8 minutes to get from cold start-up to where it triggers. This happens consistently. Pretty close to the same amount of time/distance when leaving the office.
Warm up time is considerably different between leaving my condo and leaving my house, yet the distance/time to trigger has stayed the same.
Its like the ECU is expecting and event within n time, irrespective of conditions and if the event doesn't happen it triggers the code.
Why this code? There are LOTS of things that fit that bill in the ECU, but none that trigger THIS - and ONLY this - particular code. <img src="/forums/images/graemlins/confused.gif" alt="" />
Just thinking out loud ... When I leave from my condo it's entirely up hill against the wind to the trigger point. When I leave my house it's entirely coasting with tail wind to the trigger point. Average speed over the period is virtually identical. I have almost exactly the same 30 MPH distance and 55 MPH distance to trigger for both. So, condo is much more throttle and house is very lite throttle. Those two scenarios drastically affect A/F ratio. Yet the trigger time/distance is almost identical.
From a mechanical/electrical standpoint - the problem occurs on two completely different engines. The only common parts are the water pump, TB and MAF. Everything electrical on 3.5L either came with the 3.5L or is new Mitsu parts.
I replaced the O2 sensors at engine install time. Exhaust stayed the same except mods to the down pipes to fit them to the 3.5L. No leaks, I checked. Down pipes have the equivalent insulation to the stock set. Forward sensor position in the pipe has not changed. The rear has by about 6-8" (rearward) but that happened long after the problem cropped up.
ECU has been replaced. I have another one on order which should be here in a couple days as well as two Mitsu OEM O2 sensors.
Sigh. Like I said. Stumped.
Edward
