Emissions monitors wont go ready - Problem with ECU?

[phxZ31]

2000 Cherokee Classic RWD 4.0L
My registration has just expired because I cannot get my Jeep to pass emissions. No codes or check engine light coming up, Jeep runs absolutely fine, gets great gas mileage, etc..

Can't pass emissions because the ECU reports not ready for testing. The three monitors in particular that won't go to ready are:
1) Evap. system
2) O2 sensor
3) Catalyst
I can pass emissions if only just one more of these becomes ready.

These three monitors have been "not ready" for testing for over 3 months now, and over 1000 miles of total driving. All other monitors switch to ready within about 75 miles of driving after resetting the ECU. The catalyst in the car is new. I've put 350 miles on the car since the last time the ECU was cleared, still not showing ready.

I'm at a loss.. I don't really drive a lot, so its really been difficult just to put enough miles on to get through a single tank of gas in under two weeks... I've had to just go out and take a 75 mile long drive at night just for the sake of putting miles on the car to get through the drive cycle. I have 1 more week to figure this out before I'm out of temporary registration and it becomes illegal for me to keep driving the car.

Any suggestions how I can check the components or ECU, or anything, to get just one of these monitors to report ready? All I need is one. Any one.

 

[joejeep92]

Evap monitor only runs under certain conditions. Fuel must be between 15 and 80 percent level wise and it can't be to hot or to cold. Can't remember the exact temp parameters but being in Arizona I bet you have exceeded them. As far as the catalyst monitor it compares the wave form of the front and rear O2 sensors. Front O2 oscilates to enrichen and lean out the mixture to assist in the emission process. The rear O2 should flatline as all the oxygen should be used up in the catalyst process. Without the O2 monitor running it shouldn't run the catalyst monitor. The evap monitor is your best shot.

 

[ParadiseXJ]

I know your not getting a code, but it's just possible that the computer is having issues. That's the only thing I can think of that might be a problem, but then I know squat about a 2K Jeep.

I had a problem with my Nissan throwing a constant emissions code. I fixed all the sensors, gas cap, plugs, oil, vacuum, everything crystal, squeaky clean. I sent it to the shop finally. They charged me $350 for diagnostics, not fixed, said I needed a new computer. Retail $600 + 2 hours labor + reprogramming = $850

I got a used computer off e-bay with a 90 day warranty, 4 years ago - $200. Replaced in 5 minutes, plugged in, no reprogramming necessary, code gone, smogged it that day. You might want to look into a replacement computer.

 

[joejeep92]

Found it...
WHEN MONITORED
Immediately after a cold start, with battery/ambient temperature between 40 °F and 90 °F and coolant temperature within 10 °F of battery/ambient temperature.

 

[phxZ31]

Found it...
WHEN MONITORED
Immediately after a cold start, with battery/ambient temperature between 40 °F and 90 °F and coolant temperature within 10 °F of battery/ambient temperature.

This is for Evap Monitor, correct?
Seems this step should have completed successfully numerous times by now, I would think. What sensors are used when this system is functioning? Maybe its just a loose connector somewhere?

 

[joejeep92]

Yes it is. Oh and the computer will not set a code if the monitor has not run so you could have problems you aren't seeing. There is a leak detection pump, an EVAP purge solenoid, leak detection filter all located in the engine bay on the passenger side of the firewall.

 

[lazyxj]

Found it...
WHEN MONITORED
Immediately after a cold start, with battery/ambient temperature between 40 °F and 90 °F and coolant temperature within 10 °F of battery/ambient temperature.

Three possibilities, an out of calibration water temp sensor, intake air temp sensor or battery temp sensor.
Using a ScanGauge, I can monitor the intake and water temps but not the battery temp.

 

[joejeep92]

They run battery off ambient. In theory battery should not heat up above that.

 

[lazyxj]

They run battery off ambient. In theory battery should not heat up above that.

97+ OBDII models have separate battery temperature sensor, located in the bottom of the battery tray.

 

[phxZ31]

Three possibilities, an out of calibration water temp sensor, intake air temp sensor or battery temp sensor.
Using a ScanGauge, I can monitor the intake and water temps but not the battery temp.

Coolant Tempe Sensor was just replaced (before the most recent 350 miles of driving). It was previously throwing a code and turning on the check engine light. The Jeep has run MUCH better since replacing the sensor, and the temp gauge is back to where it should be, but the ECU has never been testable since.

I'm curious - The heated O2 sensor monitor is working, but the O2 sensor isn't.. Isn't the heated sensor the post-cat one?

 

[phxZ31]

So I understand that I won't get a code for a bad O2 sensor since the O2 sensor monitor isn't running... However, is it reasonable to then assume that a bad O2 sensor would prevent the monitor from becoming ready in the first place?

 

[sidewaysstarion]

Here's what you do, start the jeep up cold in the morning and let it idle for 10 minutes without touching the gas or putting it in gear, that should run the O2 heater monitor. After that go for a drive down a flat road and try and maintain 50-55 mph and try and keep a very steady throttle position, do this for 5 minutes and then stop the vehicle and let it sit for 3-5 minutes idling in park, that should run the catalyst monitor and O2 tests. As for Evap you need to fill the tank all the way up and drive it around and it should kick off the monitor on its own. if you have a faulty fuel sending unit it wont run the Evap monitor.