Bad Thermostat???

The Lure Washer · Dec 23, 2008

Could a bad thermostat be the cause of all my emissions troubles? I never really gave it a thought till I used the search feature and found a few posts about it. My 90 does not ever reach 210, It rarely makes it past 200 and then as Im driving it drops close to 150. Which if I inderstand correctly means that the therm thats in there is sticking open. Im really just learning and starting to understand my jeep.

5-90 · Dec 23, 2008

The Lure Washer said:
Could a bad thermostat be the cause of all my emissions troubles? I never really gave it a thought till I used the search feature and found a few posts about it. My 90 does not ever reach 210, It rarely makes it past 200 and then as Im driving it drops close to 150. Which if I inderstand correctly means that the therm thats in there is sticking open. Im really just learning and starting to understand my jeep.

Got test results? That would be very helpful.

Also, verify your coolant temperature with a non-contact thermometer (if you can) at the upper hose, radiator entry, or at the thermostat housing proper. The IP gages on RENIX are notorious liars - to the point where I've marked the lense with a grease pencil at the "nominal" readings (my temperature gage gives me 210* at 180*, my voltmeter reads ~12VDC @ 14.5VDC, ...) They're more "indicators of relative state" than absolute instruments, and should be verified using instruments known or believed to be accurate.

But, giving with the "failed" results you've gotten would be more instructive than pretty much anything else you can (post the "fail" results and the "acceptable max" - both numbers for each measurement should be on the report you'd have gotten when you left.)

The Lure Washer · Dec 23, 2008

first test: HC Limit:160/319 fail, CO limit:3.24%/7.59% fail, NOx limit: 4200/70 pass
Replace O2 sensor and ran a bottle of G2P after the first test.

second test: HC:160/296, CO: 3.24/7.11, NOx: 4200/120

Still failed.
Checked MAT sensor and CTS Both were good.

MapleDitch · Dec 23, 2008

I know you have been fighting this problem for a little while. I think you need to move on to a more significant test, and see if your cherokee is running in closed or open loop when warmed up.

I know you already have a new o2 sensor, but check to see if your o2 sensor relay is functioning properly(next to your fuel pump relay).

Originally posted by Ecomike

If you can rig up a backprobe or wire tap to the two smaller black wires (not the larger gauge orange wire) on the O2 sensor wires with the the O2 sensor still connected to the harness, then with engine runnning and using an analog volt meter you can watch it rapidly oscillate from lean to rich across the 2.5 volt threshold at idle. At idle it will oscillate from about 1 to 4 volts about once per second in the closed loop mode. At 2000 rpm or higher it closes the gap to a 2 volt to a 3 volt oscillation across the 2.5 volt target. Rapid decel will peg it rich for about 5 to 10 seconds (less than 1 volt as I recall) before it goes back to a 1 to 4 volt swing. If it is running open loop, and rich it will display anything for 0 to 1 volt at steady idle. More importantly it will not rapidly oscillate back and forth across the 2.5 volt mark in open loop.

If your O2 sensor's heater is working and getting 12 volts it will go into closed loop shortly after start up on the Renix.

Edit: Oh, and check your grounds! They can mess with all your sensor values.

Bad Thermostat???

The Lure Washer

NAXJA Forum User

5-90

NAXJA Forum User

The Lure Washer

NAXJA Forum User

MapleDitch

NAXJA Forum User

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