1990 Jeep YJ Smog Check

Smokin Jeep · Posted at Wed Apr 22, 2009 8:03 am

Engine Mechanical problem
1990 Jeep YJ 6 cyl Four Wheel Drive Manual 128000 miles

I have a 1990 Jeep Wrangler 4.2L that I have been trying to pass smog in CA. The Jeep has been running pretty good for an old vehicle and my mechanical experience has been growing vastly since I have had her. She is running 33's w/ stock gears.
Here are the Max and Gross polluter limits
15mph (HC-124(MAX)311(GP),CO-0.75(MAX)2.05(GP),NO-1020(MAX)1807(GP)) for
25mph (HC-104(MAX)261(GP),CO-0.95(MAX)2.25(GP),NO-880(MAX)1607(GP)).

Here are the results of my first test.

15 mph (RPM-1984, %CO2-13.9, %O2-1.0,HC-102, CO-0.53,NO-1965)GP
25mph(RPM-1902,%CO2-14.0, %O2-0.9,HC-105,CO-0.52,NO-1870)GP.
They said the high NO had to do with my EGR system. So I looked at it and the plastic nipple from the EGR temp switch was broken off, so the EGR had no vacuum. I fixed that w/ super glue and EGR gets vacuum and diaphram moves when revved.

Test2
15 MPH(RPM-1952,%CO2-12.3,%O2-0.6,HC-198,CO-3.44,NO-114)Gross P
25mph(RPM-1905,%CO2-11.9,%02-0.6,HC-201,C0-4.02,NO-99).

Now its running super rich. I went through all the vacuum hoses and replaced an re routed them per the vacuum schematic in my chiltons, and now she is idling super high, like 1300 RPM. I'm stuck, does anyone have any idea of what to do?

racefan966 · Posted at Mon Apr 27, 2009 5:04 pm

OK here is a factory vacuum diagram. Check to make sure that everything looks right first ok. Then get back to me after that and let me know how it went.

Smokin Jeep · Posted at Tue Apr 28, 2009 7:33 am

After my second test I started to look at my vacuum hoses. They were not right at all. One line that was supposed to go to the rear of the carb was not there and the nipple on the carb was capped. I have since replaced most of the old vacuum hose and routed it the correct way. I also checked my timing and it was at 9 deg. so that is at factory setting. I still have to take it in for a third smog check.

racefan966 · Posted at Wed Apr 29, 2009 7:27 am

Did the vacuum diagram I sent help at all as this is a factory diagram. How is the idle did it go back to normal? I would also say run a bottle of seafoam in the gas tank to clean anything out before the test too. Get back to me.

Smokin Jeep · Posted at Wed Apr 29, 2009 11:45 am

My idle went close to normal. I adjusted the idle on the carb sol-vac, fast idle and curb idle. It is now idling better than ever. I also ran some seafoam in my tank, down my carb, and some in the oil. I changed my spark plugs, pcv valve, air filter, changed oil 3 weeks ago, and I checked my timing and it is at 9 deg. I took another test yesterday and it did much better, but still not good enough.

Here are the results of my third smog test.

Test RPM CO2 O2 HC CO NO
15 mph 1964 14.0 1.0 124 0.46 219 Pass
25 mph 1929 14.2 1.0 133 0.39 210 Fail

I don't really know what to do now. It is weird that at higher speeds the CO and NO went down, but the HC went up. Now I just need to see what to do to get the HC down. Thank You.

Smokin Jeep · Posted at Wed Apr 29, 2009 1:02 pm

I also noticed after my 3rd test that my pcv air in tube going to the back of my air cleaner housing had fallen off. I don't know if that would affect the emisions, but I do think it is supposed to have vacuum and that may have been why the motor was running a little rich.

racefan966 · Posted at Thu Apr 30, 2009 7:16 am

It very well could as if it makes the car run lean then the O2 sensors pic this up and try to correct the issue which in turn would make it run on the rich side.

Smokin Jeep · Posted at Thu Apr 30, 2009 1:40 pm

I was also using high octane gas. Would that leave more unburned fuel in the exhaust. My jeep is not made for high octane , I don't know it was just a thought. Also I heard some people put on smaller tires and that helps them pass.

racefan966 · Posted at Fri May 01, 2009 7:05 am

Smaller tires does nothing more then change the speedometer rate. As for high octane fuel should not have any affect that way. Most all cars are made to run on 87 octane any higher octane is just really a waste of money. I must ask have you checked the coolant temp sensor? If not then unplug it and check the resistence across the terminal of the sensor (not the wiring harness). Get back to me with the reading in ohms and if you do this cold the air temp at the time of the test.

Smokin Jeep · Posted at Fri May 01, 2009 7:50 am

I am at work so I just did a quick test. The motor was warm and I just unplugged the sensor and the idle changed so I think that it is working. I will check it with a meter at lunch.