fiatslug87 Posted February 23, 2008 Share Posted February 23, 2008 I know this has been covered, I searched but couldn't find what I needed. '89, 4.0, AT, 2WD failed smog test in CA. It passed 2 years ago here's the comparison (in CA it's done on a dyno at 2 speeds): Test..................Max........"Gross Polluter".......2006 Test.......2008 Test HC@ 15MPH......123...............310.....................32...................188 HC@ 25MPH......103...............260.....................26...................182 CO@ 15MPH......0.73...............2.03...................0.03................ 2.83 CO@ 25MPH......0.93...............2.23...................0.02.................2.83 NO@ 15MPH......1015..............1800..................163...................776 NO@ 25MPH.......875...............1600..................294...................772 So it was high for hydrocarbons and a gross polluter for carbon monoxide. I've only put 7000 miles in the 2 years but look at the differences. What do you guys think it is? I have an idea but don't want to dismiss any options I haven't thought of. Thanks for any input. Link to comment Share on other sites More sharing options...
dragonrider477 Posted February 23, 2008 Share Posted February 23, 2008 well,here goes,could be any one or a combination.bad o2 sensor or wiring problem,bad or insufficient sensor grounds,bad egr or control system for it,fuel pressure regulator bad,leaking injectors,map sensor bad or vacuum supply to sensor compromised,wicked plugged air filter,wicked dirty throttle body/intake,valve timing off(timing chain jumped or just worn badly),bad computer,coolant sensor bad or just a little bad and lying to the ecm,too cold thermostat(engine running too cold,computer never takes it "off the choke" and is rich),manifold air density sensor problems.this is only a partial list.i am sure other posters on this site will come up with more.if the thing runs good and idles good and you did not want to pay a shop $$$$$ to test it i would take a stab at changing the o2 sensor.the high co readings point to an out of control feedback fuel system which will also raise the hc's.if it was a leaking intake gasket the hc's would be off the scale and the co would be low.the o2 sensor is the main component the ecm uses to control fuel trim with the map sensor a close second.map sensors are much more reliable than the o2's hence the suggestion to change it (the o2)first.good luck. Link to comment Share on other sites More sharing options...
jeepdoggydogB Posted February 23, 2008 Share Posted February 23, 2008 Hello Neighbor, I have heard of this problem before and it usually involves the O2 and Catalytic converter. I know you have three trucks and 7K in two years isn't a lot of driving. Is this the truck with the weird short when you depressed the ebrake that made it cut off? :cheers: Link to comment Share on other sites More sharing options...
fiatslug87 Posted February 23, 2008 Author Share Posted February 23, 2008 Hello Neighbor,I have heard of this problem before and it usually involves the O2 and Catalytic converter. I know you have three trucks and 7K in two years isn't a lot of driving. Is this the truck with the weird short when you depressed the ebrake that made it cut off? Hi Joe, No, this is the red '89, that was the blue '90. I was thinking along the same lines, replace the O2 sensor and retest or should I replace both O2 sensor and cat? I had this happen before to the '90, I checked all sensors and replaced the 02 and cat which was rattling and it passed. However the cat in this truck isn't making any noise. Is the cat's main function to reduce NO? Since I had to take it to a Smog Only test center, I can now take it to a qualified "Gold Star Center" (after approval) pay the first $100 and the State will pay up to $500 for the fix. It sounds good but I really don't like anyone working on my MJs. That's why I'm thinking of 02 sensor $50 + $50 for retesting, that's what I'd pay through the program anyway. If that didn't work cat $100, if that wasn't it go through the program. Any comments? Link to comment Share on other sites More sharing options...
mfpdm Posted February 24, 2008 Share Posted February 24, 2008 Hello Neighbor,I have heard of this problem before and it usually involves the O2 and Catalytic converter. I know you have three trucks and 7K in two years isn't a lot of driving. Is this the truck with the weird short when you depressed the ebrake that made it cut off? Hi Joe, No, this is the red '89, that was the blue '90. I was thinking along the same lines, replace the O2 sensor and retest or should I replace both O2 sensor and cat? I had this happen before to the '90, I checked all sensors and replaced the 02 and cat which was rattling and it passed. However the cat in this truck isn't making any noise. Is the cat's main function to reduce NO? Since I had to take it to a Smog Only test center, I can now take it to a qualified "Gold Star Center" (after approval) pay the first $100 and the State will pay up to $500 for the fix. It sounds good but I really don't like anyone working on my MJs. That's why I'm thinking of 02 sensor $50 + $50 for retesting, that's what I'd pay through the program anyway. If that didn't work cat $100, if that wasn't it go through the program. Any comments? Had the same thing happen when I lived out in San Diego. Guy told me it was either the cat or O2 sensor. My advice would be to start with the cheapest to replace. That's what I did. Change the O2 sensor and had it retested and pasted by a little margin. I was able to take mine to the base being military and the retest didn't cost me anything. Is it 20 or 25 year old cars that no longer require smog checks? :cheers: Link to comment Share on other sites More sharing options...
FxRacing282 Posted February 24, 2008 Share Posted February 24, 2008 in the great state on nh i believe it 87 and newer need exhaust testing. luckily for me i gots an '81 Link to comment Share on other sites More sharing options...
Tracker Posted February 24, 2008 Share Posted February 24, 2008 In Ca. it's 1975 and below that get to skip smog tests. The bummer is that there is no longer a limit on how much you have to spend to make it pass. Anything Jeep between 1976 and TBI is doomed. It make for a good supply of truggy and trailer queen donors though. This may sound silly to some of you but if you put on a set of street tires inflated as high as you dare your motor will spin that dyno a lot easier. It wouldn't be enough for your problem but it can make the difference when you are right on the line. (I know a good smog man) Link to comment Share on other sites More sharing options...
Randy in Maine Posted February 25, 2008 Share Posted February 25, 2008 Been here? http://www.ratwell.com/mirror/interro/techgas.html A little tuning time with an LM-1 is worth it. Link to comment Share on other sites More sharing options...
fiatslug87 Posted February 26, 2008 Author Share Posted February 26, 2008 A little tuning time with an LM-1 is worth it. Yeah, got one I can borrow :brows: ? Don't want to spend an additional $300!!! Link to comment Share on other sites More sharing options...
Randy in Maine Posted February 26, 2008 Share Posted February 26, 2008 There have to be lots of folks out there with a wide band that you can use. Mine is loaned out right now. :driving: Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now