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How to bring down COs?

904 views 12 replies 8 participants last post by  Bbannongmu 
#1 ·
I can't pass smog mostly because the COs on my 89'YJ are thru the roof. It's the carburetor 4.2L engine.
I have replaced the carb, electronic ignition, coil, distributor wires, cap & rotor, fuel pump, fuel filter and airfilter.
Where do I go from here?
 
#3 ·
Agreed,

This is the next step.

You can test your catalytic converter with a infrared temp gun if you have one.

The catalytic converter should be hotter on that connects to the tailpipe, and cooler on the side that connects to the engine.
 
#4 ·
Cat appears to be fine.

These are the numbers for the CO after various changes:

Original carb 4.82
New carb 5.73
Removed secondary fuel filter 8.25
Tweaked new carb 6.21

Max is 0.80.

Clearly something is wrong big time somewhere. So the question is what!!
 
#5 ·
Cat can look fine on the outside. Bad inside. How is your thermostat? Is it reaching operating temp? Chrysler/Jeep gauges are not known for accuracy. Need to verify with an infrared temp gun. Does your state have a waiver program? $150 fee paid to a local certified mechanic. Cheaper than throwing parts at the vehicle.
 
#6 ·
I believe there is no thermostat because shop I took it to did the temperature test an suggested there might be no thermostat. But why would that affect the COs? If there is no thermostat doesn't that jut mean that the water always circulates?
 
#7 ·
Hmm. I've never had a 4.2L jeep wrangler, but my suggestion is you probably have an automatic choke.

The thermostat regulates the heat of the jeep wrangler, so you jeep may never actually be hitting operating temperature... you're jeep is therefore running richer. A richer running vehicle can produce higher CO levels.

The shop you took it to should have put a thermostat in. For a thermostat, and gasket it will run you maybe $20 parts. You can do it yourself.
 
#8 ·
Put a 195 thermostat in it. Make sure its up to temp before you take it in . A lot of garages have a sniffer setup . To make sure they will pass. Before you take it in . As a last resort get her warmed up and within a mile of the place lean out carb , pass test fatten mixture back up around the corner from the place. Leaner mixture makes it run a little warmer there for getting the cat hotter in turn burning cleaner . Just dont leave it leaned out too far or you could burn a valve .
 
#9 ·
Put in a thermostat, Made sure it was nice & toasty , made it leaner, but failed again. The numbers were almost as high as the last time.
I can't do the retirement program either because it has been more than 60 days since I paid for registrati0n & I can't sell it because I can't pass smog.
I really don't know what to do with it if I can't get the cos down.
 
#11 ·
OP stated that his COs are "thru the roof". Even if changing the plugs would help, I doubt if they would get it to pass.

Next step is get an infrared lazer thermometer. (Harbor Freight, about $35.00.) Use it to check your cat. Visual inspection of a cat, or simply touching it won't do. If it is the cat, change it for a new aftermarket one. If it isn't, report back for more suggestions.

There is one county in CA that doesn't require smog testing. I dunno which one. Make a buddy in that county and register it at his address or advertise the Jeep for sale in that county.

Good Luck, L.M.
 
#12 ·
I understand what he mentioned. If everything was changed, the plugs should have been replaced as part of the tune-up which can only further help. If that was done as part of the tune-up and there's no improvement, I would bet that the O2 sensor was never replaced. It might have even been removed or bypassed by a previous owner. It's supposed to be replaced on an 89 4.2 at 88,500 miles, max. Not knowing the condition of the cat, I agree that's probably due to be replaced also.
 
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