1986 MJ 2.8L V6 failed emissions.

[justinmartinez001]

I recently bought a 1986 Comanche 2.8L V6 and had an emissions test to register it. It failed for high CO levels at "Low Speed RPM". The reading was at 2.61 and the limit is 1.20. The "High Speed RPM" barley passed with a reading of 1.10 and the limit being 1.20. I replaced the air filter and did an oil change before the emissions test. What could it be? Hole in the exhaust? Bad O2 sensor? Any help would be greatly appreciated. 

 

-Thanks Justin.

[Green Mesa XJ]

What kind of 2.8 is it California emissions or federal ? ( sorry if the answer is in you signature I can’t see them in this app)

My fist thought is the AIR pump and pipes/valves still operational


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[justinmartinez001]

It’s the GM 2.8L V6 and I believe it’s the federal. I live in Albuquerque New Mexico. It says my vehicle has “failed the tail pipe emissions inspection. 

[Green Mesa XJ]

Ok on the front of the engine left hand side should be a pump below the alternator, it’s a AIR pump, all it does is pump air into the exhaust. See if you still have one because a lot of people bypass it. If it’s there the follow the tubing back to the I want to say solenoid on the left hand side of the motor, there’s vacuum line going to it and from there it splits off to tubes on each exhaust manifold. Those tubes have a check valve if I remember right.

AIR system is a mess, that’s why you’ll hardly find a old 2.8 /any 80s carbureted engine with one anymore.

Now if you federal emissions the good news is no computer and no O2 sensor, you do have a catalytic converter.

I live in s no emissions testing state so I don’t know much more about what you might need to pass in ABQ

I’d guess either tune the carb out, or fix the AIR system and/or catalytic converter. But I’ve really got no idea what help pass or fail a system. Surprised they care to test a 32 year old Jeep.


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[justinmartinez001]

Thanks so much for the detailed information I’ll check it first thing in the morning. And unfortunately if it was one year older I wouldn’t have to worry about emissions in my state. I plan on swapping a 4.0 inline 6 in it eventually I just want to get it registered and in my name. 

[Green Mesa XJ]

Glad to help if I can. I don’t know much about the AIR emissions system because when I bought my Jeep, in CO, it already had the AIR pump removed, I’ve been pulling pieces of the POS system out bit by bit for years. Never tried to make it work and never registered the Jeep in a place where I’d have to get emissions done.

BTW the 4.0 swap is not that easy with the 1984-86 Jeeps, they were not designed to fit it so you’ll have to find a complete 4.0 donor to swap all the front end parts to make it work. Plenty have done it, so it’s not an impossible task. However upgrading to a Chevy v8 or even v6 is much easier to fit. The 1993-5 camaro 3.4 is basically a stroked 2.8 v6 and will bolt in with a few modifications like swapping over all the hardware and getting the flywheel balanced if remember.

Anyway Lots of possibilities. I remember well how gutless the 2.8 was on the highway especially going up steep inclines or high passes.




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[Jargon]

4 hours ago, justinmartinez001 said:

It’s the GM 2.8L V6 and I believe it’s the federal. I live in Albuquerque New Mexico. It says my vehicle has “failed the tail pipe emissions inspection. 

I know this is basic, well-known emissions test trick, so sorry if you already know about this :) . But have you tried driving it at highway speeds for like 45 minutes prior to testing? I only bring it up because my friend has an XJ with 2.8L V6 and he fails every two years for the exact same thing: "failed the tail pipe emissions inspection". Then he takes it on the highway for a bit, comes back, and passes. I don't know if it's legit, or just coincidence. 

[Green Mesa XJ]

Probably the catalytic converter getting to temperature. That’s my guess anyway.


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[zomeizter]

Agreed, carb tune and operational cat air supply system will clean up emissions. Also, ensure the choke is operating properly, it may be contributing to the high CO reads...

[grumpiebill]

Ok on the front of the engine left hand side should be a pump below the alternator, it’s a AIR pump, all it does is pump air into the exhaust. See if you still have one because a lot of people bypass it. If it’s there the follow the tubing back to the I want to say solenoid on the left hand side of the motor, there’s vacuum line going to it and from there it splits off to tubes on each exhaust manifold. Those tubes have a check valve if I remember right.

AIR system is a mess, that’s why you’ll hardly find a old 2.8 /any 80s carbureted engine with one anymore.

Now if you federal emissions the good news is no computer and no O2 sensor, you do have a catalytic converter.

I live in s no emissions testing state so I don’t know much more about what you might need to pass in ABQ

I’d guess either tune the carb out, or fix the AIR system and/or catalytic converter. But I’ve really got no idea what help pass or fail a system. Surprised they care to test a 32 year old Jeep.


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Same...I'm quite surprised they're testing. As long as I've been wrenching I've forgotten more than most will ever know about smog pumps and air diverter valves. I wonder if they inspected for system application to be sure everything was there that is supposed to be. Make sure the pump is there and there is a belt on it. If no belt pump could be seized...that is my step 1...

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