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Unread 06-09-2013, 11:34 PM   #1
KillZone47
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1995 YJ Wrangler 
 
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2.5L YJ Smog BS again...

Tried looking around for answers haven't found much but so far everyone says replace the Cat some say has nothing to do with the cat...

My jeep is a 2.5L runs like a champ!

but failed "No (ppm)"

15mph-1675 MAX-539
25mph-1398 MAX-554


Any tips?

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Unread 06-10-2013, 06:04 AM   #2
EABiker
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High No is cause by high cylinder temperature. This can be from a lean mixture, (vacuum leak, faulty O2 sensor), or a malfunctioning EGR system. A bad Cat can also cause it, but if all your other readings are OK, it's most likely not the cause.
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Unread 06-10-2013, 06:22 AM   #3
ashland82391
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O2 sensor
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Unread 06-10-2013, 07:38 AM   #4
Que89YJ
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High Nox is running lean or bad cat. Run diagnostics:
http://www.jeepforum.com/forum/f12/h...codes-1257145/

Check your coolant temp sensor, MAT and O2. Last is cat because of $$$
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Unread 06-14-2013, 03:37 PM   #5
KillZone47
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1995 YJ Wrangler 
 
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I got three Error codes but im still little confused.

12. = Battery disconnect
33. = Air conditioning clutch relay circuit
17. = Engine is cold too long (thermostat stuck open)


Also im pretty sure i have an exhaust leak. would that make it not pass?
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Unread 06-14-2013, 03:55 PM   #6
idaholtby
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#17 needs to be addressed. If you are not reaching normal operating temp, then your ecm will not use the O2 sensor among others for proper fuel trim. What temp are you running at? Your rig is designed to have a 195 deg t-stat and then the normalized engine running temp is typically 210deg. There is no EGR systems on your model year and it has to rely on a 3-way catalytic to compensate. So address your temp issue. If you are running at the correct temps, then your ecm seems to think otherwise, which case, replace the temp sensor on the t-stat housing. If temps really are that low, then bad or incorrect t-stat is likely.
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Unread 06-14-2013, 04:42 PM   #7
KillZone47
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it was running around 145. im swapping it all out right now.
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Unread 06-14-2013, 06:26 PM   #8
Que89YJ
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exhaust leak before the o2 sensor must be fixed.
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Unread 06-14-2013, 07:31 PM   #9
KillZone47
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its running at 210 now and the exhaust leak is before the cat but after the o2.
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Unread 06-14-2013, 09:43 PM   #10
Noltz
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Exhaust leak will suck in air, venturi effect. Air, with it's oxygen, passes the oxygen sensor. Sensor thinks there's too much air, adds fuel, causing rich run and a cat running very hot (lots of air and fuel getting into the exhaust). Normally this would reduce NOx, but this needs to be fixed anyway.

Has your cat been swapped? When it was replaced did they use a 3-way cat? Your 2.5 doesn't have an EGR (Exhaust Gas Recirculation) valve. EGR's were the primary way to control NOx levels in engines back then but Chrysler used better combustion chamber design and a 3-way cat. If there's a cheaper 2-way cat on there it will not pass a 3-gas sniffer test.

Don't assume because (if) you bought it with a Pass certificate that means there's a 3-way cat in there. Many car lots are shady, and many would have no problem putting a DIFFERENT jeep on the tester and punching/scanning in your VIN.
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'91 Frankenheep YJ. 4.0, 4" BDS, Richmond 8.8, Titan 12k, 35" KM2's, rust.
'88 YJ, 4.2/4.0 head, +4½" & shackles, BFG 33's (sold)
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Unread 06-17-2013, 06:19 AM   #11
Que89YJ
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If you have an exhaust leak after the O2 sensor the calibration should be fine but the capability of the cat is being compromised. The cat does the job of getting rid of the NO. Get the leak fixed. High NO happens from lean burn and from the cat not doing its job.
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