I love this site! Have 1996 Grand Cherokee Laredo, all stock, 181K, and now my sweetie needs attention. High HC(3X), High NOx(3X), High combustion temp. Bought a code reader, reads nothing, nada, no codes. I do believe it's the CAT, and I will change out the EGR too. How tough is it to replace the CAT? A big hammer, or a bigger hammer? Is a torch necessary? Should I learn to cuss in five languages? This CAT business is new to me, anyone got words of wisdom to share?

 

Before you take it for emissions, drive it around for an hour or so. It'll help to get things running where they need to be and could save you of you weren't too far out of range.

 

WAAAY out of range. Changed plugs, old ones had HUGE gaps, been running premium fuel, and still tripple the passable levels, so I think it be the CAT, any tips?

 

On the cat, I've never replaced one myself, but i have replaced everything behind it. I think it depends on if your system is welded or not. If your system is just clamped, i think you can just unbolt it and slide it off the muffler. If it's welded, then you'll have to do some cutting. Don't forget to replace the gasket!

 

Does the jeep seem to run good, no spark knock, hesitation, rough idle etc?

High NOx is the result of high combustion temps, and the main purpose of EGR is to reduce high combustion temps by recirculating exhaust gasses (bad air) into the engine. If your jeep has egr you might check that its functioning properly. If you remove the valve then make sure the passage is not clogged up too. There are many other things that can cause high NOx too. Things like a lean condition, ignition timing, high engine temps, carbon build up, catalytic converter, along with many other things.

With high HC too, high HC is usually a result of weak or faulty ignition components but things like lean conditions, low compression, timing or catalytic converter.

These things listed below are popular guesses but may not be what you need.
check vacuum leaks, hoses, PCV/CCV, gaskets.
oxygen sensor(s) ( sensors before the cat, possible lean running condition)
carbon buildup (seafoam treatment, or a good brand top engine cleaner)
catalytic converter.

 

x2 on the above post!
I lived out there in CO for quite a few years and fought with their emission's requirements on all my older vehicles! In fact a few times I said screw it and rode on bad tags for a while...

But to answer your question I would start of with a really good look at all your emissions componets and vacuum hoses make sure there are in proper condition. Also you should consider replacing your 02 sensor too. I re[laced a CAT on one of those before and it wasnt to bad... We did end up cutting it off because it was welded. But that aint to bad just a little elbow grease and some ringing in the ears from all the noise. I would also recomend a full tune up with high octane gas and a long trip around C-470 to burn up any junk in the combustion chamber.

I know there is a shop that partners with the Colorado emssions dept tht will take your car in and diagnose it for free. Just a little FYI if you still have issues.

 

I replaced the cat on my 97 ZJ. It was clamped on, but it didn't "slide off"! I had to use a Sawsall it cut thru the case behind the connector, score the side of the connector with the blade (that is, cut almost thru it lengthwise), and split it with a chisle and a BMFH!

Otherwise, I think the other guys did you right about suspecting the EGR and 02 sensor.

Another suspect might be the injectors need cleaning, replacing.

 

What gasket?

 

Answer = move to Oregon. No emissions .... no sales tax. Fantastic trails fishing etc.....not much snow in the valley but snow an hr away . 2 ye plates for next to nothing. CO issue beautiful but the NPW is awesome w/ lots less people and lots of salmon ... steelhead. You'll live longer!

 

Isn't there a gasket between the cat and the pipe comming off the engine? Or am I unknowingly making **** up again...
(Sorry if i am!)

 

There is a donut gasket where the pipe bolts to the header, but it will take a lot of abuse. After hammering on mine, it was still okay. I did put a piece of 2X4 behind the pipe where it crosses from the driver's side to the passenger's side to take up the shock, however.

That's on the 4.0. I don't know about the V-8's though. I quess there's two but I don't know how they will withstand the shock.

 

thanks for your reply, got the "bolt on" out. and bolted another on. missed the gasket, but did remember the muffler bearings. thanks. keep yer powder dry, brother.

 

thanks for your reply, my process was pretty much the same, but there is no EGR post 1995. confusing, yes?, happy Jeeping!

 

thank you, everybody! getting to know my beauty is a treat! all the insight, experience, and words of advice have helped me so much! by the way, apparently, there is no EGR post 1995.