Signs Of A Clogged Catalytic Converter

I have a 2000 4.3 GM V6 engine in my 48 CJ2a. In the swap I elected to keep the catalytic converter. I have driven it for several months and as time has progressed it has run a bit off.

Lately it has created an odor like firecrackers, as my 9 Year old says when I drive him to school in it.

Oil pressure is fine, timing is not adjustable, all plugs, wires, cap, rotor and distributor are new. 02 sensors are new and entire wiring harness is new.

The exhaust goes from stock cast manifolds to custom Y pipe to the stock resonator and catalytic converter out the back through one line thats tucked up between the frame rails. The catalytic converter has unknown miles on it and came from the donor vehicle. When I welded it together, I could see light through it, but there was noticeable soot in it.

Engine sounds as if its missing a bit, when cold its got a lot of off balance engine movement and there is a slight lag on initial acceleration. Above idle, power is great.

Stock in tank electric fuel pump is new and the PO said the fuel spiders were replaced with upgraded versions.. I don't really believe him. Anyway, it wont run under 58 PSI and it starts without issue.

It is making a sulphur smell, firecrackers...

Whats the verdict?

 

My experience has been that I get power loss and hard hot starts, bad idle, etc, and progressing eventually to complete undriveability except at very high rpm. Was extremely frustrating to diagnose.

 

these symptoms as well, but not always.

 

Think it got hot?

 

You can rig up a pressure gauge in where the o2 sensor goes. They do make a special exhaust backpressure tool to do it. It should be just about nothing if it gets over like 2 or 3psi its clogged. But it doesnt sound like thats your problem

 

A vacuum test on the engine may be revealing, also.

 

"but not always"

In one case of mine, the core was crumbled and blocking the pipe. Fairly straightforward.

But in my YJ, the 02 sensor was bad, and the symptoms were erratic, intermittent. It acted as if it were flooding/rich. I *think* the cat was getting alternately clogged with carbon, then burning off, somewhat randomly depending on driving conditions, and very confusing to me.

 

I'd suspect the injection spider or the cat is the culprit.
Wonder what brand of injection spider the PO installed?

 

Runs rich, cut the cat out, plugged in vac gauge, no erratic readings.

 

I got a bit overzealous and cut the cat off wrong, so I had to pull the Y pipe to fix it.. oh well.

 

If you have a misfire at idle, you're dumping raw fuel into the cat where it burns and overheats the cat. Running too rich can cause the same problem. Solving the misfire/mixture would save the cat if it's not already melted into a wad.

 

I cut off the cat and am welding in new exhaust. I shined a light into the resonator and cat and can see dim light all the way through, so its not clogged or melted yet. Im going to order the spiders and all associated replacement components to do this job.

Since the spider poppets going bad is a common problem with these engines and it sat for a , possibly, long period of time, I will throw these parts at this engine. It does have an occasional hard warm/hot start and it smells of unburnt fuel at initial start up with rough idle.

 

It would also be worth giving the ignition a good inspection. Plugs, wires, ...etc.

 

All new, but I agree and will check.

 

Retarded timing will cause the same symptoms also. Fuel not getting burned properly. IAT sensor or water temp sensor not regulating the injectors.

 

If it’s a 95 throw the injection out and put a throttle body or carb on it.

 

My buddy had a Ford ranger burn to the ground due to a neglected cat. converter, happened pretty quick. Only cats around here now either eat rodents or push dirt.

 

I know someone who lost their house and barn that way. A block away from the fire station.

 

Alright, so I cut out the cat and welded in new pipe, connected it all up and guess what? It doesn't run as rich. That lack of a cat shouldn't make a bit a difference in my mind. So what gives here?

I can smell exhaust, but no more sulphur or firecracker smell.. And the exhust isnt bad at all. A gloved hand over the hot exhaust has no unburnt fuel or other weird or burnt odors.

Its still has a bit of a lopey idle, but its not short on power...

Also its loud now. The single turbo style muffler aint cutting it, but I care about a lot less now because loud Vroom Vrooms are all the rage, right?