Look what I found in my exhaust

So began to replace my trans mount, trans pan, plastic accumulator modulator, and install b&m shift kit.
But first, remove exhaust. I decided to take off entire mid section from mid muffler up to second cat convertor. Upon removing, a bunch of crap (big chunks of honeycomb 1" thick) fell out from the section between both cats! Parts of them looked melted. Here are some photos. Did PO break first cat apart, or can this happen in its own?


Presumably, if the PO had busted them up, he would have cleaned them out. Dunno how it happened on its own, though. While you’re playing games, you might as well drop the downpipes and clean the corrugation out of them.

It can happen on its own. I’ve seen it on various cars a few times over the years


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I live in a fire prone area of southern California and on a regular basis there are fires that flare up along the main interstate and state highways. Often afterwards the fire officials have attributed these fires to chunks of red hot catalyst coming out of exhaust systems of cars driving by and then igniting the dry grasses along the side of the road.

I wonder if the irregular flow of gases through your exhaust system could be contributing to your uneven idle. If I were you I would remove the entire exhaust system for a visual inspection. This is what I did in my wife’s 1990 XJ-S convertible (5.3 L V12 w/ Marelli ignition) shortly after getting it in 2005 and I discovered the two right catalytic converters hard been completely destroyed by a Marelli meltdown some time in the past. I shook out all of the chunks of destroyed catalyst that were in the front and rear mufflers and then installed new front and rear catalytic converters on the right side. Before this the car had failed the CA Smog Check and afterwards it easily passed with very low numbers.


I’ll remove downpipes next week, I think what I’ll do is clean them up and have muffler shop cut out old cats and weld in new cats. And I’ll replace mid pipes/mufflers with straight pipes and no 2nd cat.

How badly clogged up was your exhaust before you pulled do you think? Looks pretty substantial from the quantity of melted down material that came out.

Did you experience less power at higher speeds than you would have expected to have? I am thinking my exhaust may be similarly clogged as at speeds above 70mph the car is really lethargic and barely willing to accelerate. There’s also a hissing/whooshing noise that starts up and becomes loud very fast if I give it more gas above that speed. I haven’t taken it over 80 ever but given its struggles at 70 I don’t think it could even do much above 80-90 now if I wanted it to.

Also, anyone have a good (ie. indicative of no clog in/along the exhaust) pressure to look for out the tailpipe? (5.3 89 XJ-S w/ Lucas ignition)

I probably purchased the car like that, so I have no ‘before’ reference. I only found out because I had to do trans mount!
And because I haven’t replaced old tires yet, I haven’t taken her past 50mph.

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Best way to test for exhaust restriction is to remove the oxygen sensor and hook up a pressure gauge at that point- upstream of the converters. Back pressure should be minimal, no more than 1-2 psi at wide open throttle.
Another test is connect a pressure gauge as described and hold the throttle at a steady 3000 rpm until the gauge stabilizes, then blip the throttle; gauge should momentarily rise but fall immediately to near zero.
Hiss you describe and lack of power at high speeds sure sounds like restrictive exhaust. My ‘88 accelerates better from 70-90 than it does from a stop.

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Thanks Robert! Makes sense to test at the oxygen sensor upstream of all the cats. I will try that and report what I discover. I expected the acceleration on these cars would be quite good in that 70+ range so I appreciate your confieming that your car has some real pep still there.

One quick check is to hold a strip of paper (Reynolds Wrap better, maybe?) of equal size behind both exhaust pipes, and let her idle. They should both blow back/“wave” about the same amount, else something is amiss in one of the exhaust systems on that affected side (i.e. less blow back).

btw, Paul #2, what do you think of the fed’s new effort to replace the CA emissions standards with the “federal” standards applicable “to the other 49 states”? :thinking:

You just gave me an idea, Greg … Since here in Texas cars older than 25 years do not have to pass emissions inspection, what’s to keep me from having all the cats taken out? Or would that somehow screw up the engine management/computer system settings? Should improve engine HP, too, I would think … :thinking:

Yep, cats internally are basically just a “honeycomb” of platinum … not sure if pure platinum (should be, given their price! :roll_eyes:) or an amalgam of platinum and other metal(s). As the cat is used over time, parts of the honeycomb eventually burn up and give their all for the team, so to speak. :baseball: btw, LTNS DD … Glad to see you posting again … :smile:

:confused: It was barely a week after owning it before I found somewhere to see if my car could do at least 120mph! Might as well be driving a Prius. :woozy_face:

I did that with my XJ40, (same engine) no problem at all, I also did it to my brothers 3.2 Lt X300 (AJ16) and again no problems arose.
In fact I had mine tested to the NZ standards (not a mandatory requirement for Pena cars) and it would have passed with flying colours.

Unless your cats are clogged or broken (like mine), you probably won’t notice much difference, except your exhaust will smell more (think 60’s car). Although you ‘may’ notice a difference if you get your car up above 80 mph :wink:

Shouldn’t affect engine management whatsover, as long as you don’t have a second O2 sensor AFTER the cat.

Also, even though you have no emissions inspection, it is still illegal to remove cats, so no muffler place will do it. Doing it at home is the only way, as long as your next door neighbor isn’t a federal emissions inspector.

To quote the American philosopher Yogi Berra, “it ain’t over til it’s over”.



Seems more than reasonable to me. However, folks around here think, “Democratic republic of California”.
Implied superiority over the other 49.

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Here in NZ its not illegal to remove cats from cars produced prior to 2000, on the 3.2 of the brothers he noticed an improvement in pick up (seat of the pants) I’m talking the I6 engines here (AJ6 and AJ16) Strangely enough there are other places on this earth other than the USA :slight_smile:

Worse, one of my buds there refers to it as Commie-fornia … :laughing: I can’t figure out if he’s not happy with the state, why not move out … he can always sell his businesses or at least run them from another state … :confused: