centuryhouse

Help on fuel / exhaust / cat issue.

My 94 XJ 4.0 seems to be losing a little power and the carpet around the rear of the passenger front seat is 'cooking' meaning the carpet is hot to the touch and the seat frame is burning hot to the touch.

The muffler shop says the cat is good and it is a fuel mix issue most likely. It also just passed a smog inspection.

No bad smell from exhaust, not 'rattling' sound from cat when driving or when beating on it.

If I flip the key on 3 times to get the ODB1 codes, it is just 55 (no codes).

Recent work: new fuel filter, plugs, wires, cap, rotor and I've run some fuel treatment (Seafoam once, and Marvel).

Thoughts? Is there any kind of heat shield above the cat that I could be missing? What should I check that controls the fuel mix?

EZEARL

On my '96 there's nothing above and separate from the converter but there is a 2pc shield on converter itself. 1pc on the top and 1pc on the bottom

http://www.rockauto.com/en/moreinfo....180213&jsn=384

97grand4.0

Had something similar to this recently with a 2010 honda crv, Driver said the floor was hot. Also noticed loss of power...Thought she was nuts, ...turned out her caliper was sticking and the rotor was getting red hot. Fix was the caliper rotor and brake line just to be safe.
Now, this isn't your problem maybe, but you did say any help..

EEVEE

hmm that makes sense if the brake is sticking the engine has to work much harder

centuryhouse

No brakes hanging. No rough running, no stalling, no overheating, no idle surges, no noises, no bad smell, no codes.

Just a hot cat and shop telling it isn't bad.

97grand4.0

What is the before and after temperature of the cat as measured FULLY hot, with a digital thermometer? Should be 100F hotter aftere than before.
No codes, passed smog? Does it have an O2 sensor after the cat? If so and no codes, and the temps are right as above, I'd call it good enough for now. I would be concerned that you may have a fuel issue or other tune up issue.
You can change it if you want and if high miles undoubtedly it will be better, but, you may still have the same problem.
One odd thing I would suggest, which I did to the 2010 Honda crv (also had a P420 code though) is a product called "guaranteed to pass" sold at NAPA. Cleans the cat screens up. I think it works but my problem was the air cleaner clamps were loose , and they are after the MAF sensor, so the rear O2 was seeing unmetered air and setting the code. So if you have a vacuum leak that might also do it.
All that said, if your heat shields are missing, you will get hot carpet, not a good situation.

centuryhouse

No idea on temp as I have no thermometer.

Only one o2 sensor on the 94, before the cat. No codes, and passed emissions test a month ago (after problem with power loss started, not sure I noticed the carpet getting hot yet then). Due to power loss I had just changed the cap, rotor, plugs, plug wires, air filer and fuel filter.

I just noticed the tail pipe has a black ring of soot around the tip, which was not there a month ago.

extrashaky

The catalytic converter burns excess remaining hydrocarbons (fuel) out of the exhaust before it's dumped into the atmosphere. If it's getting hotter than it should, that's a sign it's receiving more fuel than it should. In other words, you would be running rich. That could also explain the soot around your tail pipe.

You may be able to confirm a rich condition by pulling your plugs and comparing them to one of the many spark plug charts available on the internet. A rich condition will leave the plugs black.

You mentioned you don't have a thermometer to check the actual temp. You can get a decent IR thermometer for $20-$30. I have a Harbor Freight one and can't recommend it (it's not very accurate), but there are now plenty of other companies selling good ones in the same price range. You may not even need to do this if the plugs confirm a rich condition.

If you do have a rich condition, I would start by replacing the O2 sensor, even if it's not throwing a code. O2 sensors are strange little liars that can be failing and still tell the PCM they're fine.

centuryhouse

Replaced the o2 sensor yesterday. When I pulled the plugs 2 weeks ago (after the problem existed) they looked white-ish.

How hot should the cat be after fully warmed up?

97grand4.0

From 2 posts back and yesterday "What is the before and after temperature of the cat as measured FULLY hot, with a digital thermometer? Should be 100F hotter after than before."

Ive heard the 500-600F range thrown around as figures for an obd2 cat.

centuryhouse

This is an obd1 - does that matter?

97grand4.0

Yes.
In terms of the converter operating temp at the inlet and outlet, no, still ~100F difference ballpark.

s346k

my obd2 cat was 310 +/- 25 degrees at full operating temp after a 20 minute drive. i checked the entire exhaust end to end trying to diagnose a problem. read the plugs. if it's lean you'll see it. if it's *that lean it will spark knock and ping, also.

centuryhouse

No knock and ping or other issues with the way it drives. A little lacking in power but I can't tell if that's my imagination or not I think it is more an issue of 3.55 (?) gearing and running 31 tires.

I bought an infrared thermometer at lunch. I'll test tonight after work.

centuryhouse

Well here's an interesting twist...

I measured the temps with the new infrared thermometer. To have a basis for comparison, I tried it first on my 2000 XJ (which has no issues and which I drove to work today). Then tried the problem 1994 XJ.

2000 XJ after 20 minutes driving:

508 degrees in front of cat
636 degrees behind cat

1994 XJ (the one with the issue) after 20 minutes:

415 degrees in front of cat
530 degrees behind cat

:-o

And yet the back passenger floorboard of the 1994 was burning hot under the carpet - to the point that I could only stand to keep my hand on it for 3 seconds before yanking it away because it was so hot. And that 'heating up' smell from the carpet again.

What's going on?

The previous owner took out the carpet and padding, and rhino lined the floor. Then laid the carpet back in place (no padding). So other than the floor itself, there is no insulation.

Could it just be that is the problem? I need a heat barrier?

Then again, there is the 'heating up' smell from the carpet which was never there in the entire year I've owned it, but which now happens every time I've run it for 15 minutes, as it heats up.

Thoughts??