Plugged CAt on Lexus

[bigbadchev84]

got a head scratcher here.

My brother in law owns a 97 lexus es300 V6. its got 187,000 on the clock and he told me its been running like crap and the check engine light is on. I had him go to autozone and have the codes read. It said engine misfire.

So had him pick up some plugs and head to my place, when he got here it sounded horrible, thing was chugging and sounded muffeled. he said it didnt have any power and crappy gas mileage. it idles ok, but when you put it in gear it starts chugging and running really rough.

Since he bought it it has always smoked a little bit from burning oil. I pulled the plugs and they had a little burnt oil build-up on them, put the new ones in and only a slight improvement. I guessed his cat was plugged, as it sounded like the thing was having a hard time breathing.

we took it to the muffler shop yesterday to have it tested, sure enough it had 6lbs before the cat, he said 3lbs was really bad and needed replaced.
he also said that it was not the problem gauranteed and that he would put a new one on, but would not warranty it because the check engine light was on.

So anyone know where to go from here? he dosent want to dump alot of money into this, but needs it running good enough until he can trade it in. i noticed there was a 02 sensor behind the cat, would this have any effect on it since the cat is not breathing the way it should?

 

[Hogback Fabrication]

Have you replaced/inspected the wires, coil, cap & rotor, etc?

The O2 sensor after the cat is there to monitor the effectiveness of the cat, when the cat stops working well it trips the sensor and throws a code (but not a random misfire code).

Did the code say random engine misfire or did it specify a single cylinder?

 

[bigbadchev84]

i will have to ask him tomorrow, i have been reading up on this and all i did was put plugs into it, i will have to test the coils and check out the cap/rotor and wires

 

[jonathon]

I looked into this on my dad's CVPI since it's in the same boat with 180K on it with bad cats. My research told me that if you ditched the cats and put in an MIL eliminator(O2 simulator) it would be fine. Not much to the MIL eliminator(resister and a capacitor if I remember right), and that 2nd O2 sensor does not do anything but monitor emissions. Of course this isn't emissions legal, so YMMV and at your own risk. Living in BFE has it's advantages...

Now of course his transmission is slipping so we said f*ck it and we are looking for another rig for him(this time a Chevy truck unless he gets another surplus PI for $800 with 80K on it, which isn't likely). Of course my dad's philosophy is who cares about gas mileage when you don't have a payment

 

[dyeager535]

If the cats plugged I'd really expect it to throw a code for the cat as well, although I'm certainly not an OBD2 expert...the ONLY code was for a misfire? And that code can't in any way relate to the pre/post cat O2's?

If the cat isn't that much to replace (Lexus, so who knows) replacing it certainly can't hurt.

 

[bigbadchev84]

ok took it in today
throwing p0300 engine misfire
p0301 cylinder 1 misfire
p0441 EVAP emission control system purge flow fault
p0302 cylinder 2 misfire
p0305 cylinder 5 misfire

The cat is plugged for sure i seen it while testing, he said he reccomended getting the problem fixed before replacing cat.

Will check for broken vaccume lines tomorrow and throw some new wires on it.

Does anyone know where to find out how to test coil packs?

 

[Hogback Fabrication]

ok took it in today
throwing p0300 engine misfire
p0301 cylinder 1 misfire
p0441 EVAP emission control system purge flow fault
p0302 cylinder 2 misfire
p0305 cylinder 5 misfire

The cat is plugged for sure i seen it while testing, he said he reccomended getting the problem fixed before replacing cat.

Replace the cat and see what happens.

Does anyone know where to find out how to test coil packs?

Does it have individual coil packs for each cylinder? I would think it would still have one for all six and then plug wires running to each spark plug. If it only has one coil, coils usually fail all-together or pull a random misfire (rather than a specific misfire code).

 

[odin]

If the cat is clogged I would replace it AFTER you find the source of the misfire.
Thats the entire point of misfire monitors...to protect the cat from being destroyed by raw fuel in the exhaust.

I would start by checking compression and spark. Is there individual coil packs?
Im not sure, Im a Honda Mechanic. If there is try moving them around and see if your misfire also moves. Other things to check would be cam timing and injector pulse.

 

[nvrenuf]

Does it have individual coil packs for each cylinder?

This car should have 3 identical coil packs and 3 plug wires.

 

[nvrenuf]

I ain't sayin I know much but I do have the advantage of working at a dealership. That said...

I talked to a tech, showed him the codes and told him about the cat. His opinion is a bad coil. With the car running, he suggested unplugging the wiring harness from the individual coils one at a time - the one that doesn't effect the way it's running is obviously the bad one.

As for the cat, he said he can't remember the last time we replaced any convertor on any model because it was actually plugged. Typically, the only time we sell one or replace one in the shop is because it's damaged (wrecked, etc).

An OE coil is about $92.00.

 

[dyeager535]

As for the cat, he said he can't remember the last time we replaced any convertor on any model because it was actually plugged. Typically, the only time we sell one or replace one in the shop is because it's damaged (wrecked, etc).

That's a good point...didn't notice that before, but what were the AFTER cat numbers? Nothing saying something else isn't screwed up after the cat, however unlikely that is.