Help!!! Signs you have fried your cats...?
08-20-2008, 09:25 PM
#1
Help!!! Signs you have fried your cats...? Playing around with MAF tuning I may have cooked the cats. No rear O2 sensors so Cat overtemp couldn't save them I think. No codes or misfire or severe knock retard which explains it.
Regardless of the tune I go back to, at part throttle it seems to struggle. It feels like it's not cleanly accelerating. On WOT and letting it go up through the rpm at part throttle, I've heard numerous "thumps" and pops coming from the exhaust. I've tried the "rattle" test but no dice, cats sound solid.
when I took a look at the MAF this evening, I found it to be covered in a layer of thick dirt. Some carbon, some really just fine dirt. It's had a K&N for it's life so I figure this is eventual buildup over 10 years, but it made me think if I was messing with the MAF settings, I may have told it more air was coming in than actual and running it rich. I cleaned it up and while I can't directly compare to earlier logs, LTFT correction is <10 with maybe 1 value of 14 but mostly single digits. A far cry from the 21-24 I saw when I first logged the car.
Either way, something feels "wrong" when I drive, like the exhaust note changed but I'm not noticing any funky smell out the exhaust yet. Back when I was tuning, I did note the exhaust had a rich smell to it but I didn't think too much about it.
Regardless of the tune I go back to, at part throttle it seems to struggle. It feels like it's not cleanly accelerating. On WOT and letting it go up through the rpm at part throttle, I've heard numerous "thumps" and pops coming from the exhaust. I've tried the "rattle" test but no dice, cats sound solid.
when I took a look at the MAF this evening, I found it to be covered in a layer of thick dirt. Some carbon, some really just fine dirt. It's had a K&N for it's life so I figure this is eventual buildup over 10 years, but it made me think if I was messing with the MAF settings, I may have told it more air was coming in than actual and running it rich. I cleaned it up and while I can't directly compare to earlier logs, LTFT correction is <10 with maybe 1 value of 14 but mostly single digits. A far cry from the 21-24 I saw when I first logged the car.
Either way, something feels "wrong" when I drive, like the exhaust note changed but I'm not noticing any funky smell out the exhaust yet. Back when I was tuning, I did note the exhaust had a rich smell to it but I didn't think too much about it.
11-04-2008, 08:11 AM
#5
Do an exhaust gas backpressure test. You need the gauge made for this test. You test at pre and post cat bungs to compare the values. The pressure should go up a little at the post cat bung(say 0.5lb)from the pre cat reading, but not a lot. Also the pre cat reading should not be too high. Say 2lb pre cat, but it depends on the vehicle. I recently had an Impala where the pre cat reading was OK, but the post cat was ZERO. I figured the cat was blocked so I expected to see the reading go way up. Instead of zero. When it goes to zero it is COMPLETELY blocked and all the exhaust has to go out through other valves during overlap. The engine is having an asthma attack when this happens. Poor performance and gas mileage. You need an exhaust gas backpressure tester.
11-04-2008, 11:37 AM
#6
Exhaust back pressure tester huh?... I'm going to see what I can find at the local part stores. I'll post results. I'm really hoping that the cats are my issue... Thanks for the suggestion. Also, These are SLP cats so if anyone has had any experience with them please feel free to chime in.
11-04-2008, 11:54 AM
#7
One test to see if they're really clogged/toasted is to tap on them and see if you hear any kind of rattling. If it rattles they're done for, if it doesn't rattle it could still be clogged, but it's a good quick check. A little less scientific than the back pressure tester but works.
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11-04-2008, 05:23 PM
#8
I already gave them the rattle test. Napa is the only place around who sells a exhaust pressure gauge... They want $250.00. Found a couple online around $170. I think I'll give em' a visual inspection first. I should be able to see thru the element. My exhaust setup is all SLP. Muffler is some what quiet. Most who hear my car say it sounds great... I'm thinking I'll gut the cats if they look clogged. What should I expect as far a changes in sound if I gut em'?
Oh BTW
Sorry.
Oh BTW
Sorry.
11-04-2008, 05:40 PM
#9
Pull them off and see if you can see thru them, if you can't, punch them out and be done with it.
I had one come apart clog my exhaust back when I still had the Y pipe on (when the big motor first went in the car) and when it did, the car lost 120 rwhp! A chunk got thru all the way back to the LM1 where it slipts to go over the axle and was clogging up teh entire exhaust.
Needless to say, a long metal rod and a couple hours took care of the problem once and for all.
I had one come apart clog my exhaust back when I still had the Y pipe on (when the big motor first went in the car) and when it did, the car lost 120 rwhp! A chunk got thru all the way back to the LM1 where it slipts to go over the axle and was clogging up teh entire exhaust.
Needless to say, a long metal rod and a couple hours took care of the problem once and for all.
11-04-2008, 06:25 PM
#10
I had that happen to my 95 nissan pickup... It wouldn't rev past 3500... Made the engine run hot as hell too... Did you have any exhaust leaking sounds from under the car?
11-05-2008, 12:01 AM
#12
Found a plug wire had just disintegrated, burned despite NOT touching the damn header. I mean it was close, but some wires are closer than others so it was strange to have that happen.
The strange part it may be coincidence, but the exhaust is a lot more muted, it seriously got quieter since that incident, and it wasn't the tune that quieted it up, it was that event. Also notice now that weather is colder, that I'm getting more exhaust out the drivers side of the true dual than before. Oh well always wanted the smaller metallic cats...
The strange part it may be coincidence, but the exhaust is a lot more muted, it seriously got quieter since that incident, and it wasn't the tune that quieted it up, it was that event. Also notice now that weather is colder, that I'm getting more exhaust out the drivers side of the true dual than before. Oh well always wanted the smaller metallic cats...
BAD smell also.
11-09-2008, 07:46 PM
#15
I passed on the exhaust pressure test... Didn't want to spend the $$$ on the gauge. So I opened up the exhaust and found my drivers side cat has been gutted and the passengers side was there but in rough shape. I gutted it... A pickle fork worked well for me... I went to put my y pipe back on and had to squeeze the header pipe together about an inch to get it to line up properly. It seems like a lot of unneccesary stress on the headers & head. The exhaust sounds nice and seems to have reduced the sluggishness i was experiencing. I'm wondering if it was pulling timing... Can an exhaust leak or lifter tap trip the knock sensor?
