88red4cyl Posted July 9, 2008 Report Share Posted July 9, 2008 Some of you may remember my threads from the winter about my fuel mileage issues with my 99 Lumi LTZ.. I am still having issues with it, and it still has yet to throw any codes, or give me any indication that there's a problem.. That being said, does anyone know how to tell if a cat. is bad or not? I have been looking for it to be glowing red, but I don't think I have been driving long enough for it to get that hot... Or if anyone wants to throw out suggestions on what they think it could be, that would be great.. Thanks! Quote Link to comment Share on other sites More sharing options...
z34mightymachine Posted July 9, 2008 Report Share Posted July 9, 2008 Does your Cat make any noises, or do you feel that you have to really push on the gas pedal to get the car going? Quote Link to comment Share on other sites More sharing options...
Euro Posted July 9, 2008 Report Share Posted July 9, 2008 no joke...stick a broom stick under neath the car or something and give it a couple good raps against the cat. If the cat's bad you'll hear something rattling around Quote Link to comment Share on other sites More sharing options...
mfewtrail Posted July 9, 2008 Report Share Posted July 9, 2008 Since I'm lazy and don't feel like typing much...read over this page here. It covers several methods to test for a bad catalytic converter. http://www.aa1car.com/library/converter.htm Quote Link to comment Share on other sites More sharing options...
kwk39018 Posted July 10, 2008 Report Share Posted July 10, 2008 Does the exhaust smell like sulfer when you get on the gas hard? If so your cat could be bad or starting to go bad. Quote Link to comment Share on other sites More sharing options...
Night Fury Posted July 10, 2008 Report Share Posted July 10, 2008 Maybe this is why my car is being such a bitch? Quote Link to comment Share on other sites More sharing options...
BXX Posted July 10, 2008 Report Share Posted July 10, 2008 Maybe this is why my car is being such a bitch? No, you have a LHO... You need to check your fuel pump, injectors, coils, ICM, and CPS... Back on topic.. A cat can still be bad even if its not getting red and doesnt rattle either. They can still be glogged to the point of causing poor mileage and/or loosing power and/or running rough.. If the cat was an issue, you should be throwing a Catalyst Efficiency Below Threshold code.. Our downstream O2s are pretty good about picking up on it.. What gas mileage are you getting and forgive me on my lack of gen1.5 engines, but was the 99 LTZ a LQ1 or a 3800??? IF its an LQ1 a stretched timing belt can cause issues that seem to be elsewhere Quote Link to comment Share on other sites More sharing options...
88red4cyl Posted July 10, 2008 Author Report Share Posted July 10, 2008 Maybe this is why my car is being such a bitch? No, you have a LHO... You need to check your fuel pump, injectors, coils, ICM, and CPS... Back on topic.. A cat can still be bad even if its not getting red and doesnt rattle either. They can still be glogged to the point of causing poor mileage and/or loosing power and/or running rough.. If the cat was an issue, you should be throwing a Catalyst Efficiency Below Threshold code.. Our downstream O2s are pretty good about picking up on it.. What gas mileage are you getting and forgive me on my lack of gen1.5 engines, but was the 99 LTZ a LQ1 or a 3800??? IF its an LQ1 a stretched timing belt can cause issues that seem to be elsewhere The 98 & 99 LTZ's got the 3800... I'm getting about 11-12 mpg city with it... In the winter I was only getting 6, but when it warmed up it went to around 12.. Either way, it's still far from what it should be getting.. I do get a bit of a sulfur smell when I get home and get out of the car, although I suppose it could be unrelated... I've never had this car throw a SES light for me (except for the time the IAC crapped out).. A buddy of mine has a scanner, and when we hooked it up, he said everything looked in spec.. One of the O2 sensors (can't remember which one now) was reading pretty flat, which he said was odd, but someone on here told me that was normal... Quote Link to comment Share on other sites More sharing options...
kwk39018 Posted July 10, 2008 Report Share Posted July 10, 2008 Sounds to me like it your cat.Replace it Quote Link to comment Share on other sites More sharing options...
per0781 Posted July 10, 2008 Report Share Posted July 10, 2008 Sounds to me like it your cat.Delete it fixed Quote Link to comment Share on other sites More sharing options...
88red4cyl Posted July 12, 2008 Author Report Share Posted July 12, 2008 Thanks for the replies!! Noticed some whisps of smoke coming from the exhaust when I was sitting at a light on my way to work today.. It appeared fairly light colored, not black or anything... It was in the 80's here today, so I know it wasn't from the cold... I smelled the exhaust when I got to work, and it didn't smell sweet or anything, so I think I can rule out burning coolant... Quote Link to comment Share on other sites More sharing options...
1990lumina Posted July 12, 2008 Report Share Posted July 12, 2008 An exhaust back pressure test will let you know if the cat is plugged too. Quote Link to comment Share on other sites More sharing options...
88red4cyl Posted July 12, 2008 Author Report Share Posted July 12, 2008 An exhaust back pressure test will let you know if the cat is plugged too. How do you do that? Quote Link to comment Share on other sites More sharing options...
1990lumina Posted July 12, 2008 Report Share Posted July 12, 2008 You need a guage that is meant for doing this test (we had one at school)...anyway, it screws into the pre cat O2 sensor and measures back pressure in the system. There really shouldn't be any, but definately not anything over 2psi. It might spike when you rev the motor but should drop instantly Quote Link to comment Share on other sites More sharing options...
88red4cyl Posted July 12, 2008 Author Report Share Posted July 12, 2008 So if there is pressure then the cat is plugged, right? I had more smoke today.. Smelled like sulfur for a bit and then started like smelling like regular exhaust, but the smoke was still there... I revved the motor, which made more smoke come out and I sprinted back to smell it, and it's hard to describe the smell, but it almost smelled like a charcoal barbeque grill... Another question, although it may be a stupid one (ya'll should be used to that by now )and it's raining so I can't work on the car anyway.. I drive .7 miles to work in the morning (I know I should walk, but I have to be there at 6 am and I don't want to get up any earlier than I already do (which is 5)).. Anyhow, car is usually on for like three minutes from home to work. When I get to work, this car always makes the hot exhaust cooling off noise.. You know the one I'm talking about, the metal clinking sound after trip when you get out.. Should the exhaust be getting that hot from three minutes of running? I don't run it hard either.. The max I ever go is like 2000 rpm's (on the way to work)... Could this be related to my problem? Quote Link to comment Share on other sites More sharing options...
jasons96 Posted July 15, 2008 Report Share Posted July 15, 2008 I just had mine replaced not too long ago. I would drive 50 miles and used almost 1/4 tank of gas. Sevice Engine light never came on. Mines is a '96 Cutlass Supreme w/ OBD2 and Cali emissions. I took it to a muffler shop and they let it sit to cool down. After a while, they put it on a lift with the engine on and took a temp reading at the front and rear of the cat. After the "light-off" point, the front was hotter then rear when it should have been the same at both ends. After cutting off the cat, the inside was melted and plugged up. They put a new cat on ($300 for Cali emissions, $240 for Fed Emissions), I now get between 18-23 mpg mixed driving. So, take it in, have the temp checked and go from there. BTW, if you have Cali emissions, get the Cali Cat, Using a Fed cat on a Cali car will turn on the SES light on some '95s and all '96 and up cars!!!..... Good luck.......Jason Quote Link to comment Share on other sites More sharing options...
AWeb80 Posted July 15, 2008 Report Share Posted July 15, 2008 Since I'm lazy ya you are. Quote Link to comment Share on other sites More sharing options...
w-bodys_are_the_best Posted July 15, 2008 Report Share Posted July 15, 2008 When my cat plugged up on my Z24, I could tell cause it would get quieter and lose power, but I had nothing but straight pipe from the cat back. It was actually pretty quiet with just a cat. I took the pipe off after the cat, and using a crow bar broke the few remaining pieces into small enough chunks to empy it out completely. I put the rest of the pipe on and drove it like that for around 2 months, but it was insanely loud as the empty cat acted like an echo chamber. I ended up putting all new pipe on from the manifold back, cat deleted, and put a thrush glaspack where the muffler would be because I'm cheap and didn't want to pay $175 for the cat, and $86 for the OEM muffler, and an additional $26x2 for the OEM tailpipes/tips. My 3.1 is probably a little too loud and raspy for most people's taste, thank god we don't have e-testing around here. I think I have $85-95 for my entire system and it was all brand new. Quote Link to comment Share on other sites More sharing options...
88red4cyl Posted July 15, 2008 Author Report Share Posted July 15, 2008 I just had mine replaced not too long ago. I would drive 50 miles and used almost 1/4 tank of gas. Sevice Engine light never came on. That sounds like mine exactly!! I get ~50 miles for a quarter tank.. I don't understand why it's not throwing a SES light though... Quote Link to comment Share on other sites More sharing options...
mra32 Posted July 16, 2008 Report Share Posted July 16, 2008 cat AND an O2 sensor possibly? Quote Link to comment Share on other sites More sharing options...
jasons96 Posted July 16, 2008 Report Share Posted July 16, 2008 you might also want to check your air filter. My cavalier got crappy mileage until I changed my dirty filter. Quote Link to comment Share on other sites More sharing options...
88red4cyl Posted July 16, 2008 Author Report Share Posted July 16, 2008 you might also want to check your air filter. My cavalier got crappy mileage until I changed my dirty filter. Air filter's clean.. I actually just replaced it at the last oil change.. Wouldn't a bad O2 throw a code though? Quote Link to comment Share on other sites More sharing options...
mra32 Posted July 16, 2008 Report Share Posted July 16, 2008 you might also want to check your air filter. My cavalier got crappy mileage until I changed my dirty filter. Air filter's clean.. I actually just replaced it at the last oil change.. Wouldn't a bad O2 throw a code though? I dunno, it could have failed in some strange way where it wouldn't show in the computer. Its a possibility. Quote Link to comment Share on other sites More sharing options...
jasons96 Posted July 16, 2008 Report Share Posted July 16, 2008 you would think so but mine didn't. i think mine failed due to the fact that raw gas got into the exhaust earlier because i was in need of a tune up and it was barely running on 5 cylinders. raw gas and hot exhaust don't mix well in the cat. bad things happen. Quote Link to comment Share on other sites More sharing options...
88red4cyl Posted July 16, 2008 Author Report Share Posted July 16, 2008 Could someone post a picture of where exactly the cat is at? I don't think I've been looking at the right thing.. I see one o2 sensor, but I don't think that's the cat that I'm seeing... Quote Link to comment Share on other sites More sharing options...
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