Billy Sacco

Hey all this is kind of a weird one. As thread title states lately my car runs much better in D4 mode then in D5 mode. The backstory to this is for a few months now off and on I pull the P0420 code. The car seemed to be a little "jerky" too. So I changed oil. took off the intake manifold and cleaned that out. I replaced plugs like 30,000 miles ago so those should still be good. Seafoamed in gas, oil and intake per the directions here hoping maybe that would take care of the jerking and the code. Well I had pulled the battery cable while doing all this and the car seemed to have a little more power but was still pretty jerky and of course came up with the code again. I took it to a local honda mechanic here and he had the car all day, I asked him to take a test drive. Not sure if he did. He said "well you need a new cat that will be $1200". I think he might have just pulled his code reader, read the code and then left the car in back all day but I can't say for sure. He said he tested my O2 sensors and they were fine he said my cat was just breaking down internally, not sure what kind of test he did on it. But anyhow I told him I did not have $1300 bucks right now and he said he did not know of any bolt on cats that would fit my car. So anyhow I started running the car in D4 mode and it runs very smooth in D4 mode. Shift like a dream. Go back to D5 mode and not so good. In D5 mode it seems to want to shift right away at low rpms and as a result the shifts are very rough. But in D4 mode the car shifts great. So is this a problem with the tranny going bad? Could it at all be related to the Cat? I think my motor mounts are bad so I might have vac leaks there I was going to plug the lines and see if the car ran any better. But any suggestions or insights anyone can offer would be much appreciated.

jjashaa

iTrader: (23)

for the cat...

Excelerate sells a 2.5" High flow cat. would go really well with your comptech headers

I believe its like.. $300????

Billy Sacco

Yeah for sure man I was probably going to buy and get that one installed. I just would hate to replace that and continue to have problems .

ChucksCL-S

The top of the intake has a cover plate, and under that is a very thin gasket. Make sure that is installed correctly, not backwards or upside down. When installed wrong it covers small holes that are part of the EGR system. My '03 did what you are describing, and the dealer discovered the error, egg on my face big time.

01tl4tl

good call chuck!!
I remember that one being popular problem a year ago-

the top cover gasket needs to line up with the cover,,not the manifold,, or its flipped over and blocks important port
remove and redo

also have a real muffler shop do a cat test- they look at temps and flow rate pressure to see if its clogging or destroyed inside
Banging on it will tell it its come apart with your wild high rpm driving style

01tl4tl

excelerate and others have plenty of cats fine for the TL at less than 200-300 dollars

pzhoward got hers for a good price- Pam- what and where for your cat?

jdjohn84

I would say running better in D4 is not related to your code. D5 should only be used while on the freeway, or at least up at highway speed. I only shift to D5 when I hit 70mph or so. Many here do the same. "no bolt-on cats for our cars"...ridiculous.

datax976

I just looked at my car and i dont have a D5. I only have D4 down to 1. I have a 99 TL though so maybe it didnt come with a D5

jdjohn84

Yep, 99 was 4-speed, and 00-03 were 5-speed.

ou sig

hey all - I have had the same code for a while and was wondering if you can replace the cat easy by yourself in the garage? Most muffler shops are quoting me $400 - $500 to install a cat. I would think I could buy one for $2 or $300 and put in myself if possible...maybe the O2 sensor would be a pain to get off after 12 years and 173000 miles...!

jdjohn84

I haven't actually replaced my cat (yet), but I can tell you there are two ways to attach a cat: bolt-on and welded. The stock cat is a bolt-on that can easily be removed. You will probably have to special order a bolt-on replacement since aftermarket bolt-on cats are not that common. If you see the term 'universal' in describing a cat, that means that it just has straight pipes on either end that have to be welded onto existing exhaust pipes, so don't buy that kind if you plan on doing it yourself...unless you have welding equipment Obviously replacing a bolt-on cat with a universal cat would mean that the flanges on existing pipes also have to be cut-off in order to weld the universal in place.

01tl4tl

ck our sponsor/vendor Excelerate for the right cat for your type driving
way less than what those shops are quoting

HondaProtegeX2.3

lol according to the manual it wants to drive in D5 all the time... but hey if D4 drives smoothly then so be it your car wants to be a 4 speed auto!! lucky my tl drives like brand new it usually shifts like butter even in the cold weather im in 25 degrees and i only let the car warm up for a couple minutes before i head out... car warms up quickly. im guessin the tranmission has be replace cause the cars got 145k now and tranmission feels brand new. overall imma try to take this car as far as i can take it!

Billy Sacco

Well minor update I checked the gasket like was recommended and it was indeed the right way looking at the diagram in the shop manual. I almost wish it were that simple . The only thing I had not done besides all the other maintenance items was clean the air filter. Holy crap there was a small pile of gravel pooled up next to it and a cigarette butt. Cleaned it out with the injen kit and the car is actually running pretty smooth now, even in D5 mode. Hopefully thats all it was but things never seem to be that easy . Either way I might be due for a new cat so I think I will go with the excelerate cat and use the non fouler trick on the o2 sensor. Thanks all for the suggestions.

01tl4tl

excelerate has cats you need an anti fouler trick, and others with a long tube off the side that O2 sensor goes in- the distance reducing the flow to normal- for reading purposes