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2000 eclipse GT performance issues and P0420 code

111 Views 2 Replies 3 Participants Last post by  WhiteSpyder
I’m 18 years old, bought my 2000 eclipse GT at the start of ‘22 and have been trying to figure out what is wrong that’s throwing the P0420 code. I have a small budget so i’m trying to avoid replacing this and that in order to figure out whats bad.

The car has 183,000 miles but it’s been issue free since i got it (at 172k) aside from this. I always do an oil change after 3000 miles w/ OEM filter and mobil 1 oil but otherwise haven’t done a thing. It had a new cat installed just before I bought it. the first 8 months there was no codes at all, and then it started to pop up and go away, sometimes every few weeks at random. This makes me think the previous owner replaced the cat when it got damaged, but didn’t address the cause of the cat’s failure, and obviously i don’t want that to happen again.

I made a list of all the car’s symptoms, maybe someone can make sense of it?
-P0420 code
-lags when accelerating(sometimes more than others)
-there is a hissing sound under the hood close to the firewall (vacuum leak??)
-gurgle sound when feathering the gas from a stop
-rattle/gurgle sound lasts 2-5 seconds, only after startup, sounds like it’s coming from the rear, and doesn’t always happen but usually worse in cold weather
-when steering wheel is turned nearly all the way, it makes the RPMs change and sounds way worse than other cars would
-when driving ~2500 rpm, seems to have trouble shifting gears up, like i need to gas it excessively, and the exhausts tone makes me cringe
-idle is sometimes rough, but sometimes flawless
-battery has died a couple times in the cold
-lifter tick that goes away when warmed up (usually)
-gas mileage fluctuates, but seems a bit lower than it should be

I know not all of those are relevant but figured i’d include it all for good measure. i know all the basics of what the engine code can mean, but maybe there’s someone out there with more knowledge that can help me discern the problem. or even if my engine is running rich or lean, i can’t tell, it seems like it has been both. any help i’d be grateful for!!!
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Welcome! I'd start by finding that vacuum leak; unfortunately there's a lot of places it can be coming from. Any other codes that would help focus your troubleshooting? Have you tried spraying starting fluid or using an unlit propane torch while the engine is running, to pinpoint the vacuum leak? You should also check for exhaust leaks, especially where the PO installed the replacement cat.
You might look in to checking out the O2 sensor on that side [bank 1]. It could be giving the ECM a false reading. sometimes they go bad, but not bad enough to get an O2 fault code. The usual cautions are valid, as with all these cars. If you decide to replace the O2 sensor, make sure you get the correct one, not just a generic O2 sensor. This may have contributed to the original problem. ...J.D.
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