Lanos w/ P0301 & P0420; Short version

[2woo4you0]

I haven't really gotten any help yet so I'm making a shorter and better organized post to make it easy for you guys to help me out. My two codes stand for; P0301=Cylinder 1 Misfire detected and P0420=Catalyst System Efficiency Below Threshold (Bank 1). I had a CEL that said my upstream O2 sensor was bad but that hasn't been seen since I replaced that o2 sensor.

2002 Daewoo Lanos. Several mods but all of them were done long after the problem started. The car runs great, nothing notably wrong with the ONLY exception that rarely it wants to stall at idle but if I tap the gas it'll be okay until it does it after another 10mins of idling. I always get 29-30mpg with a bit more city than highway driving and sometimes up to 35mpg with more freeway or careful driving. The PO420 has ONLY come on with the other code and not every time, not even that often. The P0301 has ONLY come on between 70-83mph almost always at about 3330rpm/75mph or exactly 3352rpm/77mph.

I have a decent code reader so if you want me to post live data let me know. When I check the code after less than a minute of it coming on I usually have these blinking at the top of the code reader "HTR", "EGR", "o2", "CAT", and "EVA" but I don't always have all of them. Also after switch around injectors, EGR, and coil-pack the CEL came on the sec I hit 75mph but no code was there. I deleted it and next time it came on the code was there. CEL seems to come on less since switch those things around and the CEL definitely comes on on average 4mph less than before. Which is strange considering it was very predictable in what speeds it would come on at.

A few months ago, several months after the CEL started I noticed the head gasket was bad and the spark plug holes were FILLED with oil. I replaced the head gasket, and everything the oil messed up (see list below). There is no rotten egg smell from exhaust nor does it feel clogged so I think the CAT is okay only based on that.

Things I've done/replaced:
-Checked for vacuum leaks.
-Checked for TB or intake manifold gasket leaks.
-Replaced head gasket (Three months ago, no oil since)
-Replaced & gapped spark plugs (two months ago)
-Replaced Spark wires (two months ago)
-Replaced upstream 02 sensor (two months ago)
-Switched around injectors (early this month)
-Switched EGR with a used one (early this month)
-Switched coil-pack with a used one (early this month)
-Checked & replaced oil (Last night)

Things I'm going to try:
-Triple check with other methods other than just inspecting for vacuum, TB gasket, intake gasket, ect leaks.
-Check spark plugs for any signs of anything as well as double checking the gap
-Switch around spark wires


Things I think could be my problem but need confirmed/info:
-Camshaft position sensor?
-Evaporative something (not even familiar w/ that system so need info on what&where I'd be looking)?
-Switch ECU? (which one do I need to switch? I see a couple computers in the car and don't know which is which)
-Fuel pump? (Don't think so since it's not a random cylinder misfire but a specific cylinder)
-Fuel filter? (Same as above, and not sure if Lanos has intake filter, inline, or both)
-Downstream o2 sensor?


Advice/help is greatly appreciated.

[benzino]

have you done a compression test?
when you did the head gasket, did you get the head machined and did you use new head bolts torqued to the factory specs?

[Daniel]

This problem at a specific engine speed makes me think at a mechanical resonance phenomenon: springs, valves, ...

[2woo4you0]

have you done a compression test?
when you did the head gasket, did you get the head machined and did you use new head bolts torqued to the factory specs?

Sorry I've been gone for awhile.

No I didn't, am I supposed to? My service manual says nothing about that and neither did my Renos service manual when I replaced it's gasket. I did torque to factory specs though of course.

This problem at a specific engine speed makes me think at a mechanical resonance phenomenon: springs, valves, ...

But with absolutely no other symptoms or issues othr than the CELs?e

I'm going to replace my other o2 sensor for the hell of it as and if that doesn't do anything I'm going to try an o2 sensor extension as I found my spare one. I'll be trying these within two weeks, gotta replace the alternator in one car, and oil change as well as brakes in two of my cars this coming week.


Any other ideas please guys, keep any ideas you got coming. I've had a header back exhaust waiting to go on for many months as well as I've been planning since I lost my Reno like a year ago to put it's old 2.0/D20 in my Lanos this Febuary. I don't want to do any of this with a CEL though.

[Rust Never Sleeps]

I had both the 301 code come up and the 420. The 420 was an easy fix. Just replaced the O2 sensor and that went away. The 301 would come and go and was almost impossible to trace so I just put up with it. Sometimes it would stay off for couple hundred miles and then re-set. Good news/bad news here. The 301 code went away completely after my recent timing belt and head replacement so I am guessing I had some bad valves that weren't seating or sealing setting the 301 code. I mean...with 16 vales and a 100,000 mile motor and head its a pretty good guess.

[2woo4you0]

I had both the 301 code come up and the 420. The 420 was an easy fix. Just replaced the O2 sensor and that went away. The 301 would come and go and was almost impossible to trace so I just put up with it. Sometimes it would stay off for couple hundred miles and then re-set. Good news/bad news here. The 301 code went away completely after my recent timing belt and head replacement so I am guessing I had some bad valves that weren't seating or sealing setting the 301 code. I mean...with 16 vales and a 100,000 mile motor and head its a pretty good guess.

As I said in my original post I had an additional front o2 sensor code and replaced it. That code went away but still had the other two. I was going to try to replace the rear o2 as well.... but now I'm wondering if I should bother since I want to do a 2.0 swap soon. Plus my rear shoes need replaced so I'd rather spend my money on disk swap and hold off for coil-overs as I almost have enough rather then dumping money into fixing a CEL on an engine I'm replacing soon.

Still though if anyone has any ideas let me know...esp if it's something that won't be resolved when swapping to a 2.0

Thanks Rust.