dtguitarist

Here it goes:

Car is 00 civic dx 103k
-Just replaced timing belt, and timing is confirmed correct
-Full tune up 3000 miles ago (spark plugs, wires, dist cap and rotor, fuel filter, oil x, trans oil change)
-Tanabe catback, dc headers, ex intake mani swap

Probs:

-p041 (only code) heater circuit malfunction

-bogging (hesitation) during acceleration from idle and sometimes during sudden braking

-burnt tailpipe

-poor gas mileage

-acceleration doesn't seem consistent...misfire?


Brief history-my car didn't have any problems until about 2 years ago, and had it for 7 years.

I didn't know anything about cars when I started having problems-which was low compression in 1 cylinder, and did a "wet test" and that didn't help-so not the piston rings I'm guessing. There was also no apparent vacuum leaks after using the smoke test. I did all this in my first auto class, and didn't know what the hell was going on, so I didn't do anything because the teacher said it wasn't a big deal if the check engine light wasn't on.

A year after that, my check engine light came on-turns out it was a cracked manifold. Instead of getting the oem cast iron crap I decided to switch to an ex exhaust setup (headers, cat, catback) after the p0420 code for the cracked manifold, and even switched the o2 sensors and had a full tune up.

P0420 gone, but suddenly a few months later the p0141 code came on. I switched the o2 sensors with ntk oem spec sensors (primary and secondary). Light went off for a few hundred miles and came back on, so I replaced the o2 sensors again with oem denso o2 sensors...a hundred miles later the light is on again.

I have researched this extensively, but usually there's compounded symptoms and codes, or usually it's obvious (wires rubbing, frayed wires, unplugged, etc.)...yet almost everyone says just to replace the sensor which didn't work for me.

Probable causes- Short circuit in the wiring (could it be in the main harness? how can I fix that?), bad egr (don't have the tools to test), fuses (checked-they're okay)...and other people said fuel filter, fuel pump, spark plug, wires, dist, injectors, pcm, ecm-but besides the last 2, the other causes seem p0420 related and could be the cause of misfires,but not with electrical-at least relating to the o2 sensor.

What can I do? If there wasn't such poor fuel economy and struggling, I could ignore this longer-but it only seems to be getting worse. I am getting desperate and absolutely frustrated and about to just sell my car...I'm stumped.

Is there any unique instances where an unlikely fix worked? I've tried taking it to several shops to be troubleshooted, but they say just to replace the o2 sensor. When I tell them I have, they all say just to replace the cat, which is unrelated to the p0141, and I say that-they also say the same thing: you can do whatever you want, or go somewhere else.

hyperblu

The rear o2 sensor only takes readings. A rear o2 malfunction will not affect driveability or fuel economy. Sounds to me like your cat is bad.

Texas4door

Yep, second O2 sensor is bad or the cat is bad.
Easy way to check the cat:
Tap on the side of it GENTLY with a rubber mallet
If it sounds like shattered glass or something rattling inside the cat, the media inside it is broken down and no good.

If not, then it's the O2 sensor

PS: don't worry about having to test the EGR system---unless you have an HX Civic, you don't have an EGR!
^^

Also...have you ever had the computer memory cleared with a code reader rather than just yanking the battery cable?
Sometimes it stores major codes like O2 sensor issues until you clear the computer manually
The battery cable trick DOES work most of the time, but the code reader method ALWAYS works 100% of the time.

Also when you had your tune up done..did you or whoever did the spark plugs gap them correctly?
That pre-gapped from the box claim is crap
Check them before installation cuz if they're off, that could well cause the misfire code.

Also check your timing-if it's off, you can run rich/lean, get bad mpg, toast your cat/O2 sensors, misfire, etc.

Good luck!

akacoke

since u a auto student just like me i assume u have access to scan tools , use a oscilloscope to check your TPS, what u mentioned is all related to a TPS. TPS is often overlooked when troubleshoting, its basically a poteniometer with a resistor and signal pickp arm, where the 1/3-1/4 throttle is used most of time that tps have wears around that area, so it would send all kinda wrong signal to ecu, so you driveability is like ****. your teacher should be able to quide your through, if you cant get a real scope, use a good graph meter like snap on vantage, the reason you want a good meter is you wanna catch the artifacts and spikes during the test. also check ECTs and MAP those are real important too. also, misfiring could be the ign. coil and module in the dizzzzy, i would check those parts with meter for res. try to figure out your A/F ratio too, so you will know how is the engine running.

also a compression test would be good to know how is your engine sealing oil, your problem would be a combination of few problems together, so just get your mind straight dont be depressed and all, this is the best time to learn.

good luck, let us know wassup.

akacoke

like others said, check ign timing, check vavle clearance , your burnt tail pipe usually mean youre burning oil or running rich. test or replace pcv valve. bogging when brake idle rough could be IACV. just begin with real simple stuffs. you cat is most likely gone. you can check it at any smog test station, you just drill a very small hole right before the cat you they can get the tester in there, and put another sniffer in the tailpipe. after just put a self tapping screw on the hole.

akacoke

double post

dtguitarist

Thanks for the reply! Yeah, I was told that. Wouldn't it set a p0420 code? it's still pretty new...I made sure the sensors are in the correct location as well

dtguitarist

I'll do all that this week. I had the codes cleared several time with the code reader and it always comes back on. I didn't gap the spark plugs, and I had the tune up done before by a shop and I guess they didn't know anything was wrong cuz they didn't notice anything weird...I had the timing belt done professionally about 8000 miles ago professionally (by Signal Auto) and I saw him check timing with the timing light...Actually that was when he noticed there was smoke but I didn't ask him to check that cuz I knew it was there from before..he said it could be head gasket, broken valve, piston rings, and a whole bunch of other things...And for the spark plugs, would that only cause a misfire or low compression in only 1 cylinder? One of my spark plugs looks kinda brown


Thanks for the help!

dtguitarist

Man, I wish I had access to all that stuff...reason why I wana rule things out is cuz I'm in debt and once I come up with money I wana try as much as possible to try the "right" methods. I don't have any reliable shops I know about, so idk...tps is a good idea tho-actually I used to work at a shop and a coworker said it could be that, but he was a joker, so I didn't take him seriously..but ya, no access to a shop anymore-ill let you know-thanks!

Also, is it worth it to get a code reader? would this help?

dtguitarist

Ya, I'm just gona clean out everything I can for the idle at least...for the o2 sensor i'm stuck cuz I keep replacing them and they just go bad...not a fuse, and I just need a multimeter to start testing if there's a short...just not good with electrical, but I'll go out and get a helms

motegicivic

Check the wiring to the O2 sensor as well, make sure it was not burnt by the manifold, gently cut the loom and trace it back.

A bad ground or wire for an O2 can make the car run like a bad o2 sensor itself.

you said ex mani swap, what year ex did you take it from?

akacoke

begin with the stuffs thats free or very lil money. code scanner is money down the drain IMO, there is a way you can pull out codes no scan tool required.

hyperblu

I have a code scanner, but I can afford to have it, lol. As far as the smoke, it's most likely a valve seal. However a compression test or leak down test would be the best way to identify where the oil is getting in the combustion chamber. A PCV valve should be replaced anyway and it's very cheap and worth the $5. Sometimes the rear o2 code is inevitable and requires modifying the bung to set the sensor farther back, so I wouldn't really add that code as a symptom until you check the easy things first.

Texas4door

LOL yeah, Autozone!
*shot*

J/K you can also jump the ECU test connectors and count the flashes...but that kinda sucks
XD;