jj_diamond

ok everyone hope someone can shed some light on this. 2002 civic lx AT coupe. 100,000+ miles. a few weeks ago i started experiencing CEL with some rough idle and loss of power when accelerating. i changed my oil abd spark plugs. a few days later same deal. it first started one day that was really hot and i was in traffic. so a buddy told me change your O2 sensors. did that. same CEL. now if i'm driving highway with no traffic the car runs fine. it's if i'm doing city driving and there's some traffic it happens. i did a ECU diagnose with a code reading of P0420. emissions.

a few nights ago i was on the highway and ran into some traffic. when i pulled over to check the engine the manifold/converter was cherry red. i let it cool down for close to an hour, reset the ECU and it was fine until i got home. i was thinking maybe my converter is done or clogged. when i called the local muffler shop)very reputable). the old man told me he'd get back to me because his book was showing 2 different converters for my year vehicle. when i called him back he said it was in the $500 range for a new one replaced. then he asked me why i thought it was the converter. i told him what i just wrote. he said it sounds like a bad fuel sensor not the converter. i told him that i had done the diagnosis and he said sure youre gonna get an emissions code if you're dumping fuel into the engine. that didn't make sense to me. why would the converter get red with too much fuel. wouldn't the engine bog out if something's dumping fuel?

please help. thanks.

pheaton

iTrader: (6)

hrm. Is your temp gauge normal? How's your air filter?

Have you done a full tune up on it?

There isn't anything obstructing your intake or exhaust?

Did you gap the plugs and torque them to spec.?

jj_diamond

temp is normal even when it heats up. haven't checked the air filter. no full tune up just oil, plugs and O2's. no visible obstuctions in intake or exhaust. i assumed the plugs came gapped. they are torqued to specs. but the problem first happened before the plug change.

would a bad fuel sensor give me an emissions code and cause the engine to lose power and cause the manifold to turn cherry red hot?

speedfoos

iTrader: (17)

No, your mechanic is right. The mani will get ridiculously hot if the motor is dumping too much fuel. That's why seriously built motors run EGT (Exhaust Gas Temp) sensors, it's a quick indication that an engine is running too rich or too lean. Too rich can seriously bump up the temperature of the exhaust, by as much as 2-300 degrees. That's why your converter is glowing a nice cherry red.

Rough idle and crappy power are also two indications that you're dumping too much fuel. Sounds like your ECU has a fault and it's dorking up your LT fuel trim.

Our ECUs are a "learning" ECU. In otherwords we have two types of fuel adjustment curves, or "trims", long term and short term. After an ECU reset, you car uses a Short Term fuel correction (fuel trim) or adjustment to maintain the desired AFR, dependent upon engine load vs RPMs (MAP vs RPM), and other sensor variables that the ECU takes into consideration. The ECU then takes the ST Fuel Trim and uses the trends it sees there to write to the Long Term fuel trim.

It sounds like the ECU is dorking up the ST/LT fuel trim corrections and dumping way too much fuel. Unfortunately, this is going to be a dealer fix only, unless you swap the ECU and either get your key flashed for the new ECU, or swap the ECU, lock cylinder, and appropriate key. I'd take it to a dealer.

I initially thought it might be a stuck injector, but since you said it's fine right after you reset the ECU, and you replaced both O2 sensors, it's got to be something in the ECU.

jj_diamond

ouch.


it could also be a loose O2 sensor. since i have not been able to properly tighten the bottom one. i will be torquing them both tonight. if that doesn't work i was told by my g/f's dad who's a mechanic to check the fuel sensor and fuel pump.

hopefully it's not a dorky ECU. but i have considered that.

speedfoos

iTrader: (17)

What fuel sensor are we talking about? We don't really have a set "fuel sensor". The ECU controls the injectors by using a fuel map hard-coded into the ROM. Plus it's not going to be the pump. You're getting too much fuel, not too little. Unless the pump circuit is shorted somehow to throw like 24 volts at it (you would hear the pump constantly for a day and then it would die), it's not going to throw too much fuel.

Didn't know your O2 sensor was loose, that may be it, but I doubt it since you were having this problem beforehand. Do you have a decent OBD2 scanner? They're like $70 on Ebay and you can use them to read your LT/ST fuel correction and that will help you diagnose the problem better before taking it to the stealership. That might not be a bad investment before taking it in for diagnosis. That way if you do take it in, you save the dealer some time (and you labor charges) by having checked several things first.

jj_diamond

O2 sensor torqued. drove around for a bit. CEL came on. i'm gonna try and get to a buddy's garage this afternoon and have it diagnosed. this is very frustrating.

jj_diamond

OBD2 scanner reads 1 of 2 codes. 1 of 2 P0420, 2 of 2 P0420. catalyst system efficiency below threshold (bank 1)

speedfoos

iTrader: (17)

That may be the cat being clogged then. Pull it off and shake it. If it sounds like a maraca, then the element has busted loose and you need to either replace it, or convert to an EX exhaust set-up and run a spark non-fouler to trick the ECU into thinking a cat is there. That's if you don't have to worry about emissions.

jj_diamond

i think so too. the CEL comes on but there's no loss of performance or anything. i only drive the car to work and back, so if the CEL comes on i just reset it before i drive again. but like i said if it's really hot and i'm city driving for too long with the CEL on then the manifold gets really hot.

any other manufacturers other than this..

http://www.meganracing.com/products/...d=762&catid=67

can you recomend one i can use for the LX automatic coupe? no emissions tests here.

jaycee

ps...this is the post that sounded similar to my problem though my idle just drops. I don't know if it's "rough", just sounds like something is "stuck" and even with the pedal to the metal, it just stays at 20 mph. My Civic also runs fine in smooth moving traffic, but any creeping along or sitting at very long lights seems to provoke the problem.

Thanks again!

jj_diamond

update-

still no fix. it went into the rough idle and no power 'safe mode' today again on the way to work. seems that if it's really hot out like today and i have the a/c on it does this. i have the ODB2 with me so i plugged it in. besides the 2 po420 codes it also had a p0361 code if i remember. which is ignition malfunction/timing. which makes sense since in 'safe mode'.

i guess i'll stop trying to DIY since i can't find any info online and take it to a mechanic i know.

jj_diamond

changed the O2 sensors to OEM. CEL came on again. could it be the PCV valve or EGR valve? if not, the only two other fixes would be the cat is bad or the PCM is bad, correct?

jj_diamond

catalytic was bad. installed header with downpipe. modified primary O2 with spacers. CEL came on. haven't checked the code yet.

jj_diamond

secondary O2 sensor wiring was loose. made a better connection until i get time to solder it right. NO CEL.

ugabuga

hi
I think i've been having a similar problem. When I start the car cold and sometimes warm but always soon after starting, and I take off all of a sudden the car would loose all power.

If I put it in neutral idle is around 400-500 rpm and sounds bumpy. If I floor the gas pedal at this moment nothing happens. This goes on for 2-3 seconds then I get the response back and car runs fine. A few feet further I get the same thing ... and so on until it more or less warms up completely.

I dont get a CEL but I used to a few months ago, and I think it was the same 2 codes.

So you fixed it by making a better connection? Where was it loose? I checked mine when I replaced the cat shields and it seemed fine ....

jj_diamond

yes. the wiring on the secondary O2(before cat) was loose. i had to make the wiring longer because of the placement for it on the new header.

if you need to make your O2 sensor wiring longer you can also grab one of these, which i just found. hate when that happends.

http://passwordjdm.com/PasswordJDM-O...P1767C364.aspx

ugabuga

Thanks. I will ccheck it out. I just started getting this problem every day (had gone away for a few months).

ugabuga

update: I replaced both sensors with new Denso ones ($65 for both from rockauto), and this morning I didnt experience the annoying problem. I hope that cured it.

oh and when I checked the codes I had a primary and secondary sensor error and cat efficiency below threshold. Dont remember the exact codes though. P0420 and some other ones

jj_diamond

just a FYI on this... since changing the OEM manifold/cat to header, the annoying rumble sound i was experiencing in heavy rain went away too.

jj_diamond

DAMN!!!

CEL came back this morning with the same "safe mode" puttering. WTF?

it was working fine since i changed the manifold/cat.

jj_diamond

happened again. only during the day with the a/c running or after the a/c has been running for a bit.

rahenry00

iTrader: (4)

Those O2 spacers go on the secondary O2 sensor...not the primary. If you had a cat the secondary sensor sees less oxugen b/c of the cat....so those spacers simulate that by putting the sensor further away from the air flow. Move you spacers to the secondary o2 sensor and reset your ecu. Also you might want to consider replacing your secoindary o2 sensor if the wiring is not 100% intact. My care did the same thing a few months ago, the sputtering and what not.

jj_diamond

the spacers are on the bottom O2 sensor. the top O2 sensor has an extension added. wires are intact. there's no space on the top O2 sensor to add spacers since the alternator bracket is right there. i get confused as to which is primary and secondary. on the stock O2's, one has a light blue wire shield oand the other a black wire shield with clips.

rahenry00

iTrader: (4)

I an earlier post you said you had to solder your secondary sensor wire...that could easily affect your sensor's operational ability. The secondary sensor is the one furthest away.

jj_diamond

which one is the primary and which one is the secondary?
like i said it confuses me. i tried to splice the top sensor, the stock one with the blue wire shield. but that kept giving me CEL. so i bought an extension. there are no spliced wires on either O2 sensor now.

how EXTREMELY frustrating.

rahenry00

iTrader: (4)

The secondary sensor is the one that would normally be AFTER the catalytic converter. That's the one the spacers should be on. Did you get your CEL code read? Your problem sounds very similar to mines a few months ago so I will do my best to help you.

jj_diamond

well then the spacers are on the secondary sensor. haven't had the code read yet. and none of the wires are spliced.

it was fine for a week and now i get the CEL again and as soon as it comes on the car goes into that awful "protect mode" or shuts off.

rahenry00

iTrader: (4)

My car did the same thing...it would sputter then take off full speed and you could smell all the unburnt fuel.

jj_diamond

mine doesn't take off. it sputters and boggs. no power when i accelerate.