Si_chRis

Car is a 2000 Honda Civic SI with the original B16A2.

So I just changed the cat converter along with a new secondary o2 sensor since I had a code for a bad cat converter (P0420) since my car is burning oil. I used a spark plug defouler for the secondary sensor to space it out of the exhaust gas this time around to make sure the code stays off since I don't want to see the code again. Also considering that cat converters and o2 sensors are expensive and I don't want to waste more money on new ones after this, I figure this could work for the P0420 code and would be ok to do since the secondary o2 sensor doesn't affect the air fuel ratio and there are countless threads on other forums on using the spark plug defoulers to solve the P0420 code problem.

Well, the P0420 code did not come up again but after going through some drive cycles, usually 2 cycles putting 40-50 miles, I get a P0172 and P0170 which are system too rich and fuel trim malfunction.

I just put in new spark plugs about two weeks ago and I pulled them recently to look at em. They are normal and no fouling.

The car has a stock fuel pressure regulator, OBD 2 JDM ITR fuel injectors with 20K miles on them (one of my old fuel injectors were damaged so I replaced them all) and a AEM fuel rail.

I've never gotten these codes before until I put in my new cat converter and o2 sensor about 2 days ago (they have like 150 miles on them).

Other codes prior to the new cat converter were always the P0420 for a bad cat and no other codes.

Car idles fine, drives fine with no hesitation at all. MPG is normal and no serious bogging at all.

Could it be bad gas? I only use Shell 93 octane V power though.

Bad primary o2 sensor? Fuel pressure regulator?

Where should I look first to diagnose? Cause I don't want to start replacing parts and waste money on them if they are not going to solve the problem.

I also checked for vacuum leaks...didn't find any. I also checked all connections on the TPS, IAT, fuel injectors and MAP sensor...all are secure. Checked the fuel lines for any bends...none at all. No fuel leaks around the injector o rings and checked each injector for pulsating...they're fine.

Former User

Have you checked for exhaust leaks following installation of the new cat?

Si_chRis

I did jack up the car and re-tighten the bolts associated with the cat converter. But I did see some exhaust residue coming out where the donut gasket is...where the header meets the cat converter. No exhaust smells or noise though while the engine is idling, running from underneath the car.

I don't think it would cause the CEL cause it's after the first o2 sensor. Or could it?

gearhead16

make sure u didnt damage the o2 wires

i have one question,

Y DID U PUT A CAT BACK ON IT

ive got a test pipe and no check engine light and i just passed emissions with a test pipe lol

trick is to not put the second o2 in the exhaust system or get the extender.

gearhead16

i would clear the codes and see if they come back

Si_chRis

Well, I did extend the after cat secondary o2 using the spark plug defouler trick. And it works cause I am no longer getting the P0420 code for a bad cat. I also made sure the wires/sensor were not hitting the chassis or rubbing against anything.

Reason I put the cat on there is because my state does a visual inspection along with the OBD2 code scan. So I have no choice.

I also cleared the codes twice and the CEL comes back on after about 40-50 miles with 2 drive cycles. I get the same codes for system too rich and fuel trim malfunction.

gearhead16

ah that sucks

CrackThatTec45

po420 is a bad cat code.....po170 & 171 are O2 sensor related codes. Dont think you have yourself a bad cat on your hands as you might have some bad O2s. If not the O2s then you may wanna double check your "defouler" mod for that might be botched up........thats really the only thing it could be honestly

CrackThatTec45

also notice the gas mileage.....should be getting real shitty gas mileage

Ran4it2

HELLL ****ING NO
i just did my smog
and the ****-er checked my cat with a mirror
but i have a test pipe
so it didnt pass plus numerous other things

Si_chRis

Well if you read my original post, I no longer have a "bad cat" code but now the P0170 and P0172. And the cat on the car now is a brand new Magnaflow OEM replacement direct fit bolt on. The secondary o2 sensor is a brand new NGK/NTK sensor. The secondary sensor has nothing to do with the air fuel ratio but only sole purpose is monitor for a properly functioning cat. Only the primary o2 monitors the air fuel ratio.

My MPG is normal as of now. I recently filled up with 93 octance and have gotten 45 miles and the needle barely moved.

Si_chRis

Only things I think might be causing the system too rich and fuel trim malfunction is possibly a bad primary o2 sensor or an exhaust leak.

But the funny thing is I never got these two codes prior to installing my new cat converter 3 days ago. I don't think my primary o2 went bad all of a sudden and I have no visible exhaust leaks that I know of.

Former User

The two CEL codes actually signify that the engine is running both too rich and too lean.

Si_chRis

I only have the P0172 for system too rich. I never got the lean code. Out of all the possible things on that list, which one do you think is the most probable cause?

Former User

Oh, in your first post, I mistakenly thought I read P0171 and P0172. Based on discussion in your thread, I'd start by checking the primary O2 sensor and its wiring.

Si_chRis

I'll check it out once the weather clears up (no garage). I'm just going to let the car sit till then and drive my other car.

The primary o2 wires did seem fine last time I looked at them, they were zip tied away from the down pipe or any other moving part.

I guess I'm also going to change out the donut gasket where the header meets the cat also since it won't cost much and see if it helps.

Any other ideas, feel free to post.

Thanks.

Si_chRis

Just cleaned my air filter and letting it dry since it was VERY dirty. Hoping it could help.

I also just bought an OBD2 scanner. I cleared the code and drove around for 10-20 miles. Scanner shows no stored codes or any codes for the matter right now and is "ready" for an emissions test according to 7 monitors that are good to go.

Hope the codes doesn't come back.

Khoald

did you put in an aftermarket O2 sensor? i have had issues not using OE sensors

Si_chRis

Well I used an NTK/NGK sensor. It's an OEM replacement with an identical plug.

Khoald

interesting sounds like if any A/M part would work it would be one that makes parts for the Car Manufacturer

Si_chRis

So after playing around with my OBD scanner and going through some drive cycles, my primary and secondary o2 sensors seems to be working fine since they are "ready" for emissions.

But there is always one engine monitor that is incomplete which is Evap after going through some drive cycles. There is a pending code that I get which is the P0170 for "fuel trim malfunction" which does not set the CEL off. If I go through some more drive cycles, the P0172 for "system too rich" sets the CEL on and those are the only two codes I get.

All other monitors check out fine which include Catalyst, O2 Heater Sensor, O2 Sensor, Comprehensive Components, Misfire and Fuel System.

So I am guessing that the CEL is something to do with the Evap system?...I checked all connections on the charcoal canister...everything is connected.

Former User

Good job.

As indicated in the diagram, check for a leaking EVAP purge control solenoid valve.

Si_chRis

Alright, I'll check that out asap.

Thanks

gsrhatch2356

the purge is really easy to check, just unplug the canister side and check for vacuum coming from the valve and if there is then check to make sure that there isnt a short to ground causing the valve to be active and replace if neccesarry. the other thing is with trying to diagnois a lean or rich code, it is always good to have a actuall scan tool that shows fuel trim so that you can better see what the car is doing. if you notice that you have like +20 fuel trim and it goes down with throttle then you know that it is fuel related since you are getting the air coming in closer to the 14.7\1 ratio so it dosent require as much fuel trim but if it just stays the same then you need to look at map sensor output and make sure that key on engine off that it is somewhat close to 29" if at sea level. then also alot people dont know that there is a baro sensor on the ecu and it also should read that same reading if at sea level. you should try to make or create a lean condition like a vacuum leak to see if the 02 sensor (primary) is capable of getting down to a .1v or lean condition cause of the sensor can not read or mimic a lean condintion than that is your problem.

MugenHonda

u got the wrong o2
cali and fed emission double check