Hows it going guys,
I have 98 civic ex with an y7 bottom end/ y8 head.
after doing the swap i put an entire headerback off ebay to get it running, no cat.
afterwards i threw both po135 and 141. i replaced both o2s to make sure they werent bad, one is off amazon and the other is denso from auto zone. after putting new ones in, i still threw both codes. also, my engine harness was a mess, and the ecu plugs. so i replaced the entire wiring harness, and still im still throwing both codes, even with a defouler on the secondary oxygen sensor.
Need advice on this,badly. anyone else ever experience this?
thinking either putting cat back on, defoulers on both o2s, or putting oem o2's in since ive heard aftermarket dont always work.

Thanks guys.

update:
put a y7 cat and it took away the p0141, but the p0135 persistst

 

bump

 

Ya. Its telling you you have no CAT. You gotta tell the ECU to stop trowing the codes, or put the cat back in. Defoulers=bandaid, and can make the car run strange as the O2 isn't reading correct information.

 

P0135 and P0141 are heater circuit codes. They result from an electrical problem. The first thing to check is if the yellow-black wires to each sensor have power with the key on. This power comes from fuse 15 under the dash. It is very common for the harness to get frayed and short out where it goes across the intake manifold bracket on the back of the engine. This will blow fuse 15 and cause several codes including 135 and 141.

Once the sensors are working, it will throw P0420 after a period of driving because there is no cat. An anti-fouler on the second sensor might prevent the P0420. Really though you should have a cat. Do not put an anti-fouler on the first sensor that will only mess up the performance.

 

thank you for the reply, as for what i said about replacing the wiring harness. ive done all of the following you have said before getting a new one. and still have not thrown p0420

 

but wouldnt it throw the cat code and not heater circuit for the o2s.

 

With a P0135 it doesn't even consider the sensors reliable to check for a P0420. You have to fix the heater problem first. Yes you replaced the harness but you still need to make sure the fuse is not blown and check with a meter for power actually reaching the sensors.

 

the fuse was checked, never blew, and all of the heater elements have voltage going to them. that is why i am so confused here because i have checked every possible aspect for the electrical issues.

 

update,
threw a left over d16y7 header on and connected it to the test pipe. got the the p0141 to go off but the primary code p0135 is still showing. what could be the issue? test all o2s and theyre fine

 

wiring issue

 

all the wires are fine. brand new harness. the junction plugs under the intake are good. the o2 sensor heater element itself is putting out resistance as it should, and the harness side o2 plug is getting voltage. the #15 fuse is good, and the ELD is fine and not throwing codes. im ******* tearing my hair out over this i feel like im overlooking something so simple

 

bump please someone must have some insight. im currently only throwing p0135, am i running too rich possibly. the car really hasnt moved should i go through a drive cycle and let the computer lean it out? need to get this car inspected. would there be any reason a y7 bottom end could cause a/f ratio problems. the car runs fine, vtec everything else besides block. any advice

 

bump

 

new harness? as in new from honda or new from salvage yard?

 

brand new, off ebay though. i matched it up to the old and its the correct one, and all the looms are in great condition.

 

bump
just going to get a magna flow cat, see if it helps.
if it doesnt, probably going to trade it off for a obd1 civic. anyone in ny interested. lmk