I keep getting an occasional code 43 when on the highway and driving near WOT, but NO performance loss is noticed. About the only difference besides the CEL is that when I come off throttle to idle, it idles between 1200 and 1250 RPM's, normally ~750 RPM's any other time. I've searched and half the people say to replace the O2 sensor if you get the code and don't see any drop in performance and half say that they did that with no luck. I also followed the Helms troubleshooting flowchart and came up with a conclusion of "intermittent failure, system is OK. check for poor connections at right shock tower, O2 sensor, and ECU". I have not had a chance to check my plugs to read them yet. Current plan is to rewire my O2 sensor and possibly move it.

Exactly where should I put my O2 sensor?
In the #4 runner, at the bottom of the header downpipe (might require some modification because it is right in line with my rear crossmember), or in the test pipe?
Does it matter where I put it, and why?

.:car, engine, and engine management:.
1990 Honda Civic SI
D16Z6 with intake, header, test pipe, exhaust and JG head w/ JG cam
newer (less than 1000 miles) universal 4-wire O2 sensor wired into Rywire OBD0-OBD1 conversion harness with crimp connectors and in-line plug
stock (unmodified except for auto-manual conversion) P28 ECU

.:things recently changed before code started showing up:.
replaced OBD0 injectors with freshly cleaned and balanced (by KGParts) OBD1 injectors, also rewired injector harness at left shock tower to remove resistor box
moved O2 sensor from test pipe location to bung on #4 runner of the header because my plugs looked like i was running a little rich and i wanted to put it above a small header leak that i have between the 2 parts (4-2-1 eBay special 2-piece header)
replaced stock FPR with another stock FPR
changed fuel filter
changed fuel pump

Now, the O2 sensor was the same one that I used for my car when it was boosted for a very brief time (about 150 miles), but it was just running on a street tune (assuming pretty rich).

Any ideas, tips, or solutions are appreciated. Please don't just say "replace the O2 sensor" without anything to back it up.


Modified by DelSolDon at 12:32 PM 6/22/2007

 

fix the header leak, that will cause the car to run even richer. and may cause this problem.

the best O2 location for OBD1 ECUs is a few inches from the final merge in the header. locating it in the #4 cylinder will result in spikes in the readings that the ECU is not expecting and may cause this CEL.
locate the O2 in the correct location and go from there. If the CEL still shows up... yes I'm going to say it... replace the O2. Go with a OEM replacement NGK for the best result.

 

yeah, i have plans to pull the header off and just weld the 2 parts together. right now, i just have a bunch of hi-temp gasket maker qunked up around the leak... it seems to help a little.

also, while it is off, i think i'll have to weld on another bung for at the end of the downpipe (right before flange for cat. converter) since the one that is there right now is so close to my rear crossmember and sway bar i don't think it would fit and would always be concerned with it breaking off due to engine movement.

do you think that the O2 could have gone bad that quickly? what causes an O2 sensor to fail? it is a Denso (not bosch) universal O2 sensor if that matters.


Modified by DelSolDon at 12:35 PM 6/22/2007

 

usually O2s don't go bad that quickly, more than likely there is something else wrong.
Unless you have a wiring issue...

 

i'm leaning toward a wiring issue, because wouldn't i also be getting a code 1 if the O2 was bad? or no?

 

i've seen that code show up from a slightly bent valve as well...it was on a 94 gsr in a del sol...kept getting code 43 and idle was a little shitty, but it ripped up top...I checked everything, fuel pump, injectors, dizzy, compression test (good results)...finally got sick of it, and yanked the head...one very sightly bent valve...not saying that is your problem, but if you check everything else...then it might be

 

thanks for the idea, but the head was freshened up before i put it on (about 900 miles ago). valve seals were replaced, valve seats were ground, and valves were checked for straightness.

 

i had cel 43 once, and changed fuel filter, o2 sensor, etc. the code came back. it ended up being my ground on the thermostat housing was loose. might wanna check that.

good luck.

 

yeah, forgot to add that i changed the fuel filter also.

i'll check that thermostat ground also, thanks.

 

ok, took a closer look at where the O2 bung is in the header downpipe and when an O2 sensor is put in there, the top of the sensor hits my axle boot.

how much of a difference would it make if i just put it back in the test pipe (about 12" downstream)?

 

OK, i finally got a chance to pull my plugs and they looked great, so I chose to leave the O2 sensor in the same spot, but replace it with an OEM O2 sensor and I resoldered and rechecked all of my connections.

driving home from the garage, it seemed OK **crosses fingers** now lets see if the code stays away.