Help Meeeee!!!!!

[fastwhipyo]

Ok, this post has nothing to do with the celica but Ive been a member here and recently built a 91 crx hf w/ B16a swap. I am posting this on this forum because you guys seem to know alot more about cars in general than most of the honda guys on my other club. So here goes, My engine is a JDM B16a and it came with 2 02 sensors installed but I got a DC sports 4-1 header and was forced to drive it 40 miles to the exhaust shop to get an exhaust put on it. I spliced the wires so that the ECU reads both 02 sensors as only one which is mounted about 2 inches from the end of the header. My question is, would running open header with the 02 sensor soooooo close to outside air (about 2 inches) could that cause the engine to read some of the 02 that was outside of the exhaust that might creep in while at low RPMs and make the engine run really rich?????? I wasnt throwing any engine codes but under 3k RPMS if I didnt floor it or give it alot of gas it would sputter a little like it was running super rich. right when I gave it alot of gas it would lean right out and drive fine. If I kept the RPM's above 3k then it seemed to do fine no matter what I did with the throttle. what do you guys think??? and tech I guess I will find out for sure when the exhaust is finally fitted, but I dont wanna be driving it around if Im hurting it all.

[Griffin]

Well I don't know the ins and outs of Hondas ECM logic but I'm going to assume its pretty similar to Toyotas when i answer this.

The Dowstream O2 sensor (after Cat) reads Catalyst efficiency. Untill recently I thought all it could do is set a CEL and a code to let you know your cat wasn't working, but it turns out that Toyota at least is using it to adjust fuel trim if it senses catalyst readings far out of the norm. Hondas probably is the same. The Primary or Front O2 sensor is what the ECM uses to make corrections to the base fuel trim map the eCM is running, it is what allows it to maintain stochiometry. How this relates is that you are indeed forrect that 4" from the end of the pipe at low RPM there will probably be times when he negative pressure pulses allow air to enter and come back towards the O2 sensor. Add to that teh fact that its probably trying like crazy to add some more fuel because of all the oxygen it thinks it sees coming out the back of the cat. So yeah, I imagine this current setup has the potential to make you run both extremely rich and extremely lean.

My prediction is that you will wind up with a CEL, some misc codes, including possibly Catalyst efficiecy codes, Rich/Lean Codes, and maybe even misfire. Will any of this hurt your engine? Outside of fouling your spark plug probably not, but you will get lousy gas mileage. However running open headers does pose some other dangers in the way of exposing the car to flame from the exhaust and whatnot. I would very much suggest putting a temporary downpipe on or not driving your car like that as there is a potential danger to you and your car.

[fastwhipyo]

aight sweet, thanks alot man, thats exactly what I was looking for. All the people on the honda forum werelike "02 sensors....ya I think I have one of those" but just to let you know, the japanese dual 02 sensor set up is just two 02 sensors side by side, each one reads 2 cyl. thats all, there isnt one after the cat. its an odb0 engine so its not really focused as much on emissions....not to mention its JDM. But thanks alot for the help, im pretty sure when I get the exhaust put on it will fix everything, well see I guess

Thank you
Jason

[Lord Banshee]

i wish i had the money yo have project cars lol, its hard enough paying for my celica. oh well maybe in 5 years when i am out of college and being a computer programmer i will make LOTS OF MULA! and i can go buy an integ and put a b18c1 or a ls vtec. or maybe find my self a 240sx qand get a sr20det ohhh!!!

[Griffin]

Originally posted by fastwhipyo
aight sweet, thanks alot man, thats exactly what I was looking for. All the people on the honda forum werelike "02 sensors....ya I think I have one of those" but just to let you know, the japanese dual 02 sensor set up is just two 02 sensors side by side, each one reads 2 cyl. thats all, there isnt one after the cat. its an odb0 engine so its not really focused as much on emissions....not to mention its JDM. But thanks alot for the help, im pretty sure when I get the exhaust put on it will fix everything, well see I guess

Thank you
Jason

Ahhh I got ya - we use a very similar setup on the straight 6 and V style engines as well as the 1AZ 4Cyl. Engines with Toyota. Its cool because it lets us fine tune the control down to just 2 cylinders as a single bank on the 1AZ. What you are doing is probably okay, the only possible issue I see with it is that the O2 generates a very weak voltage signal and I'm not sure if making it drive a parallel circuit will invalidate the feedback its giving the ECM. If you have access to an oscilliscope, check and see what the waveform looks like for the current setup, and then unsplice it and check it. If teh voltage range increases significantly with the splice removed you may have to get a second port tapped into your exhaust manifold.

[fastwhipyo]

ya, good call griffin, Ill check into that, I dont have an ocillsicope but I can probably borrow one from school, I can always use a voltmeter though and just check it out like that at first to see what kind of difference were looking at right?

[Griffin]

I've never found DVOMs to be adequate for O2 sensor diagnosis becaus ethey give an "average" voltage. Maybe an ultra-low impedence analog, or a digital with a fast reading bar graph like a fluke 87, otherwise I prefer Osciliscopes.

[fastwhipyo]

hey griffin, I got my car back from the exhaust place yesterday and although its too loud, it runs great now, it must have been that whole open header deal. My only problem now is that Im all bitter because i dinged up my brand new 4-1 header pulling into my driveway and broke my short shifter in half (yup all 6'3" of pure 155lb muscle snaped that sucker right off.....cheap ass 30 dollar shifter)