I have recently purchased a crx with a b16a and a pr3 obd0 ecu. the car came with the knock sensor and secondary o2 sensor disconnected. i hooked up the knock sensor and that code went off, then i welded up the secondary o2 sensor and did the required wiring. i also welded up an additional bung to hook up my wide band to. i did an inital test with the secondary o2 sensor still disconnected and while the car was idiling the car was running 14.7 and more or less held stoich up untill the point of vtec ingagment, when vtec hit the fuel ratio droped way down to high tens low elevens. i figured hooking up the secondary o2 may help this problem so i did my next test with everything hooked up as honda would recommend, the airfuel ratio had a lot less spikes than previously, and still held stoich up untill vtec, once again vtec hit and the ratio plumeted back to low elevens. i do not believe that honda had this setup like this so what could be causing this? any help would be greatly apprectiated and i really would like to get this fixed because it cause a distinct doggy feeling in vtec, and i no that if the air fuel ratio was leaned out a little bit the car would pull so much better. thank you for the help i really apprectiate it.

 

The secondary O2 sensor doesn't help with air fuel ratio at all, it's simply there for emissions reasons to tell your ecu if the cat is working or not. With it disconnected or connected you should have the same a/f ratio. You will throw a code if it's not hooked up. Though I'm not sure what car the PR3 came out of. Is it 99-00 civic si?

My first guess would be your ecu isn't stock. An o2 sensor is just a fine tuning **** to the a/f ratio and won't cause it to change that dramatically. And you'd see a problem off vtec as well. So I'd rule out the o2. Maybe who ever had the car before you put a chip in the ecu or had it tuned. You are right that you should see around 12-12.5 a/f for the best perfromance and I'd think that's how Honda would tune it. So maybe just crack open the ecu and see if it's been chipped, if not maybe the ecu has gone bad. That seems a little strange to me, but you never know. Swap it with a buddy or something and see what you get.

 

dude. what the hell are you rambling about!
PR3 is a B16A OBD0 ecu. either out of a 2nd gen integra or 2nd gen crx

to op, YES the second o2 is needed. there was a confusion of which oxygen sensor belongs to which runners.

make sure you wired it correctly.

 

i have the o2 sensors hooked up in the right ecu ports, but i do not have the stock b16a exhaust manifold. i have the two oxygen sensors in the collector of what looks to be some b series obd1 exhaust manifold, i believe this may make a small difference but would it make that drastic of a difference that the o2 sensors are in the collector of all 4 pipes insteade of haveing one in each collector for the 2 cylinders? what else could be making the ecu run so rich?

 

has the ecu been chipped?

 

i do not believe the ecu is chipped, how would i know for certain?

 

open the ECU. and it might look something like this... never seen an obd o ecu b 4.
http://www.superhonda.com/tech/honda...installed1.jpg

 

what elso could possibly make the computer want to run the car so rich when vtec hits. I haven't taken the ecu apart and looked for a chip yet,but is there anything else that may do it?

 

the ecu is not chipped. my car also back fires rather heavily under deceleration. I also notice that when im cruzing at around 3000 rpm it has a slight misfire that occures every 10 or 20 seconds. could I have a bad map sensor or bad primary o2. the secondary o2 is brand new though. also when I wired up the secondary o2 sensor I also didn't pay much ateention to wire size, could that play a differnce. basically id like it if some one could possibly point me in the right direction on where I should look.