I got a test pipe on a 00' si. I have heard you can make your own o2 sensor simulator with a 555 timer or something like that. Can anyone tell me the parts I need to buy and maybe a web site with some pics of it or explains this futher?

 

where did u get test pipe or did u make it any pics ?? thanks

 

Made it out of SS. Sorry no pics

 

wrap the 02 sensor in aluminum foil...it'll work I swear

 

I know but i want to make it with that 555 timer.....any one know how???

 

Being a EE, I'd like to know how this works. I can only assume that the 555 is in an astable mode of operation, which sorta simulates the Primary O2 (swinging back and forth). But the Secondary O2 does NOT swing in closed loop operation, it monitors the Catalytic Converters effiency. In theory, the Cat USES oxygen to do its job, thus the 2nd O2 is usually giving a reading of about .8v to indicate a rich condition (or rather, the absence of air, thus the Cat is doing its job nicely).

Is this simulator something for people who have Primary O2 problems because they have a header, thus locating the O2 to far away to get heated?

Whats the website addy, I'd like to take a look and critique?

 

ya, the 555 is configed as a VCO. A pot across vcc allows you to manually vary the control voltage, allowing you to vary the # of "cross points" that is the # of times the ocsillator swings past the magical 450mV value.

automotive O2 sensors are crude devices, only really capable of measuring full lean or full rich. when you are in around the stoich region, the sensor is 'lost' bouncing back and forth. the faster it swings, the closer you are to stoich. I think this 555 cct atttemps to recreate this 'hunting' The ECU input probably only really responds to an extreme lean or rich condition anyway.

 

or just buy one from zip

 

Yeah - Stock O2's are quite crude...they are more like a switch that turns on/off at stoich (but yet people will swear by them for tuning).

But in a closed-loop system, the ECU is always monitoring this input for trimming the fuel...so to say that the ECU ONLY responds to extremely rich/lean conditions, is a little mis-leading.

Now as far as this circuit recreating the 'hunting'...I can see that...but I thought this circuit was supposed to eliminate the 2nd O2 codes given by test pipes...and if this is the case, well, the 2nd doesn't hunt around, like I said before...its usually sitting at around .8v.

So I'm still wondering what exactly this thing is used for, unless it was specifically made for people who have headers that relocate the primary O2 so far away from the engine that it doesn't get hot enough to do its job....so this circuit takes its place.

 

Youre right about the secondary o2, I was thinking of the primary...
Maybe the 555 cct was being used for trying to fool the car into thinking it was lean in an effort to get more fuel in, for people running turbos and stuff.

As for the secondary, a simple voltage divider could feed the ECU. I don't know why people dont do this. People here have said they get away with just tying the secodary o2 to the frame rail. There are 2 problems with that - one, it doesnt get hot enough to work, 2 since the cat consumes 02 to work, the output (as you said) should remain higher than .5V, indicating a lack of oxygen. If it is left dangling, then there is lots of excess o2, and the reading should be low - but this is a moot point, as the sensor isnt hot enough to work anyway.

Here are my thoughts on why it works sometimes...
-The ECU is likely very 'lenient' with the output of the #2 o2. maybe on obd1 they even ignored it??
-if #2 sensor is close enough to the exhaust, maybe it is just warm enough to produce something to keep the ECU happy. This would depend on the sensor, the ecu setpoints and luck....

 

there is no O2 sensor after the cat on an OBD1 car