daeron Posted April 28, 2007 Author Share Posted April 28, 2007 the instance i had with my maf the ecu did not throw a code, but changing the maf did improve. check all the grounds on the engine harness and at the intake bolts Grounds are checked and re-enforced, MAF has been swapped with another to no effect. Sorry I forgot to mention those two points in the original "update" Quote Link to comment Share on other sites More sharing options...
Cougar Posted April 28, 2007 Share Posted April 28, 2007 One thing you can do to see if the O2 sensor changes is disconnect one of the plug wires. The rich unburned fuel mixture should make the sensor show a rich condition, a voltage greater than .5 volts. If the sensor voltage doesn't change then, I would say there is either a ECU problem or the sensor may be bad. I would suspect the sensor first as the trouble. Quote Link to comment Share on other sites More sharing options...
daeron Posted April 28, 2007 Author Share Posted April 28, 2007 One thing you can do to see if the O2 sensor changes is disconnect one of the plug wires. The rich unburned fuel mixture should make the sensor show a rich condition, a voltage greater than .5 volts. If the sensor voltage doesn't change then, I would say there is either a ECU problem or the sensor may be bad. I would suspect the sensor first as the trouble. BADA BING, another smack on the forehead for not thinking of the obvious. thanks again cougar, going out for the warmup right now. pray that i dont get zapped in pulling the plugwire. Quote Link to comment Share on other sites More sharing options...
daeron Posted April 28, 2007 Author Share Posted April 28, 2007 ahh hey.. I *should* be striving to maintain the connection between the sensor and the wire while testing, correct? I am NOT supposed to be unplugging the O2 sensor, and putting my positive lead into the wire coming from the sensor, correct? all voltage readings thus far have been with the sensor plugged in... Just now with the engine at temp, but without driving it at all, i tried unplugging the sensor and testing voltage JUST between it and ground, and got zero.. Engine is up to temp now, about to go for a warm up drive to make sure the O2 sensor is adequately heated.. EDIT Okay, just drove around the block a bit, got her good and heated.. and the O2 sensor was showing a voltage of .28-.35, with or without the spark plug wire pulled... SO I am guessing I need to get a NEW NEW O2 sensor and not some junk out of the garage.... now, about that magic wand.... If only there was some way to TEST a junkyard O2 sensor... Well, off to the telephone to find the cheapest one I can get, and then call the parents to bum the cash... THATS always fun.... Quote Link to comment Share on other sites More sharing options...
Cougar Posted April 28, 2007 Share Posted April 28, 2007 After thinking about this I seem to recall another incident like this with a O2 sensor. The problem turned out to be with the ECU if I remember correctly. Since you can get a spare one for $25 dollars it is cheaper than a new sensor. You may be able to check the sensor using your ohmmeter across the sensor and heating the sensor with a torch. Quote Link to comment Share on other sites More sharing options...
Gloyale Posted April 28, 2007 Share Posted April 28, 2007 After thinking about this I seem to recall another incident like this with a O2 sensor. The problem turned out to be with the ECU if I remember correctly. Since you can get a spare one for $25 dollars it is cheaper than a new sensor. You may be able to check the sensor using your ohmmeter across the sensor and heating the sensor with a torch. The single wire O2 sensors in EA82s are dirt cheap. Like 20 bucks. Some are listed higher but they are all basically the same generic single wire sensor. Quote Link to comment Share on other sites More sharing options...
daeron Posted April 29, 2007 Author Share Posted April 29, 2007 so.... Does ANYBODY think that I likely have an issue that is NOT either the O2 sensor, or the ECU??? When I was "testing" the sensor yesterday, I tried unplugging it from the wire and checking voltage between the sensor and ground, independent of the ECU and got zero. I dont know if thats normal or not... *I* was under the impression that the catalytic action of the sensor generated voltage in and of itself, and by THAT knowledge this sensor isnt doing SQUAT. I am kind of agonizing through the decision here because I have nothing to spend on either, so I am going to HAVE to borrow money from someone (all my friends and family are almost as broke as me) to buy either an O2 sensor or that ECU... Thus far I see a couple options: One is to borrow $30, go to the junkyard, POCKET the O2 sensor out of the subaru thats there, come home and try it, and if THAT doesnt change anything, go back and buy the ECU. Another option would be to just try the ECU first, and risk the chance that the "new" ECU will not make a difference and I am just buying a "spare..." NOT a scenario I feel like finding myself in... Third would be to try buying a new O2 sensor, and be willing to take it back if it doesnt change anything (AND *if* I can pull THAT off) In any case, ~$30 is something I should be able to bum off of SOMEONE easily enough.. ~$60 (for new O2 AND ECU) would be MUCH more difficult. I hate to have to think of pocketing the O2 in the boneyard, but I really think that course might be my best bet.... Plus, I hate the idea of trying a junkyard O2 sensor in the car. That what I have in there already; replacing the fuel filter, or the FPR with junkyard parts is no big deal, but the O2 sensor is more like using a junkyard spark plug, or fuel filter.... So, does anyone think that my problem is likely to be anything OTHER than either the O2 or the ECU? AND, if everyone agrees that I am on the right track, what would be your next move given my options? Quote Link to comment Share on other sites More sharing options...
Gloyale Posted April 29, 2007 Share Posted April 29, 2007 Disconect the o2 sensor. With key on /eng. off mesure the connector for voltage. Greater than 0.1 V? Should be some voltage there. If not, mesure for voltage at the ECU connector for pin 34. Greater than 0.1 V? Basically the ECU sends a small signal current to the o2 sensor. this is the only test the FSM gives for the o2 sensor circuit. I was under the impression that there is voltage generated by the o2 sensor as well. I believe it only happens when it reaches high temps, 300-400 degrees. and very small amounts of voltage Quote Link to comment Share on other sites More sharing options...
daeron Posted April 29, 2007 Author Share Posted April 29, 2007 Disconect the o2 sensor. With key on /eng. off mesure the connector for voltage. Greater than 0.1 V? Should be some voltage there. If not, mesure for voltage at the ECU connector for pin 34. Greater than 0.1 V? Basically the ECU sends a small signal current to the o2 sensor. this is the only test the FSM gives for the o2 sensor circuit. I was under the impression that there is voltage generated by the o2 sensor as well. I believe it only happens when it reaches high temps, 300-400 degrees. and very small amounts of voltage Yes, I get 0.21 volts from the ECU with the engine off OR on.. According to the FSM flowchart, it is time for me to "Replace O2 Sensor (already dont with questionable junkyard unit) or replace control unit. My query was regarding the O2 sensor ITSELF, heated up, and unplugged from the ECU lead. I was under the impression, based on the page here excerpted from the FSM (and other reading I have done) that the O2 itself should be generating a few tenths of a volt by its own catalytic action inside there.. "Examination of the oxygen concentration in the exhaust gas makes it possible to show whether the air/fuel ratio is leaner or richer than the stoichiometric ratio. The O2 sensor has a zirconia tube (ceramic) which generates voltage if there is a difference in the oxygen concentration between the inside and the outside of the tube. Platinum is coated on the inside and outside of the zirconia tube for the purpose of catalysis and electrode provision. The hexagon screw on the outside is grounded to the exhaust pip, and the inside is connected to the SPFI control unit through the harness." It then has a diagram showing a cutaway view of the sensor, and indicates a large, circled V in between the ground, and the center of the tube. It also has a handy-dandy little graph of the function of the O2 sensor, indicating low voltage at lean ration, and high voltage at rich ratio... SO I am taking ALL of that to mean that YES, I should be seeing SOME sort of voltage down there between ground and the conductor of my unplugged O2 sensor.... Which means that the damn RX-7 sensor my dad gave me was BUNK. I shoulda known, my brother said that thing always ran rich.... So what about the junkyard O2 sensor? anyone want to warn me away from trying that first?? if it works, then I will replace it with a new one at earliest possibility.... but I HATE to get it and have it NOT work... Any chance someone could check the output of their O2 sensor after a good spirited drive, with the sensor unplugged from the harness? just leave the engine running, the voltage measured is unimportant.. I just want to know IF you get a voltage off of it... Quote Link to comment Share on other sites More sharing options...
mikeshoup Posted April 29, 2007 Share Posted April 29, 2007 The 02 sensor needs to reach 600F before it works properly. This is not always easy to do at idle. The O2 sensor is self powered, and you should be able to register a voltage once it has warmed up properly. To test it on the workbench, you need a torch. Put the O2 sensor in a vice, clamp the positive lead to the signal wire on the O2 sensor, and the negative lead to the body of the O2 sensor. Use a propane torch set to high and the inner blue flame tip to heat the fluted or perforated area of the sensor. The voltage should go above 0.6V within about 20 seconds. Remove the torch, it should drop to under 0.1V within about 4 seconds. Apply the heat again for a couple minutes, making sure the voltage doesn't drop. If all of that passes, the O2 sensor is most likely good. Quote Link to comment Share on other sites More sharing options...
mikeshoup Posted April 29, 2007 Share Posted April 29, 2007 One thing that came to mind, what Voltmeter are you using? If its a digital one, you're probably good. However, cheap analog meters generally have too low of impedance and won't be accurate enough. (they'll start to absorb the voltage) Digital ones are usually fine in this department though. Quote Link to comment Share on other sites More sharing options...
daeron Posted April 29, 2007 Author Share Posted April 29, 2007 I idled in my driveway until the engine came up to operating temperature, then gave it a good spirited drive around the neighborhood, BEFORE i checked ANYTHING With the O2 sensor. I have no way of knowing what temp it was at, but the car was fully warmed up before I even started the drive. thanks for the bench test procedure, I will try that before I buy anything, and base my decision off of that.. that ALSO lets me "test" the JY O2 before it goes into the car. Anyone else want to sound off, feel free... i doubt I will have a chance to work on this until tomorrow.. household projects to be dealt with, too. Quote Link to comment Share on other sites More sharing options...
MilesFox Posted April 30, 2007 Share Posted April 30, 2007 here is a long shot but try making a ground lead for the o2 sensor from the heat shield to the firewall, if the o2 doesnt have a good ground thru the exhaust pipe Quote Link to comment Share on other sites More sharing options...
subie_newbie Posted April 30, 2007 Share Posted April 30, 2007 I think NEW single wire O2 sensors are around $30, so don't go blowing $30 at the junk yard when you might be able to get a new one for the same price. I stand corrected. $15 ebay FTW! Quote Link to comment Share on other sites More sharing options...
MilesFox Posted April 30, 2007 Share Posted April 30, 2007 if you ask for a "subaru " o2 it may be more expensive than the "generic" unit, the only difference is you will have to add the spade terminal to the generic unit. its the bosch single wire Quote Link to comment Share on other sites More sharing options...
daeron Posted April 30, 2007 Author Share Posted April 30, 2007 gotcha.. Well, I think I'm gonna get a cheapo sensor from the junkyard to check the theory first, and I plan on checking the one already in my car as was mentioned above. If I get a sensor that passes bench check and STILL don't resolve my problem or my code, then I am going to borrow the 25 to pick up the ECU from the boneyard.. For the longest time the tuning buttons on the OEM stereo only worked once in a GREAT while.. so i had to keep my stations set. Any time the battery got unhooked it took me days to weeks of pushing the buttons waiting for the up or the down to work, so I could re set the presets. SO, once or twice, when changing batteries, I played some games with two sets of jumper cables to maintain voltage to the stereo... So what I am saying is, I HAVE played stupid games with the battery cables, minor ones.. and "games with battery cables" fall under the category of "the very few things that can hurt these ECUs" Basically, I *do* have a decent explanation for why the thing may have gotten a tad frizzled..... I am almost tempted to pull it apart; but not yet. I dont have a chance to work on it monday or probably tuesday, but I will let everyone know what happens as it comes. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.