O2 Sensor Voltage? July 02, 2010, 12:48:25 PM Can anyone tell me what the voltage from the O2 sensors should be going into the EEC? Since I bought the Sport a month ago, when the engine's warmed up, its had an occasional high-speed miss, an intermittent rough idle and it will stall at idle from time, to time as well. I pulled codes (did both KOEO and KOER tests) and got a code 42 first and then a code 34 out of the scanner. The first code that's spit out is the one you should address first obviously. As I'm sure most of you know, a code 42 designates "O2 sensor voltage signal always rich-does not switch" and a code 34 designates "EGR Valve Position Sensor, or Pressure Feedback Sensor signal voltage out of self-test spec limits."Instead of throwing parts at the car, I'd like to test the O2 sensors and verify if they really are bad, or not. I already verified proper TPS voltage and verified that the IAC is clean an working properly. I made sure there aren't any vacuum leaks (good old propane test), I replaced the old fuel filter, plugs (gapped at .050"), plug wires, cap and rotor. The fuel pressure is on the money (37 PSI with reg hose on, 45 PSI with hose disconnected). There's no hint of fuel in the regulator to indicate a bad reg. The diaphragm in the EGR valve doesn't leak. The diaphragm in the MAP sensor also doesn't leak. Since a bad ignition module can cause a high-speed miss, I removed the TFI from the distributor and took it to Advance Auto Parts and had them test it. It tested fine. I'm pretty sure it's either a bad EGR Pressure feedback sensor, bad O2 sensors, or dirty fuel injectors. I'm gonna run a can of Seafoam through the fuel tank to hopefully clean the injectors if they are in fact dirty. I already replaced the EGR Valve Position Sensor when I did the tune up, so the possibilities of what's causing this should really be narrowed down. What should the voltage coming out of the O2's be? Quote Selected
O2 Sensor Voltage? Reply #2 – July 02, 2010, 06:21:09 PM Hey, thanks for posting that chart. That's just what I was looking for. Quote Selected
O2 Sensor Voltage? Reply #3 – July 03, 2010, 09:18:34 AM That is a nifty little chart but is just doesn't do it for me. The part there were it tells you appx .55 volts isn't sitting well with me. Yes that is in the range of the sensor and about in the middle. of the range from 0-1volt. That part that gets me is how do they know it should be .55volts and not some place other in the range. I guess they are assuming that the air fuel ratio is dead on . Then it still doesn't seem right. When these cars are all warmed up they go into closed loop. That is when the o2 sensor is full heated and the EEC start taking what the O2 sensor says into consideration. Once its fully into closed loop that voltage varies up and down within that 0-1volt range. So I just don't get how testing the sensor for .55volts is gonna tell you much. Maybe there is something I' missing and someone else with chime in and set me straight. Stuckman Quote Selected
O2 Sensor Voltage? Reply #4 – July 03, 2010, 12:39:42 PM Quote from: ipsd;327157I just don't get how testing the sensor for .55volts is gonna tell you much. Maybe there is something I' missing and someone else with chime in and set me straight. StuckmanThe o2 sensor(s) switch several times a second, so the meter is only going to read a average of the switching voltage, which is usually approx .4 to .7 on a system without a problem... Thus the average is going to be .5-.6v, if you read say .3v or .8 there is a definite problem... With a oscilloscope a accurate pict of the switching points can be viewed... Quote Selected
Well... Reply #5 – July 03, 2010, 05:51:30 PM To update my progress... Just a bit ago, I went out and cleared the codesI cleared the codes and did a KOEO, KOER and cylinder balance test. Today, after the KOEO test, it threw a code 34 again just like yesterday. After the KOER test, it threw the 34 again, but instead of throwing the more ambiguous code 42, it threw a code 92 instead, which designates the passenger side O2 sensor as being bad. It passed all 3 phases of the cylinder balance test with flying colors though, which was good to see.While I was out there, I had planned on testing the voltages at the O2's, but I'm gonna have to wait until the engine cools down. It's way too tight in there to be able to unplug the O2 sensor harnesses without getting Kentucky fried! Even after the engine has cooled down, that passenger side O2 looks like an absolute nightmare to get to. It's buried under the emissions tubes and looks impossible to get to from under the car. Hopefully I won't have too much trouble getting my hands in there to disconnect its harness for testing.Last night, I went to the gas station and dumped a can of Seafoam in the tank before putting 16 gallons of gas in the almost empty tank. This car had been sitting for the past three years, so I wouldn't be shocked if the injectors had gotten at least a little gummed up from that inactivity. If the injectors were, or are still gummed up, I hope the Seafoam works as advertised and cleans things up in there. Shortly after dumping the Seafoam in, I did notice fewer problems the idle. Even the intermittent miss hasn't reared its ugly head since I did that. The car IS still throwing codes though which I'm gonna have to get resolved. Even though its idling smoother than a baby's fart right now, something still isn't right with the car and that doesn't sit well with me. When I test the O2's, I sure hope I find that one, or both of them are bad. I'm running out of options fast here. If both O2's test bad, that would leave the EGR Control Valve, or emissions system as being the only other possibilities I can think of.Aw man. Aren't driveability issues fun to deal with! I'M OUT! :D Quote Selected
O2 Sensor Voltage? Reply #6 – July 03, 2010, 05:53:13 PM Quote from: TurboCoupe50;327167The o2 sensor(s) switch several times a second, so the meter is only going to read a average of the switching voltage, which is usually approx .4 to .7 on a system without a problem... Thus the average is going to be .5-.6v, if you read say .3v or .8 there is a definite problem... With a oscilloscope a accurate pict of the switching points can be viewed...Tom. You DO realize that your knowledge of all this stuff is sickening don't you? You must have forgotten more about this stuff than most of us will ever know! Quote Selected
O2 Sensor Voltage? Reply #7 – July 03, 2010, 09:14:57 PM Quote from: 88 Blackbird 5.0;327191Tom. You DO realize that your knowledge of all this stuff is sickening don't you? You must have forgotten more about this stuff than most of us will ever know! Really??? :DIf you want to get rid of that code 34, Replace your EGR position sensor, make sure the sensor is sealed to the EGR actuator(mounts with a "O"ring)...I have drilled a small hole in the housing and shot some contact cleaner(or WD40)in them and then resealed the hole with silicone rubber... This usually fixes the problem, but may not have a long lasting effect... Quote Selected
O2 Sensor Voltage? Reply #8 – July 03, 2010, 10:11:19 PM Quote from: TurboCoupe50;327204Really??? :DIf you want to get rid of that code 34, Replace your EGR position sensor, make sure the sensor is sealed to the EGR actuator(mounts with a "O"ring)...I have drilled a small hole in the housing and shot some contact cleaner(or WD40)in them and then resealed the hole with silicone rubber... This usually fixes the problem, but may not have a long lasting effect...As always, thanks for the advice Tom. I already replaced the EGR Valve Position Sensor a week ago though. I was really careful to get a good seal with that O-ring, but I'm still getting that code 34. Do you think it might be a sticking EGR Control Valve possibly? This evening, I went out and tested the passenger side O2 sensor. I'm confused about something though. When I followed the instructions that were posted earlier in this thread to see if the O2 sensor was switching, I was getting nominal voltage. When I think about the fact that I'm checking voltage between the Signal wire and the negative terminal of the battery, I'd expect to get nothing but a nominal voltage reading, because there's no voltage coming in to the O2 sensor in the first place. That sensor was disconnected per the instructions. Can you steer me straight on this? It sure wouldn't make sense to me that I WOULD get a .55 volt reading under those cirspoogestances. Where would the voltage be coming from? Quote Selected
O2 Sensor Voltage? Reply #9 – July 04, 2010, 01:08:35 AM After doing more homework on this, I found out that O2 sensors create their own voltage when they react to changes in oxygen levels (such as when your engine is warm enough to go into closed-loop). The passenger side O2 sensor I tested today must be bad, because it didn't react at all (no voltage output from it) when I tested it with the engine running in closed-loop.At least I've confirmed it's bad. Since I now know it's bad, I'm going to replace both of them. I'm hoping my code 34 is somehow being caused by the bad O2, or bad O2's. Hopefully this will kill the driveability issues with the car.I'll keep you posted on how this turns out. Quote Selected
O2 Sensor Voltage? Reply #10 – July 04, 2010, 08:21:14 AM Yes the o2 sensor should be connected to get a switch voltage, the system(ECU) is constantly switching from slightly lean to slightly rich trying to get the A/F ratio perfect... Quote Selected
O2 Sensor Voltage? Reply #11 – July 04, 2010, 11:06:58 PM I see what you're saying Tom. When I asked about whether the O2's needed to be hooked up to check their voltage output, I was thinking they had to have power supplied to them via the vehicle for them to put out the .55 volts. I now realize however, that the O2 sensors will create their own voltage when they react with oxygen in the exhaust gases passing through the exhaust manifold. On another note... I replaced the O2's today. After I replaced them, I reset the base idle. After the base idle was reset, I did another KOEO test as well as a KOER test. The KOEO test threw a code 34 again and the KOER test threw a code 34 and a code 44 (thermactor system fault). After running these tests, I took the Blackbird for a nice, long drive. There's no longer any hint of an intermittent rolling idle, or any stalling problems. The intermittent miss also seems to be gone. The car is also much easier to start. It fires up like it should now. Now that I replaced the bad O2's, the car isn't displaying any driveablity issues at all. I still want to address that code 34 I've had for a while though, and whatever issue is causing that code 44 to be thrown too. It looks like I've got more homework to do on these issues. I still wonder if my code 34 isn't being caused by a bad EGR control valve. It's just a vacuum switch. As old as it is, I wouldn't be shocked if the switch mechanism in it is sticking. Like I said though, I'm gonna do more homework on this. I'm sure I'll figure out what my next best course of action should be with this. Quote Selected
O2 Sensor Voltage? Reply #12 – July 05, 2010, 12:51:49 AM Well you're making progress, glad to hear the idle is OK... The older o2 sensors didn't have nearly the life of the newer ones, often were bad by 50-60K mi...Is the 34 a continuous code(KOEO), or running???The EGR control valve could be bad, but I'd think it'd cause a idle problem, with that I'm kinda assuming it isn't closing all the way but I suppose it could have a ruptured diaphragm(which should not cause a KOEO code)... If you can pull a vacuum on the valve it's diaphragm is OK(oops I forgot you tested that)...BTW is the sensor in a black or gray housing??? Should be gray, the black ones have a different calibration... Quote Selected
O2 Sensor Voltage? Reply #13 – July 05, 2010, 12:58:36 AM Quote from: TurboCoupe50;327328Is the 34 a continuous code, stored in memory or both???The EGR control valve could be bad, but I'd think it'd cause a idle problem... I'm kinda assuming it isn't closing all the way but I suppose it could have a ruptured diaphragm(witch should not cause a continuous code)... BTW is the sensor in a black or gray housing??? Should be gray, the black ones have a different calibration...It's both continuous AND stored in memory Tom.As far as the color of the sensor's housing goes, that's a good question. I'll have to check that tomorrow and get back with ya on that. I'm gonna test the diaphragm in the one on the car tomorrow to see if it's ruptured, or not. I'm gonna test it for proper switching too and go from there. I hate throwing parts at a car.Now that I have the O2 sensor problem resolved, I'm gonna focus on resolving the EGR issues. After I have the EGR system squared away, I'm gonna focus on the Thermactor system. Quote Selected
Hey Tom Reply #14 – July 05, 2010, 03:09:36 PM I checked the EGR control valve and it has a black housing. You said it should have a gray housing. Does the black housing mine has indicate it's the one the car came with 23 years ago? Quote Selected
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