Cougar Posted August 20, 2007 Share Posted August 20, 2007 To verify the ECU end of the wires disconnect the sensor and then measure the voltage of each wire but use the car body ground as reference. The sensor voltage should be a small voltage and ground will be zero of course. Link to comment Share on other sites More sharing options...
salewit Posted August 20, 2007 Author Share Posted August 20, 2007 Well I think I'm going to run out and get a new one. I measures the resistance between the heater wires and got 4 ohms. My book says it should be 30. What's $40 after spending hundreds? Link to comment Share on other sites More sharing options...
OB99W Posted August 20, 2007 Share Posted August 20, 2007 [...]The coolant sensor was behaving properly. I had 5v on the harness, and the ohms ranged from 2480 cold to 460 when the engine warmed up and I stopped. According to my book 2480 = 75F and 460 about 158F.[...]Actually, this is a bit suspect. If the ambient temp was about 75F when you started, then of course the 2480 ohms reading when "cold" makes sense. However, 158F when "warmed up" is somewhat on the low side. I believe the thermostat spec for your engine should be that it opens at about 170-175F, meaning the coolant sensor resistance should be equivalent to that when the engine is warm. I also seem to remember that if below 160F, the ECU may remain in open loop. Assuming I've got those temps right (and hopefully someone else will say so if I'm wrong), there are three possibilities: 1) The engine wasn't fully warmed at the point you stopped taking the resistance reading. -or- 2) The engine was warmer than the coolant sensor resistance would have us believe, i.e. the sensor isn't accurate. -or- 3) The thermostat is of the wrong temperature range, not OEM, defective, etc., so the engine isn't coming up to high enough temp, and the coolant sensor is accurately reporting that. This, of course, is aside from the possible O2 sensor issues. Link to comment Share on other sites More sharing options...
OB99W Posted August 20, 2007 Share Posted August 20, 2007 Well I think I'm going to run out and get a new one. I measures the resistance between the heater wires and got 4 ohms. My book says it should be 30. What's $40 after spending hundreds?The correct heater resistance depends on the temperature. Four ohms would appear to be "in the ballpark" when "cold"; the O2 sensor needs to be rapidly heated to quite a high temp, and three amps (12 volts supplying a four ohm load) wouldn't be outside the range of possibilities. Since the heating isn't needed once the exhaust system comes up to normal operating temp, 30 ohms may be correct at that higher temp. EDIT:By the way, you can measure the resistance of the heater, but shouldn't measure that of the sensor itself; measure its voltage output to check it. That's because applying voltage to the sensor can damage it; therefore, if the sensor was miswired and heater voltage went to the sensor itself, it's good that you're replacing it. Link to comment Share on other sites More sharing options...
salewit Posted August 20, 2007 Author Share Posted August 20, 2007 OB: I don't think I let the engine get fully up to temperature, so I'm thinking the CTS is probably about right on. Alright I just put the old O2 sensor back in with the white from the harness connected to the black on the Bosch replacement and stuck a pin in the connector on this signal wire. The engine had fully cooled at this point. The cat was cold. I started it up, and put my voltmeter on it right away and it was jumping all over the place from .1 - .9 volts. From what I understand this is what is supposed to happen after two minutes or so. I never got the "open loop" mode of just .1-.2V. I have one muffler strap I missed, so when it cools down, I'm going to fix that strap, test it again cold, and maybe go for a spin. Then what? Smog test? Link to comment Share on other sites More sharing options...
Cougar Posted August 20, 2007 Share Posted August 20, 2007 The voltages now look ok. You may want to now drive the car a little and let the engine get to normal temp. Then see what the voltage of the O2 sensor is at idle and around 2,500RPM. Hopefully it will be about .5 volts. If that checks out then maybe see what the test shows you. Link to comment Share on other sites More sharing options...
OB99W Posted August 20, 2007 Share Posted August 20, 2007 [...]The engine had fully cooled at this point. The cat was cold. I started it up, and put my voltmeter on it right away and it was jumping all over the place from .1 - .9 volts. From what I understand this is what is supposed to happen after two minutes or so. I never got the "open loop" mode of just .1-.2V. I have one muffler strap I missed, so when it cools down, I'm going to fix that strap, test it again cold, and maybe go for a spin. Then what? Smog test? It's a bit strange, if the system was truly cold, that it didn't seem to go open-loop for a bit. However, in order for the cat to work correctly, it has to get an exhaust stream that oscillates in content (the engine is alternately being fed a mixture to either side of the stoichiometric point), and the voltage range you're reporting would seem to indicate that the O2 sensor is seeing such a change. You could see what the sensor reading is when forced lean and rich. Lean is easy to accomplish -- disconnect a large vacuum hose such as the one to the brake booster. Rich is done by adding more fuel; some people inject propane at the intake, but you can often accomplish the desired result by blocking off the air intake somewhat. EDIT:You might also accomplish enrichment by partially restricting the fuel return line momentarily, as you did when checking fuel pressure. If the sensor seems to swing correctly, it's probably time for a road test. I don't know how you feel about being vulnerable to a ticket, but if the engine no longer seems to be running rich, it would probably be good to get things up to temp so the cat has a chance to burn off any fouling. (That doesn't mean you still won't have a damaged cat to contend with, but you might just get lucky.) After that, if it seems to run okay, I suppose an emissions test is next. Best of luck. Link to comment Share on other sites More sharing options...
OB99W Posted August 20, 2007 Share Posted August 20, 2007 [...]Hopefully it will be about .5 volts.[...] Yes, an analog meter (depending on certain physical and electrical characteristics) would likely result in an averaged reading around 1/2 volt. A digital (such as that being used) samples the voltage periodically, and might indicate an erratic voltage anywhere between 0.1 and 0.9 volts; you'd have to do your own averaging. Link to comment Share on other sites More sharing options...
salewit Posted October 11, 2007 Author Share Posted October 11, 2007 I hate to bring this old thing back to the top, but I just wanted to thank everyone that helped me out with this beast. The car finally passed smog! The culprit was apparently the mis-wired O2 sensor. Cat didn't need changing either. The numbers were all below average. The car is running unbelievably well. Thanks again for all the help! Link to comment Share on other sites More sharing options...
OB99W Posted October 11, 2007 Share Posted October 11, 2007 [...]The car finally passed smog! The culprit was apparently the mis-wired O2 sensor. Cat didn't need changing either. The numbers were all below average. The car is running unbelievably well. Thanks again for all the help! Great! Thanks for getting back to us with the outcome. Link to comment Share on other sites More sharing options...
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