smokin5s Posted March 18, 2008 Report Share Posted March 18, 2008 on our 2001 Malibu it was throwing an engine code that the EGR valve was bad... I replaced it with an Autozone EGR valve and the code has not come back since, but the mileage has dropped about 100 miles a tank. I have verified that the air filter is clean, plugs are good, EGR valve is good, and tire pressure is right... any other ideas on what could be going one? any help would be appriciated. Thanks! Quote Link to comment Share on other sites More sharing options...
Casper Posted March 18, 2008 Report Share Posted March 18, 2008 I've had this happen a few times. All three times it was an O2 sensor. No code thrown either. Its like it was still within spec, but out enough to fuck up my mileage. Quote Link to comment Share on other sites More sharing options...
smokin5s Posted March 18, 2008 Author Report Share Posted March 18, 2008 downpipe O2 or before the CAT? those are 60 dollars a pop, so I'd like to get the right one. Quote Link to comment Share on other sites More sharing options...
Casper Posted March 18, 2008 Report Share Posted March 18, 2008 Find the specs for the O2 sensors. Pull them and check the ohms. Replace whichever isn't to spec. Also check the cat. Drive the car around tonight sort of hard. Pull in the driveway, and jump under the car. See if the cat is glowing at all. If so, its clogged and needs replaced. Shouldn't be the cat, but definitely could be. Quote Link to comment Share on other sites More sharing options...
MrMeanGreen Posted March 18, 2008 Report Share Posted March 18, 2008 Before the cat. The post-cat sensor only monitors for cat functionality. Quote Link to comment Share on other sites More sharing options...
smokin5s Posted March 20, 2008 Author Report Share Posted March 20, 2008 anyone know the specs of the O2's? Also, do I check the resistance while it is plugged in or can I leave the car off, unplug the O2 and put my multimeter on it? Also, what wires am I testing? Quote Link to comment Share on other sites More sharing options...
JaSSon Posted March 20, 2008 Report Share Posted March 20, 2008 Before the cat. The post-cat sensor only monitors for cat functionality. +1 If both 02 sensors are the same, just swap them. The 2nd O2 sensor is basically just a pass/fail test for the Cat. Hardly important. Quote Link to comment Share on other sites More sharing options...
Buck531 Posted March 20, 2008 Report Share Posted March 20, 2008 +1 If both 02 sensors are the same, just swap them. The 2nd O2 sensor is basically just a pass/fail test for the Cat. Hardly important. GM sensors are different between the front O2 and the back. (most of them). Quote Link to comment Share on other sites More sharing options...
Casper Posted March 20, 2008 Report Share Posted March 20, 2008 GM sensors are different between the front O2 and the back. (most of them). That's what I was going to say. With Ford you can do that, but I don't think you can with GM. I don't know what the spec is for your O2 sensor. Call a dealer. They can probably tell you. I'd check both, but most importantly the front. Disconnect it, pull it from the exhaust, and test it. I'm pretty sure there are only two wires. Quote Link to comment Share on other sites More sharing options...
99FLHRCI Posted March 20, 2008 Report Share Posted March 20, 2008 That's what I was going to say. With Ford you can do that, but I don't think you can with GM. I don't know what the spec is for your O2 sensor. Call a dealer. They can probably tell you. I'd check both, but most importantly the front. Disconnect it, pull it from the exhaust, and test it. I'm pretty sure there are only two wires. I think it should have 4 wires. 2 for the heater and 2 for the input/output on the sensor. Quote Link to comment Share on other sites More sharing options...
Dave1647545494 Posted March 23, 2008 Report Share Posted March 23, 2008 th easiest way to check is to watch the o2 on a scanner and see if the volatge switches slow or is always low if you need access tot a scan tool let me know and I'll bring mine home so you can look at it Quote Link to comment Share on other sites More sharing options...
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