urbex Posted August 1, 2011 Report Posted August 1, 2011 Ok, so I had been looking online, and I'm starting to wonder if perhaps a failing crankshaft position sensor is what is causing my surging issues on my Lumina (3100)? In case you haven't seen my thread about it, I'm having issues when accelerating (between 40-55mph) like when passing, the car feels like it's surging. It has never set a code though. I also have a sporadic rough idle and sporadic delayed/long starts sometimes. The surging happens more when it rains, and does not happen during the winter months. I've replaced the TPS, coils, ICM, and cleaned the MAF, EGR, IAC. So my questions are... 1. Does it sound like a failing CPS could be to blame? I've seen online other people had similar symptoms where that was to blame. 2. It says in my manual that the dealer must repgrogram/relearn the PCM for the sensor after changing. Is that true? Do I really need to have the dealer reprogram my car after I replace it? 3. Is there any way to tell which sensor may be bad? I know there are two, but I didn't know if I just have to replace them and see if that takes care of it? I figure if they're kinda a pain to get to if I've got them off I might as well just put new ones in anyways. Quote
slick Posted August 1, 2011 Report Posted August 1, 2011 I'm gonna say that the cps is doubtful to be the issue. Hook up to a scanner, and see what's wrong. Or take it to a shop that can actually diagnose the issue, rather than just throwing parts at it. Quote
urbex Posted August 1, 2011 Author Report Posted August 1, 2011 Well like I said, nothing shows up as being wrong when you do hook it up to a scanner. Quote
Schurkey Posted August 1, 2011 Report Posted August 1, 2011 Well like I said, nothing shows up as being wrong when you do hook it up to a scanner. A REAL scan tool, or some consumer-grade junk tool? What is the short- and long-term fuel trim when the engine is surging? What is the O2 crosscounts when the engine is surging? Quote
urbex Posted August 1, 2011 Author Report Posted August 1, 2011 I can't remember exactly what the fuel trims or O2 readings read when it would surge. I just remember that neither really changed when it was doing it. I mean I wouldn't have a problem taking it in, but since it does it so sporadically there's no chance in hell that it would do it while it's in... I mean first of all it'd have to be taken in on a rainy day, and even then it might not do it. I mean, I could just wait until it gets worse, but I'd really like to get it taken care of before it gets that far... Now's the best time to fix this shit since I'm not driving it 80 miles a day and we have a couple cars at home that I can drive a different one if it's getting worked on. The last thing I'd want is to get stranded in a not-so-nice area. Quote
urbex Posted August 1, 2011 Author Report Posted August 1, 2011 So if I take it into the dealer or a shop their scan tool would be better and it'll pick up what the issue might be? Even though there are no stored codes or anything? I might just have to have them at least diagnose it... I wouldn't think it'd cost too much to at least have them do that. Quote
Schurkey Posted August 1, 2011 Report Posted August 1, 2011 (edited) So if I take it into the dealer or a shop their scan tool would be better Yes. (or buy your own. Snap-On MT2500 is readily available, and not all that expensive any more--although price varies with the included software and cables.) and it'll pick up what the issue might be? Depends on the skill and integrity of the guy doing the work. Even though there are no stored codes or anything? I might just have to have them at least diagnose it... If it's in the data stream, a skilled tech using a professional-grade scan tool can figure it out. I wouldn't think it'd cost too much to at least have them do that. First Guess: Diagnosis is done at hourly rate. Around here, that's ~$100/hr. Edited August 2, 2011 by Schurkey Quote
urbex Posted August 2, 2011 Author Report Posted August 2, 2011 Ok well.... I did plug in my scanner while I drove today, and will do it in the following days. Tonight I WAS able to replicate the surging, and had rough idle at stop lights. First the surging.... Of course I could only get it to do it once, and I wasn't able to change screens and do it again. I was on the screen that showed the MAP sensor values (whatever they are...) Now, normally when you accelerate the number goes up (must be as vacuum decreases?) however during EACH single surge the number would quickly drop to 8, then back up to approximately 20. Now the appx. 20 was the consistent number that was being read during normal acceleration. So basically for a split second during each surge the MAP sensor would read ridiculously lower than normal. Now, the only thing I noticed as far as the rough idle at the lights, was whenever the car is idling in park foot on brake, I noticed that the first O2 sensor has a lower voltage reading than the second. I don't really know how to interpret that data, but I was under the impression that the first sensor should read a higher voltage than the second? For example, the first O2 sensor would read 0.070v wile the second O2 sensor would read 0.700v. During driving for the most part I noticed that the first sensor would read higher than the second (say 0.700v/0.400v respectively).... Not sure if any of that means anything or not..but that was all I was able to see today. Tomorrow it's supposed to rain, so hopefully I'll be able to drive during it... Quote
AL Posted August 2, 2011 Report Posted August 2, 2011 The front 02 sensor should be reading below .2 and above .8 and keep bouncing back and forth while the rear one should stay around .45 Quote
urbex Posted August 2, 2011 Author Report Posted August 2, 2011 The front 02 sensor should be reading below .2 and above .8 and keep bouncing back and forth while the rear one should stay around .45 Oh, ok that does make sense... Thanks! Although the rear sensor reads around .6...but I doubt that's an issue since it isn't too far off. Quote
urbex Posted August 2, 2011 Author Report Posted August 2, 2011 I also did notice today that the LT fuel trim is always a negative number. Usually not higher than -8 though. It hovers anywhere from -4 to -6 for the most part. But I think some of that is probably from my driving, since I'm always light on the throttle and coast as much as I can. Quote
AL Posted August 3, 2011 Report Posted August 3, 2011 Its running leaner than it did when it left the factory Quote
urbex Posted August 3, 2011 Author Report Posted August 3, 2011 So maybe that's why I get good gas mileage! Hmm... So now to figure out why it's running lean.... Quote
AL Posted August 3, 2011 Report Posted August 3, 2011 It sounds like your front 02 sensor may be going bad Quote
urbex Posted August 3, 2011 Author Report Posted August 3, 2011 You think? I mean it does jump around a lot more than I would have thought it should, but again I don't know much about the values. I suppose if that's all it is I'm not going to worry about it until it gets to the point that it starts throwing a code or running worse... BUT.....a bad O2 sensor could be causing my surging, so it may fix it.... But I don't want to spend that much money if it's not it. I'd rather be sure. At least everything else I've replaced is cheap. Thanks man! Quote
AL Posted August 3, 2011 Report Posted August 3, 2011 Its supposed to jump around like crazy, I would have to look at the datastream to see if its working quickly and accurately enough Quote
urbex Posted August 3, 2011 Author Report Posted August 3, 2011 Hmmm... Well I figure that it's probably only going to get worse, and hopefully when it does it'll throw a code then. Like I said I don't really want to replace it if that's not it, and I don't know how to read a datastream (or what that even is...) It's not that I'm really stupid, it's that I don't have a fucking clue about any of this, and I'm trying to learn it as I try to fix it... I appreciate your help! Quote
AL Posted August 3, 2011 Report Posted August 3, 2011 The datastream is what you look at when your reading sensor data Quote
urbex Posted August 3, 2011 Author Report Posted August 3, 2011 The datastream is what you look at when your reading sensor data I was picturing like a big chart or graph or something.... I dunno why... Quote
urbex Posted August 6, 2011 Author Report Posted August 6, 2011 (edited) Yeah after driving again today with the scanner plugged in I see for sure it's running lean. The LT fuel trim never went above -3.0.... It does seem as if my gas mileage is going down...but then again I'm not driving 70-80 miles a day to school, so it's hard to tell... Edited August 6, 2011 by urbex Quote
alec_b Posted August 6, 2011 Report Posted August 6, 2011 To really watch O2 sensor values you need to have a scantool that can graph history. That way you can see the O2 activity in something graphical. They really move too fast, what you're seeing by watching the voltages is only part of the picture. A lazy O2 sensor can cause all kinds of weird issues, because the PCM needs it for precise metering of the A/F ratio. When you can watch the graphs, you should have a nice tight up and down sweep, with peaks being longer the more load and valleys being longer when you're coasting. If your O2 isn't responding fast enough the PCM can get late signals and won't always be able to keep you in the optimal A/F range. Quote
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