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    VWVortex


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    Thread: Will a bad O2 sensor cause drivability issues?

    1. 12-20-2006 12:56 PM #1
      I'm trying to figure out why I'm getting such bad gas millage. So many people say just replace the O2 sensor. I'll do it, but what confuses me is that the car really seems to drive and respond well. I've never had a VR6 before, but compared to the 16v I just sold it drives well. Also, when the 16v had a bad O2 sensor, it really shows in hesitation on throttle. So would the VR6 be the same, or does the bad O2 sensor just cause improper fueling with leads to less power and bad millage?

      Thanks


    2. Member CBHVR6's Avatar
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      12-20-2006 01:24 PM #2
      Front O2- yes, it will adjust fuel trims accordingly

      Rear O2- no, it just makes sure the cat is filtering. You can still get a CEL from the rear but not drivability issues.

      I've been rocking one since my highflow cat install


    3. 12-20-2006 01:34 PM #3
      OK perhaps I should be more specific. When I say drivability issues I mean hesitation or sputtering, something like that. If you say yes to drivability issues when the front O2 sensor is bad, but you're referring to bad milage and improper fueling, leading to lacking power - that's not something I'd really see or know about since I've never driven a VR6 before.

      So I'm looking for mre evident signs, if they exist. It seems to me that that simply don't. I'm getting the impression that a drive could drive the car for months and not realize they have a bad O2 if they aren't in tune with the power the car should have, or the expected fuel consumption.


    4. Member c25porter's Avatar
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      12-20-2006 01:42 PM #4
      That is a true statement with VR's. If you are not in tune with it, there are a lot of things that you wouldn't notice wrong. I still has more power missing on one cylinder than the 16V but there are some feelings that go along with missing on one.

    5. Member craigt-from-atl's Avatar
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      12-20-2006 10:14 PM #5
      Quote, originally posted by CBHVR6 »
      Front O2- yes, it will adjust fuel trims accordingly

      If bad, the O2 would throw a code, correct? I've never replaced mine and I'm at 119k. No codes.

      -Craig

    6. Member CBHVR6's Avatar
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      12-20-2006 10:43 PM #6
      Quote, originally posted by craigt-from-atl »
      If bad, the O2 would throw a code, correct? I've never replaced mine and I'm at 119k. No codes.

      If you don't have a code, you are fine.


    7. 12-21-2006 06:48 AM #7
      how bad is "bad gas mileage"? Are we talking 12mpg on the highway or something? Check the actual mileage by doing the numbers game with how many miles it takes to run through a full tank until the empty light comes on.

      If you don't have any codes than you probably don't have much to worry about but a bad MAF sensor could cause some minor problems without throwing codes. Usually results in weird/jumpy idles, though.

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    8. 12-21-2006 09:47 AM #8
      Well I should have provided more details in the begining, but I'm greatful for the response thus far.

      Its a 95 Passat, ODB1. So only 1 O2 sensor. I don't have a CEL on. I'm averaging 450 km's per tank of gas (remeber thats 70 liters in a Passat, not 50 like in G/J's). I'm using 93 octane from Esso or GTO. My MFA tells me an agverage of 12.5 - 13 l/100 km's but if you work out the milage for 450 km's on 70 liters (I worked it with 65 liters actually because it wasn't right on empty - and no gas light on B4's) you get 14.4 l/100 km's. Yuck BTW, this is mostly non spirited city driving. I have like a 10 minute drive to work down a single street. Traffic isn't really stop and go. Just a few lights.

      So getting back to the original question, are there noticeable driving differences between a VRsick with a bad O2 and one with a good O2. Like I said, if this were a 16v, you'd be hesitating when giving gas under load, and the motor would drink more too. But the 16v isn't efi, its CIS and therefore a lot more sensitive to improper fueling.

      Last night I ordered an OEM O2 sensor anyway. For the $130 CND it cost me, it isn't worth fretting over. But for the sake of discussion, I will keep this thread alive and post back my findings when I change the O2. From reading these forums, I'm getting to see how the VR6 is more along the lines of a performance motor and so if one component isn't working quite right the whole kit goes to the crapper.


    9. 12-21-2006 09:53 AM #9
      If ur o2 doesnt work properly the car will run pretty rich, rich enough for u to notice at idle and when u romp on it. do you smell unburnt fuel when the car idles? A bad o2 will not cause the car to sputter, it will make it drive like sht tho. what condition is your maf in?

    10. 12-21-2006 11:08 AM #10
      The MAF is apparently new. Previous owner replaced it along with the entire intake elbow this spring.

    11. 12-21-2006 11:12 AM #11
      hm.. have u pulled ur plugs? what do they look like?

    12. 12-21-2006 12:01 PM #12
      Ya, plugs... I should just buy new ones. I haven't pulled them (kinda thinking that's a need to replace part)

      But good to bring it up. I'll get on that too.

      What I might do is replace the O2 and drive the car for a week and see how the milage goes. Then I'll replace the plugs. Of course I need to eTest this car ASAP, so I might need to do all the work at once, which really wont tell me definitively what part had the most impact to the milage.


    13. 12-21-2006 01:48 PM #13
      how many miles since the last good tune up ( plugs, wires filters etc..)

    14. 12-21-2006 10:26 PM #14
      I'm gonna go with about 25,000 to 30,000 km.

    15. 12-22-2006 08:54 AM #15
      yeah, it may be that time for a tune up.

    16. Geriatric Member need_a_VR6's Avatar
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      12-22-2006 09:09 AM #16
      Quote, originally posted by CBHVR6 »

      If you don't have a code, you are fine.

      Absolutely untrue.

      The first signs of a failing O2 are surging/misfiring below 4500 and it running PERFECT after that at WOT. If you unplug the O2 and the problem goes away, it's a bad O2 sensor. Some of the later cars do have some diagnostics for this, but the primary O2 can already be on the way out (and you notice it) before it gets caught by the computer.

      -Paul
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    17. Member CBHVR6's Avatar
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      12-22-2006 09:32 AM #17
      Thanks for the correction man. i'll remember that

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