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Car issues - not sure where to begin looking

AridholAridhol Daddliest CatchRegistered User regular
edited August 2011 in Help / Advice Forum
I have a 2001 Nissan Sentra 2.0L front wheel drive, auto and I think I have broken something.

I accidentally left the e-brake on and drove about 200 feet before I noticed. I was giving the car a lot of gas, not pedal to the metal but close.
After that the "service engine" light came on and I drove home (about 1k). A friend told me to disconnect the battery to reset the computer because driving with the ebrake may have tripped something so I did that.
The "service engine" light now does not come on but when I first start the car (starts fine) I put it in drive and press the gas and it feels like it limps along, trying to go (it moves a bit but not much).
After about 30 seconds to 1 minute of that it runs and drives fine. No knocking, stalling or anything. It's only when I start it up.

It's in a covered car park so it's not getting cold or baked in the sun either.

Things I've done:
Checked coolant - lots
checked the oil - tiny bit low so I put a quart in last night. Nothing changed this morning
reseated all the fuses

I'm not sure where to go from here and my mechanic is away for the next few days.




Aridhol on

Posts

  • EffefEffef Who said your opinion mattered, Jones? Registered User regular
    edited August 2011
    Burnt out or clogged oxygen sensor. There are a few of them, and they sit downstream of the combustion chamber in the exhaust system to monitor the amount of oxygen in the exhaust, so that the ECU knows how much fuel to put in the air/fuel mixture when the engine runs. They all go bad or get glassed over eventually, and need to be replaced.

    The engine will run without them completely, but you will get far worse fuel mileage and rough running until the engine warms up like you are experiencing. This is because the ECU does not know how much fuel to feed the engine, and essentially just uses a baseline and guesses. What could have happened is that the sensor was close to failure, and you running the car hard like that (I am guessing you usually don't ) could have broken it. If this is the problem, the warning light will come back on after a while.

    You probably don't know this, but back before the days of the ECU and emissions monitoring, all cars ran like shit when cold.

    Effef on
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  • AridholAridhol Daddliest Catch Registered User regular
    Any idea how much that might run?

    It seems to run pretty much perfectly when warm. This morning it did the issue above and just now 20 minutes ago it started and drove with no issues.

  • EffefEffef Who said your opinion mattered, Jones? Registered User regular
    Depends. The part itself is about a hundred or so bucks, but a dealership or repair shop will charge you a couple hundred in labor.

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  • EffefEffef Who said your opinion mattered, Jones? Registered User regular
    edited August 2011
    The light hasn't come back on because when you remove the ECU from a powered state it reverts back to its hard coded engine maps, which are not always ideal and the car can run rough. Over time, it learns what parameters make the engine run better, and it will hold off on throwing a trouble code until the car is driven for a while. After the required drive time is up, it will sense that the OX sensor is fucked and the light will come on again.

    Effef on
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  • AridholAridhol Daddliest Catch Registered User regular
    Thanks Effef you've been very helpful :)

    Everything you said sounds bang on so I'll see with the mechanic on wednesday. He's a good friend so labour will just be a case of beer.

  • EffefEffef Who said your opinion mattered, Jones? Registered User regular
    The trick is finding out which sensor is the broken one. If your friend has a diagnostic tool it should tell you.

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  • SpudgeSpudge Witty comments go next to this blue dot thingyRegistered User regular
    Auto parts stores like AutoZone and Advance will run a check engine diagnostic for free. If the light comes on and you can limp it to the store, they can pull the code and tell you exactly what is wrong

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