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Author Topic: Severe misfire update  (Read 2391 times)

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ikebaddog

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Severe misfire update
« on: May 25, 2016, 06:29:55 AM »
If you remember some time ago whilst investigating a severe misfire , I disconnected the upstream lambda sensor, missfire disappeared, yesterday the old girl passed the MOT, with the sensor still disconnected!!! I had just simply forgotten about it, my point is, if it hasn't affected the emissions, what the hell, does it do???
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Jonny Jeep

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  • Vehicle: TJ 4.0 Sport
  • Year: 1997
Re: Severe misfire update
« Reply #1 on: May 25, 2016, 10:42:17 AM »
The upstream sensor does control emissions. If however it is disconnected the computer has to use it's programmed fuel tables with data from other sensors to set fuel trim.

It's possible it may run just slightly rich with no sensor, but when I had a bad one I didn't notice any change in MPG whilst waiting for a replacement NTK sensor from Rockauto. They don't seem to set codes very often with bad sensors so no check engine light normally which I think would be a fail these days.
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