940 & 960 Buggered Oxygen Sensor? 1991 940GLE 16valve.

Recent work:

-new fuel filters and ‘newer’ intank pump

-AMM replaces with known to be working 2nd hand unit

-new air filter

-IAC cleaned and operational

-new spark plugs

-KS cleaned and retorqued

-dizzy cleaned; it’s not the best but it’ll be replaced soon with a wasted spark set up.

-good plug leads.

-Injectors cleaned

-probably other stuff I can’t remember.

-oh yeah, vacuum hoses done too.

The story:

I removed the O2 sensor when dropping the exhaust to fix leaky joins. Discovered, to my great delight, that someone has beaten me to gutting the cat. There’s no pipe in it so it has a really annoying resonance at certain revs

When I was putting the O2 sensor back in I noticed the cable was twisting about itself like a spastic snake.

It’s a weird mental image I know.

I got it all straightened out, took the car for a drive and all was peachy. Or so I thought. It was a short drive, less than two minutes.

Next day, warmed it up before going out and when I got in the car say the CEL on and noticed the engine sounded tougher than usual. Fumey too.

Turned it off, disconnected the battery for a bit then restarted it and same problem.

When driving it, the car was sluggish and phark mee!😳 she loved the fuel! 80km and used a bit over half a tank.

Checked codes, got 232–>running rich (no kidding) or too much fuel pressure.

I checked the signal lead lead from the O2 sensor using a DMM and saw that instead of sweeping from 0.1 - 0.9V it was bouncing around in the 0.1V range. I saw 13.5V supplied in one of the white dot heating so I guess that side of it ok.

i can’t rule out a faulty FPR. I don’t have a pressure gauge. The vacuum line has a mild odour de petrol but nothing more. Diaphragm could be stuffed.

Has as anyone else had an O2 sensor go from good to useless in these kind of circumstances?

Is it possible that during its interpretive dance if the spastic snake I’ve damaged the wiring inside the unit?

Any light shed on this will be much appreciated?

Thanks in advance.



  • We spoke about this the other day Mark,

    You mentioned you had some wiring to do because it may have snapped, what was the result?

  • Its possible for them to just stop working. Check the codes as well.

    When i converted my car from 8v to 16v, the first start came up with a CEL. The codes were indicating that the CTS was screwed, spent all week trying to diagnose and tracing wires, doing resistance checks etc etc until we eventually decided fuck it just replace the O2 sensor, and low and behold thats what the issue was.

    It was running perfect with no issues before and all of a sudden just stopped.

    Got a new one from AFI in Sydney for around 110$ iirc , cheap insurance for something that makes such a massive difference to how the car drives.

  • edited September 2019

    Wiring was good Sam as far as continuity goes. Sat the sensor in fuel for 2 nights and still no improvement.

    I think I’ll have to bite the bullet and replace it.

    Im still questioning the FPR. It looks newish but the car has always had a stumble coming down to idle when decelerating to standstill below about 20kmh. There’s always been a hesitation on takeoff too. From what I’ve read (getting my masters in google mechanics!😂) the diaphragm can harden up and be slow to redpond. I’ll check it out soon with a known good one and see how it goes.

  • I'm pretty sure the FPRs are the same between 8v and 16v as well so you shouldn't have a hard time trying to find a used one just to check

  • Often when an FPR fails, it will leak fuel into the vacuum hose to the manifold, so that's easy to check.

    o2 sensors do fail eventually, and as it's been handled recently it would be worth checking/replacing.

  • There’s no fuel leaking through the vacuum hose of the FPR although it does have a mild smell of fuel.

    Yes, the FPR is a normal 3bar item.

    Probably used across many makes and models.

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