Dumbass lambda sensor question

[Helz]

Because I'm so good at them

Last week my frontpipe was fuzzing slightly, a corner of the flexi section had come loose, but the car was still performing as normal and getting 50-55mpg. Said frontpipe has now been fixed, I'm now getting 35-40mpg. I reckon the garage might have been a tad rough with the sensor when getting it out to change the frontpipe (the boss was off, it was left to a lackey) and that's why it's not working any more and why it's using so much petrol. Garage reckons it wasn't working before (guessing, they haven't done a diagnostic). Well if it wasn't working before, surely the mpg wouldn't change so drastically as the lambda sensor (or any other sensor that did or did not happen to be working) wouldn't have been able to detect any change in air concentration/ flow? And surely I wouldn't have got such good economy before? Or am I being a div and missed something?

Anyway, this is just a question about the principle of it because I'm not going to argue with them over £20, just want to know if I happen to be likely to be right. So i can avoid them By the way, for any potential customers, it's NOT Jordan's dad as he's away at the moment (and probably wouldn't have broken it).

 

[e_cag]

IMHO you are right. Last Saturday i got lambda sensor of my Palio changed. Mileage increased noticeably. About your story, everything seems so clear to me.

 

[T14086]

Not really easy to break even during removal,however you have to remember there is a heating element inside which could break if dropped.Alot of lambda faults are due to failure of the heater element,the rest are normally 'out of range/limit' faults which can indicate a fault elsewhere(air leak etc)...a simple cheap 'deflection' multimeter can diagnose if sensor is at fault or not.

 

[Biz]

^ - as above

I think your injection system is constantly running in "open-loop" mode

Basiclly means the ECU isnt re-using the values that are constantly sent from the lambda sensor as it sounds like its broke

Broke lambda = No values = not as good mpg

You lost? lol

 

[Helz]

Oh I know it's likely broken now I was just thinking was garage man right when he said it was likely broken before? I think not........

 

[jug]

if you had 50-55mpg before and only 35-40mpg now then it is obvious that something has gone wrong, and that it definately wasnt wrong before. i'd say it is very likely to be the lambda.

maybe they havent reconnected it, or dmaaged the wire (pulled on it). i'd check the sensor is connected and the wiring is ok, if you open the engine bay and look for the small plastic cover in the middle of the bay right at the back near the windscreen you'll see there are 2 knobs you can loosen to allow the cover to be pulled off. under the cover the lanbda sensor wiring connector should be there, if there's only one side of it with nothing plugged in BINGO :idea:, if it looks as though its been pulled on and has damaged wires thats also a good clue.

you should see a white wire going down from under the cover to the lambda sensor, check for it, and check it doesnt look damaged at the connector or sensor. i can imagine the garage disconnecting the lambda sensor and leaving it dangling while they did the exhaust, leaving it in an easy place to get caught on something and pulled. i've done it before, so have other people i know so maybe its happened.

 

[Helz]

Thanks guys Just got the car back tonight so I haven't had chance to assess economy yet, but they've sorted something as it's now passed MOT on emissions (which it wasn't before) I've been charged nothing so as you suggest Jug, either something was left unplugged or they've fitted a new one FOC for them having broken it. Thanks for you opinions, I just wanted that nice smug feeling that I was right and said garage were talking rubbish......