Faulty Lambda sensor ?
Turbo Mini Forums

My car has not been used for some months but it started right up and ran fine today BUT the AFR readings only moved around 14.5 -14.7 even after a good towsing.

Never been a problem before, even after standing.

Does this indicate a faulty sensor ?

If so what should I look for as a replacement as there are so many on Ebay varying in price from over £100 to as little as £23 ?

you need to replace with the same sensor you have.

If it's a wideband, a new sensor most certainly will not be £23

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

If it's a innovate AFR gauge (everyone loves innovate at the moment) you can recalibrate it, you're meant to do it every year or so.

If it's Innovate, probably lucky if it lasts a year lol

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

The gauge is an AEM and it has lasted )so far) over 5 years and nearly 17000 miles.

It is all very well saying replace with the same, but I don,t have a clue what the specification or part number is !

No one has yet indicated whether it IS a faulty sensor or another reason ?

The only real way to tell if it the LSU (the sensor) or the controller (the electronics that work the sensor) or the gauge itself is to plug a known working LSU in.

Assuming it's the common version of the AEM where the controller and gauge are all in one package there are really only two parts you can replace anyway, the gauge/controller package or the LSU.

First thing I would do is take the LSU out of the exhaust and look at it. They are usually killed by either excessive heat, ie, mounted too close to the turbo, or carbon build-up. Both are fairly obvious visually.
The other killer is water hitting them when hot (starting a cold engine sometime after the contoller has been powered up) but that isn't obvious visually.
Then leave it out in the open air and power the thing up and (a) see if it gets hot (make sure it's on something non-flammable because they get VERY hot if they are working correctly) and (b) see if the gauge goes up to 20 plus after about 30 seconds (which it should in free air). Or you could expose it to butane or propane, cigarette lighter or plumber's torch but NOT lit, just the gas, and it should go down to 10 or less.

As for a replacement LSU you just need to know whether it is a 4.2 or 4.9 version.
The 4.9 is more common now but as you say five years it's probably a 4.2
The difference is easy to tell, post up a photo of the plug and any number of us could tell you, the plugs are obviously different (well, obvious when you have seen and used both....)

4.2 vs 4.9 is really the only difference or specification you need when searching eBay etc. if it's just the LSU but beware of cable lengths, whilst the LSUs are simply 4.2 or 4.9 the cable length will vary depending on what vehicle it was intended for.

4.9 here (I've bought from him without problem) http://www.ebay.co.uk/itm/LSU-4-9-WIDE-BAN...ZYAAOSwnDZT~Eg6

For 4.2 take your pick but they tend to be a bit more expensive as everyone is moving to 4.9 now.

They are NOT interchangeable, for a start they run at different temperatures, the control algorithm is different, and that's why Bosch made the plugs different so you can't fit the wrong one although many people are stupid enough to cut the plug off and try even though the plug contains a resistor that was calibrated at the factory to match the LSU internals and that resistor is essential for the good controllers to work (not Innovate, they don't use it hence why you have to pull the LSU out and re-calibrate it every few hours if you use Innovate.... well that is if an Innovate lasts more than a few hours....)

EDIT - typo and bit added.

Edited by Rod S on 3rd Nov, 2016.

Schrödinger's cat - so which one am I ???

Thanks Rod. Your usual incisive and complete explanation.

I owe you from way back when I had even less of a clue than I do now 11