AFR Gauge

[e21Mark]

I run an air / fuel ratio gauge in my M3 and the usual reading is around the 14.4 to 14.8 range. On lift off (if lifting off whilst approaching a corner, whilst going down hill) the gauge usually reads LEAN, which as the throttle is then closed, I assume is correct. Recently however, I note the gauge no longer changes the display on lifting off the throttle pedal. I've scrolled through the functions on the gauge, but it still just reads the usual AF ratio. (I hope I've explained this clearly enough?)

The wideband lamda AFR gauge in question is a Tech Edge LA1.

Please excuse the lack of knowledge my end. This is the first car I've owned with such a gauge and I generally just use it to make sure the mixture remains in what I am told, is the safe range.

Does the failing to show as LEAN on overrun point to a fault with the lambda sensor, or am I worrying over nothing? It just seems odd, that it simply stopped displaying this.

Thanks in advance.

[e21Mark]

Steve - the gauge stays at the usual range of 14.4 to 14.8, which I was told was about the correct level "on throttle" ?

I'll look into the potential for a TPS issue. I know next to nothing about Alpha N but have a few places to mail for advice. There has been a slight hesitation issue recently, which was mostly sorted by replacing parts on the ignition side, but could also suggest the TPS was deteriorating. Could a fault with the lambda sensor cause the same issues?

Thanks in advance.

[e21Mark]

Thanks Steve. I've just been reading the instruction PDF from Maxx and I'm thinking the TPS or the wiring was disturbed recently, when the exhaust manifold studs and cam cover gaskets were replaced?

I feel like I'm on the correct path towards sorting this now anyway. I'll let you know how I get on.

[e21Mark]

Pumaracing said:

e21Mark said:

Could a fault with the lambda sensor cause the same issues?

No. The problem is as I've already described.

Thanks. I think I'm going to replace the TPS as a matter of course anyway, as it's a few years old now.

[e21Mark]

Put a meter on the TPS yesterday and got a reading but am I right in thinking it acts as a potentiometer in this application?

I've been trying to source a new one, but neither BMW or Bosch have stock. It could be a month minimum, so still searching or else it'll be an overseas supplier.

After messing with it yesterday, it cured itself briefly but issue soon returned.

I'm at Santa Pod today so long shot, might find a used one as a temp' fix?

[e21Mark]

I'm trying not to worry about the gauge (honestly) but it's now reading HEAT, which I've not seen before. The poor running is still there but I'm going to replace the TPS anyway. Could there also be a problem with the lambda? Hence the HEAT reading?

[e21Mark]

I'm guessing / hoping that the sensor issue and rough running are both lambda related. I'm just trying to identify which lambda it is and will replace it anyway.

[e21Mark]

Thank you to all who've responded. I really appreciate all your help as till now, my usual cars have nothing more complicated than points!

Anyway, there should be a new sensor awaiting collection shortly and I bought a TPS as one presented itself. At least I'll then know when these parts were replaced, instead of having to hazard a guess. I'll let you know how I get on, once I've fitted them.

[e21Mark]

TPS replaced (it wasn't hugely expensive and as I had it anyway) and a marked improvement in throttle response. Still some hesitation though and clearly over fuelled judging by the popping and banging on overrun. New lambda (Bosch part to replace pattern item) and over fuelling cured. Still hesitating intermittently though. A quick check of the rear fuel filter and it looks decidedly "second hand". Decided to replace it and all is well once more. I realise the TPS might have been an avoidable expense, but the condition of the fuel filter typifies why I wanted to work my way through the car and replace these parts. At least now I know exactly when all these parts were fitted and can be confident the car is less likely to fail, down to neglect.

Many thanks for all your input chaps. Much appreciated.

[e21Mark]

The saga continues...

As I wanted to get everything in good order, I replaced pretty much everything on the ignition side. I also replaced the TPS, as already mentioned, where things appeared to have returned to normal. Unfortunately it didn't last for long though and the rough running is now between 2 & 3k revs, whilst under load. The AFR gauge has started to read HEAT pretty much constantly.

I checked the fuel pressure and found the filter was pretty much blocked, so replaced it. I have also bought a new lambda sensor, which I'll be fitting tomorrow morning.

I know that E30 M3's running Alpha N can often suffer some flat spots but this has only started recently. Is it possible for maps to be corrupted in any way? Am I being misled by the odd AFR gauge readings, or do they point to a fault somewhere, that would explain the rough running?

Clutching at straws, I was caught out and bought my last fuel from Tesco. I have heard that other people suffered poor running after filling up with Tesco fuel, so am topping up with Esso just in case.

Finally, can anyone advise on the lead needed to connect a laptop and check the map?

Thanks in advance.

[e21Mark]

Thanks. I've just posted a thread there, so fingers crossed.

[e21Mark]

It turned out to be contaminated fuel. I replaced pretty much every sensor and ignition component, with little or no improvement. As a final straw we drained the tank and the fuel looked decidedly suspect. Once replaced, it cleared and now runs better than ever. The AFR gauge is also working perfectly.