Nanocom Lambda reading question

I've still got loads of running issues with the car after I've done the heads. Using my Nanocom to run through some values I've noticed something about my Lambda sensor readings. I thought the Lambdas switched between 0 and 5 volts. While I'm watching the values on the nanocom I'm only seeing values of 0.03 to 0.98 (ish). On the Nanocom is that actually showing true voltages ie am I only seeing between 0.03 and 0.98 volts. Or is it some type of scale?


Cheers all

doz said:

I've still got loads of running issues with the car after I've done the heads. Using my Nanocom to run through some values I've noticed something about my Lambda sensor readings. I thought the Lambdas switched between 0 and 5 volts. While I'm watching the values on the nanocom I'm only seeing values of 0.03 to 0.98 (ish). On the Nanocom is that actually showing true voltages ie am I only seeing between 0.03 and 0.98 volts. Or is it some type of scale?


Cheers all

Click to expand...

I don't know the answer to that but I would expect to see the voltage swing, if it were a scale reading it would not be 0.03 to 0.98, it would be a single number.
Have a look at the info on the BBS site.

Just done some reading. Lambdas are 0 to 1 volts. So I'm guessing I'm seeing the full scale as they swing from rich to lean.

doz said:

I've still got loads of running issues with the car after I've done the heads. Using my Nanocom to run through some values I've noticed something about my Lambda sensor readings. I thought the Lambdas switched between 0 and 5 volts. While I'm watching the values on the nanocom I'm only seeing values of 0.03 to 0.98 (ish). On the Nanocom is that actually showing true voltages ie am I only seeing between 0.03 and 0.98 volts. Or is it some type of scale?


Cheers all

Click to expand...

5 Volt sensors are usually wideband.

From your other posts I take it your P38 is a Bosch controlled Thor engine.These ran the cheaper Zirconia 0-1v sensors,so your readings are within range as the threshold for crossover is 420Mv. 0v being lean, 0.8 or 1v being rich.The engine ecu will try to widen or narrow injector pulse width each time it goes either side of the threshold to maintain an average value.
The 5 - 0v Titania sensors,(5v rich, 0v lean) fitted to earlier Gems equipped cars are not wideband sensors,they just use an applied 5v feed which they then use to switch down for rich to 0v, then back up to 5v for the lean part of the cycle.
What are the running isses with the car ?

Runs very lumpy, Multiple fault codes relating to misfires on the odd number bank. Fault codes relating to Lambda sensors. Even number Lambda is slow to switch, odd number lambda has almost stalled. However I switched Lambdas around and the misfire fault codes remain on the odd number bank. Good spark on all cylinders. Excellent compression on all cylinders, Dis packs appear OK and firing order is correct. I've removed the LPG kit which has made no difference. Had Fannymould on and off several times so no chance of air leaks. Unplugging the MAF makes no difference. Will get new Lambdas tomorrow but if that doesn't cure it I'm stuffed........ Just had a thought. When car is cold it doesn't use the Lambdas(?) Will check again tomorrow and see if it's ok when cold and gets worse as it warms. Wondering also if the odd number bank's Cat is damaged as it was run for quite sometime with damaged valves. It doesn't rattle when you knock it but still maybe blocked and causing issues. Owning a P38 is like slamming your genitals in draw everyday.

Oh and I lifted the rocker covers and cold cranked the engine to check for cam wear. All seems OK. One last thing. When I first turn the key on the engine check light comes on then goes off when I start the car. However I've had it running with both Lambda's disconnected as well as the MAF and it didn't light up.

Lambdas being slow to switch or not switching at all may be symptomatic of the mixture being miles out. The fuel trims might be miles out because of another fault. If it's missing badly in open loop (warm up cycle) then there's likely to be another fault. Do you know what the long term fuel trims are?

I chased a missfire on mine for months. Eventually located it to the ECU plug. Check it for corrosion. I would also look at the continuity to the crank sensor.

ECU has been checked as I had to remove it to get to some of the LPG wiring. Trims appear to be around 1.00 to 0.98 if I've read that right

Trims don't look too bad. Disable the ignition system then turn it over for a few seconds. Remove plugs and give em a sniff - no petrol smell - duff injector or injector not being triggered.

Right the plot thickens. New Lambdas fitted. Near side still reading stalled. So I checked all the wiring again and it's all sound. So I bridged the two data wires from the Lambdas and sure enough both start reading. So this rules out a duff ECU. So spark is good, fuel is good and the lambda in theory should read but it doesn't. I have only one last thing to try really and that's a blocked cat on the nearside. Problem is I know the rest of the exhaust is just hanging in there so I bet it all goes Pete Tong and I end up buying full system.








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Exhaust and Cats off. Back boxes full of crap. Centre section unable to tell. Cats appear OK but I can't see all the surface of them nor can tell if they're blocked. I was wondering if a Cat could block up as it heated up? Thinking out loud now if this doesn't fix it I haven't a clue what to do next.

A bit late to this thread as I found it on a google search for other stuff, and joined so I could answer. I may be able to answer at least one of the questions.
Titania lambda probes are often 0v/5v switching, but not always. However the scantool representation of them can be significantly different than what you'd see on an oscilliscope.
For example My Volvo S40 has 0v/5v switching Titania lambda sensors. On the oscilliscope observing their signal directly they go to nearly 0V for rich and 4-5volts when lean. Yup, low for rich. In the scan tool showing live data, in this case ScanXL Pro, they show as low for rich and high for lean still, but the scantool signal waveform is -
a) truncated, so you only see 0V to 1.275V portion of the actual waveform, and,
b) isn't sometimes an accurate representation of the finer details of the real signal due to the update rate of the scantool, even running single PID updates.

Have you tried doing a running compression test and better still with a pressure transducer viewable on a scope?

How long was the LPG kitted to it and which make model was it? Active or passive injectors?

Just reading the rest of your post. With a scope you can see if the cat is bad by looking at the front & rear O2 sensors during and after a propane test.

From what I read cats can go into melt down through excessive heat.

An exhaust back pressure test would tell you if the cat was blocked.

Take a look at ScannerDanner on you tube. I've learned a ton of stuff from those videos.

Cheers for the info Pete. I only have one probe per a bank so can't do the before and after test. I'm not 100% sure but Thor P38's don't use Titania however I can't vouch at all for the Gems motor however they do seem to swing from 0-5 volts where as the Thor is 0-1. 0 being lean and 1 rich. LPG kit was fully sequential system. Had been fitted in 2006 and had covered nearly 80k miles. At the moment I've junked it and am running on Petrol. I will have to refit a LPG kit at some point but I will be fitting a STAG system next time purely as it is a system I have fitted to my car in the past and have been involved in several installations on other cars. Mind you this has always been on big old VX's not RR's. The car is now running sweet without issue however I can't say what I actually did to fix it. Possibilities are, a battery which dropped to 5v when cranking, Air leak which took up when the gaskets expanded (probably the best idea as I used metal gaskets not composite ones when I redid the inlet) or the fuel trims were so buggered up from the LPG and shagged inlet valves it took a while for the ECU to get a grip again. So I'll keep on running her as she's OK and see what happens.

Little update, Car has covered 150 miles now in all weathers and is excellent. Runs spot on, however I must get it back on gas before it bankrupts me