RR Classic LPG Lambda (oxygen) sensor readings

[TerryG]

I have a KME Bingo S kit with an OMVL R90/E Vaporiser fitted to my 4.6 Range Rover Classic.
As part of my engine and vaporiser upgrade I bought the cable to plug the kit into my laptop and reconfigure it.
The thing that is concerning me at the moment is the reading from the Lambda Sensor that the kit is wired up to. When the engine is idling or if i gently blip the throttle in neutral up to about 2000 rpm the lambda probe reads 0. If i take it above 2000 rpm or when i am driving along at a constant speed it seems to bounce about in the middle of the gauge as it should but it has periodic dropouts to 0 volts. If i boot it then it goes up to the top of the gauge at a steady 0.9-1v with no dropouts. Does anybody know if this is normal for titania lambda sensors or if it is an indicator of a failing sensor?

[Gilbertd]

I'd say it's on it's way out. If it's a 3 wire generic, there have been numerous failures with the Chinese made aftermarket ones. I had one that did exactly as you describe on my Saab.

A 4.6 Classic? I thought the biggest engine fitted to the Classic was the 4.2 in the LSE with all the others having the 3.9?

[rossko]

Guessing this is the standard 3-wire 3.9/4.2 sensor, it might be poorly. Or it might be telling the truth. Does it work much the same way on either fuel? How confident are you the fuelling (petrol map) is actually correct for the 4.6? Air or manifold leaks? Sensors will behave like that if cooling off too, check that the sensor heater feed circuit is working.

[TerryG]

Hi,
The biggest standard classic is indeed the LSE with a 4.2 from 1992-1995. This is a 1994 LSE and was a 4.2 until 6 weeks ago. with 150,000 miles on the clock the engine was well past it's best (down to 90psi of compression) so i swapped it out for a recon 4.6.
The sensors are factory LR items but there is no record of them ever having been replaced (i have a FSH for the car).
It does the same thing on both petrol and gas. I will check for a manifold leak tomorrow. i have new gaskets on but the exhaust is definitely tired. the cats have been "removed" at some point in the past so there might be a leak there.
The petrol fuel map is definitely not ideal for the 4.6 but is close enough to run without causing any problems.

[rossko]

The petrol fuel map is definitely not ideal for the 4.6 but is close enough to run without causing any problems.

mm, I'd agree it won't be far wrong because of the MAF control ... but if it is little out here and there it's likely to look just as described?? The sensor can only report 'lean', not distinguish 'very lean' from 'just a tiny tad lean'. You might take a view if the behaviour is consistent (external causes) or truly random (possibly sensors). There are two sensors, how do they compare?

To set against that, most manufacturers expect a sensor life of around 60,000 miles so they are on borrowed time and at least more sluggish than they should be.

Another thought is worn throttle position sensor causing the map to go into idle or overrun areas. Could meter for dead spots across the TPS range.

Have you kept the distributor? Gapped the plugs to suit that, not the 'book' 4.6 setting?

[TerryG]

Because it is doing the same thing on petrol and gas i was assuming there wasn't a fault with either fuel system but it was either "normal" or duff sensors.
I have the front panel from my origional serpentine 4.2 so i have a distributor and Lucas ECU rather than GEMS or Megasquirt.
I'll get my soldering iron out and try connecting the ECU to the other sensor and see what it shows when I check the exhaust for leaks. I'll check the TPS too hopefully I'll get a chance to investigate it tonight.
Fingers crossed it is something daft rather than something expencive!
Thanks all.

[TerryG]

I have checked my TPS and it is OK, both lambdas are doing the same thing and the heaters have the correct impedance and are getting power. There are no exhaust leeks so i am leaning towards this being "normal". I have adjusted the Idle mix on the Vapouriser to get the Lambdas moving off 0 when left at ldle and run an auto configure on the LPG kit to re-tune it. The idle screw is almost all the way out (it actually fell out while i was fiddling and i had to put it back in 1 turn)

Here are some screen dumps of what my LPG kit says is going on:
Petrol at idle:


LPG at idle:


Petrol at 2500rpm:


LPG at 2500rpm:


Do these look like i am worrying about nothing?