lambda signal cable +1.5 till 2 volts

[richardix]

Interesting question. If cold, the engine runs smooth. As soon the Lambda's are read out by the 14CUX, the engine is running rough.
When I measure the voltage between signal cable (black) and ground (white), the signal is between 1.5 and 2.5 volts. But according to all information I read, it should have a maximum of 1 volts.
So, disconnecting both lambda's and just measuring the black signal cable (with Rover gauge I swich on the fuel pump and thus the lambda's) I measure alread 0.5 Volts - 1.8 Volts. I had assumed it should be zero
I measure the same between signal and engine block or earth on the battery. So doesn't seem to be an earthing problem.
Also measured the cables itself on bad contact or a bad cable, cannot find anything.
Has anybody any clue where I have to look for ?
thanks!

[ric355]

The RV8 lambda sensors are unusual in that they are Titania type sensors (most cars use Zirconia type sensors which is what most of the information you are reading on the web is about). Titania sensors generate a 0-5v range instead of the 0-1 ish volt range you are reading about, assuming a 5v reference signal.

https://en.wikipedia.org/wiki/Oxygen_sensor#Titani...

and

http://www.tomco-inc.com/Tech_Tips/ttt20.pdf

I understand it's a 5v reference signal on the RV8.

[blitzracing]

You are getting confused here with wideband probes that are 0 to 5 volts. The 14CUX are resistive probes so have to have an external voltage source to provide an output voltage- thats what makes them "odd". The normal range is 0 volts to 1.2, but could peak at 1.8, but Ive not seen it higher. The out put voltage will go above 1.5 volts if the mixture is very rich, so for cold starts thats not unreasonable. The shift in running you hear will correspond the the ECU trying to weaken the mixture to get the probes to start switching- so you should see a 0 to about 1.2 / 1.5 volt cycling voltage at fast idle- Ive seen lots of TVRs stop cycling at normal idle so try running at say 1200 rpm if the probes don't switch. If they stick at above 1.2 volts then you have a problem with a rich mixture. The old RV8 does not like running at 14.7:1 AFR at idle, its much happier at 13.5:1 or so, but the emission control forces it to be leaner than ideal to reduce pollutants.

Dont measure anything without the probes plugged in - its meaningless. The voltages are red- 12 volt heater and lambda supply. Black- voltage out- white ground.

Edited by blitzracing on Thursday 17th May 12:35

Edited by blitzracing on Thursday 17th May 12:40

[richardix]

Thanks for all your help and information. I solved the problem.

I measured 1.6 Volts at the inlet of the CUX, during running of the engine with an engine temperature above 85 degrees (Celcius) between ground and signal cable. Probes were not cycling.

I measured the resistance between the signal cable and the ground cable of the extension cable (the cable between the probes and the connector located near the injectors, which is basically the first part of the cable. I didn't measure "infinite" between ground and signal cable, but like 10-20kOhm. So it seems that the connectors have internally a connection.

I tried to clean the connectors , but that didn't work out. At the end I by-passed the extension cable connectors and made a direct wired connection between the probes and the "first"cable . After starting the engine, I measured cycling between a few volts and 1.1 Volts. I connected Rover Gauge and I see the trim fluctuating as a sign the CUX is controlling the mixtures.

My conclusion, the connectors of the extension cable, which are hanging in the "mud" and were cleaned with "contact spray" made it even worse than the situation before the action of using contact spray. Seems to me, that care must be taken with those connectors. Especially because the voltage of the signal cable is very low with 1 volt. So a new extension cable will do.