5 replies to this topic

[serfa]

Hello,

 

Long time user of this website but first time poster - phenomenal amount of technical information on this site which has saved me countless hours and hundreds of dollars so thank you to all. Time to now hopefully contribute.

 

I have been having problems with my 1999 Mpi for a few months - sometimes won't start, sometimes rough idle, misfire at partial or full load, etc. I have pretty much cleaned all earths and sensor plugs and the car runs mostly fine however the O2 sensor is reading way off the charts. I have an ACR4 and all sensors are working (including lambda sensor heating relay which I physically sighted working myself) however the O2 readings fluctuate from 0.02 to 4.6 V. I understand that it should fluctuate between 200 and 500 mV.

 

I recently replaced the sensor (believing it to be faulty) however it gives the same readings. I do not believe it is possible for a zirconia lambda sensor to produce more than 1.0 V so how is this reading possible? Do I have a short or is my ACR4 incorrectly calibrated?

 

Thank you in advance

[Fast Ivan]

the readings indicate that its running rich, it should be averaging .45v. are you having any other symptoms that would indicate over fuelling? sooty plugs etc.

I must admit I do have my doubts about the ACR lambda voltage readout on the mpi, but I've only got mine and a mates to play with so I don't have enough info to draw any conclusions.

[serfa]

Rob, Thanks for the reply. I recently changed the plugs and they weren't overly sooty. I think my Cat may be stuffed due to some large misfires. Even if the mixture was rich would it read over 1.0 V? The readings are changing several times per second so the sensor seems to work, just impossible voltages. Would a non-operating heating element cause this?

[FlyingScot]

The sensor cannot produce over 1.0 volts. You can measure it with a multimeter either in or out of the car.

See here http://mr2.com/TEXT/O2_Sensor.html

What pod and cable are you using in your ACR 4?

FS

[serfa]

Thanks FS - that is what I thought. I am using a Rover V5 pod and universal ISO harness. Interestingly I was on the Blackbox solutions website the other day and read through their page on the MEMS 2J. It stated that for the O2 sensor, the readings should alternate above 2.025V and below 1.575 V. Link to the page is here: https://blackbox-sol...help/SM072.html 

 

This aligns with what my ACR4 is reading. Is it possible that the MEMS could amplify or convert the original voltage in order to accord with other sensor outputs (I understand that the system uses 5v as the 'baseline')? Maybe to simplify calculations, etc. If so, this means that my sensor is working correctly and just that the computer / FCR output is different.

 

Serfa

[FlyingScot]

I could be wrong, but AFAIK a voltage higher than 1.0 volt implies the sensor is no good. I am going by Rover Technical Bulletin number 13.
If you look at page 16 onwards for information.

You can download the bulletin here http://ukcooper.co.u...ems updates.pdf

My theory is that the high voltage you are seeing is either a calculated number that the MEMs unit throws out when the sensor fails or that the heater section of the sensor is leaking current into the actual measuring part of the sensor.

FS