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Super Spec Lambda signal error


geordie40

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Hi

This is mainly for those with a Super spec but all input welcome.

Just finished fitting my new exhaust and decided to look at the ECU readings (Rover Mems ECU) and car starts & runs fine but when I look at the errors its showing a Lambda signal error after a few minutes. I have tried the new one I bought and the original from old exhaust but no change , so I checked wiring back to ecu and all meters fine, next step was to check Lambda itself so with help of Youtube found how to test and when not running it sits at a few mV and when I start it jumps to around 40mV and drops when engine stops so the sensor is reading something

Could a leak in one of my new exhaust joints cause this, it doesnt sound like its blowing 

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OK, a few points first:

1.   Your statement that the sensor is reading something is not correct.  When you start the engine the ECU puts a voltage of 0.435 V across the sensor so that it subsequently swings between 0.1V and 0.9V to signify lean and rich mixtures.  So what you are seeing is the sensor NOT reading anything.

2.   it's no surprise that the car is running OK.  The car will run perfectly with a failed sensor, in fact it will run better without a sensor than with a working sensor because the Rover engineers set the default mixture to slightly rich if there is no reading from the sensor.  The downside is that will fail any emissions test.

3.   Once the engine starts the ECU gives the sensor anywhere between 1:00 min and 2:00 mins to start working.  If it doesn't get a signal by then it enters the 'limp home' mode and uses the default settings.

4.  I need to see your log file to check, but if it never starts to work then either the sensor is not working or the wiring has failed.  If, however it stutters (see picture) then it could be interference, you may have disturbed the wiring while fitting the new exhaust.  I had similar readings until I replaced the lambda signal wire (between the lambda sensor and the loom up around the alternator/water pump with shielded cable, making sure it was earthed at only one end.

Can you send me the logfile ?

Al

 

1.jpg

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It sounds like you need to check your lambda sensor wiring. When using Al's MEMS logger, if you're not getting any output at all on the lambda plot, and the status drops to 0 after a minute or so, then the ECU isn't seeing the sensor. The voltage should start at 0.44 and then start cycling between 0.1 - 0.9 as it warms up. Even a duff O2 sensor usually gives some sort of output.

When I first got my car the O2 sensor was wired incorrectly, and I've seen the same problem on many other Superspecs. Seems to be a common problem. This is the wiring from my car. You should check continuity to the ECU.

Also, you could check you're using the right type of O2 sensor for the Rover T-series, as I believe some types don't work.  Recommended is a NGK NTK OZA739-EE13 (96722) or the older OZA527-E9 (0498). Or a Bosch 0258003229.  I've used both those NGK and Bosch sensors successfully, but I've also got another Ford one that won't give any output.

1321965338_Lambda-ECUwiring.jpg.e285b6f750df1e813aeeea44b76cd7ba.jpg

 

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Thanks Al & Andy

I have put old sensor back in and hey presto, luckily I left just enough wire on the old one to use the good ole choc block connector.

A friend who has a garage that was a Rover one said they are fussy about what Lambda sensor you use and universal ones are a bit hit and miss, so its off to fleabay for a genuine one.

Only taken me all weekend but live and learn 😉

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  • 9 months later...
  • 2 weeks later...

I have wired in my lambda sensor as per Andys drawings. I have the shielded wire going from lambda to the main loom. On Andys drawing it is joined shielding to shielding part. Could I not just take the new shielded wire and connect it to earth or does it need to be connected back to the ecu?

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I think actually have a slightly different wiring setup to Andy so I'll let him comment on his.   As I see it, on his diagram he has both the signal & earth (Black/Grey) inside a shield.   I actually have them totally separate and keep them physically apart, and in turn physically separate from the heater wires.   So only the signal wire is a shielded cable and the shielding is earthed to the chassis at the Lambda end and NOT connected at the loom end.   I suspect both methods are OK, but all I can say is mine works 😀

 

lambda.jpg

Edited by alanrichey
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My understanding is that shielding should only be earthed at one end to prevent transmission of electrical noise, so it’s normally earthed back through the ECU. But yes, if you earth your new sensor shielding and keep it separate to the engine loom shield you should be ok. Unlike Al’s wiring I used 2 core shielded cable to follow the Rover wiring diagrams where both signal +ve and -ve are shielded. No idea if it makes any difference though. 

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