Lambda wiring mod

[Stunned Monkey]

Sagi Badger said:

3 wire sensors stay as they are.

The 3 wire sensors benefit just as much from having a decent ground on their heaters as the 4-wire sensors.

Yes, cut the loom north of the connector on the wire corresponding with the white from the sensor, and ground it well. Be careful with which wire is which because the rubber grommet on the plug can be twisted in so the wires don't line up.

I've done this to my Cerbera and saw an immediate improvement.

The reason for the problems is that the ground for the heating elements is taken via the ECU, and the loom is long enough that this can lift the ground at the ECU causing it to mis-read the output. The lambda sensor is unique in taking a 12v feed, all the other sensors that use a supply run off an isolated 5V

Sagi Badger said:

The lambdas generate a very small voltage so any interference causes problems.

Titania sensors don't output a voltage, they are resistive and exhibit a very fast change in state between low and high resistance across stochiometry. They can be implemented however the ECU manufacturer felt like on the day they designed the system. MBE saw fit to ground them via a biasing resistor in the ECU and it is the voltage across this that the ECU reads (and hence why it goes skew-wiff when the ground drifts) - hence the unique output given in the software of 0-2v.

[Sagi Badger]

I am not clever enough to quote but I am correctly corrected by Stunned Monkey, although I did understand that we were not generating voltage and were in fact changing resistance, my terminology was incorrect, the point being it is a small voltage in a long cable.

What I don't understand is earthing the heater - ve giving an improvement. Can you explain further, where you earthed it and did you keep the wire continuous in the loom or break it to make the connection? The ECU earth is on the back of the block so did you piggy back this?

Does anyone recall who on PH is working on an interface to input UEGO's into the MBE, I have a pair fitted in my decat pipes and would like to use these to control fuel. Interesting is that AFR stays 13.5 to 14.7.

J

[johnboy111s]

Yes this is what I am not sure about dose the loom wires stay intacked or do you sever the wire altogether and earth the white wire coming from the sensor. I really need an idiots guide and a PIC so I don't fry something.

[Stunned Monkey]

Actually doing it either way should be fine if you ground to the engine. If like me you ground to the battery, you need to cut the wire in to protect the ECU if the main engine ground ever starts to get resistive.

Sagi Badger said:

I

What I don't understand is earthing the heater - ve giving an improvement.

Correcting an oversight in the loom design. The heaters draw quite a lot of current and are grounded at the ECU (this is the mistake). This means that the slightest resistance in the ground path for the ECU causes an effective increasing of the value of the biasing resistor across which the lambda reading is taken.

NB I can not fully explain the mechanism because I've not studied the circuit diagram (anyone got one?), but it is an observable effect

[mk1fan]

Seeing has we have a few knowledgeable people on this thread I have a question.

I have a spare set of manifolds that I bought to get ceramic coated. This was done to avoid 'down time' of the car. The manifolds are an early set with the smaller boss for a 3-wire lambda probe. Can I buy 3-wire sensors and wire them into the 4-wire loom.

The mod that started this thread suggests this is possible as the 3-wire is self earthed on the manifold.

I have m18 bosses to fit to the manifolds but it would simpler to just fit 3-wire sensors if that is going be the resultant wiring after doing the earth mod.

Please help an idiot.

ETA

I just read the lambda wiring link and seen that there is a m12 threaded 4-wire available. Perhaps I should just buy a pair of them and then do the wiring mod. Would be easier me thinks.

Edited by mk1fan on Tuesday 3rd March 19:05

[Stunned Monkey]

mk1fan said:

Seeing has we have a few knowledgeable people on this thread I have a question.

I have a spare set of manifolds that I bought to get ceramic coated. This was done to avoid 'down time' of the car. The manifolds are an early set with the smaller boss for a 3-wire lambda probe. Can I buy 3-wire sensors and wire them into the 4-wire loom.

The mod that started this thread suggests this is possible as the 3-wire is self earthed on the manifold.

I have m18 bosses to fit to the manifolds but it would simpler to just fit 3-wire sensors if that is going be the resultant wiring after doing the earth mod.

Please help an idiot.

ETA

I just read the lambda wiring link and seen that there is a m12 threaded 4-wire available. Perhaps I should just buy a pair of them and then do the wiring mod. Would be easier me thinks.

Edited by mk1fan on Tuesday 3rd March 19:05

You can do either

[mk1fan]

Thanks for you help.

[KenInOntario]

PetrolHeadPete said:

Over the year's i've tried various things to improve low throttle stability (aka "shunting"). Bodies- bearing mods, pot mods, better tune / balance etc. Even tried a new coil pack etc (the latter made no diff btw). The body mods made the biggest improvement...got close to good, but when watching the consistency of the adaptaives at idle and at very low throttle opeings (@1500 rpm you can hardly see that you've moved the butterflies !) I realised I was wasting my time...you could change the reading from lovely and stable to +/-10% different just by a brief fast idle spell (2K-2.5K ish) and then release back to idle -> adaptives would hunt to a diffent point (and hence be wrong)...eventually returning to close to where they started (meaning several minutes of dodgey running). I've had several experiences in the past where after an M-way blast, then come off to a traffic queue, the engine wanted to die on light throttle application...only to correct itself a few minutes later (would idle fine but was clearly hopelessly lean as you pressed the throttle to creep forward)

Finally tried the lambda ground mod...what a difference. Stable, easy to drive at low revs, nice throttle pick up, predictability of throttle response after a long M-way stretch etc etc.

If you haven't had it done...its a no brainer.

Any chance of a few photos? I had to splice my sensors in, so already have as access to the ground wires. But a few photos would be helpful.

[gkronberg]

Hi all
Can I ask someone here to help out a complete idiot ( idiots guide to grounding a Lambda )

Maybe a diagram or two ?

Pm me if you have to.

Rebuilt engine chasing high adaptive %
TP’s balanced ...
No air leaks on TP’s
New leads

Getting 15.2% at idle for TP’s
Adaptives start low but go up to 30%
Lambda’s at 0.0 but you see a flicker now and then
Ohms 2. Something

We had an issue with the lambda’s earlier as they were all over the place . Noted my year 2000 appears to have 4 wires and we have 3 wire lambdas . One lambda was dead so we replaced with a near new from a friends cerbera v8 ( spare )
Not sure if we rewired correctly?

Now we are thinking this earthing might help but being an idiot need images or pictures ...

Hope you can help

[PetrolHeadPete]

Test the lambdas using a bit of carb cleaner puffed into a throttle...the lambda on that bank should go high within a second and hold there for a couple. If the adaptives continue to head north and the lambdas are proven working, you must have too much air relative to the amount of fuel-> so either too much of the former, or too little of the latter. Also try putting you hand over one throttle mouth and see what happens...should go rich i.e. lambda will go high until adaptive pulls it back down. Have you proved that correct lambda is wired to correct bank ?

The wiring mod is "finessing" only...wont help with something significant like you describe (unless of course there is a big voltage offset in the lambda path causing it to offset negatively (*very* unlikely imo)).

Try the carb cleaner test