P0420 sports cat - read pls !

MikeS

Oki I knew this was going to happen and i have had the dreaded p0420 code as a result of the sports cat , i was going about 90 mph then came to idle and the light kicked in

now i also noticed that once the voltage of the rear lambda started reading rich averaging over .5 volts the front lambda was trying to compensate by leaning the mixture below .45 volts

now a lot of people say the rear does nothing but monitor the cat efficiency however i got proof with the support of live data graphs showing the front lambda compensating the rich readings from the rear lambda by way of leaning the mixture, i watched the front lambda lean the mixture and noticed how the rear lambda responded by lowering the average reading then once at the specified average of .45 the front resumed normal duty and once more the rear lambda voltages started to creep up again until the front lambda started going lean, it is like a cycle to stop high emissions going past the rear lambda

this is quite serious stuff if proven meaning that sports cat are messing up the performance of the engine by way of high emissions flow going past the rear lambda

love to hear your views

this could also prove my theory that sdbulters overfueling issue was a result of his rear lambda showing extreme lean averages

Muncher83

I'm not sure I agree, I know Jon at Courtenay has spoken to the guy who calibrated the second lambda, I don't think it provides any feedback in that manner at all.

MikeS

well tomorrow i am going to unplug the rear lambda to set the reference voltage at .45 volts [ideal average volts for lambda] and monitor the front lambda sensor readings

there is no reason for the front lambda to go from averaging rich to averaging lean at minutes at a time other than it being faulty

now for it to be running rich then it is usual a faulty map / maf sensor or it is simply overfueling [ fuel pressure]- all my sensors are showing correct stable readouts

for it to run lean it might be missing / air leaks

now at 90C when idle the front lambda should not average outside .5 volts otherwise it is overfueling and it should not drop below .45 otherwise it is lean

MikeS

he hasnt calibrated the lambda

all he has done is change the threshold values on the ecu to like desensitize it from throwing up the code

there is no way u can change the readout of a lambda sensor

sdbutler10

im with you mike. why else would the companys use 2 lambdar sensors? its to help the emmisions and help the car run right on fueling.
as with mine my front sensor is reading rich all the time but drops to lean quick to go back up but my rear sensor is always reading lean!
that is why my car is overfueling on ticker over as the car thinks it running ok but really it not it just has a faulty sensor so it just keeps chucking in the fuel.
as soon as my new sensor turns up i will check again my more than 90% sure that this is going to sort it.

Sjdickso

This is intresting reading, Keep us up to date on your progress Mike.

Also do you think that a 02 sim will stop this?

Does this situation only happen once the code has been thrown up and the EML is on?

MikeS

the 02 sims i have seen are pretty crude, they just drop the voltage pulsing to say like .1 volts meaning very lean

now this is a big IF but if sdbutler is having problems with overfueling as a result of his lean pulsing rear lambda then an o2 simulator needs to be pulsing constant between .3 volts and .6 volts IF the PCM uses both lambdas for optimized fueling

quite a few manufacturers such as audi use both lambdas concerning pcm air / fuel mixtures

MikeS

been informed that the rear lambda should stay steady between .68 volts and .7 volts when at operating temps

sounds like my front lambda could be buggered considering it was bent by the free flowing pre cat

MikeS

i am going to get an o2 simulator and see how the front responds

Sjdickso

Are you going to get a new front sensor and carry on the testing?

Sjdickso

MikeS said:
i am going to get an o2 simulator and see how the front responds

Have you decided which 02 sensor sim you are getting?

what about this one?

http://www.eliseparts.com/products.php?product=300

MikeS

i might well do that
🙂

MikeS

here is two images

one is a comparision of both working lambdas and the other image is a reference for the engine rpm

the startling finds was the voltage of the rear lambda when under full load and high revs, it is showing very rich

also you will notice the voltage of rear lambda after blasting it and settling down to around .65 - .7 which i been told is correct

dont understand from looking at that why p0420 would pop up unless it goes over .8 volts for rear lambda

the o2 simulator i gone for is from

http://www.o2simulator.com/
Universal o2 simulator single output

if u havent noticed i think my rear lambda is shot as it is not pulsing very well and it is dropping voltage at idle then flying back up for no reason - looks to me like resistance is gone

MikeS

The most common type of Lambda sensor, and the type used on all Omegas, is termed a "narrow band" sensor. This is because it measures the fuel mixture over a very narrow operating region centred around the chemically correct mixture. Such a sensor can be viewed as indicating whether the mixture is "lean" (too little fuel) or "rich" (too much fuel) with respect to the chemically correct mixture. Basically, the petrol ECU will use the output of the lambda sensors to adjust the quantity of fuel injected (the injector duration) so that the lambda sensors are always at the point of switching between "lean" and "rich", so the average mixture is correct.

It does this by maintaining a variable called a "fuel trim" for each bank of the engine (on a V6 - just the one on a 4 pot). If the lambda sensor reads "lean" it will increment the fuel trim periodically. If it reads "rich" it will decrement it. The fuel value from the map is multiplied by the fuel trim before calculating the injector duration so the fuel trim has a negative feedback effect, adjusting the injector duration read from the fuel map to keep the mixture correct.

The fuel trim is used to compensate for variations between engines, fuels, injectors, etc. to ensure the mixture is always right for the catalytic converters. However, it has a maximum range based on how much trim would normally be expected. If the fuel trim exceeds a threshold programmed into the ECU, a fault code is stored and the EML comes on.

now if a buggered rear lambda isnt pulsing right or being lazy then surely it will affect fuel trims based on what the ecu feels is necessary to stop the cat from being shagged thus affecting fueling

hence why i think sdbutlers overfueling is a result of incorrect fuel trims based on the lean voltage by his rear lambda trying to protect his cat

sdbutler10

it looks good mate. im still convinced that is my problem with my car.

MikeS

i forgot to mention i was trying out a coil pack i got 2nd hand yesterday and since i replaced it back to my old one and reset the codes and given it a blast the p0420 code hasnt come back

but i am still not happy with the pulse of the 2nd lambda

SriSte

Theres definitely something happening to the fuelling, mine now sometimes pops through the exhaust on high rpm gearchanges,
Not always though. And my mileage per tank seems quite random.

I don't have any obd software that remembers values unfortunately, and its not safe watching the laptop lol

MikeS

so it is suppose to sit under .5 volts when operating normally to get a .45 average

i think the p0420 is due to the high averages of the rear lambda which i initially thought anyway, replacing the rear lambda will prob help but not stop the fault code appearing if you start booting your car about for long periods, from looking at my graph the rear lambda voltage increases around 3500 revs and max emissions around 4500 revs based on the fuel mapping

i would go down the 02 simulator route imo to ensure that your get optimum fueling at all times, i have spoken to 02simulator.com and their simulators work on pulsing .3 - .6 volts and not a static voltage of .1 volts so effectively your getting the simulation of a healthy fuel / air setup

MikeS

oki i fitted the 02 simulator

i will post up a how to guide and photos of it in action plus how it was wired up

give me a few days 🙂

Sjdickso

MikeS said:
oki i fitted the 02 simulator

i will post up a how to guide and photos of it in action plus how it was wired up

give me a few days 🙂

Look forward to seeing the results and having a look through the how to.