Lambda readings

Daz

A m8's coupe turbo has started playing up today, its a strange one, he fitted a sub and disconnected the battery + terminal , and it fell back down onto the post and arked a bit....now since this happened the car has started to bog down on hard throttle,
So he paid a visit 2 night, went about checking items, he'd already tried a new afm on it and it the same, so he's refiited the old one, swapped a few items from alys car ( coil pack/map sensor/boost solenoids etc) and its still the same....so fired the laptop up.

Now the only thing i can see that maybe dodgey from readings is the front llambda.

on idle its

fluctating 98 - 764mv
heater is on and off constantly

2nd sensor

45mv stable
heater inactive

b1 long term fuel trim -1%
b1 short term fuel trim between 0 and -2%

its also smelling very rich from the exhaust...

do those readings sound right......As tho i've been a mechanic for 20 years doesnt mean i know everything( :lol: ) and i never willl

MikeS

need to check front lambda on idle and fast idle when warm to truely find out if it is buggered

should pulse .1 - .9volts then zig zag at around 3k rpm [when warm]

overfueling then look for air leaks first before looking at afm & lambda

symptoms of failing front lambda is like an electrical misfire at low revs when planting it, just over fueling really

does sound like air leak post AFM - worth looking for cracked hoses

Daz

its very boggy and misfirey ish at low revs.....now to add summa telse to the equaution he had a total decat fitted 2 weeks ago....no eml issues at all, but wondering if it killed the sensor....

MikeS

just unplug front lambda sensor

it will give default value of .45 volts should show a difference in response if it is lambda related before it throws up a code

it should go into closed loop before throwing up a code - wont have long though

it is rare for front lambdas to throw up a code before they start misbehaving

Daz

Unplugged the front one....threw up a code as soon as i unplugged the front one mike....and made no differnece in the running...still boggy....

MikeS

if it is pulsing like this at idle or similar then it is fine

sign of a faulty lambda is when it is not pulsing like this and sticks at certain voltages for seconds at a time or doesn't respond to RPM

what is the front lambda average say over a few minutes cos simply pulsing up and down wont give a true reflection on the fueling

Daz

waveform is alot closer than that mike....changing less than every second. cant remeber the average of the top of my head...but somewhere bewtween 98 and 764...

MikeS

then the lambda is healthy

sounds like it is pulsing every second 🙂

i dont think it is lambda related on what information u have told me

it pulsing to above .75 volts though it should go above .8 but that would not mean it is faulty and it is pulsing below .1 volts

all looks normal

short term fuel trim is showing rich condition as it not going above 0

you want to see the short term fuel trim pulsing between _ & + when in closed loop

ltft = long term fuel trim

LTFT Adaptation Value negative (-), 0<LTFT<1 (ECU thinks mixture is rich)
Too much fuel, Lack of air.
This could be due to leaking injector for example or faulty air flow meter

deffo fuel system related and you are correct when the car is overfueling

Daz

hmmmmm.... he changed the afm as reccomended by his local garage....but made no diff.....so he took it back off.... got opcom coming shortly so will try again once it arrives as my software kept hanging all the time....cheers for the input mike....will report back as and when

MikeS

concerning shorter term fuel trim if it is negative all the time it can be caused by high exhaust back pressure, or stuck open injectors

personally i be looking at the whole fuel system in terms of CTS, MAP, AFM, Lambdas, air temp sensor

i take it no codes yet ?

Daz

No egr on the z20lets ....did think of the temp sensor but after he had gone...

MikeS

yeh i removed egr valve lol cos i googled it haha 🙂

MikeS

AFM is common fault on the z20let

apparently your suppose to use the uprated vxr one instead

Daz

To use the vxr one it needs to be mapped to the car apparently....as its 80mm as opposed to 70mm on the zlet.... seems odd to me this has happened since the + batt terminal fell back and arked to the post....

He did have a code. which was the tps but he that cleared b4 he came to see me and it hasnt reapeared...

MikeS

try swapping over the ecu's m8 next time u see him

he could of damaged the ecu

as for TPS then that measures the throttle position at idle and calculates engine load along with MAP sensor to adjust injector pulses - i.e fueling

Daz

Wud have to swap the immob etc aswell then mike....and i dont fink my mrs wud let me go that far in taking her car apart lol.....will report back when i hear more.....

MikeS

personally i wouldnt though daz as you dont know what state the leccys are in

it is not uncommon for ECU problems after fitting in subs & amps as they are not fused or earthed correctly

MikeS

i just remember a member on here with a p0300 code that appeared after he fitted an amp & sub

could not get down to the root of the problem though he replaced every sensor like i have and many other members have done lol

king larry with p0300 found out it was an ecu problem

Daz

it cud well have spiked the ecu mike,,,,did tell him that,,,

Daz

He tetx me today to say that when the car is cold it drives as normal, its only when it gets up to temp that it has issues