I'm suspecting I have an upstream Lambda senor that is faulty, poor MPG and very high emissions CO,HC, and lambda. Left/2nd bank is running lean with lots of black soot in the exhaust.

So I purchased and OBD2 reader from ebay which will be delivered Wednesday. I hoping to test my feul trims throw the results on here and some-one that knows about them can tell me if it is a lambda thats gone.

So first question, how do I test my trims, what state does the engine need to be in - idling/revved and hot/cold engine?

Thanks for your help.

 

Did you reset the ECU ( fuel-trims ) after cats + catback change? You can do it by disconnecting the battery for 30min. Then drive with different rpms ( not WOT ) for 50-100miles. Then look at what fuel trims do you see.

 

I believe the bloke that put my cats on disconnected the battery for a few hours while fitting the cats, not sure why he would do this but he went in the boot and said this was what he was doing. The MPG is noticeably worse after he has fitted the cats......

To summarise take fuel trims after car has been on a good run without switching off?

 

Here you can see my O2 Sensors output voltage. Bank2 is ok. Voltage goes up and down within right range. Bank1 sensor is faulty. The voltage is stable. . Both sensors were 10K miles old orginal Denso ones.
Here you can see, that bank1 was running lean at idle:
Fuel trims - YouTube
Repaling the bank1 sensor fixed the problem.

 

Ok in a couple of hours I'll put up my readings, in the mean time what do I need to be looking for..... Stable readings or up and down? What is a sign of a faulty Lambda or airleak?

Going to test STFT & LTFT @ Idle and 2500rpm

 

The reading from the sensor should fluctuate around the 450mV centerline. If it stays at one position or changes very slowly you likely have a bad one.

I wouldn't bother looking at the fuel trims until you've remedied the sensor issue.......

good luck!

 

Right here we go, they don't make much sense to me so I hope they do to you.

No error codes in ECU.
Car failing emissions on all three test OC,HC, and lambda. Very poor fuel consumption (16mpg average, max 20MPG - careful driving).

Open loop: IDLE
Bank 1 - LTFT=14.8 STFT=19.5
Bank 2 - LTFT=14.8 STFT=19.5
Both fuel trims never moved.

Open loop: 2500RPM
Bank 1 - LTFT=14.8 STFT=19.5
Bank 2 - LTFT=14.8 STFT=19.5
However I noticed when letting off the pedal @ 2500RPM both STFT's dropped down to "0" and slowly climbed back up to 19.5, is this normal?

Here's a couple of pictures of the results:

 

Your bank 1 lambda sensor is bad...

 

Ok excellent, can you tell me how you work that out for future reference.

Also the readings are the same on bank 2, is this not bad as well?

 

Those values look awful to me. I question the accuracy of the output.
Check out the link below for a good discussion on fuel trims.

https://www.jaguarforums.com/forum/g...ed-quiz-49317/

 

If it's stuck in open loop it's in such pain it can't do proper fuelling (it would be closed loop).

It may be trying to flag codes but unsure what's wrong so can't guess what to flag.

Any recent work is #1 suspect.

Open loop means it's not using any more sensors that it has to as it can't trust the values. May not be using the O2s. Probably has to trust one or both of TPS & MAF. Will aim to run rich as lean damages engines. It's aims are: if possible keep engine running at all no matter how badly, protect very expensive parts (engine & cats).

If you want to DIY this you need to study lots of JTIS and read how closed loop is meant to work (any articles about modern engines will do, keep reading till you get it). I'd be using DVOM to measure O2s I think.

 

I’ve tested my reader in a Civic Fn2 this morning and it read the fuel trims fine, up and down but stable.

I think I might have told you wrong, it was perhaps in closed loop, when the car was cold there was a message that perhaps said Open loop, then as it got warmer the message turned to now using O2 sensors for mixture (I defiantly remember that part as it got warmer). I was too busy trying to take note of the fuel trims I didn’t take much noticed of it.

If the readings are correct am I right in saying both O2 sensors are dead? Or big air leak? Isnt it impossible to have both ST and LT trims high at the same time and not moving.

 

Fuel trims are just a factor by which the computer adjusts the fuelling to the cylinders on each bank. The computer depends on correct readings from the lambda (O2) sensors to make these adjustments. Your fuel trims will never be right if the lambda sensors are faulty.

The video shows a non responsive sensor on bank one. That alone will keep the computer from adjusting things properly. My recommendation is to replace both upstream lambda sensors (position 1 on both banks) before even thinking about the long term and short term fuel trims....

After correcting the sensor issue, look closely for intake and exhaust leaks. The obvious ones will be gaskets but even things like a throttle body shaft leak can affect these readings...

Good luck!

 

The video above isnt mine or my car some-one just posted it as an example, the pictures above from the Torque app are...

 

It is strange that your fuel trims are exactly the same at idle and at 2500 rpm. But if they are accurate, the computer is dumping more fuel into the engine than it thinks is normal with the high positive fuel trims. This could be due to O2 sensors not registering the mixture properly or a vacuum leak that the computer has to compensate for (I guess you knew that already). Are you getting any ODB codes at all ?

 

The bloke at the MOT station thinks, that if it fails all 3 emission tests than its 9/10 an O2 sensor failure.

No ODB codes. Going to take it for a proper run tonigh and get it nice and hot see if the trims change.

 

If it will run closed loop for goodness sake post the trims with a hot engine. Complete waste of time posting open loop values.

 

They are closed loop trim values and just retested after a 50mile run, same values.

 

If they don't change between open & closed loop or between idle & 2500rpm I think your tool doesn't work.

 

Been and tested 3 readers now all with the same results....


Open loop shows LTFT only @ 14.8
Then when closed loop kicks in LTFT @ 14.8 and STFT @ 19.5 both banks both at idle and 2500rpm.


I doubt its the readers so both LT & ST fuel trims are stuck until I let off the revs @ 2500rpm then ST will drop to "0" and climb back up to 19.5 again.


What can this suggest?