Fuel Trim Issues

[nicked95]

Hi Guys,

I've recently finished my Meglio project but have one (hopefully last) issue to solve, when the car is up to temp and left idling the revs drop to almost stalling before picking back up again. So far I've replaced both lambda sensors with new genuine, checked for vac/boost leaks and swapped out the MAP sensor for a known working one.

I've noticed that when this is happening the STFT drops to -100% briefly before recovering. This also happens when cruising at a steady throttle input and can be felt as a slight hesitation before continuing as normal.

I think my next move might be a fresh set of injectors (its currently on 630cc injectors and has been mapped by Chris at EFI)

Any suggestions?

Cheers

 

[Red21]

If the short term fuel trim is going negative 100, the engine is over fueling and the ecu is trying to remove fuel to keep it at the AF ratio set for that area on the map tables. The other possibilities is oil burning or unregulated fuel from the Hydrocarbon canister system or as you mentioned injectors

 

[DaveL485]

I've noticed that when this is happening the STFT drops to -100%

STFT?

 

[andybond]

Short term fuel trim

 

[Adey]

too suddenly shoot to -100% is huge like an intermittent fault by the looks of it. Mine currently is currently a map for a 1.2 running Megane 225 injectors so massively oversized but what it does is fluctuate, you can see it run down the numbers as it adjusts (mine gets to between -60 and -90 at idle currently). the lambda will start to go rich and the ecu will then progressively remove fuel trying to correct it. For it to suddenly pin at -100 makes me think there's possibly a failing lambda at play. Can you monitor primary lambda voltages? A stuck or sticking injector could also cause the same.

 

[nicked95]

too suddenly shoot to -100% is huge like an intermittent fault by the looks of it. Mine currently is currently a map for a 1.2 running Megane 225 injectors so massively oversized but what it does is fluctuate, you can see it run down the numbers as it adjusts (mine gets to between -60 and -90 at idle currently). the lambda will start to go rich and the ecu will then progressively remove fuel trying to correct it. For it to suddenly pin at -100 makes me think there's possibly a failing lambda at play. Can you monitor primary lambda voltages? A stuck or sticking injector could also cause the same.

It doesn't shoot straight to -100% but it does get there fairly swiftly and then recovers back to +50ish before settling nearer 0. I can monitor lambda voltage, from memory it goes to 0.7V when the STFT drops off, then reads 0.1V when it's settled back down (I'll see if I can log these tomorrow).

I've changed both lambdas for new genuine ones already so I guess it rules them out but there could always be loom issues. Out of interest, do you know what would happen if the two lambdas were plugged in the wrong way round?

Cheers

 

[Adey]

not sure actually ive never tried it, do you have a cat in place?

worth firing an email to Chris too just to ask him for some input.

 

[nicked95]

It has a sports cat, so I guess the two lambda will be reading different things. I would have though that if it was ready the post-cat sensor it would never read rich enough to pull all the fuelling?

I'll ping Chris an email, while he was mapping he said it seemed like a lambda problem hence I changed them (although I do seem to recall him saying the injectors weren't behaving exactly how he was expecting as well)

 

[Adey]

were the 630s from a known source? genuine?

 

[nicked95]

They were second hand so not fully known. Chris checked they were genuine, but no idea on mileage covered or age etc hence me leaning towards those probably being the issue (the joys of second hand parts!)

 

[Adey]

Fire them off for a quick clean and check

 

[andybond]

Do you have any way of monitoring the lambda voltage?

 

[Adey]

It doesn't shoot straight to -100% but it does get there fairly swiftly and then recovers back to +50ish before settling nearer 0. I can monitor lambda voltage, from memory it goes to 0.7V when the STFT drops off, then reads 0.1V when it's settled back down (I'll see if I can log these tomorrow).

I've changed both lambdas for new genuine ones already so I guess it rules them out but there could always be loom issues. Out of interest, do you know what would happen if the two lambdas were plugged in the wrong way round?

Cheers

Do you have any way of monitoring the lambda voltage?

Could still be a faulty lambda, ive had a dodgy brand new one previously.

 

[nicked95]

So this is a recording from this morning, I've just noticed that I also get a sharp rise in manifold pressure when it's all going on.

What do you guys think?

 

[Adey]

you might also notice that the throttle is adjusting its position and ignition is changing to compensate, both would change manifold pressure a little

 

[andybond]

Could still be a faulty lambda, ive had a dodgy brand new one previously.

I missed that completly!

sounds like a failing lambda to me. My upstream exige one is doing exactly the same at the mo

 

[Brigsy]

Assuming its hunting all the time?

Id say this could be throttle body related, as have had this issue on the mrs 225 twice over the years, cleaned throttle body, reset throttle and fuel adaptives with clip and its been ok. Do this first as very common.

I have had this issue with my megane converted Kangoo recently too, it was almost stalling then picking up idle to above 1k and repeat.

I had a couple of stuck 630cc injectors/old injectors on first fire up which i got working and had this issue, opted to replace injectors for new flow matched 630cc from Efi. Reset throttle and fuel adaptives and it runs absolutely great now, can rest a cup of tea on the engine, and thats on an old map as ive just fitted some hotter cams. I instantly noticed improved idle and fire up after doing this.

Also, if its idling ok from cold and if you stop the engine before fully warmed up, i.e. temp gauge between bottom and 1st mark, it will hunt like fuck on restart until it settles down even with good injectors. This is also a common trait on the megs for some reason, blue megane done this on new stock injectors, and same on new 630cc’s.

Regarding Lambda sensors, if using the megane loom you should have the front lambda sensor wiring on the cam cover, its tied into the map/injection wiring. rear lambda plug is in the same shroud as the reverse sensor.

 

[nicked95]

Assuming its hunting all the time?

Id say this could be throttle body related, as have had this issue on the mrs 225 twice over the years, cleaned throttle body, reset throttle and fuel adaptives with clip and its been ok. Do this first as very common.

I have had this issue with my megane converted Kangoo recently too, it was almost stalling then picking up idle to above 1k and repeat.

I had a couple of stuck 630cc injectors/old injectors on first fire up which i got working and had this issue, opted to replace injectors for new flow matched 630cc from Efi. Reset throttle and fuel adaptives and it runs absolutely great now, can rest a cup of tea on the engine, and thats on an old map as ive just fitted some hotter cams. I instantly noticed improved idle and fire up after doing this.

Also, if its idling ok from cold and if you stop the engine before fully warmed up, i.e. temp gauge between bottom and 1st mark, it will hunt like fuck on restart until it settles down even with good injectors. This is also a common trait on the megs for some reason, blue megane done this on new stock injectors, and same on new 630cc’s.

Regarding Lambda sensors, if using the megane loom you should have the front lambda sensor wiring on the cam cover, its tied into the map/injection wiring. rear lambda plug is in the same shroud as the reverse sensor.

Cheers for this. I'll give the throttle body a good clean out and see if it helps before ordering some new injectors. Is it vital to reset the adaptives as I don't have clip to do this?

 

[Brigsy]

Ideally its best off resetting the adaptives. Can prob do it with delphi or failing that snap on if you cant get access to clip.

 

[nicked95]

not sure actually ive never tried it, do you have a cat in place?

worth firing an email to Chris too just to ask him for some input.

So it turns out this is exactly what happens when you plug the lambdas in the wrong way round