Leon mk1 fueltrims high on throttle

[mmisch]

Hello everyone,

I just got 1 more issue with my car, and that's the fueltrims..
I have a leon Mk1 1.8 20v (APG engine), NA

My STFT only will go up when i'm on throttle, but because of that, if i am driving at cruise speeds, the LTFT slowly will take over and it goes up to 20%

I doubt i have a vac leak, i have checked every hose but no results..
Also the STFT is 0% at idle

1 other thing i noticed;
On idle, i feel slight bumps/shocks, like a misfire, but i don't feel that while driving.
Could this still be a misfire? (I have taken the spark plug wires slightly out so u hear a ticking noise and it did?)

things i checked/replaced:
- fuelpump (new, included in the major service)
- fuel filter (new, included in the major service)
- fuel rail, all fuel injecors, FPR (replaced with a other mk1 with low mileage)
- whole intake hose (with some PCV piping) (replaced, was broken anyways)
-sparkplugs (new, included in the major service)

this defenitely cannot be a fuel problem.

 

[mty12345]

Weird one. It's possible the MAF might be under reading slighty. That may not show during acceleration/deceleration during city driving etc, but might become an issue at a sustained rpm when cruising. Is it a Bosch MAF or some sort of cheap brand?

Seeing as you have already replaced practically the whole fuel system, then that's about the only thing i can think of.

 

[mmisch]

Yeah but the STFT does go up while driving? Is that normal? Or should the stft still be ~0% while on throttle?
It's a genuine bosch. Probably still the original one

I tried a delphi one (new) but the car didn't like that at all.. didn't go above 50kmph or 2000rpm

I tried cleaning it with maf cleaner but it didn't work

I did some tests some time ago, did not go to redline but highest i got on 4000rpm was about 70/80 g/s

 

[mty12345]

Yeah it's normal for the STFT to move around a lot, as that is what the ecu is doing at that exact moment. Then if the STFT moves in one direction for an extended period of time, the LTFT starts to adjust to compensate.

That way the STFT doesn't get maxed out and still has room to adjust itself. as each trim only has a range of +/-20%
I hope that makes sense.

I'm not sure of the numbers on the N/A engines, but 70/80 g/s sounds about what i'd expect.

Are you 100% sure you have no leaks in your intake or PCV system? Squeeze the hoses while looking with a flashlight. That often causes the lumpy idle and would also explain the high LTFT at cruise.
Maybe a leaking inlet manifold gasket? If it's easy to get to on the N/A then may be worth replacing the gasket and seeing what happens. They are fairly cheap/

 

[mmisch]

On my engine (APG) its very easy to replace the intake manifold gasket.

To be honest, I had to remove the intake manifold alot of times due to troubleshooting/removing the fuel injectors/rail, and now i'm missing 1 hex screw for the inlet manifold (out of the 7), but i don't know if that causes the LTFT to go to 20% positive


If I did have vacuum leaks, it would show up at idle where my stft is +20? And get better while on throttle?
Because if so, that's not my problem

So squeezing the hoses also work for finding leaks? Didn't know about that one.
Sometimes it's quite difficult to spray brake clean because of the orientation of the bottle

 

[mmisch]

This is what i meant with a vacuumleak
(i resetted the fueltrims) :

stft high because of vacuum hose loose (in this case from the FPR)

Fueltrims normal after vacuumhose connected

Stft +~10% while holding revs on 2000rpm

 

[mty12345]

To be honest, I had to remove the intake manifold alot of times due to troubleshooting/removing the fuel injectors/rail, and now i'm missing 1 hex screw for the inlet manifold (out of the 7), but i don't know if that causes the LTFT to go to 20% positive

I'm not sure, but it's definitely possible. I think i would eliminate that first if i was you.

From the STFT data logs it looks like an intake leak too. Higher at idle than at 2500rpm

 

[mmisch]

From the STFT data logs it looks like an intake leak too. Higher at idle than at 2500rpm

What do u mean with "higher at idle than at 2500rpn?

I tried spraying brake clean in that screw hole that was open but on idle i got nothing different

I will try and find another hex screw for it

 

[mmisch]

I tried recording some data, including TPS/fueltrims/maf reading/speed (kmh)/afr

I wanted to record with my camera too but i don't know how to both record screenn+rear camera. Hopefully this will lead to something?

I didn't go like above 2000rpm because of cold engine. I also resetted the fueltrims.

While on cruising speed (holding throttle to maintain xx Kmh / driving with cruise control) the STFT actually does stay within limits (+/-10%), but it's actually only when accelerating that the fueltrims spike up.

 

[mmisch]

While on cruising speed (holding throttle to maintain xx Kmh / driving with cruise control) the STFT actually does stay within limits (+/-10%), but it's actually only when accelerating that the fueltrims spike up.

use earphones so u also kinda hear at what throttle input i'm at


here's another video of exactly what i described. Watch the throttle input/stft. U can also slowly see the LTFT rising with within the 3 minutes (from +10,94% to +15,62%)

 

[mty12345]

Right mate, the screenshots misled me because it had 850 rpm with 15.6% STFT, then only 10% at 2100rpm, but the video logs make it a LOT easier.

From the videos I don't think it's an intake leak at all. I agree that it's short of fuel when on the throttle, and short by a lot too. Seeing as you have replaced everything in the fuel system, my best guess would be that the O2 sensor is possibly faulty, so the car thinks that the engine is short of fuel when it is actually ok.

I really can't see what else it can be tbh. If you decide to replace it then make sure you get a genuine bosch one.

 

[mmisch]

The +15.6% was to show how to fueltrims were with a vacuum leak created just to clarify.

But good to know the video logs makes it better.

I did replace the afr o2 sensor (upstream), but i didn't replaced the second one. Sorry for not mentioning already.

Could the second one (downstream) also be a problem?

(The old upstream o2 sensor gave me -40% values in vcds, that's how i knew it needed to be replaced, and it did make the car run better too)

 

[mmisch]

So, i've just been troubleshooting a bit again..

I've removed all the hex bolts on the intake manifold, started the engine, hold revs to 2k but still nothing different.
The intake manifold is also like bolted to a hinge so it doesnt move. So i think we can rule the 1 missing bolt out..

I don't know why but i have a feeling it's still some sort of misfires, but could it be the block or the sparkplug wires? (yeah.. the old wires, my 2003 does not have real ignition coils, coil on plug)

I dont know which one goes bad faster

But it gives me 0 misfires..

 

[mty12345]

The +15.6% was to show how to fueltrims were with a vacuum leak created just to clarify.

But good to know the video logs makes it better.

I did replace the afr o2 sensor (upstream), but i didn't replaced the second one. Sorry for not mentioning already.

Could the second one (downstream) also be a problem?

(The old upstream o2 sensor gave me -40% values in vcds, that's how i knew it needed to be replaced, and it did make the car run better too)

No only the 1st upstream sensor affects the mixture, the 2nd one is just to monitor the efficency of the catalytic convertor.

 

[mmisch]

Idk if this is something useful but on cylinder 2, 3 and 4 it sparks to the housing? Is that normal?

Order is:
Right top = cyl 1
Left top = cyl 2
Left bottom = cyl 3
Right bottom = cyl 4

Also, the fueltrims apparently did not change when running on 3cylinders (and holding revs with 1 disconnected)

 

[mty12345]

No i don't think it's anything to do with misfires, as that would lead to negative fuel trims due to the unburnt fuel at the O2 sensor.

It can only be one of 3 things really: Drawing in un-metered air somewhere that hasn't been through the maf
Fuel Supply issue
Bad O2 circuit

Seeing as you seem to have covered all 3 of those, really not sure what else it could be. Maybe get a fuel pressure gauge plumbed into the fuel rail and see if you have the right fuel pressure. I know you've replaced most of the fuel system components, but at least then you can rule that out

Not really sure about the spark issue, the turbo engines are all coil on plug, but if you had spark issues you would be getting proper misfires on the misfire counter.

 

[mmisch]

And there is no possibility the misfire counter could be wrong? This is also my first time with a ignition coil pack (instead of Coil on Plug)

The other thing is, my car was used for lease (before i had it), and after i got the car and changed the fuelfilter, it came all black. I am 99% sure it was the original or atleast a very old fuel filter.. maybe the fuel lines could be clogged because of it ?

Edit:
I ordered a fuel pressure gauge, hopefully the plugs fit. Anyone knows what kind of tests (on idle or while driving?) i should do and how much bar should i expect?

 

[mty12345]

I'm not sure on the fuel pressure on the N/A, on the turbo it's 3 bar. It's possible fuel lines are clogged somewhere, but unlikely as fuel filter should prevent the vast majority of it getting through

 

[mmisch]

I'm not sure on the fuel pressure on the N/A, on the turbo it's 3 bar. It's possible fuel lines are clogged somewhere, but unlikely as fuel filter should prevent the vast majority of it getting through

Yeah, but as i mentioned, the old filter was like pitch black so maybe it could've clogged the lines at that time.
I better hope i get around 2 bar i think

 

[mmisch]

Well.. 3 bar constant, 44psi
No weird hickups in fuel pressure..

maf results look okay, could it be the o2 sensor then? (Bought new but from ebay) exactly this one:

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The reason i went with the ebay one is because of the connector that I needed, and the OEM number was the same