Leon mk1 fueltrims high on throttle

[mmisch]

Changed the new ebay o2 sensor with the old one (apparently bosch), still same results....

I've been driving for 15minutes now;

I'm almost out of options and the whole fuel system is ruled out... it could only be to much air, but no vacuumleaks...

Must be one of the sensors then (besides the o2..)

 

[mmisch]

Well.. did a full run to redline in 3rd gear..
Do those maf readings look okay or was i in the wrong gear?

Here's the full youtube video, run @ 0:20

 

[smutts]

Looks quite complex. But perhaps there is a duff sensor input throwing the fuelling calcs out. It's a computer, therefore GIGO.

 

[mmisch]

Looks quite complex. But perhaps there is a duff sensor input throwing the fuelling calcs out. It's a computer, therefore GIGO.

could it be the MAF? (as mentioned, at redline, 3rd gear, 78,2 g/s)
I did try an new delphi MAF but i've read on multiple forums that u absolutely should NOT go for aftermarket?
(my car was behaving weird with that delphi MAF, sort of limp mode @50 km/h and did not go above certain RPM)

 

[smutts]

back of fag packet, 1200g air is 1m3, 1000 litre,
78,2g/s is (78.2/1200)*1000 l/s

that's 65 litres of air a second,
Is that believable?

6000rpm, 100 rps,

engine, 1800cc? half the pots breath per turn, pumps 0.9l per turn.
pumping volume 100x 0.9 litres a second.

That's 90 l/s at 100% no losses breathing.

Breathing efficiency 65/90 = 73%

It's believable.

Best check the figures, as I am having a couple of beers.

 

[mmisch]

Does that mean the MAF is good or bad ? Wasn't good at math lol
I've heard of the formula that your maf reading should be around 80% of the HP of my engine, in this case;
125HP / 100 x 80 = 100 g/s

 

[mmisch]

Well.. i think i found the problem

New full redline run with a new BOSCH MAF.

Here's the video:
(Starts on 0:22, 3rd gear pull)

Going to top of my fuel and see what mileage I get (instead of around 300/350km on a full tank)

 

[smutts]

On the GIGO theme.
A few years ago, I was having crappy MPG, finally tracked it down to the coolant sensor.

It was only with my VCDS that I found the engine thought it was at -40c.
while the dash instruments were showing the correct temp.

The sensor has two separate thermistors.
One sends signal to the instrument panel,
The other sends to the engine management.

New coolant sensor sorted it.

 

[mmisch]

On the GIGO theme.
A few years ago, I was having crappy MPG, finally tracked it down to the coolant sensor.

It was only with my VCDS that I found the engine thought it was at -40c.
while the dash instruments were showing the correct temp.

The sensor has two separate thermistors.
One sends signal to the instrument panel,
The other sends to the engine management.

New coolant sensor sorted it.

Oh yeah my ECT was just working as it should, reported good temps so that wasn't it for mine

 

[mty12345]

Well.. i think i found the problem
View attachment 35977
New full redline run with a new BOSCH MAF.

Here's the video:
(Starts on 0:22, 3rd gear pull)

Going to top of my fuel and see what mileage I get (instead of around 300/350km on a full tank)

Glad you got to the bottom of it in the end. That's quite the difference in maf readings.

 

[smutts]

Does that mean the MAF is good or bad ? Wasn't good at math lol
I've heard of the formula that your maf reading should be around 80% of the HP of my engine, in this case;
125HP / 100 x 80 = 100 g/s

Looking at the video, seems you heard dead right!

 

[mmisch]

Glad you got to the bottom of it in the end. That's quite the difference in maf readings.

Yeah, but let's see the fueltrims on the end of this week.. there's still something wrong tho.

STFT don't spike up at all on throttle so that's good, but currently the LTFT is at around 12% positive.. I do hope it doesn't get higher so it doesn't trigger the CEL (for selling purposes)

 

[mmisch]

Well, last time i checked (last week) my LTFT was +10,94%, and it still is after a week.

So good thing: fuel trim not causing CEL
Bad thing: there's still something wrong, but minor.

STFT is on 0% while driving and idle (because LTFT took over)

And yes, mileage is 100% improved, but would like to see it just a little bit better (caused by the 10% LTFT)