Considerably more power with fresh fuel ?? Any help

Rhys

Active Member
Nov 20, 2018
15
0
Hi I’m trying to diagnose a sorta problem with my Leon if fuel has been sat for a day or 2+ she’s still quick but really lacks enthusiasm put some fuel in weather that me 5 quid or 80 quid it’s a night and day difference,

Obviously theres always a little difference in power with fresh fuel but not this much it’s massive anyone have a clue? She will stay that fast fora bout half aday.

Only thing that even slightly makes sense is the intank Lpfp?? Works harder when colder new fuel is cold?

ima do a fuel filter on it soon as i couldn’t tell you when the last owner did one but I doubt it be that?

anyhelp will be much appreciated tia
 

Legojon

I only wanted a remap
Staff member
Moderator
Jul 7, 2015
5,191
2,635
How low do you let the fuel go? When it drops below 1/4 tank, the intank fuel pump will have to work harder. What engine / model do you have?
 

Jester

Active Member
Aug 17, 2018
31
8
Hi I’m trying to diagnose a sorta problem with my Leon if fuel has been sat for a day or 2+ she’s still quick but really lacks enthusiasm put some fuel in weather that me 5 quid or 80 quid it’s a night and day difference,

Obviously theres always a little difference in power with fresh fuel but not this much it’s massive anyone have a clue? She will stay that fast fora bout half aday.

Only thing that even slightly makes sense is the intank Lpfp?? Works harder when colder new fuel is cold?

ima do a fuel filter on it soon as i couldn’t tell you when the last owner did one but I doubt it be that?

anyhelp will be much appreciated tia
Could this be some sort of tank venting problem? Next time it does it try just removing and replacing the fuel cap, see if that makes a difference.
 
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Rhys

Active Member
Nov 20, 2018
15
0
Hi guys yeah sorry I forgot to mention it’s the 2.0tfsi stage 1 few mods nothing fuel related tho.

it doesn't matter if the tanks full or empty nor does it matter how much fuel I put in (min £5) it makes a difference she’s currently 250bhp
 

Legojon

I only wanted a remap
Staff member
Moderator
Jul 7, 2015
5,191
2,635
Hi guys yeah sorry I forgot to mention it’s the 2.0tfsi stage 1 few mods nothing fuel related tho.

it doesn't matter if the tanks full or empty nor does it matter how much fuel I put in (min £5) it makes a difference she’s currently 250bhp
When's the last time you checked the cam follower?

Actually just noticed... I assume yours is the EA888 gen 1 so prob has a roller follower?
 

Rhys

Active Member
Nov 20, 2018
15
0
Could this be some sort of tank venting problem? Next time it does it try just removing and replacing the fuel cap, see if that makes a difference.
Hmmm possibly that’s the only other thing that happen when filling up (removing the cap to vent) I didn’t think of that think they have a purge valve too
 

Rhys

Active Member
Nov 20, 2018
15
0
When's the last time you checked the cam follower?
Can follower Changed 500 miles ago done 3 oil changes every 3k since owned it.

had plugs r8coils

every service item except fuel pump no expense spared as she’s my baby
 

Legojon

I only wanted a remap
Staff member
Moderator
Jul 7, 2015
5,191
2,635
You got any logging equipment you can check eg fuel rail pressure, expected vs required?
 

Rhys

Active Member
Nov 20, 2018
15
0
You got any logging equipment you can check eg fuel rail pressure, expected vs required?
Unfortunately not and really can’t justify vagcom and no where near me is a vag specialist apart from seat or Audi of corse was hoping to find an the issue on the forum but worst case I’ll have to bring her to the dealer and get ready to faint with there prices
 

mty12345

Active Member
Jun 17, 2011
3,196
208
bristol
Unfortunately not and really can’t justify vagcom and no where near me is a vag specialist apart from seat or Audi of corse was hoping to find an the issue on the forum but worst case I’ll have to bring her to the dealer and get ready to faint with there prices
I agree with what the other poster said about opening the fuel tank. I can't see any way that new fuel would affect it, but if you have a vacuum forming in the tank, then that could be stopping the pump picking up fuel properly. There is usually some sort of one way valve that allows air into the tank as the fuel is used up. That would be my first suspect.
 
Last edited:

martin j.

Active Member
Feb 11, 2007
1,249
406
Fife
Can’t help re fuel but I would change the filter, if you don’t know when it was done it’s a good idea, 10 minute job, cannot do any harm.
 

andycupra

status subject to change
RE opening cap. easy to find out if this
I agree with what the other poster said about opening the fuel tank. I can't see any way that new fuel would affect it, but if you have a vacuum forming in the tank, then that could be stopping the pump picking up fuel properly. There is usually some sort of one way valve that allows air into the tank as the fuel is used up. That would be my first suspect.
to test if this is an issue simply take the cap off and don't fill with fuel and see if it helps.

the other option would be the dreaded defeat device, or a version of it. What i mean is, there was some evidence of 'hot' starts running a nicer program. although you say its just for a few mins after fill up.
Could it be as simple as its due to something the ecu is doing after starting the car, for example is the fuel richer initially following a restart and as engine is already warm (rather than a cold start) this is noticeable.
try stopping and leaving 3 mins and restart but without a fuel fill, do you get the same affect,.

PS - i have found the same after fuel fill ups on many cars...
 

Rhys

Active Member
Nov 20, 2018
15
0
RE opening cap. easy to find out if this

to test if this is an issue simply take the cap off and don't fill with fuel and see if it helps.

the other option would be the dreaded defeat device, or a version of it. What i mean is, there was some evidence of 'hot' starts running a nicer program. although you say its just for a few mins after fill up.
Could it be as simple as its due to something the ecu is doing after starting the car, for example is the fuel richer initially following a restart and as engine is already warm (rather than a cold start) this is noticeable.
try stopping and leaving 3 mins and restart but without a fuel fill, do you get the same affect,.

PS - i have found the same after fuel fill ups on many cars...
This car is honestly so weird at Times last 2 weeks I have been driving with no fuel cap on at all and it hasn’t once gave me power loss feels as fast as when I fill up to when I need fuel today I decided to refit the cap and ohhhh boy she was even faster how on earth does that make sense sure it’s just a placebo well I hope so anyway.

Do have an ongoing issue that’s been happening this since ownership (stock) (now stage 1)

3rd gear plus floor it about half way through the revs can hear turbo vent air and slow and car obviously looses power during that then it will pick boost up will do it 1-2 time’s during 1 gear and then sometimes not at all again all the way through the gears almost as if The turbo is turning it self down sounds like boost leak kinda sound not a hole dump of air.

just weird how it goes away and boost fines higher rpm and lower rpm.

dv changed a few thousand miles ago
 

mty12345

Active Member
Jun 17, 2011
3,196
208
bristol
Sounds like you need to run some logs with VCDS, no real way to know what it going on without doing that.
 
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