S3 8p fueling/misfire issue .help needed

Post Reply
Trishen94
Cadet
Posts: 716
Registered for: 5 years 5 months
Car Make: Vw
Car Model: Mk5 gti

S3 8p fueling/misfire issue .help needed

Post by Trishen94 »

Hi guys so the s3 8p ran fine for 2days without any issues but then an old issue resurfaced ... fueling/misfire dont know which 1 it is ...so basically i need some guidence i know i can simply take it to a mech n have it sorted but id like to try myself 1st to gain more knowledge and save some cash ...so in the beginning it was giving a low rail pressure error ... upon further ispection found that the lpfp was on its way out was at 60% on idle ...mech fitted a new1 and its fine now sits at approximately 30% but sometimes at around 4000 rpm on WOT i get a sudden like fuel cut/overfuel and backfire/misfire for a split second and then car goes back to normal but with a little lack of power there after... the intercooler has a small leak which i doubt will cause this but will fix tomorrow morning plz point me in the correct direction.. so i will start with :
Log lpfp actual vs requested again
Log hpfp actual vs requested
Log boost actual vs requested (after intercooler is fixed )
Log misfire on all 4 cylinders
log all 4 injectors
Log timming pull on all 4 cylinders
What else should i check ?
The cam follower was changed , cam and old follower seemed fine no wear or scratchs
Plugs changed to BKR7EIX
Current :2008 S3 8P (panic mechanic +thanas) 227kw /309hp 473nm
viewtopic.php?f=11&t=217296

Ex :2008 mk5 gti ... really miss this car

Previous :too many to list
Trishen94
Cadet
Posts: 716
Registered for: 5 years 5 months
Car Make: Vw
Car Model: Mk5 gti

Re: S3 8p fueling/misfire issue .help needed

Post by Trishen94 »

Just to add on for those like ME who might not know ...done some research and common issues related to low fuel pressure :
Blocked fuel filter ( already changed mine )
Failing hpfp or hpfp sensor
Worn camshaft lobe ( mine seems fine will still double check )
Fuel pressure relief valve under intake manifold
Lpfp ( already changed)
So slowly but surely and hopefully i do resolve this on my own will make me smile so much more
Current :2008 S3 8P (panic mechanic +thanas) 227kw /309hp 473nm
viewtopic.php?f=11&t=217296

Ex :2008 mk5 gti ... really miss this car

Previous :too many to list
User avatar
THANAS
Forum Advertiser
Posts: 4660
Registered for: 10 years 8 months
Car Make: VW
Car Model: AW Polo GTi
Membership No: 2035
Location: Cape Town

Re: S3 8p fueling/misfire issue .help needed

Post by THANAS »

Log the following and post the log(upload to google drive or dropbox or something):

Engine RPM
High Pressure Actual + Specified
Lambda Actual + Specified
Lambda Control
Median Injection Duration (Injection Time)
Low Pressure Actual (Current Fuel Pressure)
Boost Pressure Actual + Specified
Cam Adjustment Intake (Spec)
Cam Adjustment Intake (Actual)
Throttle Valve Angle

You can also log

Ignition Timing
Ignition Retard 1/2/3/4

You can run into misfire if your injection duration becomes excessively long as a result of a drop in rail pressure (as a result of mechanical failure or boost being too high on stock HPFP internals). Coilpacks can also exhibit that kind of misfire symptom. Does the idle feel smooth or is there a stutter/shudder in the idle?
User avatar
panic-mechanic
Panic's Place
Posts: 26715
Registered for: 21 years 8 months
Membership No: 79
Location: Benoni, putfontein.

Re: S3 8p fueling/misfire issue .help needed

Post by panic-mechanic »

Bring it around one afternoon then we can log it on the dyno quick.
Stephan van Tonder - Jhb - Putfontein Benoni
'05 Audi A6 3.0L TDI Avant
'09 Touareg 3l TDI
'13 VW CC 2l tdi (repair project)
'05 Touareg v10

Perfect Power dealer. I do dyno tuning.
User avatar
THANAS
Forum Advertiser
Posts: 4660
Registered for: 10 years 8 months
Car Make: VW
Car Model: AW Polo GTi
Membership No: 2035
Location: Cape Town

Re: S3 8p fueling/misfire issue .help needed

Post by THANAS »

panic-mechanic wrote: Fri Jul 19, 2019 10:42 am Bring it around one afternoon then we can log it on the dyno quick.
Better idea :iagree:
Trishen94
Cadet
Posts: 716
Registered for: 5 years 5 months
Car Make: Vw
Car Model: Mk5 gti

Re: S3 8p fueling/misfire issue .help needed

Post by Trishen94 »

:hug: Thanks so much for the help thanas i guess its not so easy after all lol i thought id manage on my own but surely its more than i can handle will have to let a pro check it out

Hi stefan i just finish taking out the intercooler now i spotted sludge in 2 spots so suspecting 2 leaks... ive dropped it of at silverton to see if its repairable as soon as i get the intercooler back il give u shout for an appointment thanks to u also for the help im literally pulling my hairs out my head wih this car :bang:

This issue is intermittent last night it was all sick with no power and then this morning just before taking out the intercooler i went to midas to buy a 16mm socket for the crash bar and guess what it was running like a beast like all of the power came back im lost ... :crazy:
But yeah anyways hope i get it back tomorrow so i can hopefully see u soon
Current :2008 S3 8P (panic mechanic +thanas) 227kw /309hp 473nm
viewtopic.php?f=11&t=217296

Ex :2008 mk5 gti ... really miss this car

Previous :too many to list
User avatar
Killerwatt
VWCSA Member
Posts: 4819
Registered for: 15 years 10 months
Car Make: AUDI
Car Model: S3
Membership No: missing
Location: Brakenhurst

Re: S3 8p fueling/misfire issue .help needed

Post by Killerwatt »

Intermittent misfire on mine turned out to be an injector with a poor spray pattern.

Check which cylinder has the misfire. Move the coils and plugs around. If it stays then that would be my first guess.

But logs will point you in the right direction.
Trishen94
Cadet
Posts: 716
Registered for: 5 years 5 months
Car Make: Vw
Car Model: Mk5 gti

Re: S3 8p fueling/misfire issue .help needed

Post by Trishen94 »

Hi killerwatt thanks so much for the info... upon inspection i found my dv to be leaking ive replaced that ... misfire on no2 and 4 found that the plug connector clips where broken this causing a loose connection(misfire) i replaced the 2 with new connectors ... also managed to repair my intercooler... so awaiting to log at panics place to see what else pops up
Current :2008 S3 8P (panic mechanic +thanas) 227kw /309hp 473nm
viewtopic.php?f=11&t=217296

Ex :2008 mk5 gti ... really miss this car

Previous :too many to list
Post Reply