Advise needed - Fuel trims at -25 on idle (resolved)

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BdtDSG
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Advise needed - Fuel trims at -25 on idle (resolved)

Post by BdtDSG »

Hey Guys,
Looking for some advise please.
My 2011 Roc 2.0 TFSi seems to be over-fueling on idle and under vacuum, when I get off the gas pedal. I had a look at the short term fuel trims in VCDS and it's sitting and -25% (Adding fuel). It also logs a 'System too rich' code, the RPM value on the code is always on idle, 700-800 RPM.
It's now at the stage that when I let of the gas pedal, the unburnt fuel combusts in the exhaust and sounds like a fireworks show when I pull into work. I've checked for leaks by pressurizing the system, no luck. Did a readiness test on group 107 (A/F control) and it states 'System not Ok'. I checked the PCV, seems fine. O2 sensor readings seems fine while driving. The oil is also starting to smell like fuel. The car idles fine and no black smoke from the back on idle.
Mods on the car : HPFP upgrade, RS4 valve, VWR Intake, Remapped software, Forge Actuator, FMIC.
Starting to think the HPFP is bad.
Any advise will be appreciated.
Thanks
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Tman21
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Re: Advise needed - Fuel trims at -25 on idle

Post by Tman21 »

BdtDSG wrote: Mon Jul 16, 2018 8:50 am Hey Guys,
Looking for some advise please.
My 2011 Roc 2.0 TFSi seems to be over-fueling on idle and under vacuum, when I get off the gas pedal. I had a look at the short term fuel trims in VCDS and it's sitting and -25% (Adding fuel). It also logs a 'System too rich' code, the RPM value on the code is always on idle, 700-800 RPM.
It's now at the stage that when I let of the gas pedal, the unburnt fuel combusts in the exhaust and sounds like a fireworks show when I pull into work. I've checked for leaks by pressurizing the system, no luck. Did a readiness test on group 107 (A/F control) and it states 'System not Ok'. I checked the PCV, seems fine. O2 sensor readings seems fine while driving. The oil is also starting to smell like fuel. The car idles fine and no black smoke from the back on idle.
Mods on the car : HPFP upgrade, RS4 valve, VWR Intake, Remapped software, Forge Actuator, FMIC.
Starting to think the HPFP is bad.
Any advise will be appreciated.
Thanks
I would start there . . .

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BdtDSG
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Re: Advise needed - Fuel trims at -25 on idle

Post by BdtDSG »

Yeah I'm not to keen on driving the car at the moment, don't want bore wash with diluted fuel circulating through the engine. Will park it until I get the fuel trims back into acceptable range. I have a new oem HPFP laying around at home, will try that first. Guess from the it's maf, oxygen sensors etc. The boost gauge reads 22 inHG vacuum, so don't think it's a vacuum leak. Could a lazy coilpack or plug perhaps cause this without noticeable misfires on idle?
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Re: Advise needed - Fuel trims at -25 on idle

Post by Killerwatt »

What airflow does the maf register at idle and in neutral at 3000rpm?
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BdtDSG
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Re: Advise needed - Fuel trims at -25 on idle

Post by BdtDSG »

Killerwatt wrote: Mon Jul 16, 2018 10:42 am What airflow does the maf register at idle and in neutral at 3000rpm?
Hi,
About 3 g/s IIRC...
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Re: Advise needed - Fuel trims at -25 on idle

Post by BdtDSG »

BdtDSG wrote: Mon Jul 16, 2018 11:18 am
Killerwatt wrote: Mon Jul 16, 2018 10:42 am What airflow does the maf register at idle and in neutral at 3000rpm?
Hi,
About 3 g/s IIRC...
I mean 3 g/s at idle, will have to check at 3k...
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Re: Advise needed - Fuel trims at -25 on idle

Post by Killerwatt »

Sounds about right. Should be around 10g/s at 3k. -25 indicates that the ecu is trying to remove fuel. What are the long term fuel trims?

So MAF seems to have the correct readings but your car is dunping fuel. Check rail pressure at idle and part throttle as well as injector pulse time. Also pull out the sparkplugs and check if any cylinder is much richer than the others.
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BdtDSG
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Re: Advise needed - Fuel trims at -25 on idle

Post by BdtDSG »

Killerwatt wrote:Sounds about right. Should be around 10g/s at 3k. -25 indicates that the ecu is trying to remove fuel. What are the long term fuel trims?

So MAF seems to have the correct readings but your car is dunping fuel. Check rail pressure at idle and part throttle as well as injector pulse time. Also pull out the sparkplugs and check if any cylinder is much richer than the others.
Cool thanks, I'm removing the plugs now. I monitored it now while driving, it only starts when the engine is at operating temp. So starting to think it's the O2 sesnor. When I disconnected the pre-cat O2 while engine was idling, the STFT returned to -2. Not sure if that's a valid test though. If it was HPFP, it would have dumped fuel regardless of temperature right?
Will post pics of the plugs...

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Re: Advise needed - Fuel trims at -25 on idle

Post by BdtDSG »

Cylinder 4's plug seems a bit darker... Maybe fouled plug not combusting all the fuel properly, or even coilpack?ImageImage

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Re: Advise needed - Fuel trims at -25 on idle

Post by BdtDSG »

Seems I have found the issue, just updating this post if someone else comes across this thread some day with the issue.
This isn't the only thing that can cause the P0172 (System too rich) code, but can at least be checked when it does happen.

I took out the HPFP last night and saw fuel in the HPFP housing. Normally there's some oil there, not fuel. Checked the seal on the pump and it didn't even look like the correct size for the pump, or it's just worn.

I took the seal off a spare pump I have and put the pump back. The STFT went back within spec after some driving and the fireworks show stopped.
So the HPFP seal was the culprit.ImageImage

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Re: Advise needed - Fuel trims at -25 on idle

Post by Tman21 »

Well spotted! Glad she is up and running! I can just imagine the horror if you had sent the car in for a "diagnostic" . . .
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BdtDSG
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Re: Advise needed - Fuel trims at -25 on idle

Post by BdtDSG »

BdtDSG wrote:Seems I have found the issue, just updating this post if someone else comes across this thread some day with the issue.
This isn't the only thing that can cause the P0172 (System too rich) code, but can at least be checked when it does happen.

I took out the HPFP last night and saw fuel in the HPFP housing. Normally there's some oil there, not fuel. Checked the seal on the pump and it didn't even look like the correct size for the pump, or it's just worn.

I took the seal off a spare pump I have and put the pump back. The STFT went back within spec after some driving and the fireworks show stopped.
So the HPFP seal was the culprit.ImageImage

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Just updating this post as I was showing the wrong seal in the pics. Here's what the internal seal looked like...
Think this pump had quite a few miles on it and is old AF.
Just bought a new autotech, won't go for second-hand pumps again. Lesson learned.Image

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Re: Advise needed - Fuel trims at -25 on idle

Post by GTiJoe »

Well done!
It takes many bolts to assemble a car, but only one nut to scatter it all over the road.
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BdtDSG
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Re: Advise needed - Fuel trims at -25 on idle

Post by BdtDSG »

GTiJoe wrote:Well done!
Almost cost me a built motor as my oil was so diluted with fuel.

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Re: Advise needed - Fuel trims at -25 on idle

Post by GTiJoe »

BdtDSG wrote: Thu Jul 26, 2018 10:11 am
GTiJoe wrote:Well done!
Almost cost me a built motor as my oil was so diluted with fuel.

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Eina!! Gotta check mine then
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Re: Advise needed - Fuel trims at -25 on idle

Post by TimeShifter »

BdtDSG wrote: Thu Jul 26, 2018 10:04 am
BdtDSG wrote:Seems I have found the issue, just updating this post if someone else comes across this thread some day with the issue.
This isn't the only thing that can cause the P0172 (System too rich) code, but can at least be checked when it does happen.

I took out the HPFP last night and saw fuel in the HPFP housing. Normally there's some oil there, not fuel. Checked the seal on the pump and it didn't even look like the correct size for the pump, or it's just worn.

I took the seal off a spare pump I have and put the pump back. The STFT went back within spec after some driving and the fireworks show stopped.
So the HPFP seal was the culprit.ImageImage

Sent from my SM-G935F using Tapatalk
Just updating this post as I was showing the wrong seal in the pics. Here's what the internal seal looked like...
Think this pump had quite a few miles on it and is old AF.
Just bought a new autotech, won't go for second-hand pumps again. Lesson learned.Image

Sent from my SM-G935F using Tapatalk
BdtDSG, I can't thank you enough for updating your post with the issue you had. I'm convinced after reading your thread that I'm having the same exact issue as my oil also smells like fuel and my fuel trims at idle are terrible. THANK YOU once again!
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Re: Advise needed - Fuel trims at -25 on idle (resolved)

Post by NHB_R »

BdtDSG wrote:Hey Guys,
Looking for some advise please.
My 2011 Roc 2.0 TFSi seems to be over-fueling on idle and under vacuum, when I get off the gas pedal. I had a look at the short term fuel trims in VCDS and it's sitting and -25% (Adding fuel). It also logs a 'System too rich' code, the RPM value on the code is always on idle, 700-800 RPM.
It's now at the stage that when I let of the gas pedal, the unburnt fuel combusts in the exhaust and sounds like a fireworks show when I pull into work. I've checked for leaks by pressurizing the system, no luck. Did a readiness test on group 107 (A/F control) and it states 'System not Ok'. I checked the PCV, seems fine. O2 sensor readings seems fine while driving. The oil is also starting to smell like fuel. The car idles fine and no black smoke from the back on idle.
Mods on the car : HPFP upgrade, RS4 valve, VWR Intake, Remapped software, Forge Actuator, FMIC.
Starting to think the HPFP is bad.
Any advise will be appreciated.
Thanks

Quick question regarding the issue you had. Did you find that your oil temp was higher than normal? Maybe still in "normal" range but definitely higher than it was prior to the issue you started having with the seal?

Thanks


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BdtDSG
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Re: Advise needed - Fuel trims at -25 on idle (resolved)

Post by BdtDSG »

NHB_R wrote:
BdtDSG wrote:Hey Guys,
Looking for some advise please.
My 2011 Roc 2.0 TFSi seems to be over-fueling on idle and under vacuum, when I get off the gas pedal. I had a look at the short term fuel trims in VCDS and it's sitting and -25% (Adding fuel). It also logs a 'System too rich' code, the RPM value on the code is always on idle, 700-800 RPM.
It's now at the stage that when I let of the gas pedal, the unburnt fuel combusts in the exhaust and sounds like a fireworks show when I pull into work. I've checked for leaks by pressurizing the system, no luck. Did a readiness test on group 107 (A/F control) and it states 'System not Ok'. I checked the PCV, seems fine. O2 sensor readings seems fine while driving. The oil is also starting to smell like fuel. The car idles fine and no black smoke from the back on idle.
Mods on the car : HPFP upgrade, RS4 valve, VWR Intake, Remapped software, Forge Actuator, FMIC.
Starting to think the HPFP is bad.
Any advise will be appreciated.
Thanks

Quick question regarding the issue you had. Did you find that your oil temp was higher than normal? Maybe still in "normal" range but definitely higher than it was prior to the issue you started having with the seal?

Thanks


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Hi, no didn't notice a difference in temp, but the oil pressure was lower because of oil dillution.

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Re: Advise needed - Fuel trims at -25 on idle (resolved)

Post by NHB_R »

Cool..thanks


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