Jerky at low rpm / small throttle angles and down on power

[RS4RAB]

After a little help if possible

My B7 RS4 is on 113k miles and I have just completed a carbon clean, new gaskets, intake manifold clean etc, flaps removed, small vac leak fixed and new 1 way valve installed

Before this I am experiencing a slight hesitation and jerking under light throttle and the car seems to bog sometimes under WOT, but other times pulls hard.

I have taken some logs with VCDS and I will post the log later when on the laptop but for now I have noticed the following

My long term fuel trim at idle on both banks is slightly negative, around -1.5 and long term fuel trim at load was around +7.4% on bank 1 and +6.6% on bank 2

I then completed a few 3rd gear pullS from 3k to 8k

After this my long term fuel trims at load on both banks have gone up to +9.9%

After driving normally for a few days with some spirited driving thrown in my long term trims are now at about +3% both banks

whilst doing this I was monitoring MAF readings and only reached a maximum of 135 g/s

Car is stage 1 tuned with the following modifications

BMC air filter
Forge oil cooler
Aux rad removed and cold air feed fitted
Carbon cleaned less than 500 miles ago
Pre cats removed
Miltek res cat back exhaust

As far as I am aware injectors are originals, so thinking of changing them first, would I be correct in thinking the low MAF reading is a result of the engine not getting enough fuel and therefore not achieving full power or could the MAF be the cause of the fuelling problem?

Anything else I should log?

Any help would be great

[AA_954]

Definately change the injectors.

Did you log Low pressure fuel and High pressure in the pulls?

For reference I see a peak of 162grs maf read at ~7800, give it a clean first to see, I assume the air filter is new or at least recently cleaned?

The lowest I get at WOT with lpfp is 3.8 and hpfp specified and actual at around ~120


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[rs user]

before changing injectors i would check fuel is getting delivered properly to the hpfp s -nice fresh filter and a good pump at the rear

[mikep99]

is it worthwhile trying a throttle reset?
viewtopic.php?t=124222

Mike

[James1984]

Definately change the injectors.

Did you log Low pressure fuel and High pressure in the pulls?

For reference I see a peak of 162grs maf read at ~7800, give it a clean first to see, I assume the air filter is new or at least recently cleaned?

The lowest I get at WOT with lpfp is 3.8 and hpfp specified and actual at around ~120
Does the maf reading relate to power? Mine flows 177

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[AA_954]

Definately change the injectors.

Did you log Low pressure fuel and High pressure in the pulls?

For reference I see a peak of 162grs maf read at ~7800, give it a clean first to see, I assume the air filter is new or at least recently cleaned?

The lowest I get at WOT with lpfp is 3.8 and hpfp specified and actual at around ~120
Does the maf reading relate to power? Mine flows 177

Sent from my iPhone using Tapatalk Pro

Relates to flow of air calculated by the sensor so the ecu’s can calculate how much fuel to deliver for the mix, etc.

Differences can be due to carbon build, mine was done about 6k ago but carbon builds up pretty quick, air filter, cold air intake, eliminating the flap in the airbox, if your car is pulling timing, others. All these can affect maf values either up or down.

Not sure if you have done any mods but 177 is good, I’ve read in other forums that in reality its 354, because we have 2 ecu’s each ecu uses half the total value to calculate the fuel delivery


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[RS4RAB]

Definately change the injectors.

Did you log Low pressure fuel and High pressure in the pulls?

For reference I see a peak of 162grs maf read at ~7800, give it a clean first to see, I assume the air filter is new or at least recently cleaned?

The lowest I get at WOT with lpfp is 3.8 and hpfp specified and actual at around ~120


Sent from my iPhone using Tapatalk Pro

High pressure was logged and at 7000rpm to 8000 car was specifying 114.99, actual readings were anywhere from 113-119

At this pull i was reading 150grs on the MAF

Didn't have low pressure logged but had group 106 which is electrical fuel pump and between 7-8k this was between 49 and 52, think that is a percentage

It does start to pull timing at around 5k rpm? and other times randomly at low RPM?

Have taken the air filter out this afternoon and it was filthy, cleaned now and once dry i will re oil with the spray from the cleaning kit, will clean the MAF also as looks a bit dirty

[RS4RAB]

before changing injectors i would check fuel is getting delivered properly to the hpfp s -nice fresh filter and a good pump at the rear

Filter is brand new less than 100 miles ago, haven't changed the pump though, although i experience this problem more so at low rpm and light throttle?

[RS4RAB]

Definately change the injectors.

Did you log Low pressure fuel and High pressure in the pulls?

For reference I see a peak of 162grs maf read at ~7800, give it a clean first to see, I assume the air filter is new or at least recently cleaned?

The lowest I get at WOT with lpfp is 3.8 and hpfp specified and actual at around ~120
Does the maf reading relate to power? Mine flows 177

Sent from my iPhone using Tapatalk Pro

Relates to flow of air calculated by the sensor so the ecu’s can calculate how much fuel to deliver for the mix, etc.

Differences can be due to carbon build, mine was done about 6k ago but carbon builds up pretty quick, air filter, cold air intake, eliminating the flap in the airbox, if your car is pulling timing, others. All these can affect maf values either up or down.

Not sure if you have done any mods but 177 is good, I’ve read in other forums that in reality its 354, because we have 2 ecu’s each ecu uses half the total value to calculate the fuel delivery


Sent from my iPhone using Tapatalk Pro

Just for info car has just been carbon cleaned, flap removed and CAF fitted, but the car does seem to be pulling timing looking back at the logs, near the top end but also randomly so need to look at if this is at the same time i experience the jerking at light throttle / low rpm

[12th]

I had a problem with one of my fuel pumps (there are two) and this manifested itself in worsening but predictable behaviour. There were flat spots and drop-outs in the power delivery, but they seemed to be at the same 2 or 3 points in the rev range - they just got more extreme as the fault developed.

[rs user]

before changing injectors i would check fuel is getting delivered properly to the hpfp s -nice fresh filter and a good pump at the rear

Filter is brand new less than 100 miles ago, haven't changed the pump though, although i experience this problem more so at low rpm and light throttle?

did the issue start same time as filter fitted,or already present when changed?

[RS4RAB]

before changing injectors i would check fuel is getting delivered properly to the hpfp s -nice fresh filter and a good pump at the rear

Filter is brand new less than 100 miles ago, haven't changed the pump though, although i experience this problem more so at low rpm and light throttle?

did the issue start same time as filter fitted,or already present when changed?

Sorry I mean the fuel filter was brand new 100 miles ago but problem was there before , air filter has been on the car for years

[rs user]

have you thought about the throttle body itself...be good to be able to substitute and try a known good item
if injectors were kaput it wouldnt generally be all of them,and would more likely show as a missfire-not come and go like what you have

[RS4RAB]

have you thought about the throttle body itself...be good to be able to substitute and try a known good item
if injectors were kaput it wouldnt generally be all of them,and would more likely show as a missfire-not come and go like what you have

The thought has crossed my mind, difficult to swap with another as not many around where I live

The car is mapped I believe by AMD so misfire info doesn’t seem available in VCDS

I do also have a small exhaust leak before the main cat, will address that tomorrow and a throttle body alignment and report back

[AA_954]

Definately change the injectors.

Did you log Low pressure fuel and High pressure in the pulls?

For reference I see a peak of 162grs maf read at ~7800, give it a clean first to see, I assume the air filter is new or at least recently cleaned?

The lowest I get at WOT with lpfp is 3.8 and hpfp specified and actual at around ~120


Sent from my iPhone using Tapatalk Pro

High pressure was logged and at 7000rpm to 8000 car was specifying 114.99, actual readings were anywhere from 113-119

At this pull i was reading 150grs on the MAF

Didn't have low pressure logged but had group 106 which is electrical fuel pump and between 7-8k this was between 49 and 52, think that is a percentage

It does start to pull timing at around 5k rpm? and other times randomly at low RPM?

Have taken the air filter out this afternoon and it was filthy, cleaned now and once dry i will re oil with the spray from the cleaning kit, will clean the MAF also as looks a bit dirty

The readings you mention seem ok, adaptation is something you could to do but honestly I would not underestimate the injectors specially with the mileage you have, flap screws and faulty injectors are the main reasons behind these engines getting blown. A faulty TB would give a code and you would notice in some cases sudden jumps in idle moving, you could also peep down the hose between the MAF and TB and see if the TB flap has any dirt buildup. As someone else mentioned hpfp could be a possibility but you haven’t mentioned anything about misfires

You mentioned AMD tuned so are you in the US? AMD tunes here as I recall are done by UM, about the air filter just clean it but don’t oil it, theres different views but most of the owners I know including myself will go with a non-oiled filter.


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