Shaky low RPM acceleration & VagCom near Bristol

[pj_sibley]

Hi there,

Acceleration on my MRC tuned S4 at low rpm & low throttle position is occasionally a bit shaky / jerky in 1st and 2nd gear at the moment. I commute 20 miles each way to work, quite a bit of it in traffic and a fair bit at a steady 40mph in 5th gear. I wonder whether the car just needs a good thrashing to 'clear it out' or could it be lambda / EGT / MAF related?

I've not had the MAF replaced or cleaned in the last 26k miles / 2.5yrs, as it's never been a problem when I've visited MRC. Was thinking about replacing the 2 lamda sensors and 2 EGT sensors anyway.

Is there anyone within close proximity of Bristol / Gloucester / Stroud who would be happy to run Vag-Com on my car and look for sensor fault codes? I also need to clear the 'INSP' light on the dash

Thanks, Pete

[Nige_RS4]

Hi Pete, I thought you'd popped round to me before when you first got the car? I'm nr Stroud and only too happy to help you out with vag-com - send me a PM!

[pj_sibley]

Thanks Nige....PM sent

[pj_sibley]

And the culprit is:

16518 - O2S B1 S1: No Activity
        35-00 - -

17524 - O2S Heating: B1 S1: Open Circuit
        35-00 - -

So, no lambda sensor signal on bank one. Thanks to Nige for running Vag Com on my car at such short notice I'll post some logs shortly.

[pj_sibley]

Results for run number 1:

GROUP 003

TIME RPM MAF Throttle Ign

s  /min  g/s % degs

262.04 2720 18.36 9 41.3
262.95 2800 78.33 35.3 30
263.96 3160 166.44 100 7.5
264.96 3720 205.31 100 6.8
265.88 4280 212.97 100 6.8
266.84 4800 233.69 100 9
267.85 5280 239.03 100 13.5
269.03 5800 247.06 100 16.5
270.25 6280 243 100 21
271.39 6640 244.36 100 22.5
272.52 6360 12.64 8.6 20.3
273.67 5320 12.92 7.5 50.3

Group 115

TIME RPM Load Boost Actual

s  /min %  mbar  mbar

261.44 2720 22.6 1000 1010
262.34 2720 24.8 1000 1010
263.25 2840 88.7 2190 1100
264.35 3360 178.9 2130 2020
265.26 3920 182 2140 2210
266.19 4480 171.4 2080 2060
267.17 4960 163.9 1930 1960
268.31 5480 151.9 1890 1870
269.39 5960 144.4 1780 1810
270.63 6400 130.1 1720 1710
271.76 6760 125.6 1720 1680
272.87 5480 61.7 1000 1010

Group 004

TIME RPM Voltage Coolant Intake

s  /min  V °C °C

261.74 2720 13.65 94 31
262.64 2760 13.58 94 31
263.66 3000 13.44 94 29
264.65 3520 13.44 94 24
265.56 4120 13.3 94 22
266.51 4640 13.02 94 21
267.51 5120 13.23 94 23
268.67 5640 13.16 94 24
269.88 6120 13.37 94 27
271.01 6520 13.44 94 30
272.14 6840 13.51 93 33
273.33 5280 13.58 93 33

[pj_sibley]

Results for run number 2:

Group 003:

TIME RPM MAF Throttle Ignition

s  /min  g/s % degs

372.9 2360 32.08 14.1 32.3
373.91 2520 75.78 98 21.8
374.81 2880 145.06 100 9.8
375.82 3440 188.67 100 6
376.72 3920 204.39 100 9.8
377.76 4520 223.53 100 9.8
378.86 5080 235.44 100 12.8
379.89 5520 243.67 100 13.5
380.97 5920 251.17 100 18
382.08 6320 248.42 100 20.3
383.46 6760 247.75 100 21.8
384.67 5400 189.47 48.2 15
385.78 4560 14.81 7.5 48

GROUP 115

TIME RPM Load Boost Actual

s  /min %  mbar  mbar

372.31 2320 42.9 1000 1030
373.2 2400 45.1 1000 1030
374.21 2600 113.5 1900 1310
375.11 3040 176.7 2070 2000
376.12 3600 178.9 2140 2110
377.04 4120 174.4 2100 2110
378.08 4680 169.9 2010 2040
379.19 5200 156.4 1910 1890
380.24 5680 149.6 1890 1850
381.33 6080 141.4 1760 1800
382.58 6480 131.6 1730 1730
383.84 6920 14.3 1000 1640
385.13 5400 29.3 1000 1250

GROUP 004

TIME RPM Voltage Coolant Intake

s  /min  V °C °C

372.6 2320 13.65 94 26
373.5 2440 13.72 95 26
374.51 2720 13.72 94 24
375.52 3280 13.72 95 24
376.42 3760 13.58 95 22
377.35 4280 13.58 95 23
378.52 4880 13.58 95 24
379.54 5360 13.44 95 25
380.6 5800 13.37 95 28
381.7 6200 13.37 94 30
382.96 6600 13.51 94 33
384.32 5280 13.51 94 33
385.46 4920 13.79 94 33

[pj_sibley]

So, from these results:

- Peak boost appears to be about 1.1-1.2bar @4500-4800rpm
- Boost at red-line is around 0.6-0.7bar
- Ignition advance is doing a lot of the work in the second half of the RPM range (MRC custom map)
- MAF of 252g/s is lower than expected (hoping for 265g/s based upon most recent rolling road power figures, although it is only a 1Hz log and might have missed the actual peak during fast acceleration)

Questions:

- What's my FATS time?
- How much difference will new lambda sensors and an FMIC make (I already have RS4 downpipes with gutted pre-cats, 200cpi cats, a twin Miltek system and the APR bi-pipe)?

Thanks, Pete

[Nige_RS4]

Pete, I added the FATS times on the spreadsheet.

5.2 on the first run & 5.4 on the second run - that's a bit slow for a stage 2 S4 IIRC.

Pop round when you've changed the O2 sensor and we'll do it again.

You might find that MAF reading are lower at this time of the year as the engine is not having to work as hard to produce the required power?

[Nige_RS4]

B1-S1 is the upper 02 sensor on the drivers side AFAIK

[pj_sibley]

Thanks for the FATS times Nige. Yeah, a bit slower than expected TBH. The car isn't quite right at the moment. Could be lambda / MAF related I guess, needs a little work to get it right again.

Spoke to Doug at MRC earlier about all of this and will be booking the car in for FMIC (probably), lamdas, health-check etc. early in the New Year. Will get in touch after the work has been done if you don't mind doing another couple of FATS runs?

Cheers, Pete