Marc sierra

iTrader: (1)

My sapph has a slight hesitation/judder in it. It's a bit like the throttle is changing a few times per second. It continuously feels like braking on the engine at one moment and slightly accelerating straight after that.

I have a Dynojet wideband lambda kit in the car that can log the AFR, RPM and MAP signal. When cruising at constant speed the MAP signal is oscillating. The MAP signal is from -1 to 2 bar, to prevent any confusion. The RPM signal is also not completely stabile, but I'm not sure whether that is just measurement inaccuracy.

Time MAP RPM AFR W R
0.000 -0.29 3135 14.8 0 0
0.100 -0.35 3136 14.8 0 0
0.200 -0.26 3138 14.8 0 0
0.300 -0.33 3135 14.8 0 0
0.400 -0.28 3135 14.7 0 0
0.500 -0.29 3133 14.7 0 0
0.600 -0.32 3135 14.7 0 0
0.700 -0.30 3133 14.8 0 0
0.800 -0.37 3135 14.8 0 0
0.900 -0.32 3138 14.8 0 0
1.000 -0.34 3135 14.8 0 0
1.100 -0.28 3135 14.8 0 0
1.200 -0.34 3133 14.7 0 0
1.300 -0.32 3135 14.7 0 0
1.400 -0.34 3135 14.6 0 0
1.500 -0.34 3133 14.6 0 0
1.600 -0.29 3135 14.7 0 0
1.700 -0.34 3135 14.8 0 0
1.800 -0.28 3133 14.8 0 0
1.900 -0.30 3133 14.8 0 0
2.000 -0.32 3133 14.8 0 0
2.100 -0.34 3132 14.8 0 0
2.200 -0.28 3135 14.7 0 0
2.300 -0.30 3136 14.7 0 0
2.400 -0.30 3132 14.7 0 0
2.500 -0.28 3135 14.7 0 0
2.600 -0.34 3133 14.8 0 0
2.700 -0.30 3132 14.8 0 0
2.800 -0.35 3132 14.8 0 0
2.900 -0.33 3133 14.8 0 0
3.000 -0.30 3135 14.8 0 0
3.100 -0.29 3133 14.8 0 0
3.200 -0.35 3133 14.8 0 0
3.300 -0.33 3133 14.7 0 0
3.400 -0.30 3135 14.8 0 0
3.500 -0.35 3133 14.8 0 0
3.600 -0.28 3133 14.8 0 0
3.700 -0.32 3133 14.8 0 0
3.800 -0.30 3133 14.8 0 0
3.900 -0.28 3133 14.8 0 0
4.000 -0.33 3132 14.7 0 0
4.100 -0.32 3132 14.7 0 0
4.200 -0.30 3133 14.6 0 0
4.300 -0.28 3133 14.7 0 0
4.400 -0.32 3133 14.7 0 0
4.500 -0.29 3132 14.8 0 0
4.600 -0.35 3133 14.8 0 0
4.700 -0.33 3135 14.8 0 0
4.800 -0.32 3133 14.8 0 0
4.900 -0.37 3132 14.8 0 0
5.000 -0.28 3133 14.7 0 0
5.100 -0.33 3132 14.7 0 0
5.200 -0.32 3133 14.7 0 0
5.300 -0.37 3136 14.8 0 0
5.400 -0.28 3135 14.8 0 0
5.500 -0.33 3132 14.8 0 0
5.600 -0.29 3133 14.8 0 0
5.700 -0.26 3133 14.8 0 0
5.800 -0.32 3133 14.8 0 0
5.900 -0.29 3133 14.8 0 0
6.000 -0.35 3133 14.8 0 0
6.100 -0.28 3133 14.8 0 0
6.200 -0.30 3135 14.8 0 0
6.300 -0.28 3136 14.8 0 0
6.400 -0.34 3136 14.8 0 0
6.500 -0.32 3132 14.8 0 0
6.600 -0.33 3133 14.8 0 0
6.700 -0.35 3136 14.8 0 0
6.800 -0.29 3133 14.8 0 0
6.900 -0.33 3135 14.8 0 0
7.000 -0.29 3135 14.8 0 0
7.100 -0.35 3136 14.8 0 0
7.200 -0.30 3138 14.8 0 0
7.300 -0.35 3136 14.8 0 0
7.400 -0.28 3138 14.8 0 0
7.500 -0.29 3136 14.8 0 0
7.600 -0.29 3135 14.8 0 0
7.700 -0.28 3136 14.8 0 0
7.800 -0.33 3138 14.8 0 0
7.900 -0.30 3138 14.8 0 0
8.000 -0.35 3136 14.8 0 0
8.100 -0.28 3136 14.8 0 0
8.200 -0.32 3135 14.8 0 0
8.300 -0.29 3138 14.7 0 0
8.400 -0.35 3139 14.8 0 0
8.500 -0.30 3139 14.8 0 0
8.600 -0.35 3138 14.8 0 0
8.700 -0.34 3138 14.8 0 0
8.800 -0.29 3135 14.8 0 0
8.900 -0.35 3138 14.8 0 0
9.000 -0.28 3138 14.7 0 0
9.100 -0.33 3140 14.7 0 0
9.200 -0.33 3136 14.7 0 0
9.300 -0.37 3136 14.7 0 0
9.400 -0.28 3138 14.8 0 0
9.500 -0.33 3139 14.8 0 0
9.600 -0.29 3139 14.8 0 0
9.700 -0.28 3136 14.8 0 0
9.800 -0.30 3138 14.8 0 0
9.900 -0.28 3138 14.8 0 0
10.000 -0.34 3135 14.7 0 0
10.100 -0.29 3135 14.8 0 0
10.200 -0.29 3136 14.8 0 0
10.300 -0.28 3136 14.8 0 0
10.400 -0.33 3136 14.8 0 0
10.500 -0.30 3138 14.8 0 0
10.600 -0.37 3139 14.8 0 0
10.700 -0.32 3139 14.8 0 0
10.800 -0.33 3136 14.8 0 0
10.900 -0.34 3138 14.8 0 0
11.000 -0.28 3136 14.8 0 0
11.100 -0.30 3138 14.8 0 0
11.200 -0.34 3138 14.8 0 0
11.300 -0.34 3139 14.8 0 0
11.400 -0.29 3138 14.8 0 0
11.500 -0.35 3136 14.8 0 0
11.600 -0.28 3140 14.8 0 0
11.700 -0.33 3136 14.8 0 0
11.800 -0.30 3138 14.8 0 0
11.900 -0.28 3138 14.8 0 0
12.000 -0.32 3140 14.8 0 0
12.100 -0.34 3139 14.8 0 0
12.200 -0.28 3139 14.8 0 0
12.300 -0.29 3139 14.8 0 0
12.400 -0.30 3140 14.7 0 0
12.500 -0.28 3139 14.7 0 0
12.600 -0.33 3138 14.7 0 0
12.700 -0.30 3136 14.7 0 0
12.800 -0.35 3140 14.7 0 0
12.900 -0.32 3140 14.7 0 0
13.000 -0.33 3136 14.8 0 0
13.100 -0.29 3138 14.8 0 0
13.200 -0.35 3140 14.8 0 0
13.300 -0.30 3142 14.7 0 0
13.400 -0.35 3139 14.7 0 0
13.500 -0.33 3140 14.7 0 0
13.600 -0.32 3140 14.6 0 0
13.700 -0.37 3139 14.7 0 0
13.800 -0.28 3136 14.7 0 0
13.900 -0.33 3138 14.8 0 0
14.000 -0.29 3139 14.8 0 0
14.100 -0.35 3140 14.8 0 0
14.200 -0.30 3140 14.8 0 0
14.300 -0.35 3139 14.8 0 0
14.400 -0.28 3138 14.7 0 0
14.500 -0.32 3138 14.7 0 0
14.600 -0.29 3138 14.8 0 0
14.700 -0.28 3138 14.8 0 0
14.800 -0.33 3139 14.8 0 0
14.900 -0.29 3136 14.8 0 0
15.000 -0.35 3136 14.8 0 0
15.100 -0.29 3140 14.8 0 0
15.200 -0.30 3142 14.8 0 0
15.300 -0.28 3140 14.8 0 0
15.400 -0.34 3138 14.7 0 0
15.500 -0.30 3136 14.7 0 0
15.600 -0.35 3136 14.8 0 0
15.700 -0.33 3139 14.8 0 0
15.800 -0.33 3140 14.8 0 0
15.900 -0.35 3139 14.8 0 0
16.000 -0.29 3139 14.8 0 0
16.100 -0.30 3139 14.8 0 0
16.200 -0.34 3138 14.8 0 0
16.300 -0.34 3140 14.8 0 0
16.400 -0.30 3140 14.8 0 0
16.500 -0.35 3140 14.8 0 0
16.600 -0.28 3140 14.8 0 0
16.700 -0.33 3140 14.8 0 0
16.800 -0.28 3140 14.8 0 0
16.900 -0.30 3139 14.8 0 0
17.000 -0.32 3139 14.8 0 0
17.100 -0.34 3140 14.8 0 0
17.200 -0.28 3142 14.8 0 0
17.300 -0.32 3139 14.8 0 0
17.400 -0.30 3139 14.8 0 0
17.500 -0.28 3140 14.8 0 0
17.600 -0.30 3140 14.8 0 0
17.700 -0.28 3139 14.8 0 0
17.800 -0.33 3140 14.8 0 0
17.900 -0.30 3140 14.8 0 0
18.000 -0.35 3140 14.8 0 0
18.100 -0.28 3140 14.8 0 0
18.200 -0.32 3142 14.8 0 0
18.300 -0.29 3142 14.8 0 0
18.400 -0.34 3142 14.8 0 0
18.500 -0.30 3140 14.8 0 0
18.600 -0.35 3140 14.8 0 0
18.700 -0.33 3142 14.8 0 0
18.800 -0.30 3139 14.8 0 0
18.900 -0.37 3139 14.8 0 0
19.000 -0.29 3143 14.8 0 0
19.100 -0.32 3140 14.8 0 0
19.200 -0.35 3140 14.8 0 0
19.300 -0.33 3142 14.8 0 0
19.400 -0.32 3139 14.8 0 0
19.500 -0.35 3140 14.8 0 0
19.600 -0.28 3142 14.8 0 0
19.700 -0.33 3140 14.8 0 0
19.800 -0.28 3142 14.8 0 0
19.900 -0.29 3140 14.8 0 0
20.000 -0.30 3139 14.8 0 0
20.100 -0.35 3140 14.8 0 0
20.200 -0.28 3146 14.8 0 0

When it's on boost the signal fluctuates even more. The only time it is really stabile is on overrun, it was a steady -0.81 bar. Does anyone have an idea what could cause this? Is there any reason why the MAP signal could really fluctuate like this? I have checked the hose to the MAP sensor and it can't really be leaking. I also don't think it's just an electrical thing because you can feel the car judder and the signal is stabile on overrun. The only thing I can think of is something with the wastegate not keeping the boost stabile, but what exactly I don't know...

The car is a sapph 4x4 with a 320 bhp MSD chip with closed loop and wasted spark. Boost is set using a bleed valve.

Marc sierra

iTrader: (1)

Is it possible that the inlet pressure isn't really changing, but that the hesitation/judder is caused by the fueling that is constantly changing based on the changing reading from the MAP sensor?