PicoScope 7 Automotive
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Crank maths misfire
Crank maths misfire
I am looking a bit of advice on the attached waveform, I know that the car needs number 1 injector due to excessive leak back.
The trace has the following;
Channel A (Blue) - Fuel rail pressure
Channel B (Red) - Injector sync
Channel C (Green) - Crankshaft sensor
Crank Maths channel (Black)
What I am trying to understand is how do I identify using from the fuel rail pressure trace that less fuel is being delivered? I can see how the crank maths channel shows the misfire but cant see the relationship in the fuel pressure signal.
The car is a 2008 1.3cdti Corsa
Thanks in advance
The trace has the following;
Channel A (Blue) - Fuel rail pressure
Channel B (Red) - Injector sync
Channel C (Green) - Crankshaft sensor
Crank Maths channel (Black)
What I am trying to understand is how do I identify using from the fuel rail pressure trace that less fuel is being delivered? I can see how the crank maths channel shows the misfire but cant see the relationship in the fuel pressure signal.
The car is a 2008 1.3cdti Corsa
Thanks in advance
Re: Crank maths misfire
Difficult, as there are too many variables for the fuel pressure. Run the engine on brake cleaner not diesel and check crankshaft speed variation, if equal, diag is ready in exactly 2 minutes.
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ben.martins
- Pico Staff Member
- Posts: 543
- Joined: Tue May 16, 2017 1:02 pm
Re: Crank maths misfire
Hi Burt_100,
As liviu has stated, it isn't always as clear cut different fuelling stratageries, pump characteristics such as number of pumping elements, SCV and pressure control can all play a part on the signal. Sometimes it's quite clear as below -
You can try a couple of different methods such as AC coupling the rail pressure sensor and then lower the voltage to improve the resolution, use the sensor ground if capturing on a 4*25 and 4*25A where you can float across the sensor and applying bandwidth limit can also remove frequencies about 20kHz using the built in hardware filter in the scope.
Looking at your capture there is a repeating event after number 1 injector but how that relates to the system is difficult to determine without knowing more about it's operation.
Once you have the fault rectified, a known good it would be great to compare the two if you can upload to the forum.
Kind regards
Ben
As liviu has stated, it isn't always as clear cut different fuelling stratageries, pump characteristics such as number of pumping elements, SCV and pressure control can all play a part on the signal. Sometimes it's quite clear as below -
Looking at your capture there is a repeating event after number 1 injector but how that relates to the system is difficult to determine without knowing more about it's operation.
Once you have the fault rectified, a known good it would be great to compare the two if you can upload to the forum.
Kind regards
Ben
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jeffreythomas
- Newbie
- Posts: 1
- Joined: Thu May 18, 2023 12:43 am
Re: Crank maths misfire
hello,Burt_100 wrote: ↑Wed Nov 02, 2022 10:12 pmI am looking a bit of advice on the attached waveform, I know that the car needs number 1 injector due to excessive leak back.
The trace has the following;
Channel A (Blue) - Fuel rail pressure
Channel B (Red) - Injector sync
Channel C (Green) - Crankshaft sensor
Crank Maths channel (Black)
What I am trying to understand is how do I identify using from the fuel rail pressure trace that less fuel is being delivered? I can see how the crank maths channel shows the misfire but cant see the relationship in the fuel pressure signal.
The car is a 2008 1.3cdti Corsa
Thanks in advance
misfire.png
I am also having the same problem, same waveform, I think there is a misfire. Actually, nvm.