Case Study: Porsche Cayenne misfire DTC and engine warning light mystery

"The diagnostic test always reads the same DTC, one or more cylinders misfire - sometimes all of the cylinders misfire - and the DTC has a very high misfire counter. When previously repairing the vehicle, all related parts; coils, spark plugs, injectors, sensors, and fuel delivery were replaced. Each time the test drive was carried out, the vehicle passed and was returned to the customer. However, the vehicle would return a few days or weeks later with the same DTC issues."

Our latest case study is available in full on the Pico Auto website.
 

PicoAcademy Off Highway:
Preventative Maintenance and Overview

A to Z: Sampling

Waveforms can take many forms; their features can change slowly or quickly and they can cover either a long or short time span. When capturing waveforms, you must make sure you capture them in their entirety and with sufficient detail. That is, both your timebase and sample rate must be sufficiently high.

Your timebase determines how long your capture is, while the Sample rate decides how much detail you capture. It's essential to find a balance: too short a timebase might cut off important parts of the waveform, whereas too long a timebase may mean you can’t see important detail; and too low a Sample rate may mean you don’t capture enough detail, whereas too high a sample rate might not add extra useful information, just taking up more memory and disk space.

PicoScope, a tool for capturing waveforms, helps with this balance using its Sampling mode priority feature.

Sampling helps you to set the total number of samples (single measurement values at regularly spaced intervals) that make up each of your waveforms and the rate at which they are taken. To find out more about Sampling in PicoScope 7 Automotive, you can check out our new entry into the A to Z of PicoScopes.

You can also download the software for free on our website.
 

Tech Tips!

While there is no dedicated math channel selection like the Crank, did you know that it is possible to use an injector to graph the engine speed? The formula you would use is: 60/0.5freq(A), where A is the channel with the injector current.

The image above is an example from a machine where the injector current from cylinder one is captured, and engine speed is calculated from the aforementioned math channel.

This capture is zoomed in to show accuracy by using the phase rulers at each injector event, which happens once every 2 rotations of the engine. By then using the time rulers and positioning on 0 deg and 360 deg, we have the 1 rotation of the engine. The ruler overview calculates the RPM as indicated. Here, we can be sure that the math channel is representing engine speed correctly.

This formula can also be used to determine engine speed if using ignition triggers, secondary ignition, in-cylinder pressure or any other signal that occurs for every 2 rotations of the engine.

Expensive repair? Other shop
just guessed!

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