Kia Ceed 3 1.6 diesel alternator ripple test

[Technician]

I used the scope presets and followed the instructions for a PCM controlled alternator test. I was a little confused about the test setup advising me to put the probe on the alternator main battery terminal. Running the engine at idle the following trace was recorded.

Before I scoped the alternator I put the scanner on and that recorded a P0620 code. My original alternator seized in operation hence changing the unit. The code refers to a control circuit fault. I didn't think the trace looked great either, and the voltage spikes are something else!

I asked the supplier to exchange the alternator and yesterday I fitted another unit from another company they supplied. A code read does not bring back any codes, but the scope trace is the same as the one here. They don't look good and the voltage spikes look excessive to me!

Following the scope presets am I doing this test correctly! Normally I'd of thought the F terminal should have been used!

[Rfmotors1]

Hi, I am looking at your picture and here is my interpretation. (correct or not, we always find later)

There are regular waves and two spikes repeating in the waveform.
Let's say the waves are matching the alternator rotation and windings modulated by diods, then the alternator operation has predictable pattern.

There are the two spikes which may be related to engine RPM.
These spikes are not related to alternator RPM because originating always at different time in relation to wave shape from alternator.

So, I don't think the spikes are caused by alternator.

If you can invest more time, you can try to probe injector using attenuator and check if these spikes are the interference from injectors.

If you get new data or conclusion, please update us here, we all enjoy to learn from others here.

Regards,
Roman

[Technician]

Thanks Roman,

I'll do the injector tests tonight and post up for advice.

[Technician]

So I've done an injector test of all four injectors. Each injector provides the exact same waveform. During acceleration and cut off each injector performs the same and no faults can be seen using this method. I did question the operation of the injectors over time because of exhaust smoke, but tests last night indicate that I have a problem on the EGR control circuit. I tested the EGR valve operation using the scope settings in the automotive menu, but the results appeared very erractic and I thought that 200 micro seconds was a tab too fast?

Anyway I searched my Kia data last night and got the correct settings. I don't need to do further tests as I moved through the time devisions last night and the EGR operation was poor at best, so I know I have some type of control circuit fault to be found!

I've got the exact EGR waveform and settings from my OE Kia data and at those settings the EGR is not working correctly.

[Technician]

Just an interim update....

I've rectified the EGR circuit fault and the exhaust system operation is much cleaner, and the power output of the engine is significantly better. Given then that the injectors all perform the same, I left thinking about what is operating on the engine to provide those spikes are regular intervals. Something electrical that is being triggered at a given number of engine degrees? I could when I get a minute use the scope rulers/cursors and measure the duration between each, and hopefully that may provide some leading information!!

[Rfmotors1]

Hi,
The best practice to find out where the spikes come from is to use other channel and read other signals.
For example if the injectors would be the spike sources, the signal (falling or rising edge) would always match the spike on the original signal (here it would be your alternator ripple waveform)
So you would need to record both at the same time.
Regards,
Roman

[Technician]

Referring back to the injectors trace above. My exhaust tail pipe emits dense black dry smoke when I accelerate hard. Most of the smoke clears but I suspect a poor spray/lower pressure injector fault. Given the current demand test won't show that type of fault, and without dismantling, is there a good way to prove if an injector is poor in operation?

Would a back leakage test be accurate enough to prove a fault?

[Technician]

Did manage to find the time to do a back leakage test. The results speak volumes...

[wiki38andy]

Just an interim update....

I left thinking about what is operating on the engine to provide those spikes are regular intervals. Something electrical that is being triggered at a given number of engine degrees? I could when I get a minute use the scope rulers/cursors and measure the duration between each, and hopefully that may provide some leading information!!

You have 4ms regular intervals which means 250Hz frequency. This is used by ECM to actuate rail pressure/ fuel flow regulators. The second smaller spike inside this time frame strikes at about 0.3ms, roughly 16 % of the period. This matches with fuel pressure regulator duty cycle at idle. So, these spikes could come from ON/OFF ECM solenoids control.

[Technician]

Sorry for delayed reply wiki38andy but thanks for your input.