Piezo injector current - Bad ECU or...

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picowight
TwoWaves
TwoWaves
Posts: 119
Joined: Sat Oct 26, 2019 6:45 pm

Piezo injector current - Bad ECU or...

Post by picowight »

This is a Vivaro/Primastar 2008 2.0dCi
Original complaint rough running no power, there have been some introduced issues to resolve on the way but it is now mostly crank, fire, die. Occasionally it will idle badly.
Gathered all the wires at the ECU and current clamped them and synched voltage on #3 in red - it is powered at every injector firing but only grounded when needed - the difference is obvious.

This is #3 - which I believe is good as it has a good open and close current (blue) on the piezo injector (this is pilot and main firing)
Screenshot from 2022-09-08 23-08-08.png
However the next in the firing order #4 is significantly lower current and very much lower closing the crystals
Screenshot from 2022-09-08 23-09-17.png
There is a bit of a filter on this to give the recognisable shape - It is possible my Prosys C-30 current clamp has a much higher resolution forward than backwards as the opening current is around 20kHz which is the max of the clamp.
- unfiltered :
Screenshot from 2022-09-09 09-46-30.png
Screenshot from 2022-09-09 09-45-13.png
The problem is on #1 and #4 :
Screenshot from 2022-09-08 23-36-59.png
Really like peoples opinion on if this can be anything except a bad cap/driver in the ECU as I don't see a lot of Piezo current waveforms - pico file attached.
Attachments
20220908-0012 all 4 synch 3 last.psdata
(3.75 MiB) Downloaded 10 times

picowight
TwoWaves
TwoWaves
Posts: 119
Joined: Sat Oct 26, 2019 6:45 pm

Re: Piezo injector current - Bad ECU or...

Post by picowight »

This has taken a lot of thinking about, it turns out that my synch above may or may not have been reliable...
As I have a 4425a with floating ground, I hook up to differential voltage on #4 (blue) and #3 (green) injectors at the ECU- these are opposite sides of the ECU plug and one set is pierced and one set is back-probed. #4 Blue is through a 20/1 attenuator. #3 green is scaled to 50% in the pics.
At the same time I bundle the +ve side wires and amp clamp them. This is what I get;
Screenshot from 2022-09-12 22-15-45.png
#3 and #4 are both appearing to fire at the same time and the waveforms are identical. So now I can't tell which one I am synched on (this is after the fact as my CF-C2/4Gb/2 core i-5 laptop is not powerful enough for P7 :roll: and it will not zoom in to the waveforms - I can on my higher power linux desktop)
I breakout the lead for inj#4 to inj#3 leaving #3 disconnected and I get this:
Screenshot from 2022-09-12 21-52-31.png
As there is no injector on lead 3 then the green trace #3 must be accurate and the blue #4 is piggy backed. - So I'm thinking must be the ECU.. But then I go back to the 1st pic above and if you assume that green #3 is accurate and label the injectors- that means that the problem changed with a switched injector - so it must be an injector, but then look again at the differential voltages they are now showing on all firings with the injector swapped .. ECU ? :shock:
An ECU swap is not that cheap, even if a used one will take programming. An injector swap might write off the engine as they are notoriously difficulty to remove due to water sitting in the cover. Got to be right and if it is an injector I have got to be certain which one.
Attachments
20220913-0001 3-4 diff V all A.psdata
(26.29 MiB) Downloaded 13 times
20220913-0001 4 lead swapped to 3 inj.psdata
(26.14 MiB) Downloaded 11 times

Iver
TwoWaves
TwoWaves
Posts: 166
Joined: Mon May 27, 2019 2:55 pm

Re: Piezo injector current - Bad ECU or...

Post by Iver »

PicoWight
An ECU swap is not that cheap, even if a used one will take programming.
I'm not so sure you can programme a used ecu to that in the conventional way ?

However a used unit can be cloned. A search on google or ebay will reveal that there are ecu sellers that will do that for you if you send your ecu too them, or any one with "mapping" equipment certainly can. And not as expensive as you think !! Take a look. I have a good friend that does it. PM me !

An injector swap might write off the engine as they are notoriously difficulty to remove due to water sitting in the cover. Got to be right and if it is an injector I have got to be certain which one.
I learnt this the hard way ! Don't even bother trying very hard, if it does not slide out then stop. Reason being that if you damage the top of the injector it then makes it harder for the specialist to extract it and will cost more time and money.

All I have written so far does not help you diagnose the fault to the root cause. I know that.

In your shoes I would be doing the following:

CKP with RPM math channel IF you can get it run long enough. Mechanical / Spray Pattern Integrity.

Have you done a LEAK OFF ? With WPS if possible ?

Scope FRP looking for even movement as each injector fires ?

Insulation test on injectors with a Meggar or Similar tool (Bosch FSA 050) Any good Household or Commercial Electrician will have one if you don't. Test them right up to 250 - 300v. Electrical Integrity !

An Ohms test with a DVM is not really sufficient but quick and worth doing.

Since you suspect cylinders 1 & 4 to be the culprits then Im thinking those 2 pistons rise and fall together and may be fired by the same Transistor and Capacitor Combination (Think of Wasted Spark Ignition)

Extend wires on all 4 injector connectors then connect #1 to #2. #2 to #1. #3 to #4 and #4 to # 3. then scope the tits off it whilst cranking. Hopefully that will achieve some more elimination on Injector or ECU. Thats sounds all wrong but I / We do it with ABS sensors that are seized.

picowight
TwoWaves
TwoWaves
Posts: 119
Joined: Sat Oct 26, 2019 6:45 pm

Re: Piezo injector current - Bad ECU or...

Post by picowight »

thanks Iver
I have "inhaled" and stored the ECU coding on a Maxysis ready to download back to it - however there is some doubt if that covers the immo coding so yes may have to clone.

Injector removal will be down to the garage that is my customer. They have a specialist they use.

Lots of scoping gone on other than what is posted !

Meggered the injectors all nominal

Yes my thinking that 1 cap is involved with 2 injectors - hence thinking ECU injector driver.

Made my head hurt trying to work out what was going on with just one swap and one disconnect - though as someone pointed out with 1 disconnect the ECU could go into some sort of protection mode.
I'm getting an ECU and if it will not program the immo I'll drop you a line.

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