 | Home > Technical > More random scope work.. |
 
|
|
|
| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 814  
|
I thought id revisit he injectors on my 2.2 tdci engine..mainly because I've forgotten what I've done before and can't find the files I had..
Selected No2 injector and connected a channel on voltage scale to each of the injector pins..(they are piezo injectors) Put an amp clamp on a 3rd channel and connected that to one of the injector wires as well..so blue and red are voltage traces and the bottom greenish trace is injector current in the picture below..  Click image to enlarge So it appears all the injectors are pulsed with the 125v at the same time.. The injector that is fired..in this case no2 is grounded by the ecu..the voltage drops across it as seen by the missing red spikes on that trace which is obviously the voltage on the ground or ecu side of the injector, and confirmed by a current flow on the green trace below the missing red voltage spike on no 2 injector.. I'll revisit the firing event in more detail in next post..ππ |
||
31st Jul 2025 8:38am |
|
| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 814
|
Hi..not sure if follow you.. the channels are both referenced to battery ground.. that will be where the injector driver circut grounds to I believe..
My scope channel grounds are all isolated so I connected both to a good engine ground and pretty well got a trace that seemed logical and right.. |
||
|
31st Jul 2025 9:31am |
|
| eno Member Since: 15 Apr 2024 Location: Qld Posts: 48 
|
There probably is circuitry on both the high and low sides of the injector. So a single connection to one side may not show the true voltage across the injector.
To display the true voltage across an injector, connect one channel to the high side and another channel to the low side. Then select Ch A - Ch B, or whatever the channel maths function is called . It might be Ch A + (-Ch B) but the idea is to display the difference between the two channels. That will give the true voltage applied across the injector |
||
|
31st Jul 2025 11:09am |
|
| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 814
|
That is what you are looking at..
I have channel A (blue trace )on the supply or high side..its showing a 125v pulse.. Channel B (red trace) is on the ground or switched side of the injector and shows close enough to zero volts when the injector fires..ie the missing pulse on the red trace which coincides with the current pulse in the lower 3rd trace.. 125v dropped across the injector when its switched.. That's a pretty common voltage for a piezo injectors so no reason to doubt that..ππ€ |
||
|
31st Jul 2025 11:19am |
|
| eno Member Since: 15 Apr 2024 Location: Qld Posts: 48
|
Ah, all good. I probably should have looked at the posts on a PC instead of a phone with cracks all over the screen. I might read the message properly in future. π
|
||
|
31st Jul 2025 12:37pm |
|
| MK Member Since: 28 Aug 2008 Location: Santiago Posts: 2489  
|
Thanks
Can you pick all the injections (i.e. pilot(s) and main)? I cannot remember if I already ask you the same 
I guess thiis system on the 2.2 runs more "injections" on each stroke than the 2.4 Puma 110" SW ............................................................. Earth first. Other planets later |
||
|
31st Jul 2025 1:07pm |
|
| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 814
|
That's fine..I also need to make sure I'm understanding what folk are saying in case I'm not getting it right.. I do know what you were on about mind.. If you need to measure the volt drop across say a piece of wire..say the starter circut, then unlike a multimeter where you just measure between the two points you want to know the difference in, with a scope with common grounds for all channels you have to use two channels (one connected to each point you want to know the volt drop over..then use a maths channel to take one voltage (channel) from the other.. The scope i am using at present has floating grounds..and the channel ground can tolerate a + or - 30v difference between vehicle ground..so as long as that parameter isn't exceeded then you can measure a volt drop with one channel and no maths involved...just like a multimeter..π |
||
|
31st Jul 2025 1:34pm |
|
| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 814
|
Yes.. the traces in the picture above are taken over a longer time base, so that you see a bigger number of events.. The scope is powerfull enough to collect enough samples that allow you to zoom in on say the injection event in much more detail.. Ive not looked at it under decent load conditions but at tick over this is what you will see.. The 125v is applied in pulses to the piezo stack for a time determined by the engine map for the running conditions.. The current trace is showing 3 injection events ..the last one been the main pulse Click image to enlarge The blue trace is the applied voltage pulses.. The red line is the zero volts on the ground side of the injector The greenish or bottom trace is the current flow.. ill be coming back to that in a later post when I've done a bit more thinkingππ€£ |
||
|
31st Jul 2025 1:42pm |
|
| MK Member Since: 28 Aug 2008 Location: Santiago Posts: 2489
|
nice Puma 110" SW
............................................................. Earth first. Other planets later |
||
|
31st Jul 2025 2:00pm |
|
| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 814
|
Back with a close up of the injector firing event..in the space of 2.6ms the injector delivers 3 pulses of fuel..
You can see the voltage pulses of approx 120v in blue, and the corresponding current in the bottom gold trace.. The interesting bit is the current is shown as a positive and negative value .. It initially rises to about 4 amps and when the voltage is removed there is a flow in the opposite direction.. so what im assuming is that initially the piezo stack expands opening the injector on the application of the voltage.. when the voltage is removed the stack returns to normal and generates a current in the opposite direction...most probably captured by the ecu driver circut to assist in the production of the next pulse.. Anyone know if that is the way the piezo injectors work.?? Click image to enlarge |
||
|
31st Jul 2025 5:10pm |
|
| MK Member Since: 28 Aug 2008 Location: Santiago Posts: 2489
|
  Puma 110" SW
............................................................. Earth first. Other planets later |
||
|
31st Jul 2025 10:20pm |
|
| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 814
|
The next instalment is back to the glow plugs ..again just a vague recollection that last time i looked I'd established that on the 2.2tdci the max preheat period (ie light remains lit on dash) was around 2 seconds, but the plugs could go on to operate for up to 500sec in the right conditions..
And I remember the plug supply from their control unit was pulse width controlled.. So I connected all four channels up to the individual plugs and started the engine.. it was a warm day so didn't expect to see them on sor long.. Click image to enlarge They ran for 160 sec and voltage at 14.5v That view is over a longer time base, But if you zoom in this is what is actually happening..you see the individual pulses.. Click image to enlarge And if you go in a bit ore its possible to see that the pulses are staggered in such a way that only one plug is been done at any given time.. with a pulse of about 6ms.. Click image to enlarge And after that I put the current clamp on to check what current is been drawn while the plugs are pulsed.. I couldn't do it at the same time as the voltage traces as I only have 4 channels available.. Click image to enlarge And its around 20 ampsπ |
||
|
1st Aug 2025 9:02am |
|
| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 814
|
Last Post on this topic for a bitπ
Promise π€£ I bought a probe for the scope.. advertised as a vibration sensor..didn't really know what i was going to do with it but at about 28us dollars i thought why not.. Click image to enlarge I clamped it on to the hp metal pipe to no 1 injector and ran the engine..had two channels on the injector voltage... It not only capable of detecting the point of the no1 injector firing but it also picks up the pulses of the other injection events.. The red trace...largest spike is no1 and the smaller spikes align with the other Injection events.. A handy and quick way to reference any particular cylinder firing..π The probe just clamps on to the pipe..I'm sure it could be used for other things but can't think what at the minπ€π€£ Click image to enlarge |
||
|
1st Aug 2025 5:07pm |
|
| andy63 Member Since: 30 Jun 2023 Location: north east Posts: 814
|
OK.. i lied
Another post showing off the capability of a scope.. Started off with a channel on battery voltage (in blue) And a current clamp on the + battery cable to monitor current..(red trace) Disable a start and crank the engine for a few seconds.. My current clamp only goes to 600amps so the top of the red trace is cut off.. obviously the initial surge is in excess of 600 amps but other than that you can see the current settles to around 230A and the battery voltage to just under 11V... Now for the clever bit.. With the scope software you can create maths channels.. Divide the voltage by the current and you get a trace for the resistance of the circut.. Settles at just under 50mohms (black trace) so you know your earth's are good.. Then another maths channel multiplying the current and voltage, giving you the power been consumed by the starter.. (in yellow) Averaging at just under 2.5kW And finally because you know each current spike is a compression stroke and you get two of them on each revolution, then cursor placed accordingly give you the cranking speed.. A lot of info for a simple test..in fact if you looked closely at the current spikes you would see a comparison in each cylinders compression .. Click image to enlarge |
||
|
3rd Aug 2025 10:56am |
|
|
|
| All times are GMT + 1 Hour |
< Previous Topic | Next Topic > |
Posting Rules
|
Site Copyright © 2006-2025 Futuranet Ltd & Martin Lewis
