4425 Delphi injector readings

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TonyNott
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Joined: Thu Jan 17, 2019 2:05 am

4425 Delphi injector readings

Post by TonyNott » Thu Jan 24, 2019 2:20 am

Hey guys

Names Tony Nott ,
Im from Australia working as a diesel mechanic for a JCB dealer, have been working for them for close to 10 years, have only just been using the scope for the past 12 or 18months but has been a massive advantage for the work that i do.

I have a machine that has a engine running fault

i was using the current clamp TA018 to test injectors firing , everything was fine, i than went to test voltage with a 10-1 attenuator and the scope went over range so i shut it down, the machines fault required the machine to come into the work shop, now i have the machine in the work shop

yesterday i was trying to read the injector voltage and the scope kept telling me over range +2KV , thinking that maybe this machine has a issue i got a new machine and tested the injector voltage and everything was fine except, i could only read the injector voltage in reverse polarity as soon as i changed the polarity i had no reading, i also found that i could only read the injector voltage thru the green channel, i also found that reading the injector voltage and the rail pressure sensor at the same time i had a dirty signal when the injector fired, wasn't much of a issue as i added a filter and it was fine.

i have gone and checked cam signals with the scope on the channels i couldn't read the injector voltage to make sure i hadn't damaged anything but it was working fine reading the signals thru all the channels

i have attached the signal of the injector voltage with the fuel rail pressure voltage.
Attachments
JCB_TM320s_20190124-0006.psdata
(1.03 MiB) Downloaded 80 times

ben.martins
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Joined: Tue May 16, 2017 1:02 pm

Re: 4425 Delphi injector readings

Post by ben.martins » Thu Jan 24, 2019 3:28 pm

Hello Tony,

Thank you for taking the time to post and there are couple of things I think we need to try to help with your capture.

With regards to the voltage of the injectors it seems a little odd that there should be an over range issue as the scope should be able to handle most common rail injectors. As you have a 4425 the max input voltage to the scope is 200V of which I've only seen seen some Piezo injectors gone above. Great to see you using the attenuators for unknown voltages as this certainly gives us further protection from over voltage.

I have noticed that you have the channel for the injector AC coupled. For injectors there is no need for this. For most automotive signals you will only ever need DC coupling but AC coupling does have it's advantages in the right situation. If you need further information on this please let me know.

Using the current clamp is one of the best ways to determine injector operation as the current gives us an indication of 'work done.' I think I would be tempted to utilise all 4 channels on your scope and make a few changes to you set up. For channel A I would have injector current, channel B I would put one side positive or negative side of the injector, channel C would be the other side of the injector and finally place the rail pressure sensor on channel D.

With the new 4425 we do need to be aware of the floating input when looking at signals. This means we have to ensure that all the black/grounds of our test leads are individually grounded. There is further information on floating inputs here - https://www.picoauto.com/library/traini ... ing-inputs.

I hope this helps and it does seem odd that you are getting an over voltage warning even with an attenuator but if you are still seeing this after trying the setup I've mentioned then please don't hesitate to get in touch.

Kind regards

Ben

TonyNott
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Posts: 4
Joined: Thu Jan 17, 2019 2:05 am

Re: 4425 Delphi injector readings

Post by TonyNott » Thu Jan 24, 2019 7:51 pm

Just to Clarify

channel B to reference injector positive to battery negative?
Channel C to reference injector negative to battery positive?

im a little hesitant to test i have only one attenuator and have had previously seen the over voltage warning

Just for reference
The Issue with the machine is as follows
The machine starts and runs ok
Reference to another machine the same the fuel pressure at idle is approx 200 bar low (30 to 40%) but the engine does not register a pressure issue or code
revving the engine up is fine but when you back off the engine turns the injectors off as the rpm is reduced, once it reaches its desired RPM to restart the injectors i can see current flow to the injector but i cant see and dips in the fuel pressure, this would indicate a mechanical issue with the injectors , but i am just trying to confirm there is no other under lying issues as this machine is 2,500 hours old and has had two engine ecu's fail due to a coil issue.

TonyNott
Newbie
Posts: 4
Joined: Thu Jan 17, 2019 2:05 am

Re: 4425 Delphi injector readings

Post by TonyNott » Fri Jan 25, 2019 1:12 am

Ok i have a update for this issue

I have since worked out that the PIN out diagram i was using for the tests is incorrect to the actual pin outs

i must have been getting a bad signal from something whilst i was trying to test the injectors (possibly trying to test across two injectors)

i have since tested all my channels against the setup you offered and they are all working fine

one thing i am still getting is the Low side driver is still going up rather than down when the coil collapses?

i will attach my wave form

and the machine fault has been rectified also

Blue - current clamp #1 injector
Red - Injector HSD #1 injector
Green - Injector LSD #1 injector
Yellow - Fuel rail pressure
Attachments
TM320 test.psdata
(1009.07 KiB) Downloaded 74 times

liviu2004
TwoWaves
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Location: Netherlands

Re: 4425 Delphi injector readings

Post by liviu2004 » Fri Jan 25, 2019 6:34 am

For the sake of clarity.

All channels have to have the black lead connected to minus.
If you want to float measure your channels (2 or more channels connected in the same time), you have to ensure beforehand that the difference in potential between channel grounds is not higher than 30V (I've seen here). Personally, I would not do it.

It does not matter if you measure the ground side of the injector command, against minus, the injector positive feed and its internal resistance will take care you see something useful on screen.

Take care, and don't burn the scope. Its too valuable to be damaged.

ben.martins
Pico Staff Member
Pico Staff Member
Posts: 151
Joined: Tue May 16, 2017 1:02 pm

Re: 4425 Delphi injector readings

Post by ben.martins » Fri Jan 25, 2019 12:42 pm

Hello Tony,

I'm glad you have got the bottom of the fault and now seeing the expected waveform. Remember, as you are using the automotive scope you have the added protection built into the scope. If you were to accidentally put a much higher voltage through the scope, a fast self resetting fuse will trip and disable the channel. Once the signal has been removed for a period of time, the fuse will reset and the channel should be back working again. The automotive scope has been designed to cope with the harsh environment we work in which is why we have this protection in place amongst many other features. That being said, it is good practise to use attentutors when you are unsure of voltages.

Thank you Liviu for clarifying the channel grounding and pointing out the 30V capability of the 4225 and 4425 scopes. For most cases you won't need to float the channel but once your become more familiar with your scope and it's capabilities then having the option is a nice thing to have. As you are working with plant machinery there may be a time when you would like to carry out a voltage drop across something like a starter motor cable. With the older scope you would have to use two channels and then apply a maths channel to calculate the drop. This is no longer the case with the scope you have as you can use just one channel and connect as you would do with your DMM but now we can record and measure against time. It's not something you will need all the time, but the option is there if you need it.

This is a great capture you have uploaded as we can see the true relationship between voltage and current. I've uploaded your file with a couple of amendments which will hopefully highlight some additional information from your capture. I've focused on just the current and the LSD side of the injector and applied a x30 scale to the LSD signal. From the current we can see a small dip in the first current ramp which indicates a movement from the needle as it is lifted from its seat and over comes the spring holding it down. Then we enter the holding phase as current is reduced. Then as the current is stopped we have the collapse of the magnetic field which results in this large voltage spike you have pointed out. This is caused by the inductive effect from the sudden stop in current which forms the basis of many petrol ignition systems to create the high voltage required to produce a spark. Some manufacturers will place a diode on this side of a coil to cap this voltage spike but it is an effect that will always be present.

Looking further at the LSD signal but after the voltage spike you will notice that by increasing the scaling we can see a 'hump' as the voltage is dropping which is known as the pintle hump. The injector pintle hump is formed when the injector pintle passes through the solenoid winding core on closure, disrupting the magnet field on route and revealing this event in the induced voltage decay. This means the injector is moving back towards it's seated position. We have a nice case study looking at a petrol injector and looking for the pintle hump. https://www.picoauto.com/library/case-s ... techniques.

There is some great diagnostic information from this capture but I'm still not sure about the fuel pressure sensor signal. Usually you can see some form of variation when the pressure changes. Sometimes in this instance AC coupling the rail pressure sensor can help reveal these small changes. Might be worth playing about with this feature in the next adventure!

Hope some of this helps and we are all here to help with the journey.

Kind regards

Ben
Attachments
TMS320 Injector Capture with scaling.psdata
(1013.27 KiB) Downloaded 63 times

TonyNott
Newbie
Posts: 4
Joined: Thu Jan 17, 2019 2:05 am

Re: 4425 Delphi injector readings

Post by TonyNott » Sat Jan 26, 2019 2:47 am

Thanks for your input has been a great help for me and will help me a lot in the future.

I didn't notice the lack of dip in fuel pressure, on another form i had of the machine i was using AC and DC on the fuel rail pressure and i was picking up the dips than, i wasn't paying much attention to the rail pressure so didn't try get the dips in the form, i will load the form i have with the dips in it

Blue - rail pressure AC
Red - injector current
Green - Fuel pressure DC
Yellow - Throttle position
Attachments
20190120-0006.psdata
(2.45 MiB) Downloaded 80 times

lastvagn8
OneWave
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Joined: Tue Feb 05, 2019 7:43 pm

Re: 4425 Delphi injector readings

Post by lastvagn8 » Sun Mar 17, 2019 8:34 pm

Hi Tony!

Did you work it out? What was the problem?

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