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Chapter 18 Fuel Injector Testing

posted Jun 04, 2016 04:39:29 by IsshmanGarcia
In regards to your video: How to test fuel injectors with a labscope-Chrysler 3.0 "Maserati". I know injectors produce up to 100v each, so if I found a point or connection that all injectors go to,giving me access to all injector waveforms at once, is it ok for me to backprobe that connection point with a T pin and a 20:1 attenuator? Do injectors emit 100v each and together(all injectors at one connection point)? Basically i want to see all injector waveforms using one point. Do I total 100v multiplied by 6 injectors or will it be 100v total? Im using AESWAVE uScope and a 20:1 attenuator. I DO NOT HAVE A LOW/HIGH CURRENT CLAMP AT MY DISPOSAL. Thanks in advance for any help.
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15 replies
Tyler said Jun 04, 2016 17:35:35
Hey Isshman!

This is an interesting question, hadn't thought of this before. What kind of vehicle are you working on? Or, is it another 'Maserati'? I ask so I can look up the appropriate wiring diagram, better understand what you're looking at.

The point that you found to test all the injectors, is it on the power or ground side of the injector? If it's on the power side, and the power is constant, then you won't see any waveforms, just a steady 12V line (hopefully). If it's on the ground (control) side, then the voltage spike may be a concern.

The way I'm thinking of it, the inductive spikes shouldn't 'stack', and shouldn't result in a 600V peak. However, I'm not positive about this, as I've never had the chance to scope a similar circuit. I'd welcome anyone thoughts on this.

The good news is that you have a 20:1 attenuator! If I'm doing the math right, then the 600V peak would end up as a 30V peak on your scope. The max input on the uScope is 80V, so I think you're covered.
[Last edited Jun 04, 2016 17:37:55]
IsshmanGarcia said Jun 04, 2016 18:02:32
Hey Tyler, Im working on a 2004 Chevy Monte Carlo 3.4L. I do have a wiring diagram and the point i was referring to is actually a power feed.They all go straight to a fuse. The ground sides of the injectors all separately go to the computers,so I wouldn't be able to view all waveforms(together)that way.I dont understand how Paul is able to see all waveforms from that one feed wire? Is it a current thing? Thank you for your help.
IsshmanGarcia said Jun 04, 2016 18:31:21
Yeah Tyler, I just rewatched the video. Paul did Tpin those injectors separately (paired injectors). I interpreted the video wrong,but now I understand. Thanks for your help in the matter.
Tyler said Jun 05, 2016 14:30:45
Yeah Tyler, I just rewatched the video. Paul did Tpin those injectors separately (paired injectors). I interpreted the video wrong,but now I understand. Thanks for your help in the matter.

No problem! I still like the root of your question, involving multiple solenoids on one control wire. I ended up thinking of a different shorted injectors video, but that Lumina's ECM still uses two control wires externally, but one driver internally :-( Oh well.

Now I'm thinking of how to rig up some old fuel injectors in series and measure the spikes, lol.
[Last edited Jun 05, 2016 14:31:13]
IsshmanGarcia said Jun 05, 2016 17:16:12
If you do rig something up,share your results. Thanks for your help though.
AndyMacFadyen said Jun 09, 2016 17:10:27
The voltage spikes won't stack even on bank fired or engines where all the injectors fire at once the injector are wired in parallel.
BUT connecting to measure voltage at the conmmon supply won't tell you anything but battery voltage. To get any valid result for all the injectors from a single point you need to look at the current.
Without a current clamp you could go really old school and insert a cheap low resistance shunt resistor into the wiring by using a breakout and look at the waveform of the voltage across that to measure injector current.

[Last edited Jun 09, 2016 17:14:11]
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LogavaniGovindaraj said Jun 24, 2016 06:35:01
thank you for your post.before this i dont have knowledge about this..thank you so much.gangboard
Dylan said Jun 24, 2016 17:12:12
Hello Logavani. Great you find this post interesting. So do I. But would you mind not posting links to gangboard? Thank you sir.
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LogavaniGovindaraj said Jun 27, 2016 10:42:42
, this isn't a what's wrong with my car email. I'm sure you get a lot of those. My name is Rafael. I'm 30 years old and have been in the field for over 10 years now. I attended one of the famous TV ad heavy technical schools. I'm currently working at a Infiniti dealership in the Chicago land area. My credentials: tech school grad, Ford manufacture school grad (right after tech school). I am currently ASE A1-A8, L1 and B2 ASE Master current, Infiniti Master Tech current and previous Subaru Master ( non- current). With as much as I've learned in about 3 months of following your book I found it necessary to give a big THANK YOU for all you do. I've bought your book and your premium channel. I hope your students understand what kind of valuable information they are receiving and take full advantage of it. In 3 short months I have changed my diagnostic approach about 50% of the time after listening to your approach. As a employee that's completely in LOVE with their career this Shhhhh..uff has me crazy excited. Congrats on all the new material and again thank you for all your hard work and what you give to the auto tech community.gangboard

Dylan said Jun 27, 2016 16:45:23
this isn't a what's wrong with my car email. I'm sure you get a lot of those.

Of course. That's what this forum is all about. Sharing knowledge and helping each other out.

Nice curriculum Rafael. Great you appreciate Paul's work. His book is like a 'must have' if you're into diagnostics. So are his YouTube channels.

Not the right place to post this but since the new website is coming, it doesn't really matter.

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IvanKibuka-Kiguli said Jun 30, 2016 10:24:32
Isshman, I really enjoyed your question. Quite interesting to think of voltages stacking up. But because the injectors (even if fired simultaneously) would produce the inductive voltage kick simultaneously are wired in parallel and therefore their combined voltage produce cannot be higher than that produced by the single most powerful one. If they were wired in series, then things may get interesting. On most injector circuits I have tested, I have noticed zener diodes clip the spike voltage at around 35-45V. I feel like following Tyler to rig up a few in series to see what happens :-) but first, I think I would need to power them with batteries in series (same multiples of batteries and injectors) to get 12V between each injector terminals to start with...
MansiRao said Nov 27, 2017 07:38:17
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michael.techenoid said Sep 17, 2018 10:18:47
By pressurising and injecting the fuel, the system forces it into air that has been compressed to high pressure in the combustion chamber. The diesel fuel injection system consists of: fuel injection pump - pressurises fuel to high pressure.
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madhu DM said May 04, 2019 05:40:58
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meenati3 said Jun 13, 2019 07:16:31
This vehicle has an intermittent misfire that we are trying to locate. Here we will be focusing on the injectors, making sure they do not have any flow problems (restrictions or leaks) An external timer tool will be used to fire the injectors at exact intervals while watching fuel pressure drops on a pressure gauge. Since we cannot get to the injector connectors directly, we will be using the main bulk connector to access the injector control wires. This same procedure can be applied to many different systems.
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