Pulsing an eTec Outboard Fuel Injector

Thread Starter

InjectorService

Joined Apr 11, 2020
34
Hi guys, I need some help designing a system to pulse eTec fuel injectors. I am using this system to pulse the injectors outside of the motor for cleaning purposes.

I have a machine that does this already in a more complex form so I think designing this should be relatively simple. The unit I have normally runs 12v style injectors, but with the "add on box" can run a single 55v eTec injector.

I'm hoping to make this a standalone unit so I can keep using my other machine while the eTec injectors are sitting there cleaning.

The thread below is from a few years back where someone tried the same thing. It is unclear if he ever got it working.

https://forum.allaboutcircuits.com/threads/rapidly-changing-the-polarity-of-a-55-volt-dc-circuit.119221/
 

Thread Starter

InjectorService

Joined Apr 11, 2020
34
I also wanted to state that I have (I think) my power source figured out. It is a 120 - 48 volt converter.

Also I can message pictures of the current circuit boards that are in the machine, maybe that helps someone figure something out. It doesn't mean much to me as I'm not an electronics engineer or anything like that. I don't want to post these pictures to protect the company that made my equipment.

I also have a low quality oscilloscope that I can put on the output lead to get a waveform if anyone needs. I'm sure that would help.

Another thing is, I think I am able to build this myself once I know the parts required and that, but if it gets overly complicated I will need to have someone build it so if there are any of you that would build it feel free to speak out as well.

Thanks again guys, I know it's my first time in this forum, but I really do appreciate any help as this is my first venture down a road like this.
 

Alec_t

Joined Sep 17, 2013
11,637
Welcome to AAC!
Here's a relevant extract from that earlier thread :

Pyro62 said:
"The EMM keeps the injector open with this positive charge for as long as it needs too. Then it reverses the charge/polarity to close the injector for as long as needed."

To which I replied :
"That reverse voltage is to close the injector as quickly as possible in the engine application. For your cleaning application I don't see the need for rapid closure; in fact that would be a disadvantage. Hence uni-polarity pulsing of the injector would be my choice and would simplify the circuit needed. You might consider using a control chip such as the LM1949 to provide the peak-and-hold current profile to minimise power consumption and heating.

Edit: If I recall correctly, coil inductance of a typical injector is around 2mH. Can you post a link to your injector's datasheet/spec?"

Edit:
For reference, here's a description of the E-Tec injector operation.
 
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Thread Starter

InjectorService

Joined Apr 11, 2020
34
Thanks Alec, I appreciate the response! As far as reversing the polarity, I'm not sure that the injector will close fully without reversing it, but it may.

I think what I would REALLY like to do is take my scope and have a look at the signal that is generated by my current cleaning/testing box during the cleaning cycle. I think it would be the best to replicate that. The company who makes these boxes has put a lot of R&D into them and rather than trying to re-invent the wheel I would rather just replicate it.

My reason for wanting to make this "new" box is because with my current equipment I can only run 1 injector at a time. This is really not an issue when testing the injectors, but the cleaning process takes forever this way. I have to run 1 at a time for cleaning, which on a big outboard means a MINIMUM of 60 minutes, and can often be 120 minutes. I'm trying to cut that total time down to 10-20 minutes.

What are your thoughts on this approach?

EDIT: As far as getting a spec sheet on the eTec injector itself, I'm not sure that will be possible. The eTec system belongs to Evinrude/BRP and I don't think that the specs on their injectors are something they release. I could be wrong however.

"Typical" injectors have an inductance somewhere in the 5-11mH range. My machine actually tests for the inductance and diplays it for me, but unfortunately because the eTec uses a separate 55v box to power them, I can't get an inductance reading from them. Typical resistance is about 2.6 Ohms on the eTec stuff though.
 
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wayneh

Joined Sep 9, 2010
16,399
Thanks Alec, I appreciate the response! As far as reversing the polarity, I'm not sure that the injector will close fully without reversing it, but it may.
I’ve only played with automotive injectors and based on that limited experience, I’d be surprised if the injector wouldn’t close itself without applied power. If nothing else it would be a questionable design to not fail to off. Otherwise the gas just keeps coming!

But why speculate? Can you grab one and test it? It’s worth the effort in my opinion because the electronics are much simpler. Reversing current is doable, too, just more detail.
 

Alec_t

Joined Sep 17, 2013
11,637
I'm not sure that the injector will close fully without reversing it, but it may.
There looks to be a spring-return motion in the post #3 link; but doesn't it need to be open for ultrasonic cleaning to occur?
I think what I would REALLY like to do is take my scope and have a look at the signal that is generated by my current cleaning/testing box during the cleaning cycle.
Excellent idea. Knowledge of pulse timing and safe drive current would be essential for a DIY design.
 

MisterBill2

Joined Jan 23, 2018
6,997
For cleaning only purposes I do not see any need to use a pulse similar to the regular driving pulse. The primary goal is simply to open the injector to allow flow while not overheating it.
One simple way could be to use the signal from your present injector tester to drive enough transistors to exercise as many injectors as you need to do at one time. A diode to avoid any reverse base drive, and a series resistor to limit the base current to each transistor, and probably a single pull-down resistor right after the diode to be sure they all switch off. Of course, I am thinking of NPN transistors on the negative side of each injector, and a common positive supply for whatever voltage you choose.
 

MrSoftware

Joined Oct 29, 2013
1,906
The goal would not necessarily be to mirror the signals collected while running for cleaning purposes, especially at idle when the opening duration and amplitude is surely tiny. But taking readings while running would give you safe bounds to work within as far as peak voltages and durations, especially if you were able to collect some readings while the motor is under any sort of load, which is when I would expect voltages and durations to be maximized. Also the etec motors are direct injection, similar to a diesel, so the injectors are going to be a bit different than a standard port or throttle body injected motor. Gasoline is thinner than diesel so the fuel pressures won't be as high as in a diesel, but a lot higher than in a port or throttle body injected motor. I would not be surprised if their design did require some electrical stimulus to close the injector, perhaps as a way to minimize the size of the return spring. I'm guessing, but it would be interesting to hear more about it.
 

Thread Starter

InjectorService

Joined Apr 11, 2020
34
Thanks for all the replies everyone. I don't have time today to read through and answer them but I wanted to share this screenshot I took from scoping the injector output while my cleaning/testing machine was running the cleaning cycle. It looks like the signal does reverse.

20200413_205432.jpg
 

wayneh

Joined Sep 9, 2010
16,399
It looks like the signal does reverse.

View attachment 204337
If that reverse pulse isn’t too big, it could be accomplished with a half bridge and the stored charge on a capacitor instead of a full h-bridge. I built such a circuit and can show you what I mean if you want. But there are dedicated H-bridge driver ICs you can buy as well. I bet you could even buy one pre-assembled on eBay. You just need to know the specs to look for: voltage, current, frequency in particular.
 

Alec_t

Joined Sep 17, 2013
11,637
Is the negative pulse (~6mS) the one that opens the injector?
If I'm reading the scope shot correctly, the voltage is switching between -24kV and +24kV. Surely it can't be that high?
 

MisterBill2

Joined Jan 23, 2018
6,997
Why would you want the reverse pulse for a cleaning application? That really does not make much sense at all. Just use the main pulse, a single diode to prevent the reverse from getting through, and resistors to limit the base drive, and as many transistors as needed to exercise the injectors you are cleaning. But after seeing the scope trace, you might need to use PNP transistors.
 

MrSoftware

Joined Oct 29, 2013
1,906
Is the negative pulse (~6mS) the one that opens the injector?
If I'm reading the scope shot correctly, the voltage is switching between -24kV and +24kV. Surely it can't be that high?
Maybe he's got the multiplier on the probes set differently than the scope is expecting? It does look like 24kV, which for one I'm surprised the scope goes that high, and for 2 that does seem unusually high for a fuel injector.

Side note, I have no idea if this article is accurate, but if it is then I can see how the negative pulse may be necessary to help it draw more fuel, thinking that they may have kept the return spring light intentionally so the forward pulse doesn't have to work against it to build pressure:

http://www.evinrudenation.com/owner-zone/understanding-the-e-tec-fuel-injector-by-bill-grannis/
 

Thread Starter

InjectorService

Joined Apr 11, 2020
34
Wow lots of replies here, that is awesome! Ill try to answer a few questions and give some insight.

1. Seeing as the signal generated by the current cleaning box I have reverses the signal, I want to do the same. These are BIG injectors physically, and I don't think the return springs will return the pintle far enough on their own. There have also been (and continue to be) many revisions of these injectors, so I don't know that they ALL have the springs in them.

2. As far as the negative pulse, I believe that is the one that opens the injector. I believe it is actually a positive pulse, but I was fighting with my scope a bit and I only got a good reading when the leads were reversed. The longer pulse is definitely the opening pulse though.

3. The voltage is definitely not in the kV range. I would say that we can assume it is V we are seeing. (My scope is a cheap Hantek, and while it works for what I need right now, the software is known for being poor). I read it out as about 2.7V, and I am using a 20:1 attenuator. So this would make it 54V, which would make 100% sense. Inside the current injector cleaning "box" the main power (120VAC) goes into a 48V converter. I forgot to check output voltage on this but there is an adjustment on it so I assume they have turned it up a bit. In any case, this is the main power source for that circuit board, and I don't see any other transformers.

4. As far as fuel injectors go, these are COMPLETELY different than ANYTHING out there, including diesel. Thats where a lot of the confusion comes in, and trust me it's not just here, it's in the complete industry. Most shops won't work on them aside from regular maintenance. The whole motor is just completely foreign.

I hope this gets us where we need to be with this. I think we are really close, and again thank you ALL!
 

Alec_t

Joined Sep 17, 2013
11,637
I don't think the return springs will return the pintle far enough on their own.
I clearly don't understand the operating principle of your cleaning machine. What is the problem with the injector staying open?
As for the scope shot, and in view of uncertainty as to what it is showing, if the wider pulse is the one for opening the injector, could the narrower one be merely a back-emf pulse generated inductively when the other pulse terminates and the actuator coil is de-energised?
 
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Thread Starter

InjectorService

Joined Apr 11, 2020
34
It's just pulsing the injector through a "normal" operating cycle all WHILE ultrasonically cleaning it. Its just helping the ultrasonic to clean further. Also the way the eTec injectors need to be oriented during cleaning, the pulsing of the injector actually "egjects" debris.
 

MisterBill2

Joined Jan 23, 2018
6,997
I clearly don't understand the operating principle of your cleaning machine. What is the problem with the injector staying open?
As for the scope shot, and in view of uncertainty as to what it is showing, if the wider pulse is the one for opening the injector, could the narrower one be merely a back-emf pulse generated inductively when the other pulse terminates and the actuator coil is de-energised?
The problem with holding any injector open continually is HEAT. The power needed to quickly open an injector for a very short portion of the cycle time is far more than it can handle in a steady state mode.
 

bwilliams60

Joined Nov 18, 2012
1,341
I haven't read the details on these injectors but are they piezo injectors? That would explain the opening and closing pulse. Some diesels running piezo have an opening and a closing coil to make them inject properly. Could also be a priming pulse of sorts?
 

Thread Starter

InjectorService

Joined Apr 11, 2020
34
I haven't read the details on these injectors but are they piezo injectors? That would explain the opening and closing pulse. Some diesels running piezo have an opening and a closing coil to make them inject properly. Could also be a priming pulse of sorts?
Yes that is about as close as you can get to this system.
 
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