Lets talk injectors..........

[Tim @ P.I.S.]

I hope most of you already have the basic concepts of the HEUI injectors in the 7.3. If not there are several sites that give very good details on their basic operations.

First off to help you understand how I get my info lets go over the test bench. The bench is driven by a PC with software to interface a FACTORY Power Stroke IDM. THe PC gives the same signals the factory PCM would. I have control over RPM, pulsewidth and injection count. The hydraulics control the fuel psi and the ICP on the injectors. This is as cloose to an actual engine duplication as I have seen. There are a few others with simular setups out there.

For example a normal test would be programmed 3000 rpm's with 4ms/pw for 1000 shots fired. The fuel pressure would be set to 65psi and icp to 3000psi. On a normal set of 160cc/30% injectors you would get a test beaker with 170cc output.

Why 170cc? I base a set of 160cc injectors off the design of an AC code injector. That way if another test bench were used you should still get 160cc output MAX.

Other various tests would also be run to show balance through the RPM band. Just holding the injectors open for an over-extended amount of time will only show you what the fuel capacity actually is. THis basicly tells you if it works or dosn't. Running an injector at the min pw required will actually show you a balanced set. And testing at low rpm, low icp will tell you just how balanced they will run in a truck.

Now, on to the fun stuff:rockon: The factory IDM and pulse width.

Through testing I have found the limits of the factory IDM.
1000rpm = 14.2ms/pw
1500rpm = 9.4ms/pw
2000rpm = 6.7ms/pw
2500rpm = 5.1ms/pw
3000rpm = 4.1ms/pw
3500rpm = 3.2ms/pw
4000rpm = 2.9ms/pw
4500rpm = 2.5ms/pw
5000rpm = 2.2ms/pw
5500rpm = 1.8ms/pw
6000rpm = 1.6ms/pw
6500rpm = 1.5ms/pw
7000rpm = 1.3ms/pw
7500rpm = 1.1ms/pw
8000rpm = 1ms/pw
8500rpm = .9ms/pw
9000rpm = .8ms/pw
9500rpm = .75ms/pw
10000rpm = .7ms/pw

Now you can see that a perfect set of 160cc/stock nozzle injectors, that requires 4+ms/pw to empty will fall short.

It is not diffacult to build even a 238cc injector to completely empty at 4800rpms. At 5000rpm it will begin to cut short at only flowing 215cc.

300cc/200% are currently requiring 2.9ms/pw to fully empty.

Feel free to post your questions/comments/ect.

I hope this as entertaining to read as it was to learn.

 

[Tim @ P.I.S.]

One important thing to add.

For example take the 300/200 injector that can empty in 2.9ms/pw.

2.9ms is very different at 1000rpm, as 2.9ms at 4000rpm.

I just recently trouble shot a set of 250/100 injectors from a customer.

At 1000rpm with 5ms/pw this injector would give you 250cc.

At 3000rpm and 3ms/pw this injector gave reads of 125cc lowest to 220cc highest in the same set. After some work these should be able to completely empty upto 3000rpm.

So when you ask just what do you injectors flow, you may also want to know how many rpms they will empty that amount in as well.:doh:

 

[Cat_rebel]

Feel free to post your questions/comments/ect.

How do we get a 7.3L to spin 7500rpms without sending parts into the next county?



In all seriousness you did a nice job typing everything up. imp:

 

[silverpsd_06]

125cc-220cc shouldn't they all flow the same assuming all other values are equal icp, pw Or was this just one injector that will flow 125cc-220cc depending on pw? Either way 250/100's should flow 250cc max right? Guess im not following. You were out to find the limits of the factory idm or? maybe im retarded

 

[Tim @ P.I.S.]

How do we get a 7.3L to spin 7500rpms without sending parts into the next county?

Thats someone elses department. Im just working on the fueling.

In all seriousness you did a nice job typing everything up. imp:

Thanks!

 

[Tim @ P.I.S.]

125cc-220cc shouldn't they all flow the same assuming all other values are equal icp, pw Or was this just one injector that will flow 125cc-220cc depending on pw? Either way 250/100's should flow 250cc max right? Guess im not following. You were out to find the limits of the factory idm or? maybe im retarded

The 125-220 was the range the whole set didlowest to highest). And yes at any given point as long as there is enough PW to work with the nozzle size they should have done 250cc across the board. I was quite surprised myself.

Once PW is reduced to the point it can not support the nozzle size then yes all injectors will start to reduce output. The limits I found were the amount of PW the IDM will support at a given RPM. This will give you the info you need to design the injector. And to help in the tuning of the injectors.

A flow chart for a set of injectors means nothing if RPM is not a variable in the equation.

 

[silverpsd_06]

So does the problem with that particular set of injectors lie in the tuning or how do you get that much of a variance in a set? Shouldn't everything be nuts on the same? Kinda makes me wonder if there is that much of a vast gap in between eight injectors what they did or didn't do.. I'm guessing you put your own little tricks in the mix to make them all just a tad quicker to empty compared to before?

 

[DZL JIM]

At 1000rpm with 5ms/pw this injector would give you 250cc.

At 3000rpm and 3ms/pw this injector gave reads of 125cc lowest to 220cc highest in the same set.

Tim,
Are you 100% sure the discrepancy was in the rpm an not your pulsewidth change?

I've seen poor flowing nozzles (most used high performance nozzles) need more pw to empty than a comparable new nozzle.
The only time I have seen rpm affect injector operation is dealing with oil side issues.

 

[Tim @ P.I.S.]

So does the problem with that particular set of injectors lie in the tuning or how do you get that much of a variance in a set? Shouldn't everything be nuts on the same? Kinda makes me wonder if there is that much of a vast gap in between eight injectors what they did or didn't do.. I'm guessing you put your own little tricks in the mix to make them all just a tad quicker to empty compared to before?

The bench somewhat takes tuning out of the equation. All the injector is comanded is PW and # of fires.

And you are correct, yes every injector no matter what the test performed should be as you call it "nuts on the same".

 

[Tim @ P.I.S.]

Tim,
Are you 100% sure the discrepancy was in the rpm an not your pulsewidth change?

I've seen poor flowing nozzles (most used high performance nozzles) need more pw to empty than a comparable new nozzle.
The only time I have seen rpm affect injector operation is dealing with oil side issues.

I may have worded this poorly Jim. It was not a single injector that gave those crazy readings. That was the lowest in the set 125cc to the highest in the set 220cc on a single test run with all parameters being the same.

Instead of running one test and seeing 250cc across te board the results looked more like a rollercoaster ranging from those two #'s.

 

[DZL JIM]

Yes, I understand, my question still remains.

 

[Tim @ P.I.S.]

Sorry Jim,

But yes. This set we will call used for the sake they were installed in a truck. But from what i was told never left due to issues. So technically they are still new to me. I do remember are conversation on that exact topic way back.

And YES again. A big YES also. RPM has a HUGE effect on larger injectors(stg 1 & 2 not as much). That is one issue we have always had with 7.3 injectors. Without certain modifications as RPM increases output decreases. Some just way more than others.

It is quite simple to build a standard 238cc hybrid injector. You know this, as well most 7.3 enthusiasts. But on a test bench as we have both learned over the years if you speed it up(increase RPMs) it is nothing more than a glorified stg 2 injector in output.

Correct some issues and it becomes a true 238cc injector. Then increase RPMs again and see what happens. Back to a low output again. The best i have seen is to still flow 238cc of fuel out of that injector at 4800 rpms. It was not until 5000rpms that the injector would then start to reduce flow again.

Back to this set on hand here. Reduce the rpms to 1000 and stretch the pw out ot 5ms and you would get 250cc. But as soon as rpms increase the output would decrease, drastically on some. Thee were simply not built to empty at any usable RPM. I dont know anyone that drives at just 1000rpm. At a usable RPM they just dont do what they are advertised to do. I am scared to think of the number of people out there that have the same issue and dont even know it.

 

[silverpsd_06]

So at what rpm does it become overly prevalent that the larger injectors just do not flow the amount of fuel that they are spec'd out as or does this just depend on who built them?

Does having a larger nozzle help curve this problem since the resistance is less to get the fuel out without having a long injection event or am i looking at it wrong?

 

[Tim @ P.I.S.]

So at what rpm does it become overly prevalent that the larger injectors just do not flow the amount of fuel that they are spec'd out as or does this just depend on who built them?

Does having a larger nozzle help curve this problem since the resistance is less to get the fuel out without having a long injection event or am i looking at it wrong?

You are correct.

Its not "who" built them, its "how" they are built.

A large injector can flow at high RPMs. It is internal modifications and nozzle sizes that restrict their output.

The larger nozzle helps because it can flow more fuel with less PW.

 

[DZL JIM]

:thumbup: