Richard L

I can see your reasoning. It applies well for voltage acting on a resistor.
You are perfect right regarding the rise time wil be different between 3V and 14V to ther same injector. But the current seen by the injector will be different, not !A as you have stated.

For example:
- 4.5 ohm injector draws 0.67A at 3V
- 4.5 ohm injetcor draws 3.1A at 14V

Time constant of an inductor: Tc= L/R. @1A, they will both have the same rise time, regardless of voltage, 3V or 300V.

I was comparing to a 4.5ohm injector's performance between a 2 ohm 7W resistor against a FJO unit.

Richard L

The reason for the 13.3V and 15V is picked of the test is purely to demonstrate the action of the P&H function.

I agree we are both talking about the same thing, from different directions. I have borrowed a Bosch 4.5 ohm injector and a FJO unit and have tested it this afternoon.

My findings:
- I can confirm the 4.5 ohm Bosch injector does read 4.5 ohm on my tester.
- At 14.5V, the 4.5 ohm injector draws ~3.2A.
- When feeding a 3ms pulse to the FJO unit , P&H is not triggered.
- Increase the pulse width to 4ms, the FJO's time function mode kick started the P&H.
- I have found a small problem on the FJO unit not clamping the "fly-back" spike during the switching off period. It read nearly 250V!

I can confidently confirm the FJO unit behaved like a saturated driver below ~4ms. The charts posted earlier is accurate. I have no other motives other than learning how they function as our system reads the duty cycle% to meter alcohol flow. Reading P&H DC is not as simple as reading the saturated type.

gxl90rx7

iTrader: (1)

in the case with the resistor inline, there will be about 1A current with 13V supply. But the injector only sees 3V (1A x 3 ohm = 3V); a 4.5 ohm injector will see 4.5V

In the two graphs above.. the 15V graph had a faster rise time, due to higher supply voltage, in turn changing the current curve.

the 15V was .2 ms faster than 13V, or roughly .1ms per volt. Im not sure if it is nearly linear, but if you extrapolate it down, at 4.5V supply, rise time will be about 1ms! It makes no difference to me if the FJO operates in saturated mode on higher impedence injectors.. the advantage is the same becuase of teh higher supply voltage and current handling capability

Richard L

Yes you are correct, it makes little or no difference to you if the FJO is working in a saturated mode below ~4ms. (with a 10 ohm inline resistor)

The Griffin

Isn't ohm's law the "voltage drop" across the resistor? So in the case of a series /ballest resistor wouldn't the voltage the injector sees from your example be 13V(example)-3V=10 Volts?

gxl90rx7

iTrader: (1)

13V-----Injector-----resistor------ECU----GND

the voltage at the injector with respect to GND is 10V, but that is not what the injector sees. What matters is the voltage across the injector, which is 3V in this case. to help picture it, move the resistor to the other side of the injector, between 13V and injector. Does that change the voltage at the injector? no, the voltage across the injector is still 3V

JazzyFD

iTrader: (4)

Bump great thread.

Richard L

Current/voltge reading is the same across the injector regardless where you put it. Only difference is the voltage offset from ground.

Howard Coleman

iTrader: (6)

i will re-read the latter parts of this thread when i get some time as i might learn of few elec things.

in the mean time not to get too lost in the forest looking at the trees...

i installed my FJO Peak and Hold convertor and with NO changes to my map was hugely rich at secondary transition. (i had had to add a ton of fuel in that area to get good AFRs running the resistors.)

i have since removed at least 45% base fuel from that area and i have linear AFRs.

go figure.

or not.

howard coleman

Richard L

Howard,

For any injector change, there will flow, inductance changes etc.

This change will also apply to an injector driver's algorithm, requires some kind of remapping to compensate the final fuel delivery. These changes should not be constituted as an improvement, just because you are taking DC% out. As long as you are achieving the same AFR with either method. Slower "turn on" or "turn off" is just an offset or time shift, all can be nulled out during re-mapping.

The 4.5 ohm injector's minimum turn current is 1A. How fast the build-up of the 1A current ramp is governed by the current available and inductance of the winding. The higher inductance, the slower the response speed.

As far as the 4.5ohm injector is concerned, there is no difference between the FJO and driving the injector directly below 3.9 ms. The opening time will be the same, but closing time is only maginally faster due to less current dump during the off period.

There is another advantage of the FJO unit I forgot to mention, it reduces temperature rise of the fuel injector between mid to high DC%. But this improvement is nulled out by the cooling effect of fuel passing through the injector.

As I mentioned before, there is no harm using it, but the gain is not as dramatic as the opening post and the title.

Monkman33

iTrader: (28)

So... I guess now we have to extrapolate how often an injector will be running for longer than 3.9 ms. To me, that would say that the the FJO box would have its most drastic effect under high load/boost. Which, to put it plainly... Is exactly where I want the most precision in my fuel control/delivery.

Richard L

3.9 ms is only FJO's P&H threshold. It doesn't mean it perform better than the 4.5ohm injector at saturated mode. In fact, insignificant.

gxl90rx7

iTrader: (1)

not true.. did you not read my post eariler? If there is a .2 ms difference between 15V and 13V supplies, you can bet the difference at 4.5V (resistor inline with a 4.5 ohm injector) will be very significant, up to 1ms! I would say that is a huge advantage with the FJO, and it seems to match howards findings

on my 1600s, my fuel map is about 5ms at 0psi.. 1ms is almost 20% difference in fuel

Monkman33

iTrader: (28)

Which means you would be at 10ms at 15psi (or even more if your iat's are high, and you are wanting to run very rich. Correct?

gxl90rx7

iTrader: (1)

oh my mistake, i looked at it again, it is 5ms with secondaries off, 2.7ms with secondaries on at 0psi, and about 5ms at 15psi, so 20% at 15psi

Monkman33

iTrader: (28)

either way. 20% matches the findings of the OP. And either way, the FJO driver will net more efficient and consistent results. regardless if it hits P&H function or runs in saturated mode.

Richard L

On the earlier post, I was comparing the 4.5 ohm injector in saturation mode with "NO" resistor. This is no point putting a resistor on the 4.5 ohm injector at all. (post #137)

Switching 3.2A load is a relatively small current to electronic drivers.

Richard L

I think your comment is true but the switching delay can be nulled out by mapping. That was what Howard was doing, a remap.

I repeat, using smaller dc doesn't mean you get instant performance gain. It is the correct mapping that gives you the results. I can bet you anything if Howard takes the resistor out of the 4.5ohm injector, that is no need for remapping at all.

The slow reaction time is caused by the voltage change, as demomstrated on the 3.3ohm + 2 ohm resistor earlier (0.2ms delay)

I think the confusion was having too many topics in the same discussion.

Topics:

1. 4.5 ohm with resistor ........... not good. Progressively worsen with increase resistance. (original Horward's setup)
2. 4.5 ohm without resistor ........ good
3. 4.5 ohm with FJO..................... good
4. 4.5 ohm with FJO <3.9ms ....... good
5. 4.5 ohm with FJO >3.9ms ....... good (slightly better than 2 - only with the same clamp voltage)
6. 3.3 ohm with FJO at 13.3V...... normal
7. 3.3 ohm with FJO at 15V ........ normal but 0.2ms faster

Each of the above topic should be discussed individually. I was referring to topic "2 and 3" at all time, but got roped into other topic discussions. It just got more confused - please start again on each topic in detail individually. Then compare the results later.

gxl90rx7

iTrader: (1)

oh i didnt realize you were talking about not using resistors at all. stock FC ecu uses 6 ohm resistors, 1.6A max. That is a whole other discussion whether the stock ecu can handle over 3A

the problem with simply tuning out the time delay comes when using piggyback fuel controllers. Sure, when using something like the PFC, you know exactly when secondary staging occurs. But with an SAFC or simliar, it is not a perfect transition when the stock ecu cuts duty cycle by 50%. If there is injector lag, it will cause hesitations and leanouts at staging

Richard L

Sorry, I was try to relate too many variables within a few posts.

If you like I can do some comparison work on the 6 ohm with a ? ohm injector?

Please confirm the injector's winding resistance and the inductance. It should be a simple calculation.

Question: Does anyone know for sure if the FC ecu "can" or "cannot handle 3A"? Alternative, if no one knows, can anyone tell me the driver transistor' part number?

gxl90rx7

iTrader: (1)

I have a spare S4 TII ECU lying around, i can take it apart and look

Monkman33

iTrader: (28)

Richard, If you were talking about running without resistors... what were you doing in this thread? You don't want to run a 4.5 ohm injector on a pfc or a stock ecu... without a resistor OR an FJO box.


The whole point is that on a PFC, the FJO box is better than running resistors. and not just better, but better to the point where you will notice differences in tuning consistency.

Arguing for running without resistors is pointless considering the motive of this thread.

The Griffin

That's a very large flyback spike, the spikes in the 2 scope traces posted are in the neighbourhood of 36-37 volts. Just an FYI those are scope traces from a DIY "LM 1949" based Peak/hold add-on board running on a Megasquirt ecu and not an FJO peak/hold injector driver. The chap was on a quest to find the correct opening times of the injector he was running.

Richard L

Thank you very much, any information will help.

Richard L

I think it should belong to another thread, no resistor - direct drive. Once I have gathered the correct information, I can predict the injector's switch on time a wide range of resistor value.

I will be interested to know why pick a 6 ohm resistor? why not a 3 ohm or 1 ohm? Until the driver capability is established, it is just a stab in ther dark. I have said many time, 3A is not a great deal of current for a power transistor to drive.