I agree that running a p&h box is definitely better than a low imp. injector with a resistor, however it is still not as consistent as a saturated injector. When the driver switches from peak to hold mode, the injector flow usually has a slight bump leading to inaccurate fueling... It is very minimal, however I don't understand how you can claim that a p&h is better than running a saturated injector..

 

questions on FJO unit.

The instruction stated the P&H switches from 4A (peak) to 1A (hold).

If the impedence of the fuel injector is higher than 3.5 ohms, the R&H drive will be uin saturatyed mode.

Is this a correct assumption? There is no mention of this importent point on the last few pages on the "defination" of low impedance and high impedance.

As far as I see:
- 1 to 3.5 ohm = low impedance as seen by FJO
- Above 3.5 ohm, the fjo unit does nothing except driving the injectors in saturated mode. No point using it.

 

Would this be true? So running a 4.5 ohm 1680 secondary would be pointless? I better go find something with lower resistance.

 

Well, according to specifcations, this is the case.

A 4.5 ohm injectior draws 3.11 A at 14 volts. Unless the unit has other un-published capabilities, a 4.5ohm injector will not trigger the "peak and hold" circuit within the system.

I could be wrong, please do ask FJO to confirm this before make decisions based on my calculation.

 

I've had 550cc primaries stick open before. Lets just say it was smokey behind me, and it didn't fire at all. The rotary was just pumping the petrol straight out the exhaust. A LOT of smoke, but I compression tested it years later and still made 97psi front 102psi rear.

 

I just spoke with Jerry at FJO.

He mentions that the 4.5 ohm "low impedance" P&H injectors are made that way due to requiring less current to peak out. they will however still peak and then the FJO box will drop them down to the Holding amperage of 1a.

After a laundry list of reasons why resistors can't perform like this box, I am pretty convinced and will be purchasing an FJO box.

The main points that Jerry spoke with me about was what happens when you open a P&H injector with too little current and what happens when you give a P&H injector too much current through the hold stage.

The first point is that the injector will not be popping open at its full speed, and as such will be sensitive to fluctuation of fuel pressure even more so. This could create non-repeatable fueling characteristics, which would make tuning difficult. Especially in the low range and idle.

Secondly, If the injector ramps up to 2a after it hasn't peaked, which is common for a circuit running a resistor, then it will actually take longer for the field to collapse when current is cut, thus again, changing the flow characteristics from a repeatable and consistent pattern... to something else.

The advantages of running an FJO box over running resistors, according to Jerry at FJO, is that you will have much more consistent tunability, especially at low RPM and idle. And that your injectors will theoretically last longer as they are only being pulsed at high amperage and sustained at 1a, thus creating less heat.
The fueling consistencies will be apparent both at the beginning of the injector signal, and at the end.

And with that, I am sold. I will be purchasing an FJO Injector Driver Unit.


And you can get them for only $150 here: http://www.alamomotorsports.com/fjo/injdrvr.htm

 

I would think that an injector that uses high current to open as quickly as possible and then sustains it open with minimal current, thus making closing faster, would be the most consistent. Your opening and closing times would be closer to the input signal.

If I am wrong, then please correct me, it just seems to make sense to my mind.

And if saturated injectors are better, where can I get some 850cc and 1600-1680cc high impedance saturated injectors? To me, if it was better to run this way, which is how the PFC controls injectors, wouldn't there be more high impedance/saturated injectors on the market?

 

I read Jerry's reply several times, the answer doesn't make any sense to me. I didn't think the question was ever answered.

According to the FJO instruction (below), it peaks at 4 A and holds at 1A. But a 4.5ohm injector can never reach 4A at 14V.

Current = Volt/Resistance.

Anyway, no harm using it. My reason for questioning this is because I have been asked the same question. I thought I might get some expert help from here. I am no wiser so far.

 

It doesn't if they are using a LM1949 based circuit designed for a 4:1 peak/hold ratio.Those bosch 1600cc are in the neighbourhood of 2.5:1. So the best you would see is about 2.7 amps @13.5 volts, not enough to reach the 4 amp trigger.

I bought a LM1949 based DIY Peak&hold board not realizing that it was designed to be used with 3 ohm (or less) injectors. I can change the circuit "sense" resistor to either a 0.2 ohm or 0.15 ohm value giving a 2amp/0.5 amp or 2.67/0.67 peak/hold ratio.The question is if the injector will work .With the FJO I doubt doing that is possible as the case is potted and probably has SMT components. A o-scope and injector test bench would come in handy also.

 

We use to manufactue those driver a few years ago, utilising a device called CS-452 (2.4A) and CS-453 (4.4A). Made by Cherry Semiconductor. They are a 5-pin device in a TO-220 package. Very handy. Unforntunately it is now become obsolete. We still have a few lying around. We soon stopped supplying those driver kit afterward.

As you have mentioned, the LM1949 is the only integrated device left unless you want to re-invent the wheel using descrete components to achieve the same aim.

Altering the current sensing resistor will alter the peak current to switch the device to a P&H mode. Without looking at the device, but I am not sure if you can alter the P&H ratio.

I have a o-scope but not into this market anymore. I can borrow one and take a look at the waveform. Just need to find time to do it.

Back to the FJO, good solid product but a bit vague on the answering the 4A/1A P&H usage on a 4.5ohm injector. There is no harm using it, there are no negatives. The cars just weighs a bit more.

I am just surprised people just buy things based on assumptions and without questioning.

 

Your thinking definitely makes sense, which is why we developed our dynamic flow bench. Once you know the exact offset and optimal current setting (for a p+h) for each injector you can get the most accurate fueling possible for that injector. However, there are other factors that go into making a good injector such as a long linear flow range where a p+h injector isn't necessarily better than a saturated.

We offer both 780cc and 1000cc saturated injectors, nothing in the 1600 range though. Most p+h injectors on the market are old technology, OEM's have been using saturated injectors for quite some time and the saturated injectors have been getting better and better.

 

I think everyone is assuming that all P&H injectors NEED 4a trigger and then a 1amp sustained. The FJO box merely supplies those figures.

We don't know what the required amperage to trigger proper P&H behavior in each injector without looking at each injector's specifications.

What if the 4a/1a supply was enough for the 4.5 ohm injector? Hear me out with this one:

Perhaps the manufacture of the the 4.5 ohm injector knows that the injector doesn't actually need that high of signal, and as such, builds the injector with higher resistance within. Perhaps they really only require 2a/ .5a?

Just wanted to point out that we have been discussing the 4/1 issue from the wrong direction.
Known:
Supply signal is 4a/1a
Injector resistance (and thus maximum received amperage on 14.4v)
Unknown:
Signal strength required to trigger proper p&h function in each specific injector.

Once we fill in the unknown, we will be able to determine if the FJO box is the right product for the FD when using a Sat based ECU and P&H injectors.

 

therer are no "unknwn" on the current drawn on an 4.5 ohm injector. Read previous posts.

 

the FJO driver does not "inject" 4A and 1A. The impedence of the injector determines how much current it draws. I believe the FJO simply limits the current to 4A durning the "peak" and 1A during "hold"

I = V/R

If the injector is 2.5 ohms, then it will try to draw about 5 A. The "peak" period limits it to 4A, then cuts it back to 1A during the "hold" period

A 4.5 ohm injector would draw about 3A. So the peak period would be 3A, the hold would limit it to 1A

a 12.5 ohm saturated injector would only draw about 1A continuous. the peak and hold function is still operating, but a saturated-style injector wouldnt know the difference because it can only draw about 1 A of current




now when you use a P&H injector on a saturaded ECU with resistors inline, you are pretty much simply limiting the current to 1-2A continuous, so the injector turns on a lot slower than if you drove it with a 4A spike like it was intended

 

That makes a deal deal more sense.

FJO can simply say "any current over 1A" will trigger the P&H.

 

But if the inj. amp draw is less than the trigger value(4 amp. roughly), then the p/h board works on the timer function (typ. 3.9ms) to drop it into hold mode(1 amp).

I'm in the "don't know rat **** from rice crispies category" when it comes to electronics and injector operation but it doesn't sound like you are gaining much over a small ballest resistor to keep the inj. amp at about 2 amps with the 5 ohm bosch 1600's. At low pulse widths where the injector shuts before the time out can't be helping the closing times not to mention you are still heating that inj. more.

I'm not getting that warm fuzzy feeling about going and dropping the dough on the FJO to run these bosch 1600's.I'm most likely missing something though,anyone else have some proof?

 

i took another look at the data sheet and you are right, the hold mode will not be triggered unless 3.85 A is drawn during the peak period. So injectors with impedance greater than about 3.5 ohms will simply be operated in saturated (constant current) mode. Unless FJO added an external circuit that sensed injector impedance and compensated for it??

but you would still benefit from it, since your injector will be turning on a lot faster with a constant 3A instead of 1A with resistors

 

So, Just to recap.

1. There is nothing to gain by using 4A (3.85) P&H on a 4.5ohm injector
2. There is something to loose if a resistor is put in series.

Why not drive the 4.5 ohm injector direct? Provided the ECU can handle those currents. 3A is (6A total per channel) is not a problem by modern transistors.

Even a 22awg cable (UL1061) can handle 8A of current.

 

I guess it depends on what your needs are. If you are running these as secondaries, then maybe a trade off would be to just run a couple of $7.00 2 ohm/20-25Watt resistors to limit the injector heat and driver load to about 2 amps.Maybe that won't impact anything noticable on opening/closing times.

If you trying to run these large bosch inj. as primaries as well then I'm not sure what is the right approach. The timeout factor doesn't sound like it would produce consistent inj. results where the p/h circuit is supposed to drop the current as soon as triggered.

Looking at the LM1949 data sheet.You can change a couple of variables like the peak/hold ratio with a different "current sense" resistor or the timeout duration do a low value with a different cap. I'm wondering if the inj. would work correctly/consistently with a 2.0 amp peak / 0.5 amp hold current. Or maybe another bandaid is to drop the timeout value if possible to a low ( something like a 1.0 ms)? Getting back to that o-scope and inj. test bench need again.

Here's a couple of examples I dug up from the net of what it looks like on the scope. current is the yellow

5ms scope test with 3.3 ohm inj@13.3V .p&h-times out. You can see the flat spot on the top and counting the divisions it looks about 3.9ms from voltage drop to hold drop.



Same test at 15V. An almost instant drop as the trigger is reached.I think this is the way it's supposed to work

 

Another point to consider is if the FJO box will deliver enough current to reach 4a, regardless of resistance (to a point). I highly doubt that this box is adaptive.


And to those that are not paying attention to what I am saying:

WHAT IF 4a is not the universal required current to trigger P&H function. Those that are rebuking my comment are not understanding my post.

What if 4a is actually overkill, and the resistance built in to an injector is done by the manufacturer on purpose, knowing that a p&H driver will deliver at least a certain amount of amperage?

Just a thought. But until anyone can actually show me that 4a is required by the injector.... since that number has ONLY been supplied by FJO, and NOT the injectors specifications... then I will stand by the fact that there is STILL an unknown. Please. read and understand my entire post before trying to shoot it down.


the unknown has been and STILL IS: WHAT amperage is required by each injector individually to trigger proper P&H function?

We need to know what the INJECTOR wants, not what the FJO box wants to deliver. Those that are telling me that I am wrong..... think about this: Where did you get the magical 4a/1a figures from? Was it from Bosch? Was it from an injector manufacture? No. It was from FJO. So the fact remains: All we know is what the Driver will deliver, not what the injector needs.

 

It's because they can't figure out what your driving at. But hey, ask the injector what it wants. If it's an injector that's less then 3 ohms at normal car voltages, I'll probably say it wants to groove along side an FJO

 

There is no way any injector over 3.5 ohm impedance draws more than 4A below14V. As long as FJO stated 4a/1a, a 4.5ohm can not possibly peak to 4A, unless you have a 18V supply.

There are no unknown there, to me everything is very clear.

Have a good look at the OSC charts above. The instant the voltage was increased from 13.3V to 15V (hence the current), the FJO went into P&H mode.

Griffin's evaluation was spot on. Now we have the OSC traces to support it. The only time the FJO is effective is when the injection duration is over 3.9ms, On average, there is only marginal gain.

 

If you examine the current trace closer, it appeared the pinto has reached its full travel after ~1ms (13.3V) and ~0.8ms (15V). It also showed that only one amp was needed to open the pinto fully.

If this interpretation is true, there is only a 0.2ms gain between a P&H against a 3.3ohm injector + a 10 ohm resistor !!! (at 13.3V). If the inline resistor is 2 ohm, the difference of opening duration between the two is insignificant.

The major difference is $132.

 

makes sense to me. but with a resistor inline, the injector will only be seeing about 3V. I need to read up on my inductor physics, but i believe the rise time will be faster with 13V@1A than at 3V@1A?

 

You are still missing my point.
What if the reason the manufacture made it higher resistance is because it doesn't NEED 4a to reach optimum p&h function? FJO is the only person putting the 4a number out there. We STILL don't know what the required amperage and pulse times are for every injector... because we don't have the injector specs in front of us. So yes, there are still a huge number of unknowns. Where did you hear that it needs 4a to reach optimum P&H function? Who said 4a?



The point is: It doesn't need to reach 4a. What if it only needs 2?

Really?
For a bosch 4.5 ohm P&H injector, what is the required signal for optimum P&H function? what amperage supplied at what voltage? (This is my whole point I have been making; without scoping a BUNCH of injectors, we don't know the answer to this, however, we do know that a 3.3ohm injector only needed 1a, so it is safe to assume a 4.5ohm won't be far off from that.)

The injectors do not NEED 4a. Also, keep in mind that our cars are running at 14.4v, so the 13.3v test is not wholly accurate.

.2ms on a 3.9ms pulse.... Keep in mind: That's 5% timing differential. If you could improve the resolution of your timing and fuel injection by 5%... wouldn't you want to?

This is my entire point! So a 4.5 ohm P&H injector should function properly with a 4a/1a signal set from an FJO box. not only will it function properly, but it will function optimally, IF the characteristics are similar to the 3.3 ohm injector that was tested. Will a resistor work? Yes, does the FJO box work better? Yes.


So, when we were both interpreting the same thing... just in different words... why were we even arguing in the first place?

Test shows that the 3.3ohm injector only needs 1a to open fully.
Test shows that a 15v (closer to 14.4v than 13.3) is best to maintain optimal P&H function.
Test shows that The FJO box can improve injector map resolution by 5% + or -

Could be the key to idling properly, and even the key to more consistent A/F ratios all the way up to redline.

On an FD, That's absolutely worth $150.