So if I were to use 0-280-150-837 injectors would I have to jumper my '165 from d9 to d3 to put it in PnH mode? Would I need to set the firing mode to TBI also or would I leave it on 6 cylinder since I want it to fire in batch mode? I think I need 4 ohm resistors to make these 5 ohm injectors safe for my ecm, right?

 

If those are low-Z injectors they will not work with the '165. IIRC the '165 will only run a maximum of 2 low-Z injectors.

In order to run more some hardware modifications would need to be made, including a different value for the feedback or "sense" resistors and a change to the driver MOSFET.

 

Sounds like a job for a 749

 

That's the idea. I was looking at this and I want to apply the same to the '165. So I can do this with a resistor box, or just the sense resistor alone?

 

No, the sense resistor is to be able to switch between peak and hold modes, but does not increase the current capabilities of the ECM.

You could use a resistor box, but I've never been a fan of them, since it can cause some other issues when trying to use a peak and hold mode. With a resistor box you could just leave the peak and hold mode out of it.

You would have to find a MOSFET that is capable of delivering the current needed to drive 6 low-Z injectors, which may not be easy.

 

Wouldn't the one in that link work for me?

 

NM- it's not available even if it did work.

 

These are the closest I could find. Need to dig around in my old electronics stuff.

 

Closest thing I have is an IRFZ44N.

 

More.

 

The '7749 has 2 injector drivers, so the modification listed in the link splits the load between both and basically has half the current on each driver, basically equal to 4 injectors on each driver, not 6. You would have to find the actual current that will drawn, and find a MOSFET that will be capable of that, along with a proper values for the feedback circuit.

 

I haven't studied the hardware side of electronics as much as I should. I did a crude anti- engineering calc by dividing the amperage by 4 (for the '749 mod) and multiplying by 6, I'm guessing I need a mofset capable of 75 amps- as in the last post. Really need guidance on this. I'm also trying to find an answer on whether or not these are PnH injectors. Some say it's saturated, some PnH. I would believe they're PnH though because of the size and the low ohm rating.

 

Injectors are not "saturated" nor "peak and hold", those are both control schemes. Injectors are simply high or low Z when it comes to something like this. Typically a low-Z injector will be used in a peak and hold scheme, to keep the needed current lower than if a saturated control were used.

If it's 75 amps that are needed, that's 900 watts of power, you will find that will create a lot of heat (well it's really the difference of used power to input power that is dissipated, but that will usually be a good percentage of used power).

Is there some reason you don't want to swap to a '779? I have tested a '7749 in my own car running 6 low Z injectors with the stock MOSFETs, but different sense resistors.

Alternatively, why not use some high Z injectors?

 

If I understand what you are trying to do here, I think you need to recheck your math. No where near 75 amps required.

Have not looked at the 165 schematics lately,,,but I do not remember it having p-n-h drivers. You may want to look at using external hardware p-n-h driver chips and not molesting the ecm. I would use an individual hardware driver per injector to give better control and not require high current drivers.

 

Six- I'm still writing code for the '165 and it's a project I don't want to give up just yet. I'm interested in the 0-280-150-837 injectors mostly because of price. It's the least painful way to get the flow I need on E85 and still have decent control in PnH.

Alvanwie- Are you certain the '165 can't do PnH? Some PFI cars used a '165. I was looking at the continuous drain current specs on those MOSFETs supposing I need something capable of 50% more (6 inj. vs. 4) than the one in the link. Again I'm not terribly familiar with the hardware side of things but I figure it should get me in the ballpark of what I need. The one in the link is rated at 47A so I need something capable of at least 70.5A, yes?

Supposing I run these saturated with a resistor change how's response and the life of the part going to look?

 

Yes did a little checking, it appears U12 (16034984) does support PnH operation. Never tried to use it, but if you do some searches on that chip number there is some info out there. I'll bet Rbob knows something about this.

 

The '7165 has a PnH driver set up. Change the sense resistor to 0.033 ohms (4W is a good choice), and upgrade the MOSFET. Can also double up some of the wiring out to unused pins.

A low impedance port injector peaks at 2 A and holds at 0.5 A. The peak of 2 amps is only for an instant. Due to the inductance of the injector the current ramps up, taps 2 A, with the driver then going to 0.5 A to hold the injector open.

Since the one driver is running all 6 injectors need to multiply the current by 6.

So 12 A to peak, and 3 A to hold.

Use a standard MOSFET, not a logic level.

For power dissipation, that is dependent upon several factors. During ramp up to peak the MOSFET is full on. So the only heat generated is due to the resistance of the drain to source.

In hold mode the MOSFET is going to dissipate a lot more heat. This is due to the voltage drop across the device.

So, lets use 14 volts for the vehicle voltage, and 2.4 ohms for the injector resistance, and see how much of a voltage drop across the MOSFET is required to maintain .5 A of hold current.

V = IR, so .5 * 2.4 = 1.2 volts

The injector will drop 1.2 volts across itself, the MOSFET will drop (14 - 1.2) 12.8 volts.

12.8 volts at .5 A is:

W = IE, so .5 * 12.8 = 6.4 watts, times six for all injectors is 38.4 watts.

RBob.

 

well, that answers something i've been curious about(and suspected) for quite some time.... i've stared at the injector schematics for a while and could never see another way for current to be limited that wasn't manipulating the gate voltage to cause the FET to become resistive from source to drain.

since different series of FETs are different from each other in terms of source to drain resistance vs gate voltage, does the driver chip still drop to the same voltage in an open loop fashion, or is it done closed loop? it seems like the sense resistor could be used for closed loop operation, but whether it does or not, i don't know.

 

RBob,

The PnH drivers that I am familiar with pulse at a higher frequency during the hold time. Therefore during the on time the Mosfet is still fully on minimizing drop across the Mosfet but supplying the correct average holding current. I take from your comments that is not how this driver works????

Al

 

It is the sense resistor that provides the current feedback to the driver chip. This is why GM uses an external wire loop to use the sense resistor. When used in a non-PnH install, the sense resistor isn't used.

RBob.

 

In the TBI only ECMs GM ('7747/'8746) didn't use that mode. The driver chip has the capability to use that mode, but doesn't.

As far as the '7730 & '7165 ECMs, maybe they do. I figured that GM didn't as they didn't with the TBI ECMs. And the PWM feature creates a lot of electrical noise.

Likely best to bench test it with a scope to see.

RBob.

 

Learn something new every day. I always assumed on the 8746 the RC network on the timer input of the driver set up the trigger frequency, but I have never put a scope on the TBI injectors to look at it. Always something new to check out. Thanks for the info.

Al

 

Glad to have access to you here RBob, you always clear things up. I have to try this out on a junk reman ECM I have now.

 

The RC timer circuit is to force hold mode after a certain period of time (don't recall the time period). The purpose is to prevent eternal peak mode on a low voltage cranking situation.

RBob.

 

Anyone know what pin C9 is on the '165? It's A/C control on most similar ecms, can it be used as such? Or is it data? I can't find any info on it.

 

it's an input. tied to ground via a 1.2K resistor. runs to U12, pin 38, so when a read of that byte returns via SPI(i think), it will be bit 4.