I’m going to go check this thing out tomorrow (plug it in and see if it runs), but I’m trying to identify what it is and what it’s worth before I go there. It’s supposedly a DFI box (DFI 6?) with a piggyback cable for use with a 165 gm ecm. Based on a phone conversation and the owner is kind of sketchy (basically a mustang guy that was considering running a DFI and GM style harness in his mustang, so he doesn’t seem to recognize any gm stuff) this is what I know:

- box has mixture two adjustment screws labeled idle and WOT (don’t remember the exact label) and an Accel logo
- only real # on the label is:

74305-C
serial

- It has a Calmap 6.0 disk (apparently upgraded, the instructions all talk about Calmap 5.0, didn’t seem to have DFI instruction book, just calmap software books)
- Piggyback cable with a map sensor on the end of it
- ECM has '88 IROC written on it (it is a 165)
- the cable that connects to your laptop

Thanks for any info.

 

My DFI box did not have any adjustment screws, just the two terrminals at the box (same as the 165 ECM, IIRC). The 74035-C sounds like a normal part number. Give Accel a call - You can get right through to the DFI techs.

A.

 

Actually, I got it right the first time (74305-c), and I'm adding this for future refrence.

Appartently the 74305 is a Gen V Power Programmer box, where what most of you are running, a Gen VI, will have a 740xx #.

Oh well, looks like it won't work anyway, looks like the injector driver is not much better then the GM one and can't call for a shorter duty cycle then the stock one, and I couldn't get a real answer if it could use a 2 or 3 bar map without an add on box....

Oh well, I'm looking for something that will idle with the 77# injectors that I want to use

 

along these lines, does anyone know of a way to calculate the approximate duty cycle of an injector at idle? DFI claims that they can control an injector down to 1.3ms, and the injectors open 2x per power stroke so effectively, the largest injector that you can run would be one that needs at 2.6ms duty cycle to idle at a reasonable rpm.

After that you have to convert to sequential so it only fires when the valve is open...

for that matter, what are the limitations of high and low impedance injectors???

 

Staying within the same impedance and pintle weights, there are current limitations, so the opening/closing times of injectors will be nearly identical among all controllers, no matter which brand of $2 river is used inside the box. High impedance goes to about 50 lbs/hr, and over that, you'll require a low impedence peak and hold driver. Apparently the DFI can handle low impedence injectors, but it only has 4 drivers for 8 injectors. I have heard this, but not tried it. Jeff Stevens (10secZ) designed and now sells a high to low impedence conversion box that splices inline with your injectors, right from the ECM. It should be $200-$300, I think. You can also get the Accel VIC to drive the low impedence injectors and individually tune them. Anything that can handle the impedence will idle the injectors, but they might just be very rich

The MAP sensor has nothing to do with high or low impendence injectors. DFI will handle 1, 2, or 3 bar. Speaking of which, I need to get myself a 3 bar map sensor now...

 

I was actually told flat out, point blank, that GM and Gen V and older DFI’s have problems controlling injectors for pulse widths of under 3ms, and that Gen VI and VII ecms are OK down to 1.3ms. Sure the ecm can tell it to go faster, but whatever they’re using for an injector driver cannot. As per Accel, to get a Gen VI to really work well with low impedance injectors you need the VIC, the Gen V definitely needs an add on box but I’m not sure if a VIC will work with it. The Gen VII I believe is like other aftermarket ECM’s and has the functionality of the VIC built into it.

What you said about map sensors is true about the Gen VI and up, the DFI techs stated that for a V that is not the case.

To my knowledge there are very few non OEM injector driver IC’s, and the one that was being used for most apps has been discontinued (which is why the high to low impedance converters for mustang SEFI setups have disappeared). I’d be kinda curious to know what Jeff Stevens is using (not that I would go out and build my own, I hate electronics, I just try to know enough about it that I can spot crap if I have to)

OTOH, if what you’re saying is true why is it difficult to get a stock TPI ecm (whichever of the 3 that you want) to idle with larger then 30# injectors, where most aftermarket ecms will idle well with much bigger injectors???? WTF, I could see it now, injector driver via a mouse flipping a light switch…

I (and apparently the prevailing thought with the GM ecm list since there has been some discussion about trying to get them to fire every other revolution) originally thought that it was the fact that GM and DFI ecm’s fired 2x per powerstroke (once per rev), but that wouldn’t make sense considering there are people with 50# injectors that idle fine with DFI Gen VI and up. Just to double check this, my brother and I just went through the data logs for his haltech setup, and he has it running firing the injectors once per revolution (batch fire) with 36# injectors at 74psi (he needs bigger injectors). On the haltech unit this is configurable, and basically you give it a constant that tells it to fire the injectors every time it counts a specific # of ignition pulses (his was set to 4). We took the constant down to 2, (so it will open the injectors every other ignition pulse), and it still idled well with an injector pulse width in the range of 1.2ms (it blew black smoke and didn’t want to run at idle with the ~1.8ms pulswidths that it was using before, implying that the SVO 36’s were responding to pulse widths under 1.8ms) , which is below what the current DFI can constantly open the injectors (as per Accel’s techs) and supposedly way in excess of what a high impedance injector can do (according to Accel you cannot control them under 2.5ms).

BTW, 77# injectors use 36# SVO pintles and coils (they ARE 36# SVO injectors with a modified metering plate), and they are high impedance injectors. To give you some idea, I just took an ohm meter and measured some LT1 24# - 12ohms, TPI 22#-13.2ohms, 77#- 14.1ohms. (I know, resistance isn’t impedance, but I’m not going to go and build an impedometer and test the things at the appropriate frequency range, for that matter figure out that range and build/find a frequency generator and dig up the o-scope…. Resistance is close enough, if they were low impedance they would have been less then 4, I might have some of those laying around also)

 

Sorry for the bitchy tone in the last post, I was going to edit it to make it a little ‘nicer’ but decided that I couldn’t really accomplish that and say want I wanted to say. The point is that it seems like there is a lot of crap and misinformation out there about this as like with much of the world, and I’m trying to pick out the real facts….

The fact is that I find it insane that we have to spend that kind of money to by an ecm that has just about no computing power by today’s standards for a price that we could buy a fairly nice laptop for. The only thing that is expensive in it is the injector driver, which if it can drive low impedance injectors runs about $8 an injector.

As far as I can tell, the only reason great reason to go aftermarket on blown applications is that the GM ECM’s till the LT1 setup wasn’t capable of controlling injector pulse widths enough to idle with big injectors (serious NA apps have other problems).

 

<shrug> I've got my DFI idling fine at 1.7-1.8 ms with the 30 lb SVO's and 60 psi fuel pressure, IIRC. I seem to remember having 6.032 as the software revision, so it might be I have a V6 box (new in '98). If you're getting misionformation from all the racer joe's out there, call Accel DFI and get the straight scoop.

A.

 

that was my point, most of the information is based on what I got from accel yesterday (since the board was down I didn't get any from here).

I think your software is probably 6.32 (current non windows version).

Your DFI is a Gen VI, which should work down to 1.3ms...

I'd still like to know what is with the slow injector driver on the GM ECM's, if it wasn't for that I'd be going with my funky 2 maf idea.