What Impedance Injectors for DFI?

[xLusi0n]

I can't seem to get any help on my DFI 6.0 at the MR2 board, so I've come here for some help. What impedance injectors am I supposed to get (low or high)? Is there any option in the software to change between high or low? Does it vary between different firmwares? Anyway to check? I keep hearing that the DFI 6.0 uses high impedance injectors, but I have some low impedance injectors... Thanks.

 

[Chuck Leeper]

Hi/LO??

Don't think it makes any difference. I ran 55's and 72's on mine.

 

[xLusi0n]

I'm not sure I understand...to my understanding, injectors are either hi or low impedance...bad things can happen if the right one is not matched up to the ECU...am I wrong?

 

[Chuck Leeper]

Ho or lo??

You are correct. The lo impedence injectors will create more load on injector drivers in the ECM.
Most domestic injectors smaller than 55PPH, are high impedence, and work w/stock ECM's. If the injector is a lo imp., then the ECM drivers need to be changed.
In the case of the aftermkt ECM's, they already have the heavy duty drivers, and need no mods.
You can run either hi or lo imp. injectors w/ those units.
HTH,

 

[Reggie West]

One thing to remember.

If you are using an older DFI batch fire box it has one driver for every two injectors. This will work with injectors up to 72 lbs/hr with no problems. Above that you should get a VIC unit to go with it. That has one driver per injector which means better control of bigger injectors.

If you are going to buy a Gen 7 or FAST they both come with one driver per injector anyways. One of the benefits of newer technology.

Hope that helps

 

[xLusi0n]

Thank you for all your help, that helped a lot.

1) what does VIC stand for and where can I get this unit? Will this unit "attach" to the DFI 6.0? (I will be using 850 CCs which translates to about 80#s I believe)

2) So I understand that aftermarket ECUs can control either one (usually)...but is there a setting I need to change on my Accel DFI 6.0? or does it automatically power it the right way for me? Thanks.

 

[xLusi0n]

Also, I was reading the DFI manual and it says that the Spark/Fuel ECM can control 8 low impedance injectors at full duty cycle for a SHORT PERIOD of time...the SEFI can control low impedance injectors with no time/duty constraints...I think I have the Spark/Fuel version (how can I find out for sure?) and I am running low impedance injectors...does that mean I can only run it at full duty cycle for short periods of time or I'll fry my ECU? If I run it at 80% duty cycle is there still a time constraint? (Will I burn out my ECU if I'm on the track for 15 min at 80$ duty cycle?)

Does that also mean that if I run high impedance injectors, it will "be better" for the ECU because there is less load?

Does this sound right ?

1) high impd inj + high impd ECU = OK
2) high impd inj + low impd ECU = OK, but bad control of INJ?
3) low impd inj + high impd ECU = BURNT ECU
4) low impd inj + low impd ECU = OK

Sorry for all the dumb questions, but I'm running 90 PSI (@ idle) on 550CC injectors just to keep from leaning out...and I want to swtich over to 850CCs so I don't have to run such high PSI fuel pressure (afraid somethings gonna blow off and set my engine bay on fire). At the same time, I don't want to mess something up and burn out the ECU...Thanks again for the help.

 

[xLusi0n]

Ok, sorry for the triple posts...but I did some searches online and I think I figured some things out...

1) the Accel DFI manaul says that it will burn out if powering 8 low impd injectors at 100% duty cycle...that's not a concern to me because 1) I am only powering 4 injectors 2) I will be at 80% duty cylce, not 100%

2) I know what the VIC is now (saw it on WhiteRacing.com)

3) because the minimum rise time for high impedance injectors is 2.0 ms and my car idles with 1.5ms pulse widths...I will have bad idle if I switch to high impedance...stay with low impedance (because they have 1.5ms minimum rise times)

4) as long as I don't run my injectors at 100% duty cylce, I won't burn out the ECU

Thanks.

 

[Reggie West]

3) because the minimum rise time for high impedance injectors is 2.0 ms and my car idles with 1.5ms pulse widths...I will have bad idle if I switch to high impedance...stay with low impedance (because they have 1.5ms minimum rise times)

Dont count on 2.0 ms as a minimum rise time. I am seeing a Stage 2, M&A heads with a max port job idle at 850 rpm and the injectors are pulsing at 1.2 ms. That is a sign of the computer being able to handle big injectors and make them idle.

4) as long as I don't run my injectors at 100% duty cylce, I won't burn out the ECU Also, I was reading the DFI manual and it says that the Spark/Fuel ECM can control 8 low impedance injectors at full duty cycle for a SHORT PERIOD of time...the SEFI can control low impedance injectors with no time/duty constraints...I think I have the Spark/Fuel version

What they say about a Spark/Fuel ECM is the same as a batch fire unit. There is no difference.
The difference between a SEFI and a batch fire unit is the number of drivers. The SEFI (sequential unit) had one driver per injector, the batch fire had one driver for every TWO injectors.
That said, it is not wise to run injectors at 100% duty cycle anytime if it can be helped. You run the risk of the injector never closing at or above 100% duty cycle and there goes fuel control.

I am telling you all of this and I hope it helps. I was curious as to what kind of car this is going in?

Good luck

 

[xLusi0n]

Thanks for all your help.

This is for a 1993 MR2 Turbo...2.0L 4 CYL dynoed at 433 rwhp (car weighs about 2800lbs) with 110 leaded VP Fuel race gas.

T3/T4 turbo pushing 25psi max (usually 20psi), Deltagate II external wastegate, custom intake manifold, custom exhaust manifold, 8.5:1 JE pisons 20 over, Mustang TB, Greddy IC, and some other minor mods....and of course the Accel DFI...

Thanks for the help, I'll be checking this board more often, its been very helpful...not many DFI users on the MR2 board...

I guess I'll be using 850CC low impedance, side feed injectors and only need to run 80% duty cylce max, so I should be safe.

Thanks again.

 

[turbodave231]

You will be safe because your ecu has 4 low impedance drivers which will match up to your 4 low impedance injectors.

For the V6 application, we only use 3 of the drivers to drive 6 injectors. Low impedance injectors in this configuration will cause damage to the drivers at higher pulse widths.

The VIC has 8 low impedance drivers and is connected to only one of the 4 drivers in the ECU. The VIC has the advantage of being able to add fuel to the whole base map injector by injector. With this capablility you can richen up just one cylinder or all the cylinders with the twist of a knob(s).

Now if I only had thermocouples in each cylinder exhaust to find out which cylinders need extra fuel.............

DR

 

[Reggie West]

I have been using a FAST unit as of late on a Stage 2 car and I do like it.

There is nothing wrong with the DFI batch fire as long as you know how to use it. The real drawback to the older DFI is the lack of datalogging capability. But I can tell you I had the fuel and spark dialed in on the DFI before I took it to a dyno. Even the dyno guy was impressed.

So it can be done.

Let us know how that car turns out. Sounds mean.