Does the firing order you plug into the box have any contol of the injector sequence or does the injector sequence always fire the same no matter what and is only changed by moving the injector pins in the harness. TIA

 

XFI will fire them in the correct sequence with the firing order. This is why you match the correct color injector wire to the correct cylinder and you must have a cam sync signal for XFI to work in sequential mode. If you have no cam sync it will still fuel in sequential mode in the correct order but XFI will pick up the 1st crank signal and assume it's #1 and begin fueling in that order.

 

Hi Dustin, What I'm doing is a 4/7 cam swap on a Little M, so what you're saying is to swap the 4 & 7 injector wires AND change the firing order in the box? If the firing order affects the injector sequence, wouldn't changing the wires have an inverse affect and put you right back to the factory GM injector sequence. I also have an old sequential box, does it work the same way as the XFI? I'm not doubting you, I just want to make sure I understand this clearly before I do the swap. Thanks!

 

No need to swap wires. All you have to do is swap the firing order in the box. FAST and XFI function the same.

 

I could be wrong but I don't think that is true... I believe the xfi always fires injectors outputs like this EFGH ABCD e=1 f=8 g=7 H=3 A=6 B=5 C=4 D=2. The software firing order is used by the xfi to when making individual cylinder corrections for fueling and timing. plus if you watch the lights on the box when it is running it it fires EFGH ABCD. also if your correct why do they sell different injector harnesses if its controlled by the friing order.

either way i changed my pins after i figured out i had a 4/7 swap cam

 

So you changed pins and firing order in FAST? I have never had a problem with them but only have experience with one 4/7 swap. You could easily be correct as I've never looked into it. The car with the 4/7 swap has been running for 3 years but we have never tried any cylinder correction that would show us a problem. If I were using the 4/7 swap I would look into it further as i could be wrong. I guess since we're only talking miliseconds between cylinder events the motor doesn't care that the injector is a little out of sync.

Now that you mention it. I have seen a Chevy run a Ford firing order and have no issues for 3 months of racing. If the firing order doesn't matter it could easily be the wiring that determines correct order???

 

So the XFI injector sequence is the same as a LSx base engine and you can't change that unless you change the wiring around and the firing order you plug into your box is for the timing side of the ICC. What about cylinder fuel correction? Say if you add fuel to #7 cylinder will you actually be adding fuel to #4 cylinder? This whole 4/7 swap doesn't seem worth the headache.

 

I can say for certain that the old FAST unit fires the injector outputs in a fixed sequence, and it is up to you to make sure that they are wired to the correct cylinder. I think the XFI works the same way, as described by Jackstand.

The higher the injector duty cycle is, the less this issue matters. As an example, if the injector is only OFF for 10% of the time, who cares when that is? It makes little or no difference. When the injector DC is low, the ill effects of improper injector timing can be more pronounced.

 

I have never had to move any wires around. You simply buy whichever injector harness you need and it comes wired correctly. SBC, Ford, Chrysler. In your case with the 4/7 swap it sounds like you need to swap 4/7 pins in harness.

I don't think the 4/7 swap is worth it in a boosted motor.

To check the cylinder correction. Pull timing out of the cylinder and check that cylinder with a timing light. This will tell you if it's changing the correct cylinder.