As I am gathering my parts for a top end build I ran across a Facebook post where Scotty J from Parkland Auto & Machine/RHP just swapped in 26# Accel injectors into a stock 460 SD PCM. His reason for the swap was to add 8% more fuel to the fuel curve across the board along with a adjustable FPR for fine tuning. I was under the assumption that you could not just swap injector sizes in a stock PCM without some sort of tune. I take I was wrong with this assumption??


For those who dont have Facebook the conversation went like this...

I am curious about something here guys. I did not think you could swap injector sizes without a tune in the ECM?? Are you guys getting the stock ECM tuned or will the Accel 26# injectors just work??


SJ
At WOT the EFI 460's fuel maps are lean ranging from 13.5 to over 14.0
This was an emissions calculation for an engine that was underpowered and too often running in open loop while hauling.
Add headers, free flowing exhaust and a low restriction air cleaner element and the problem is even more pronounced.
Larger injectors help eliminate this as does an adjustable FPR.
When we step up the VE and make more power a combination of the 26# injectors AND additional fuel pressure help the OEM ecm deal with the upgrades. SJ

• So by the way you explained this you are changing the VE tables in the stock ECC-IV and adjusting it to use the 26# injectors?? I understand the Open Loop/ Closed loop and how that works. Just not sure how you are changing the VE tables?? Motes?? Tweecer?? or ??

• 
  The whole point of increasing injector capacity by 8% is so the average joe doesn't have to go into the ECM.
  When I mentioned increasing / stepping up VE
  I was referring to our crate engines.
  Yes it is a crutch but it is damned effective. As is an adjustable FPU.
  We settled on this by way of checking the results with a wide band. Fuel trim in closed loop can address the additional injector capacity and in some cases fuel pressure.
  I am going to utilize my personal 1997 F_250 HD as a mule to create a tweecer base tune for our crate engines for even better performance.
  
  
• Thanks Scotty J. Thats great info. I did not know you could just plug in bigger injectors on the stock SD and make it work. I would be really curious of what a good tune can do on your Awesome engines.
  
  SJ
• It works in this case because these engines operate so lean at WOT.
  Adding larger injectors past this would require a reflash.
  SJ

 

This is a unique case that doesn't translate well to other situations, the stock 460 tune is different than the smaller motors in the way it is setup, engine displacement has been increased so airflow does as well and that requires more fuel, and the injector increase is small so it's a valid strategy from a performance standpoint but all bets are off in terms of how emissions are impacted.

 

I get not meeting the emissions doing this. If you slapped a good set of heads, intake, cam and exhaust on a smaller engine it will have more airflow as well but probably not at a lower rpm like a big block stroker. So what / how do you mean the smaller engine's setup are different??

 

The OEM 460 tune is different in the way it behaves, it's designed to run open loop most of the time while the smaller motors are setup to run closed loop more. The key thing to know about that is the PCM doesn't self tune at all in open loop, while even the SD system can learn some with O2 feedback in closed loop. There is a fair bit of unused capacity in the stock 24lb injectors.. they can accomodate upwards of 350hp so it's debateable if the injector upsize was necessary, but this PCM really needs to be tuned moreso than the others to effectively manage more significant changes. I still think that is the better way to go, but considering the small difference in injector size(24-26=8%) it probably works well enough. For comparison the difference between 19lb and 24lb injectors is 21%.

 

The mid 01-04 mustang gt, got 21#'s, thats 10%, close enuff in Horseshoes & Handgrenades
2 members here, used 24's and a 460 PCM, in their 351w, and nothing else, got done, no tune, zelch nota.
460 comp & injectors into a 351 - Ford Truck Enthusiasts Forums
24 lb injectors on speed density - It can be done - Ford Truck Enthusiasts Forums

 

To me its a hack. Zero mention of pulse width.
Does it even need bigger injectors?
Where's the data log that shows the injector pulse width is greater than 80-90%?

With larger injectors, your dumping more fuel in, because the pulse width is the same as the smaller injectors. It's going to be rich.

I don't believe any mention of the Fuel Pump Unit(FPU) is increased or decreased.
More than likely decreased, probably takes some of the richness out.

Wouldn't leaving the injectors alone, and increasing fuel pressure give the same result?

 

Thanks Conanski. I didn't know there was a difference between the 460 & Small blocks PCM when it came to running in more open loop VS closed loop. I already knew about the percentage difference between the 19lb & 24lb injectors.

Thanks torq'ta 5 8. I didn't know the 01-04 mustangs used 21lb injectors. I will file that info for just in case. I already knew about the two guys that are using a 460 PCM & 24lb injectors and thanks for adding the links to refresh my memory. I already have a 460 PCM & 24lb injectors sitting in the garage. What I don't know yet is if I need to change the injector harness to get the correct firing order for the 5.8L even though they are both Batch fire??
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What I was surprised with and still have not got a direct answer on is... Can you just change injector sizes without a tune. Granted if changing injector sizes it will richen or lean the whole fuel curve depending if you step up or step down with injector size. RHP did this on the 460 PCM so I take this can be done on the small block PCM as well??

 

+1 on that.. right up there with scaled MAF meters.

Yes I have done that myself and it's a great way to increase the capacity. We also had 19lb injectors feeding a 400hp supercharged 5.0 via an FMU without any problem. If I'm not mistaked these injectors are rated to 100psi.

 

Yes. Without a tune your gambling, without a data log your just throwing parts at it, doesn't matter the engine. As an experiment, sure, have fun.

Here's a good one, take a 6cyl PCM, batch fire, throw it in the v8 batch fire. Will it run, does it work, maybe and maybe, but what's the point?

I just spent $500 on injectors...Canadian dollars, am I just throwing parts at it, no.
I will be telling the computer what injectors I have, then will be data logging to dial in the VE table.

My first upgrade to my stock engine was a tuner with data logging capabilities.
My last upgrade after headers, intake, cam and heads is probably going to be the injectors.

 

Thanks wwhite. That was the answer I was looking for. I agree without data logging & tuning ability it is just a experiment. When I start my build I am planning on installing a AEM failsafe AFR gauge that will data log for up to 3 hours. I wanted something to start out with, without going straight to the pimpxshift or one of the other's tuners. Maybe I am old fashioned by I have this mind set as to get one thing done before moving onto something else. So my first train of thought is to get all the parts installed and get it fired up and running / driving some then move on to tuning side of it.

 

I found this today and thought I would add it to this thread. I have no way to verify the information posted in the link but it shows a lot of ford injectors and different sizes.

​​​​​​https://www.stangnet.com/mustang-for...k-yard.794080/

 

I trust nothing those mustang guys, say, or post, pics of, they dont even have the blue 24's down the mustang uses, and the trucks, if you see TMOSS saying something that is believeable. they will argue over who is more wrong, for days, jmho

 

I wasn't aware that the 460 trucks didn't run in closed loop most the time and that it is the other way around. Do you have any idea why they run in open loop more often? Seem counterintuitive and possibly why they are so thirsty.

 

I don't know exactly why the choice was made, but yes, it's a huge part of why they're so much more thirsty than most people expect.

 

The open loop and closed loop code is identical for all SD, based on time, temperature, engine load, rpm and speed...a few other variables.

The only time closed loop happens is when your at part throttle. So, if you are idling, engine/speed/rpm at light load, wide open throttle, or decelerating you are in open loop.

Entry into closed loop will happen after operating temp is reached, other variables, and at part throttle.

I think it appears that the 460 is in open loop most of the time, because the engine has so much torque, the computer computes air/fuel scheduling as an extremely light load(open loop). When loaded, not at WOT, at part throttle, entry into closed loop happens, learning happens, and the computer attempts to give best power and minimal fuel usage per load/rpm.