Help with understanding fueling at different RPM's but same VMAF

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Help with understanding fueling at different RPM's but same VMAF

Post by EECBandit » Fri May 01, 2020 10:29 pm

So I'm am flowing the same MAF air and have the same VMAF at two different RPM's and load. But my KAMRF at one rpm is pulling about 7% and is roughly 0 at the other RPM.

How can I make the KAMRF the same at the two different RPM's? What in the fueling equation needs to be adjusted?


I've attached a snip of my log showing two different RPM's and loads, not sure what I need to adjust to try and get fueling to be the about the same.
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Capture3.JPG (26.97 KiB) Viewed 568 times
331, 34lb Ford racing injectors, RPMII intake, 75mm TB, AFR 185 heads, AOD with 3200 stall, custom cam 600/605 lift 224/231 @ 0.050, 1 5/8" long tube headers, 2.5" x-pipe

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Re: Help with understanding fueling at different RPM's but same VMAF

Post by jsa » Sat May 02, 2020 8:06 am

Look at pw1 and pw2.

Possibly in hi slope and lo slope.

Tweak lo slope and breakpoint.
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Re: Help with understanding fueling at different RPM's but same VMAF

Post by EECBandit » Sat May 02, 2020 9:16 am

So my FI breakpoint is 0.9969 x10-5 LB/REV, how does that relate to my PW at different RPM's? I looked at the description in BE but it wasn't clear to me.


Would I make Low slope bigger to try and reduce the PW? I think I've tried that before, even making the slopes equal, but I could never get the desired results.
331, 34lb Ford racing injectors, RPMII intake, 75mm TB, AFR 185 heads, AOD with 3200 stall, custom cam 600/605 lift 224/231 @ 0.050, 1 5/8" long tube headers, 2.5" x-pipe

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Re: Help with understanding fueling at different RPM's but same VMAF

Post by EECBandit » Sat May 02, 2020 11:51 am

So looking at my fuel injector spec sheet, there is a multiplier of .8 to .9 approx when the fuel pressure is less than 39psi.

When cruising the fuel pressure is always less than 39psi, I'm not aware of anyway to tweak the breakpoint or the high/low slope dynamically.
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331, 34lb Ford racing injectors, RPMII intake, 75mm TB, AFR 185 heads, AOD with 3200 stall, custom cam 600/605 lift 224/231 @ 0.050, 1 5/8" long tube headers, 2.5" x-pipe

Mustang Dyno - 344 Torq, 359 HP

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Re: Help with understanding fueling at different RPM's but same VMAF

Post by Paulie » Sat May 02, 2020 12:25 pm

if your fuel pressure is 39 with the vacuum line off and you have a vacuum referenced fuel pressure regulator there is no reason to use the multiplier because the pressure differential across the injector is still 39psi. With the injector firing into a vacuum we lower the fuel rail pressure to keep the differential pressure across the injector the same.
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Re: Help with understanding fueling at different RPM's but same VMAF

Post by EECBandit » Sat May 02, 2020 12:43 pm

Paulie wrote:
Sat May 02, 2020 12:25 pm
if your fuel pressure is 39 with the vacuum line off and you have a vacuum referenced fuel pressure regulator there is no reason to use the multiplier because the pressure differential across the injector is still 39psi. With the injector firing into a vacuum we lower the fuel rail pressure to keep the differential pressure across the injector the same.



excellent point.
331, 34lb Ford racing injectors, RPMII intake, 75mm TB, AFR 185 heads, AOD with 3200 stall, custom cam 600/605 lift 224/231 @ 0.050, 1 5/8" long tube headers, 2.5" x-pipe

Mustang Dyno - 344 Torq, 359 HP

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Re: Help with understanding fueling at different RPM's but same VMAF

Post by jsa » Sat May 02, 2020 4:48 pm

Don't think I can explain it any better than the material you have read.

The spec sheet has lo slope greater than hi slope, so should your tune.

Do you have a returnless system or a return system with pressure regulator and manifold vacuum reference?
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John

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Re: Help with understanding fueling at different RPM's but same VMAF

Post by EECBandit » Sat May 02, 2020 5:09 pm

stock return fuel system.

I just bumped up the low slope from 45 to 50. It seems to be trending in the right direction ( I didn't reset the eec before I adjusted). I'll clear the KAMRF's tonight and take another drive tomorrow.


I never thought increasing the low slope would/should ever be considered.
I always tried to lower it, never raised it. So we'll see how this plays out.


thanks for the help!
331, 34lb Ford racing injectors, RPMII intake, 75mm TB, AFR 185 heads, AOD with 3200 stall, custom cam 600/605 lift 224/231 @ 0.050, 1 5/8" long tube headers, 2.5" x-pipe

Mustang Dyno - 344 Torq, 359 HP

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Re: Help with understanding fueling at different RPM's but same VMAF

Post by cgrey8 » Sat May 02, 2020 5:21 pm

If you find increasing low slope helps, this could also be injector offset curve causing this. Lower all points on the curve, and see if this also helps.

But I do believe injector breakpoint/slope/offset is where the problem is.
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Re: Help with understanding fueling at different RPM's but same VMAF

Post by EECBandit » Sat May 02, 2020 6:00 pm

cgrey8 wrote:
Sat May 02, 2020 5:21 pm
If you find increasing low slope helps, this could also be injector offset curve causing this. Lower all points on the curve, and see if this also helps.

But I do believe injector breakpoint/slope/offset is where the problem is.


What confuses me about the offset is that the battery voltage is the same in both cases above. Is the offset only for low Pulsewidths?
331, 34lb Ford racing injectors, RPMII intake, 75mm TB, AFR 185 heads, AOD with 3200 stall, custom cam 600/605 lift 224/231 @ 0.050, 1 5/8" long tube headers, 2.5" x-pipe

Mustang Dyno - 344 Torq, 359 HP

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Re: Help with understanding fueling at different RPM's but same VMAF

Post by cgrey8 » Sat May 02, 2020 7:22 pm

The problem isn't voltage. The problem is that this is ADDING fuel regardless of RPM/Load condition.

The theory behind this setting is that regardless of PW, there's a certain amount of time that passes from when voltage is applied to the injector and when it starts flowing. That time is based on voltage. Higher voltage, the quicker the mechanics in the injector move. The lower the voltage, the slower.

However when more modern injectors open more quickly/easily than older era injectors did and you are running the curve for older injectors, then what happens is you wind up spraying more fuel than was calculated for. So how does that relate to this? You can attain the same MAF flowrate at different RPMs. The higher the RPMs, the more injector fire events occur, and thus the less fuel each injector fire will deliver, thus smaller PWs at higher RPMs for the same flowrate to satisfy the same airflow.

So if your offset is adding too much fuel, then it will have a similar behavior as if your low-slope is too low and needs to be raised. But in reality, the problem is a fixed adder that's simply set too high and flowing more fuel than is needed at smaller PWs.
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Re: Help with understanding fueling at different RPM's but same VMAF

Post by EECBandit » Sat May 02, 2020 8:11 pm

Thanks for the explanation, that makes perfect sense.
As a start, how much would you suggest I reduce the curve by?
331, 34lb Ford racing injectors, RPMII intake, 75mm TB, AFR 185 heads, AOD with 3200 stall, custom cam 600/605 lift 224/231 @ 0.050, 1 5/8" long tube headers, 2.5" x-pipe

Mustang Dyno - 344 Torq, 359 HP

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Re: Help with understanding fueling at different RPM's but same VMAF

Post by jsa » Sat May 02, 2020 8:36 pm

Have you set your tune to the offset values in the spec sheet?
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Re: Help with understanding fueling at different RPM's but same VMAF

Post by EECBandit » Sat May 02, 2020 9:23 pm

Yes. all parameters were set based on specs provided in the data sheet.
331, 34lb Ford racing injectors, RPMII intake, 75mm TB, AFR 185 heads, AOD with 3200 stall, custom cam 600/605 lift 224/231 @ 0.050, 1 5/8" long tube headers, 2.5" x-pipe

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Re: Help with understanding fueling at different RPM's but same VMAF

Post by cgrey8 » Sat May 02, 2020 9:58 pm

Back when I had to make that adjustment, I did NOT have the curve. So I had to guess. Even years later when the 97 Explorer EEC was deciphered and I was able to get the stock curve for the 17lb injectors I was running back then, that curve still didn't work as well as my edits did. I just assumed there were also differences in the EEC's electronics that also might play into what that curve should be. Later, when I moved over to the 331 stroker, I had the 36lb injectors...and again I didn't have the curve. I reused the one I came up with for the stock 17lb injectors. And it worked just fine.

I can't say what I would "recommend" you run for a curve. Best I can tell you is experiment and try to keep the "shape" of the curve...just lower the values so the whole curve comes down and see if this helps. Obviously if it doesn't, revert back. It's something to try when you don't have anything better to try. However if you find other adjustments work better, then run what works.
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Re: Help with understanding fueling at different RPM's but same VMAF

Post by jsa » Sun May 03, 2020 8:36 am

You can switch all your electrical loads on and off whlie watching vbat and lambse, that will guide you on your offset settings.
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John

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Re: Help with understanding fueling at different RPM's but same VMAF

Post by EECBandit » Sun May 03, 2020 2:51 pm

well, I just decided to go back with my original low slope because I was reading about the breakpoint. The spec sheet has it in LB and we are supposed to enter in lb/rev.

So I just multiplied my current breakpoint by 4.

Unfortunately, now I am dealing with winter and summer gas. I had a tank of winter gas and now it's diluted with new summer gas and that's a whole other deal.


Ultimately, I am going to just start with the bigger breakpoint and see where that gets me (as soon as I burn through the winter blend fuel).


I'll let you guys know how it goes.
331, 34lb Ford racing injectors, RPMII intake, 75mm TB, AFR 185 heads, AOD with 3200 stall, custom cam 600/605 lift 224/231 @ 0.050, 1 5/8" long tube headers, 2.5" x-pipe

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Re: Help with understanding fueling at different RPM's but same VMAF

Post by cgrey8 » Mon May 04, 2020 5:27 am

The three MAIN things I used EEC Analyzer for was MAF, mapping, and Injector Slope tuning. Run your logs through EA and get it to calculate what your injector slope/bp values should be. And even if it doesn't "fit" the datalog great, you can see the datalog and enter values that your eyes show you fits better. For anybody that is having to do injector slope/bp tuning, this is THE tool to use.
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Re: Help with understanding fueling at different RPM's but same VMAF

Post by EECBandit » Mon May 04, 2020 11:51 am

I use EA for my MAF tweaking and really like it.

I found the slope/BP to be a bit unclear. I'm not sure what data it's using other than my injector size, the manual calculation needs a bit more instructions IMO.
331, 34lb Ford racing injectors, RPMII intake, 75mm TB, AFR 185 heads, AOD with 3200 stall, custom cam 600/605 lift 224/231 @ 0.050, 1 5/8" long tube headers, 2.5" x-pipe

Mustang Dyno - 344 Torq, 359 HP

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Re: Help with understanding fueling at different RPM's but same VMAF

Post by cgrey8 » Wed May 06, 2020 2:20 pm

In order for the injector slope/bp calcs to mean much, you need a relatively long and varied datalog...that is a datalog that includes as much different RPM/Loads as possible.

So stable cruising at all speeds that you'd cruise (i.e. 40-75MPH)...meaning you need to time at each speed to capture not just flat-cruise, but cruise at those speeds going up hill (mild accel), down hill (decel), flat, and a non-WOT moderate acceleration like trying to pass or gain speed up a hill. And of course some idle-to-redline WOTs in there too.

I realize this is often difficult to get in one log which is why you can load multiple logs into EA. However when doing slope analysis, you really need to make sure that all logs that are loaded were produced using the same tune and under relatively the same conditions (i.e. outside temp, engine temp, same tank of gas, etc). You aren't going to get every possible variable particularly if you have to tweak the tune 5-6 times. But do try to get as many different running conditions as you can so you have a good representation of every possible injector pulse-width that your application is capable of producing.
...Always Somethin'

89 Ranger Supercab, 331 w/GT40p heads, ported Explorer lower, Crane Powermax 2020 cam, 1.6RRs, FMS Explorer (GT40p) headers, Slot Style MAF, aftermarket T5 'Z-Spec', 8.8" rear w/3.27s, Powertrax Locker, Innovate LC-1, GUFB, Moates QuarterHorse tuned using BE&EA

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Re: Help with understanding fueling at different RPM's but same VMAF

Post by EECBandit » Fri May 08, 2020 1:26 pm

Good info, thanks cgrey8.

I'll start putting some data logs through the slope / BP calculator.
331, 34lb Ford racing injectors, RPMII intake, 75mm TB, AFR 185 heads, AOD with 3200 stall, custom cam 600/605 lift 224/231 @ 0.050, 1 5/8" long tube headers, 2.5" x-pipe

Mustang Dyno - 344 Torq, 359 HP

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Re: Help with understanding fueling at different RPM's but same VMAF

Post by cgrey8 » Fri May 08, 2020 1:54 pm

Some other tips.

Disable KAMRFs so they aren't in the mix causing problems for the calculations

Filter your logs to remove corrupt datalog entries. If you have corrupt lines, EA will complain about missing or bad data in the datalog. To get rid of them, you'll want to filter the log of lines that have "bad" data. I have a series of filters I often use in EA if you don't have your own. I don't recall them off the top of my head right now, but later this weekend I'll load of EA on my personal PC (on work PC right now) if you need.

Oh yeah, BTW:
Image

LOL I love that GIF!
...Always Somethin'

89 Ranger Supercab, 331 w/GT40p heads, ported Explorer lower, Crane Powermax 2020 cam, 1.6RRs, FMS Explorer (GT40p) headers, Slot Style MAF, aftermarket T5 'Z-Spec', 8.8" rear w/3.27s, Powertrax Locker, Innovate LC-1, GUFB, Moates QuarterHorse tuned using BE&EA

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Re: Help with understanding fueling at different RPM's but same VMAF

Post by EECBandit » Wed May 13, 2020 8:00 pm

well, quick update. All I did was multiply the breakpoint by 4 and drove it.


So far it is the best it's ever been. in 3rd gear it's pulling about 3 to 4 % fuel across the cruising range and in OD it's +2% on one bank and -3% on the other.

It's really better than it's ever been, and consistent too. I am going to drive it for a while without making any changes and see if it does well as the weather warms up more.

I notice it really gets better closer 0 as the RPM's increase. I don't think my engine likes it below 1800 RPM, right where I spend most of my time cruising around town.

Thanks for all the help !
331, 34lb Ford racing injectors, RPMII intake, 75mm TB, AFR 185 heads, AOD with 3200 stall, custom cam 600/605 lift 224/231 @ 0.050, 1 5/8" long tube headers, 2.5" x-pipe

Mustang Dyno - 344 Torq, 359 HP

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