FIC scaling problems

[gst_Jake99]

I have a set of FIC 750cc injectors that were in my 99 gst when I bought it. Some time ago, I installed EcuFlash and EvoScan to tune. My concern is that even with scaling values set to "InjectorScalingDSM" in EcuFlash, my scaling has to be set at 586 to get proper fuel trims.

Why is the scaling value set so much lower than the actual rating of the injectors? I don't have any boost leaks, car runs great and all fuel trims are within +/- 5. I have a walbro 255 and stock pressure regulator.

Latency values are
4.69V 3.555ms
7.03V 1.290ms
9.38V 1.155ms
11.72V 1.095ms
14.06V 1.095ms
16.41V 0.900ms
18.68V 0.600ms

Any help would be greatly appreciated.

 

[kmetiuk]

Never used ECUFlash/EvoScan...

But your latency values for 11.72V and 14.06V are the same. They should not/cannot be the same latency at different voltages.

 

[gst_Jake99]

Never used ECUFlash/EvoScan...

But your latency values for 11.72V and 14.06V are the same. They should not/cannot be the same latency at different voltages.

Good to know. Being that the latency values should be different, I wonder how the low and mid trims are in range.. I do see what youre saying though. Deadtime should be less at higher voltage.

If I were to lower the latency value at 14.06V, this would increase the amount of fuel delivered, which would result in me needing to raise the scaling value closer to the rated flow rate of the injectors

 

[gst_Jake99]

Found some common latency values being used for the FIC 750s on evolutionM. They are all lower than mine. Once I get the car back together this spring, perhaps I should try those lower latency values and raise the scaling and see where that puts me.

 

[kmetiuk]

Your car runs in that range of 14V (or should if your elec system is strong and healthy) so changing values there will have an effect.

Latency is the time that the ECU needs before the fuel actually starts to flow. There is a delay between voltage/current being applied to the injector and the injector actually opening and letting fuel through. It's the time requried for the acceleration/velocity of the valve in the injector to physically move enough for fuel to flow. The delay is minuscule, but very important at low total injector pulse width.

The ECU sends the "total injector pulse width" for each injector firing event and within that value is the deadtime required for the voltage that the ECU is "seeing":
Total Injector Pulse Width = (deadtime@Voltage + base injector pulse width)

Base pulse is calculated by the ECU by using fuel trims/O2 cycling/MAS/SD/Coolant Temp/Intake Temp/RPM/Etc....
Deadtime is set by the factory (or you now that you swapped injectors)

At Idle: base width is very small
Crusing: low throttle and mid-low RPM means low air flow which means small base width
WOT: at low RPM's and 100% throttle will produce bigger base pulsewidths...at higher RPM's and 100% throttle will produce very large base pulse widths

Changing the latency when base pulse width is very small will have large affects on the AFR of the engine.

Lowering your latency will decrease the amount of fuel because, from the above equation, you can see lowering deadtime lowers the total injector pulse width which therefore lowers the total time voltage is applied to the injector. Less voltage time = less fuel.

I think you would want to raise the latency to richen up the car and then raise the injector scaling to lean it back out.




Just read your last post and re-read your first post....if common values say you should lower the latency then I think there is something else going on.

I'm wondering if using a wally 255 and a stock fuel pressure regulator is over running that stocker.

When I installed my wally 400 (with AFPR) I could not get my fuel pressure below 60 psi at idle with no vac. I swapped out my feed and return fuel lines (from tank to rail) with larger AN lines which dropped my pressure to ~57 psi. After much research I found out there is a little siphon tube that was restricting flow. Once I drilled that out my pressure dropped to 35 psi....which then finally allowed my AFPR to work properly.

Maybe your stock FPR is restricting flow causing higher than expected/wanted fuel pressures?

 

[gst_Jake99]

Alright, thats very helpful. I will definitely try that as soon as Im able to drive it again. Thank you!
Im still surprised however, that my latency values are higher (gives more fuel) and my scaling values are lower (gives more fuel globally) than others report using with the same injectors. I understand that it will vary between vehicles, but the values that work for my car are telling the ECU to supply much more fuel than I would expect.
For example, my scaling is 586 where others are around 713 (586 scaling will supply more than 713 with the same injector.) my latency is higher at 1.095ms where others are using values between 0.9 and 0.7 (as you said higher latency supplies more fuel) This means the low scaling value and high latency values are compounding to supply significantly more fuel..

Determining the cause of why my vehicle must be flashed to get more fuel is my main concern. It raises the question, Do I need new injectors, should I have them flow tested, etc.

 

[kmetiuk]

Alright, thats very helpful. I will definitely try that as soon as Im able to drive it again. Thank you!
Im still surprised however, that my latency values are higher (gives more fuel) and my scaling values are lower (gives more fuel globally) than others report using with the same injectors. I understand that it will vary between vehicles, but the values that work for my car are telling the ECU to supply much more fuel than I would expect.
For example, my scaling is 586 where others are around 713 (586 scaling will supply more than 713 with the same injector.) my latency is higher at 1.095ms where others are using values between 0.9 and 0.7 (as you said higher latency supplies more fuel) This means the low scaling value and high latency values are compounding to supply significantly more fuel..

Determining the cause of why my vehicle must be flashed to get more fuel is my main concern. It raises the question, Do I need new injectors, should I have them flow tested, etc.

I just edited my post above. More info now.

TL;DR. I think its your stock FPR with the wally 255....maybe. TBH I am not sure what the stocker will supply for fuel pressure.

 

[gst_Jake99]

That would make sense if I had to set parameters higher than the rated flow. I would have to tell the ECU that my injectors are larger than they really are to compensate for the high pressure and supply less fuel relative to the load value. Instead, I have to tell the ECU that my injectors are smaller than what they really are, thus resulting in more fuel being supplied to get proper A/F Rs (higher scaling=less fuel. Lower scaling=more fuel)
This means my injectors aren't flowing as much as they should be, correct?

 

[kmetiuk]

If you have higher pressure than expected you have to scale your injectors higher than they are to reduce the fuel injected....so ya your making sense there. Prolly not over running the FPR.

The latency has an affect but really only at idle and cruise every where else the base pulsewidth is much much larger than the deadtimes.

If your car runs and drives fine on the scaling your using then I'm not sure what else it could be as I have zero experience with EvoScan.

If this was DSMLink I'd say check you MAFcomp table or your VE table (if your SD).

As far as your injectors not flowing as much, I run FIC 2150's and they are "scaled" to 1950. My AFR's are all bang on with my WB, my BoostEst is bang on with the Boost gauge, and my latency is EXACTLY whay the spec sheet that came with them state they should be, and my VE table is all under 100%.

I still don't know why they are scaled down a bit, but all the data in my logs proves they are calibrated 100% correctly. It used to bug me, but the car drives awesome and all the data says they are perfectly dialed in.


Forgot to ask, are you running E85 or gas? That makes a difference too,

 

[gst_Jake99]

If you have higher pressure than expected you have to scale your injectors higher than they are to reduce the fuel injected....so ya your making sense there. Prolly not over running the FPR.

The latency has an affect but really only at idle and cruise every where else the base pulsewidth is much much larger than the deadtimes.

If your car runs and drives fine on the scaling your using then I'm not sure what else it could be as I have zero experience with EvoScan.

If this was DSMLink I'd say check you MAFcomp table or your VE table (if your SD).

As far as your injectors not flowing as much, I run FIC 2150's and they are "scaled" to 1950. My AFR's are all bang on with my WB, my BoostEst is bang on with the Boost gauge, and my latency is EXACTLY whay the spec sheet that came with them state they should be, and my VE table is all under 100%.

I still don't know why they are scaled down a bit, but all the data in my logs proves they are calibrated 100% correctly. It used to bug me, but the car drives awesome and all the data says they are perfectly dialed in.


Forgot to ask, are you running E85 or gas? That makes a difference too,

Sounds like I'm in a similar boat as you and some others. Maybe I should just leave it since everything seems to be in range and I don't have any drivablity issues. The datalogs look good, as well as all trims. Who knows
I'm on 93 pump has
Maybe someone else can chime in. You've definitely given some good points, appreciate it. Until then, I'll just live with knowing the scaling is a bit weird, but that my car is running well .
I believe there is something similar to MAFcomp in ecuflash. I'm pretty unfamiliar with that table though as I'm still pretty new to tuning. I always thought that should stay the same unless switching to an EVO maf or something of the sort.
I'll probably give FIC a call tomorrow to see if their tech representive can shed some light on the subject.