FIC 850s simple deadtime question

[Ravenous]

The setup is as follows:

Tuning with Moates.net Ostrich and TunerproRT (extended maps, pk code, knock gauge, etc)
Aeromotive AFPR (set at 43.5)
Walboro 255hp fuel pump
FIC 850cc ball and seat injectors (set at 920 based on 1g compensation 850s at 37psi = 920s at 43.5psi)
14b on 6 bolt with Manley 8.5:1 pistons
Pretty much stock everything else (for the moment )

Everything is in good working order, the car runs and idles decent. However looking at my low fuel trim I seem to be running rich (81%). I currently have the deadtime set at +312 across the board:

18.7v 768.00
16.35v 864.00
14v 960.00
11.68v 1152.00
9.34v 1464.00
7v 2424.00
4.7v 4368.00

The big question is, if you increase injector deadtime does it richen or lean out the mixture on the low fuel trim? Also, if anybody running 850s happen to have the deadtime that worked for them that could help too.

Any input is greatly appreciated,
Thanks
Chris

p.s. The injectors are big so I can upgrade the turbo later, or possibly run e85 on the 14b.

 

[johnnytsi]

The best starting place for almost all FIC injectors is 315.

John-

 

[Ravenous]

Well I was running them at 312, I dropped it down to 288 to see if that would improve the low fuel trim. At that point the car had a harder time maintaining idle and would die occasionally. I turned it up to 336 to see what effect that will have on the low fuel trims. Thanks for the response. I have a feeling I will go back to 312 since increasing the deadtime to 336 will most likely cause more of a rich condition, but we'll see.

 

[steve]

Increasing the deadtime adds fuel, decreasing removes fuel.

Since deadtime is a bigger factor in low injector pulse widths, you compare the low and high trims to decide what adjustments to make.

If the low is less (80%) than the high (108%) you have too much deadtime, if low is greater than high you need more deadtime, and if they are equal or very close the deadtime is a close are your going to get. This assumes that you don't have any leaks in your intake! Leaks will throw off the trims.

Once you have the deadtime in the ball park if the trims are low (rich) you need to decrease the injector global (saying you have bigger injectors) or increase it if lean.

John, +315uS isn't easily possible. The factory code is in units of 24uS.

 

[Black95TSIawd]

Problem is your math. Your injectors are rated 850cc at 43.5psi, not 37.

 

[steve]

Problem is your math. Your injectors are rated 850cc at 43.5psi, not 37.

If the math was wrong he would be lean not rich.

Since the factory injectors are rated at 43.5 that drops out and the correction is for the difference at 43.5. When he ups his base fuel pressure he needs to uprate the injectors to account for the pressure difference. Assuming that the injector really deliver 850cc at 43.5 then they deliver about the same fuel at 43.5 as 920cc injectors do at 37 psi.

 

[Ravenous]

Thanks Steve, I was looking for that info. I have searched for hours literally and could not find a clear cut way to determine the appropriate values for deadtime. I will try to check the low and high trims tonight, weather permitting. It is easy to find info for link and afc tuning but a tad more difficult with eprom tuning. Thanks again

 

[Black95TSIawd]

If the math was wrong he would be lean not rich.

Since the factory injectors are rated at 43.5 that drops out and the correction is for the difference at 43.5. When he ups his base fuel pressure he needs to uprate the injectors to account for the pressure difference. Assuming that the injector really deliver 850cc at 43.5 then they deliver about the same fuel at 43.5 as 920cc injectors do at 37 psi.

The 1g fuel system operates with 37psi base pressure. So, if FIC sells injectors with an 850cc rating at 43.5psi, why would someone set the ecu for 920cc's?

 

[steve]

The 1g fuel system operates with 37psi base pressure. So, if FIC sells injectors with an 850cc rating at 43.5psi, why would someone set the ecu for 920cc's?

Because he turned the base fuel pressure up to 43.5.

If you do the calculations based on effective size then the stock injectors are 411cc and the new injectors are 850cc.

 

[Black95TSIawd]

37/43.5 = 85%

At 37psi base pressure, Injectors rated at 43.5psi are only working at 85 % their potential. In this case, 850 * 0.85 = 722.5. At 43.5psi, they would be working at 100% their potential. 850 * 1 = 850.

What am I doing wrong? I hope nothing, as this is how I tune my car.

 

[steve]

37/43.5 = 85%

At 37psi base pressure, Injectors rated at 43.5psi are only working at 85 % their potential. In this case, 850 * 0.85 = 722.5. At 43.5psi, they would be working at 100% their potential. 850 * 1 = 850.

What am I doing wrong? I hope nothing, as this is how I tune my car.

No actually the injectors are always working at up to 100% of their potential but the potential changes with the base fuel pressure. This is the effective flow rate.

What you are doing wrong is that the injectors effective flow rate changes according to SQRT (new pressure/old pressure) X old flow rate.

* The 1g base is actually 36.3 according the the FSM. *

SQRT (36.3/43.5) = SQRT(0.8345) = 0.9135

So the 1g manual turbo ECU stock programming for injector size is set for 450cc * 0.9135 = 411cc injectors.

If you switch to 850cc injectors they are in effect 776.5cc injectors @ 36.3psi. The correction factor would be = (411/776.5) - 1.0) = (0.5293) - 1.0) = -0.47

Or ignoring the fact that the stock injectors aren't really 450cc @ 36.3 psi. The correction factor would be = (450/850) - 1.0) = (0.5294) - 1.0) = -0.47

Since the OP is also raising the base to 43.5 psi the calculations are:

SQRT (43.5/36.3) = SQRT (1.1983) = 1.0947

If you don't work from the effective size of the factory injectors then you have to correct the new injectors by the change in pressure. 850cc * 1.0947 = 930.5cc and the correction would be = (450/930.5) - 1.0) = (0.4835) - 1.0) = -0.52

If you work is the correct units for both the old and new injectors the correction would be = (411/850) - 1.0) = (0.4835) - 1.0) = -0.52

The way the injector global works inside the ECU causes the step size (delta cc's) to increase as the global decreases so you wind up with the same global for 920 and 930 cc injectors.

 

[Black95TSIawd]

No actually the injectors are always working at up to 100% of their potential but the potential changes with the base fuel pressure. This is the effective flow rate.

So installing injectors rated at 43.5psi in a 1g which runs 37psi base pressure effectively does not change their flow?

 

[Ravenous]

It does change the effective flow rate. I ran into this topic on the dsm-ecu group. I found it all very confusing as well. I could drop the base fuel pressure down to stock again and then just throw the 850cc adjustment in the mix and it would be fine. I will most likely never use the max potential of these injectors as a 50 trim is as high as I'll go with this car. However I feel as if I should run them at their rated specs.

I think the most confusing aspect is that the 1g turbo car is the exception to the rule as I believe all other models have 43.5 base fuel pressure.

 

[Black95TSIawd]

I actually can't wait for his post. This is all knowledge for me.

 

[Ravenous]

Yea I know what you're saying. It is refreshing to be able to get the how and why and not "just do this." Thanks again Steve, I'll be returning later with my findings.

 

[steve]

So installing injectors rated at 43.5psi in a 1g which runs 37psi base pressure effectively does not change their flow?

Yes, changing the base fuel pressure changes the flow rate of the injectors. That's spelled out in the post above.

New flow rate = SQRT (new pressure/old pressure) * old flow rate

It's convention to rate the injector at 3 bar pressure (43.5 psi) so that you can compare them.
So the stock manual turbo injectors are rated at 450cc/min. That's 100% of flow at 43.5 psi but when you run them at 36.3 psi their flow rate is 411cc/min. It's still 100% of their flow or potential.

If you cranked up the base pressure to 50 psi the same injectors would deliver SQRT (50/43.5) * 450cc/min = 1.0721 * 450 = 482.5 cc/min.

So we talk about the injector size but that means flow rate at 43.5 psi or what ever the manufacture used to rate them and the effective flow rate is what they do at the pressure you run them at.

 

[Black95TSIawd]

Steve, I completely understand that injectors flow what they are rated at and lowering or raising base pressure effectively lowers or raises the potential flow. What I don't understand is why the OP is setting his injector global settings to 920cc injectors. His base pressure is 43.5 and he is running 850cc injectors rated at 43.5psi. Shouldn't he just set his global to that rather than 920? Now I have a 2g. If I installed the same injectors, I would set it to 850cc global correction, but a 1g guy with base pressure at 43.5(again, same as my 2g) would have to set to 920cc's?

 

[steve]

What I don't understand is why the OP is setting his injector global settings to 920cc injectors. His base pressure is 43.5 and he is running 850cc injectors rated at 43.5psi. Shouldn't he just set his global to that rather than 920?

Because he has to make two changes in this case. One for the difference between the injectors and one for the difference in base fuel pressure. That works out to the same value you would use if you were running 920-930cc injectors at 36.3 psi

Now I have a 2g. If I installed the same injectors, I would set it to 850cc global correction, but a 1g guy with base pressure at 43.5(again, same as my 2g) would have to set to 920cc's?

You only have the first correction since your ECU is programmed to run the same 450cc injectors at the higher base pressure.

Sorry, I didn't make this clear. It's all in the math above.

 

[Black_Bullet]

Steve,
I run a eprom ecu thats chipped.
Its been ran this way for over a year, but I have a walbro 255lph high pressure, and 850cc FIC injectors and im running the non turbo fpr
which i believe was 47.6 base psi of fuel pressure and we told the ecu for 870 cc or something like that and i think like 312 us deadtime was added with 41% global.
( Its been awhile and im just pulling numbers out my head trying to remember what calculations me and a friend came up with back then. ) But what do you concur with what my inj size should be in accordance with this fpr. Not worried im off , just curious of your input.
Thanks

 

[steve]

I have a walbro 255lph high pressure, and 850cc FIC injectors and im running the non turbo fpr which i believe was 47.6 base psi of fuel pressure and we told the ecu for 870 cc or something like that and i think like 312 us deadtime was added with 41% global. (Its been awhile and im just pulling numbers out my head trying to remember what calculations me and a friend came up with back then.)

Do you concur with what my inj size should be in accordance with this fpr?

All the needed math except for the conversion to the hex injector global is above.

Injectors should be flow tested and the results used as the basis for your tuning. Initially the discussion was how does one decide if the deadtime and global are correct. Following that logic will help you dial in your parameters but if you get too far out of whack from the generally accepted values you should rethink what your doing or review your setup.

I don't accept that the N/T FPR is a fix for FPR overrun. Maintaining a consistent linear fuel pressure to manifold pressure is something the ECU depends on. I believe using the N/T FPR just pushes the problem to a higher base pressure and nothing else.

Back to your question. If you follow the thread, you understand that using a effective size of 870cc/min for that pressure doesn't seem right. Once you have real data for your setup go do the calculations.

If anybody else jumps in to ask questions, I want to see them try and apply the information already posted before they will get a reply.

 

[Black95TSIawd]

Because he has to make two changes in this case. One for the difference between the injectors and one for the difference in base fuel pressure. That works out to the same value you would use if you were running 920-930cc injectors at 36.3 psi



You only have the first correction since your ECU is programmed to run the same 450cc injectors at the higher base pressure.

Sorry, I didn't make this clear. It's all in the math above.

IF the OP would have never raised his base pressure, the injectors still would have been pumping 850cc's? Does the 1g ECU compensate for the pressure being less?

 

[Black_Bullet]

All the needed math except for the conversion to the hex injector global is above.

Injectors should be flow tested and the results used as the basis for your tuning. Initially the discussion was how does one decide if the deadtime and global are correct. Following that logic will help you dial in your parameters but if you get too far out of whack from the generally accepted values you should rethink what your doing or review your setup.

I don't accept that the N/T FPR is a fix for FPR overrun. Maintaining a consistent linear fuel pressure to manifold pressure is something the ECU depends on. I believe using the N/T FPR just pushes the problem to a higher base pressure and nothing else.

Back to your question. If you follow the thread, you understand that using a effective size of 870cc/min for that pressure doesn't seem right. Once you have real data for your setup go do the calculations.

If anybody else jumps in to ask questions, I want to see them try and apply the information already posted before they will get a reply.

Ok i just tried the formula, i dont know if it came out right because i was inputting it on my cell phone and the characters on the buttons are weird but i came up with like 933.3 for my 850cc combo w/ the 47.6psi base fp. I wasnt the one who burned my chip, thats all in my wiz friends hands as i wouldnt trust myself to do it. He's been doing it for years on several dsms on several occasions.

I asked him about it and he thinks it was set at 900something cc off the top of his head and not the 870 that i said earlier, but he was at work when i called so he didnt have time to put much thought into it...

Now as far as flow testing injectors no they arent flow tested, i just bought them new from FIC a year ago. I dont think any dsmers on the average flow test their injectors, and even if they did; typically the injs flow lessens over time thru condition, that would mean youd have to routinely pull them out every once in a while and keep flow testing them to make sure the tune is accurate. I really doubt the average joe does all that.

Now as far as the nt fpr curing over run, that wasnt initially why i or my friend ran it even though i was believe that it did at least "lessen". Why? Because on a locals car he had a upgraded rail with a fuel pressure gauge tapped to it, and he did a lot of dyno time, he said the car would always over run to around 48psi during fuel pressure over run... Well considering that my base fuel pressure is roughly that id like to assume i was just missing any signifcant overrun... Now this could be way wrong but makes sense to me. Perhaps you can elaborate your thoughts because im not doubting that i dont still have over run.

At the time me and my friend picked up the n/t fprs, we were just really getting started modding, and already had means to chip tune and he had the software to do it himself. We both had 16gs and needed more fuel from our stock 450s. This allowed me to run 17psi without leaning out on the evo3 with the 450s and I ran this way for awhile before I got the 850s in. Guess i just didnt see any need to swap back to stock turbo fpr afterwards.

 

[steve]

IF the OP would have never raised his base pressure, the injectors still would have been pumping 850cc's? Does the 1g ECU compensate for the pressure being less?

No, if he hadn't turned up the base fuel pressure the injectors would have been pumping out 776.5cc/min. That's their effective rate at 36.3 The drop in pressure caused the injectors to flow less.

Remember I said that the stock injectors aren't really 450 cc ones on a 1G, their effective rate at 36.3 psi is 411cc/min. We still call these 450cc injectors because that's what they are at their rated pressure but we aren't using them at their rated pressure on a 1G.

 

[Black95TSIawd]

Steve, thats exactly what i've been trying to say in this entire thread, minus my calculation was a bit of and not in scientist wording.

However, I am now more clear on 1g tuning. It is all in math and I missed a few steps. Thanks!

 

[steve]

Steve, thats exactly what i've been trying to say in this entire thread, minus my calculation was a bit of and not in scientist wording.

Really? I would have never guessed because you kept asking the same question and didn't seem to understand why the OP needed to tell the ECU to use a injector size parameter that equated to 920-930cc injectors.

I'm glad we are on the same page.