injector size question for a ABTC tune for FIRST injection systems

[MikeyB]

hey all!
so I have just completed a FIRST injection system install, and I have their tune applied and installed. I also read if from the chip so I could compare it to stock and hopefully learn the differences.

I see the attached for Injectors....

I have Bosch 0280155710, 22# @43.5psi /3bar injectors that I replaced the stock ones with. Should these readings be LOWER now with these new injectors? I would think they'd be the same TBH.
2023-08-05_2-21-25.jpg

the top is for the new tune, and the bottom is for the stock tune I just pulled off the stock chip from my 1987 corvette ABTC 0321.

another question, what parameter is for the Cold start injector / 9th injector to enable/disable? I don't see any that seems like it. It should be disabled in the tune I received, and I'm sure it is, I just wanna see as I'm curious ;-)

Again, I'm just trying to learn from the differences between the stock tune and what I purchased from FIRST.

thanks all!
Mike B

[dave w]

Switching to the 1227165 $6E definition (1989 TPI) will eliminate the cold start injector: 1227165 ECM Information $6E (gearhead-efi.com)

[MikeyB]

I did notice that the "startupfuel/air ratio %change vs. coolant temp" was modified by the tuner, so I assume that is for the removal of the cold start. she does start up easier now with the tune, so that's cool.

any thoughts about the injector screenshot? I would think that those settings would have remained stock, but he has 20#/HR and stock is 23.04#/HR.... I still have 22# injectors, so I would have thought he would have put in 22# instead he put in 20#, this part I dont' understand why it was done.

thanks!
Mike B

[dave w]

I did notice that the "startupfuel/air ratio %change vs. coolant temp" was modified by the tuner, so I assume that is for the removal of the cold start. she does start up easier now with the tune, so that's cool.

any thoughts about the injector screenshot? I would think that those settings would have remained stock, but he has 20#/HR and stock is 23.04#/HR.... I still have 22# injectors, so I would have thought he would have put in 22# instead he put in 20#, this part I dont' understand why it was done.

thanks!
Mike B

Setting the injector flow lower than the injector is rated to flow will make the tune rich. The computer is tricked into "thinking" the injectors are flowing less than they actually are, so the computer compensates the "Injector On Time" or Pusle Width to a longer duration of time adding more fuel.

[MikeyB]

Setting the injector flow lower than the injector is rated to flow will make the tune rich. The computer is tricked into "thinking" the injectors are flowing less than they actually are, so the computer compensates the "Injector On Time" or Pusle Width to a longer duration of time adding more fuel.

I'm glad you clarified that as I was thinking that might be the actual case and the reason that he tuned it this way. I'm not so much questioning the tuner, but trying to understand the "whys" he did things ;-)
I was thinking that if the computer thinks less fuel is flowing, it will push for more fuel and that would compensate for the overly LEAN condition that is inherently present due to the swap from the stock TPI over to the FIRST Injection system that flows so much more air into the engine.
it's interesting on another point as I do not see a location to set the fuel pressure. I have the fuel pressure set to between 43.5 - 44 right now, that's about as accurate as the gauge gets on the regulator which I think is good enough. If there was a place to set the FP, I would think that you'd want the accurate reading of the injector #/HR so it can calculate how much fuel to send. That would eliminate the "trick" by putting in a lower #/hr rate.
am I missing the fuel PSI setting in there? or is it called something strange? LOL

I have the 32B XDF BTW, I dont' think I mentioned this.

thanks for the help!

[steveo]

its very common to use the adjust constant to skew an entire tune rich or lean for LOTS of reasons.

one really common reason to do this is if you run ethanol or something that no longer burns at 14.7:1 and the bin itself doesn't have an easy to change 'stoich' constant. for example E10 runs at around 14.1:1 instead of 14.7 which is 4-5% richer so you could set your injector constant 4% lower and that'd get you in the ballpark. even if there is a 'stoich' constant its possible parts of the tune don't use it like an open loop afr table or whatever, so sometimes it's just safer to adjust the injector constant to ensure the entire tune is adjusted.

even gm botches the injector constant sometimes, like cars with 24lb/hr injectors will be set to 23.1 or something, the logic behind this isn't always clear, but i'll tell you one thing there's no such thing as a 22lb/hr injector, in fact if you have 8 injectors that haven't been to a flow lab you probably have some that are 21.8, some that are 22.3, etc.

[MikeyB]

its very common to use the adjust constant to skew an entire tune rich or lean for LOTS of reasons.

one really common reason to do this is if you run ethanol or something that no longer burns at 14.7:1 and the bin itself doesn't have an easy to change 'stoich' constant. for example E10 runs at around 14.1:1 instead of 14.7 which is 4-5% richer so you could set your injector constant 4% lower and that'd get you in the ballpark. even if there is a 'stoich' constant its possible parts of the tune don't use it like an open loop afr table or whatever, so sometimes it's just safer to adjust the injector constant to ensure the entire tune is adjusted.

even gm botches the injector constant sometimes, like cars with 24lb/hr injectors will be set to 23.1 or something, the logic behind this isn't always clear, but i'll tell you one thing there's no such thing as a 22lb/hr injector, in fact if you have 8 injectors that haven't been to a flow lab you probably have some that are 21.8, some that are 22.3, etc.

Awesome! great information to know, and it certainly makes sense about the e10 fuel, I didn't even think about that! It's all making sense now, sweet!

it's interesting as the stock tune has 23.04 for the flow rate.

yes, I am aware that "no two injectors are alike" LOL, these are not matched, nor bench tested. I was told by south bay injectors that they were 22#, and I do understand that is an approximation. but thank you for the clarification.
I'm not trying to squeeze every morsel of power of of her, she's just a project that I love to drive and wanted to get more power.... give her a treat after being with me for 30 years type thing LOL... in the process I want to keep learning about the tune process for ODB1 as that interests me... I have an EE background :-)

thank you very much once again! great information to have thank you for sharing!
Mike B