Ok... just wanted to double check a few things here before i blow myself up....
As i understand it... the GMPP SC kit for the 2.4L comes with 320cc injectors... That is what is in my car now... (some people say they are 310cc... anyone know for sure?)
my current constant with those injectors and the GMSC reflash is 0.32359
I now have in my posession a set of 750cc injectors i would like to put in....
from what i have read the best way to figure your new constant is....
New Injector Constant = Old Constant * (Old Injector Size / New Injector Size)
so I am getting....
.138065 = .32359 x (320/750)
.133750 = .32359 x (310/750) *if it is indeed a 310cc inthe GMSC kit.
Can anyone tell me if this is about right? anyone running 750's with a similar constant? Anything tried tested and true? Or do i just go with this and cross my fingers?
Ok and then wanted to qualify this as well.... My 750cc's are older Low-Imp injectors... and my car is a 2002 which used the high impedance injectors... So i understand that i can just solder in some resistors to increase the resistance from Low to high....
I read you just take an ohm reading from current injector, and one from new injector, and then get a resistor that adds the difference....
so say my old one was 12ohm... and the new one is 3ohm... i would want to add a 9 ohm resistor inline on each injector. Right? And what kinda wattage rating should i go with? The ONLY info i can find about the installation of resistors was from Nukkinfuttz....
"to size them, you will need to know the Ohms value of your stock injectors. then subtract the value of your new injectors from your stock injectors. the answer will be the value resistor you need inline, this will trick the ECU into thinking the same load is still out there. you can fudge the value a little if you cant find the exact value you need...but error on the high side so as to not overload the drivers. Try to go with about a 20W sized resistor for each. "
Again just wanted some verification on all this before i dive in and blow something up.
Yes the injectors included with the kit are 310cc which is far below what you need
I'd use your stock size injector which i believe is which is 260cc or something like that against the new one ignore all the gm kit stuff and base your constant off that, I dont have hp tuners in front of me otherwise i could give you an exact constant to go with but im sure others understand what im getting at
Yup 20 watt 9 ohm resistors wired inline, im assuming you have a multimeter that reads resistance ( they are like 20 bucks at radio shack) after everything is wired up than you can confirm the setting is right
1989 Turbo Trans Am #82, 2007 Cobalt SS G85
Good lord almighty!!!! 20watt resistors??? where does one find something that large. i have a huge collections of resistors here, and the largest one is a 1 watt. biggest radioshack sells is a 10watt, and it looks like something my grandpa made in the 40's.
we sure it is 20watt? not 1/2 watt... or 1/4 watt???
that is insane....
They are 310cc, for sure.
No, do NOT base your number off of the old injector constant. You are using the GM Reflash, and GM changed odd things and did some weird @!#$ with the injector constant, so since you're using that version of the OS, base the injector constant number off the injector size and constant that comes with the kit. Just like you have above.
You can use high impedance injectors with a low impedance injector driver but not vice versa. That is what Kinsler Fuel Injection tells me.
2001 Olds Alero (LD9)
650 whp / 543 ft-lb
@turboalero
Should add that although that is what Kinsler said a while back when I called them up, it appears you can do it vice versa as Rodimus Prime says.... (did some Googling) maybe I have what Kinsler said backwards. Lol.
2001 Olds Alero (LD9)
650 whp / 543 ft-lb
@turboalero
ok...
my current injectors (which we determined are 310cc) show a resistance of 10.8 - 11 ohms. I will measure my new ones shortly.... I found that radio shack did indeed have some 20watt 8-ohm resistors in their lil drawers o stuff. strangely they were not listed on the website. So i have 4 of those.... so if my new injectors are anywhere near 2-3 ohms, i will be golden!
i also got HPT configured to record my injector duty cycle... OUCH... yeah... apparently they have been putting in some overtime. Appearantly i hit 100% duty cycle on my current injectors at 206kpa and 3600rpm... had a blip or two as high as 126% at around 5000rpm.....
so um yeah... looks like i will be slapping these new injectors in in a hurry.
good thing it has been too cold and snowy here for me to ever try and really get into it....
Ok... and on to the constant.... I have 2 conficting reports from 2 reputable sources.... Rodimus says use factory stock injector in the math... and Ion says use the reflash injectors for the math.... Both have a valid point regarding thier opinions... but at the moment, i think i am leaning more towards Ion's side... just cuz it is better explained and makes more sence to me. I know the constant seems screwy in the reflash... but i doubt it is the fault of the injectors... i am sure it is something in the reflash itself... as as all i am changing is the injectors... makes sence i should not try to outthing GM here. they did it for a reason. unless i know what that reason was.. i am just going to stick with what works.
So for now i think i am going to go with the... .133750 constant (.32359 x (310/750)) and see how that works.
What kind of symptoms should i look for to indicate an incorrect constant? poor idle? AFR bouncing all over? etc? and how do i know which way to correct for it, and how far?
as far as interchangable injectors goes... it would make sence to me that high impedance injectors could be run by a low impedance driver, but not the other way.... think of the impedance or resistance as a load on an engine... you can put a heavy load on a little engine, and it will tug along... maybe not super effiecient but engines are designed to work against a load... But now reverse that situation... take a big old engine, and spin it at Redline on an engine stand with nothing to resist the crankshaft... and you will likely blow the thing to bits.
Sound systems are the same way.... Car stereos and some high end home systems run at 4ohms. most common home systems run at 8ohms. 4 ohm systems are more efficient and give more sound per watt. but are more sensitve. 8 ohm systems are more stable and reliable, but at the cost of efficiency. Using a 8 ohm speaker on a 4 ohm stereo works decently... but not as efficient. you loose a lil sound going this way. If you put a 4ohm speaker on a 8ohm stereo, it will sound nice and loud, and you will wonder why more people dont do this... untill one day you wonder why your stereo is smoking... and someone informs you that you over-ran your amp with too little ressitance and it cooked itself.
just my $0.02 but thought i would throw it out there... i am no electrical engineer, but that is what i have heard in the past.
so unless i hear otherwise, i am going to play it safe and use my lo-imp injectors with a resistor.
These injectors are my old ones from my Cavy... I upgraded to a set of 1000cc Bosch Saturated injectors for this season. My apologies for not remembering what resistors I used when I did these on my car man... but the constant that I was using that worked best for me was this ... 0.12850
Hope that helps some... if you have any questions don't hesitate to email me or hit me up on aim and I'll be glad to help.
President/Founder - 607 Motorsports
ok i am sitting here looking at the injector harness off an 98 Z24... got it all peeled down to the the wires.
Looking at the way it is layed out... it looks like it would be ALOT easier to solder in one resistor in the common wire. (i am not sure if the common is a ground or a positive in this case.... but the comon is a solid olive green... and all the others are various colors each with a black line, so this makes me think it is a common hot, and individula grounds)
Either way... these 20w resistors are pretty large (physical size) so it might be tricky to try in solder 4 of these inline in the individual feeds... It would be alot easier and cleaner to solder in one in the common line. OR if the common feeds more tha 20w... then i can always solder as many as i do need in paralell to increase wattage capacity.
So is there an obvious advantage to soldering each resistor in line with each individual injector? or is it all the same?
does anyone know if it is 20w PER injector... or is it 20w for the entire system? (i am thinking that it SHOULD be 20w total... as only one injector is ever firing at a time... of course batch fire might change that scenerio.)
oh... and my new injectors are indeed 2ohms each... old ones 10.8ohms... so total ressitance should be close to 10ohms... I cant imagine that an 0.8 ohm difference could damage anything.... (especially when there are people out there claiming they are getting away running 2 ohms total and no side effects.
Radio shack is where i got mine, theres plenty of room in there just be sure to soilder them in there and I perfer heat shrink wrap to using electrical tape, looks neater too
1989 Turbo Trans Am #82, 2007 Cobalt SS G85
Good Grief Charlie brown!!!!
These 750cc injectors are becoming such a pain in my arse....
Whoever said there things were interchagable with OEM injectors needs to quit smoking crack. These are longer, and wider, and thicker... The wiring connectors are totally differnt, the new wiring harness clips barely clear the fuel rail. The injector retainer clips didnt fit naturally, but with a bit of persuasion they bent to fit... but dont see how they will do any good as there is nothing to clip them to but a metal collar. The fuel rail needed to be redrilled to allow for the extra height of the injectors.
I looked it up and these injectors appear to be the "square section o-ring" style for the fit to head.
http://www.sdsefi.com/injectors.htm wrote:Sealing injectors to the intake manifold usually involves one of two methods. Older type injectors used a square section O-ring slid over the pintle cap to sit against the steel injector body. Newer injectors use a 14mm round section O-ring sitting in an isolated groove. Some new engines use side inlet injectors, notably Subaru, Nissan and some Ford/Mazda engines. These are not compatible with other types.
Manifold end 14mm round O-rings left and middle, older square section right
my injectors look exactly like the far right injector, but imagine 2 o-rings stuck on the lil brown tip there. a big o-ring near the body, and a little o-ring closer to the tip. the small ring fit into the hole and made a good seal, but it was so close to the end of the injector tip that the o-ring would fall off and/or remain in the head when you moved the injector at all. (there is no method to hold the ring in place on this style.) it just slides on the tip.
The larger o-ring didnt even fit into the socket... so was just a cause for lots of cursing.
Eventually i removed the larger oring (closer to the body) and just left the smaller one on... this worked well for ease of install and fitment... but i questioned how well the ring was sealing so far up on the injector... so i found some other "small" o-rings... and put 2 sets of small rings on each tip.
this seems to work best, but the end ring still likes to leave itself in the head.
So now i am waiting for my cordless drill to charge back up so i can finish drilling out my fuel rail. cuz the stock holes came no where close to lining up.
So yeah... any of you high impedance injector guys... probably worth spending the cash and getting the proper injectors. Had i known it would be this much headache i probably would have just gotten drop in replacements for another $100 or so. So far between between running around to find all the frankenstein pieces parts to make these work, and all the soldering and cutting and testing, and hassles trying to make it all fit... I have to estimate i am coming up on close to 8 hours invested into swapping in these injectors. with actual drop in injectors, i would guess this would be a 30min job. So 7.5 hours of my time to save $100-200, and still have injectors that arent ideally "meant" for my car anyway....
So just fair warning to anyone considering this....
Like I said these injectors were on my car and I did not have nearly as many issues as you are having to run these man... I used the larger o-ring and then a smaller one just as I sent them to you. I did not have to drill out anything on my fuel rail but I did have to compress the rail into the head using my hand and pushing down on it until the holes lined up. I never had a single leak when running my older injectors or the ones I sent you using that method...
As far the connectors those are completely different but once spliced into your existing injector harness they should fit without that much problem. I used a dremel at one point just to notch the rail a bit where the clips went to add a bit more room but it wasn't anything major like you're making it out to be... My apologies man if you feel like you got hosed or something...
President/Founder - 607 Motorsports
I dont feel like i got hosed.... and i wasnt blaming you... I do my homework before i buy.... and all my research said that these should slap in without much hassle... well there has been PLENTY of hassle... good lord i am about to start throwing things.... i just freaking snapped the aluminum post in two (where the fuel rail bolts up) trying to get a millimeter more. almost cost me a new cam tower. lucky for me the crack didnt reach the main casting.
but yeah... this has been hell.
not like there is lots of room for soldering between the supercharger and the head... and the wires didnt have any slack...
nothing fit right...
i have drilled out my fuel rail to the point the material left is about the thickness of some folded tinfoil. and i think now finally it may fit... but i just dropped the fuel rail bolt behind the supercharger, and of course it didnt come out the bottom... and there is no room for my hand, and i cant see it and my magnetic pickup tool isnt blindly grabbing anything....
i swear... i think i had more fun swapping engines.
i am sooooooo hoping that tuning it for the injectors wont be anywhere near as difficult as the install was.
Just curious... what engine did you have these injectors in? i am really doubting we are working with the same things here... there has been nothing at all about this job so far i would consider "easy"
YIKES!!!!
ok i can wrestle with all the install stuff... and got it all in and working....
fire up the car and she goes CRAZY lean.... like 19afr's rpms all over the place.. almost stalls then revs up then nearly stalls....
after keeping run for a few sec, it eventually levels out... and idles ok... but as soon as i tap the gas it instantly dies....
i start it back up, and its the same thing all over again.
i notice that the short term fuel trim seems to be a lil crazy.... and then the long term shoots off thew chart and goes red... but when it does that is when it runs ok...
i will post logs in a few min... but what could this be?
simply changing an injector constant isnt even close to tuning it, your going to need to put the car manually in open loop and work on VE
1989 Turbo Trans Am #82, 2007 Cobalt SS G85
Rodimus Prime wrote:simply changing an injector constant isnt even close to tuning it, your going to need to put the car manually in open loop and work on VE
well my VE was tuned quite nicely and working fine untill the injector swap.... as i understood it, changing nothing more than injector size required little more than adjusting the constant.
at least that is what shifted saidin a previous post. the VE tables show airflow. the injector constant adjusts how the fuel requests respond to that airflow. i changed nothing to effect my airflow... just the injector size. so i shouldnt need to re-VE-tune the whole engine...
at this point i am just assuming my math is off on the constant.
basically car runs SUPER lean... untill the STFT compensates and peaks at like 49% just sits there and car idles fine. as soon as you hit the gas (at all, even sneezing on the pedal) returns STFT to 0% and the car goes lean and dies.
after a while the LTFT goes up to like 30% and then the STFT comes down closer to 30% as well....
So as everything is seeming to error on the lean side.... I assume i should nudge my constant to make it think the injectors are BIGGER?
Maybe like .125000 (which is about right for an 800cc, so adding 50cc) as opposed to the .133750 (as is SUPPOSED to be right for 750cc)
I assume you just guess and test and tinker withit till you find something that makes you happy? so the more fuel the trims ADD the lower the constant should be. and the lower the trims, the higher the costant should be?
and ideally you want as little "trim" compensation as possible... it should hover just about 0% trim at stoich in a perfect world right?
i know that is how the car was before these injectors. would love to get it back there.
i can send my log and tune to anyone who wants it... shoot me an email, and i will reply back with them. I dont know how to attach files on jbo besides photos.
Shane @ Innovative Tuning wrote:Perhaps rather than trying tro scale your constant, it might work better to approach it from the other angle & do the math to calculate your new constant.
http://www.j-body.org/forums/read.php?f=64&i=14826&t=14742#14826
I had thought i DID the math to get my new constant.... notice that was the original posting... was double checking my math on the new constant.
There are like 100 different ways to come up with new constants. I just went with the one that seemed most commonly agreed upon. and it sounded like everyone who used it seemed to be relatively happy.
But as i pointed out, the math didnt quite work for me... engine is naturally WAY lean. and it pegs the STFT to get it to idle even at 15-16afr... and seems to get things under control pretty well with mid 30's in both LTFT and STFT. but i want to get it that way naturally.. not rely on heavy fuel trims.
What about the multiplier?? should this stay the same? or do i need to set that to 0? or mess with that in some way?
When I use PJ's formula to calculate the constant, it comes out to something like .059808 for 750's. That's a pretty significant difference. But given how far out your trims are, looks like you're going to have to take a pretty big swing at it......might just put you in the ballpark.
I haven't had opportunity to try PJ's formula yet to test it myself, so take my comments as speculation at this point. I guess you don't really have much to lose by trying it out.
ok, i have dropped my constant all the way down to .100000 and it hardly seems to change a thing.... runs just as lean and crappy till trims kick in.
trying to go the other way now... bumping up to a .140 seeing if maybe i am going in the wrong direction.
ok... 140 seemed alot more tolerable... I guess it makes sence... i was thinking backwards... i thought "ok it is too lean... so i will tell it the injectors are bigger" but that obviously makes it fire them less... which would lean it out more.
trying .150 now... just want to see it go naturally lean... then i can try to find a middle ground.
mind you... I am running the GMSC reflash for the LD9... which is known as mysterious and screwey in the injector constant area (and more)
jimmyc99z24 wrote:These injectors are my old ones from my Cavy... I upgraded to a set of 1000cc Bosch Saturated injectors for this season. My apologies for not remembering what resistors I used when I did these on my car man... but the constant that I was using that worked best for me was this ... 0.12850
Hope that helps some... if you have any questions don't hesitate to email me or hit me up on aim and I'll be glad to help.
I am starting to wonder if these are 750cc injectors at all... I am up to a constant of .23000 and it is pretty close... i am only seeing a few point of fuel trim now... but that constant should be accurate for 550cc injectors... not 750cc's
so what is the deal here?
ok... .230000 was a lil high. i found .228000 seemed to be the most accurate from my experimenting. fuel trims at idle seem to dance lightly around the zero line.
still baffled why my "750cc" injectors need a constant that should be closer to a 500cc.
Also... the thing seems to idle just fine.... and part throttle lightfooted cruising seems pretty decent.... but if i hit the gas, even mildly... it goes PIG rich.. hits like 8-9afr and falls flat on its face.
let my foot off, and it jumps right back to 14-15s and runs fine... but step on it again and it goes the rich faceplant all over.
could this have something to do with the type of injectors? the fact these are low impedance injectors, which are responding differently to the high impedance triggers. making them open slightly at idle, appearing to be smaller than they are... but once they get a lil more juice, they slam open and flood the place.
ken soggs wrote:ok... .230000 was a lil high. i found .228000 seemed to be the most accurate from my experimenting. fuel trims at idle seem to dance lightly around the zero line.
still baffled why my "750cc" injectors need a constant that should be closer to a 500cc.
Also... the thing seems to idle just fine.... and part throttle lightfooted cruising seems pretty decent.... but if i hit the gas, even mildly... it goes PIG rich.. hits like 8-9afr and falls flat on its face.
let my foot off, and it jumps right back to 14-15s and runs fine... but step on it again and it goes the rich faceplant all over.
could this have something to do with the type of injectors? the fact these are low impedance injectors, which are responding differently to the high impedance triggers. making them open slightly at idle, appearing to be smaller than they are... but once they get a lil more juice, they slam open and flood the place.
When you step on the gas its going into PE mode, if its running rich at that point you need to subtract air from your VE tables so the computer adds less fuel.
___________________________________________________________________
Hahn Stage II - Mitsu TD06-20g |3" Turbo-back Exhaust | 61mm Bored TB |
HP Tuners | Innovate WB02 | Spec Stage 3 | Team Green LSD | TurboTech Upper | Full Addco Sways | Sportlines & Yellows |
I guess i am just confused as to why my VE tables are suddenly so far off when they were nearly dead on before.
I dont see why my non-pe table is fine with these injectors at this constant... but the PE table falls on its face.
But you are right... it only went rich and choked on itself when it went into PE mode....
but why??? why is is crazy lean at idle... but super rich in PE... i am sooo confused.
According to shifted, VE should be VE... it is just a chart of the engines airflow characteristics. it should not change much at all from injectors alone.
But could the way these injectors work vary so greatly that one table is way off and the other is pretty much right there??
am i learning the hard way the difference of peak and hold and saturated?
and where do i start? should i set myself to the "correct" constant ... the one that hardly even idle and jumps to 20 afr before the trims max out to bring it within reason? and then just do major VE mods to try and compensate?
or do i leave it here with the constant that lets it idle, run, and drive (even if it is nothing close to what math says it should be)... but with a hosed PE... and just re-tune for it?
ken soggs wrote:I guess i am just confused as to why my VE tables are suddenly so far off when they were nearly dead on before.
I dont see why my non-pe table is fine with these injectors at this constant... but the PE table falls on its face.
But you are right... it only went rich and choked on itself when it went into PE mode....
but why??? why is is crazy lean at idle... but super rich in PE... i am sooo confused.
According to shifted, VE should be VE... it is just a chart of the engines airflow characteristics. it should not change much at all from injectors alone.
But could the way these injectors work vary so greatly that one table is way off and the other is pretty much right there??
am i learning the hard way the difference of peak and hold and saturated?
and where do i start? should i set myself to the "correct" constant ... the one that hardly even idle and jumps to 20 afr before the trims max out to bring it within reason? and then just do major VE mods to try and compensate?
or do i leave it here with the constant that lets it idle, run, and drive (even if it is nothing close to what math says it should be)... but with a hosed PE... and just re-tune for it?
You need to disable closed loop while adjusting your injector constant. Then you can find what is going on.
Once it idles fine in open loop, then you can start your VE tuning.
___________________________________________________________________
Hahn Stage II - Mitsu TD06-20g |3" Turbo-back Exhaust | 61mm Bored TB |
HP Tuners | Innovate WB02 | Spec Stage 3 | Team Green LSD | TurboTech Upper | Full Addco Sways | Sportlines & Yellows |
