7427 MPFI tuning

[EagleMark]

I was only referring to the injector flow rate in the bin. The xdf is set-up with six versions of the "Injector Flow Rate". These are all the same address in the bin. The only thing different is the math in the xdf.

Not sure I follow. Are you saying the ecm reads the flow rates of all of them?

That's what he's saying, if you change one all will change. He did the hard work for you!

If you have a comparable GM injector offset table for your injectors I would go ahead and use it and do all the other settings and tune it. If you run out of fuel adjust and retune. It's not like your trying to calibrate a twin turbo ferrari engine with 1000 hp and going to melt it first WOT run because your to lean. Your fueling is going to be close, tune it!

Or buy a set of injectors with a data sheet.

Since the offsets are all voltage based and all cars run a 12 volt system and usually charge around 14 volt when running the voltage is going to be very close. I'm just guessing that all injectors are designed around this voltage, why would they not? What happens at lower voltages and higher voltages may be differant from injector to injector. Look at all the offset tables and theres very little change from 12.5 to 14.5 where all cars run as Dave has pointed out.

Go for it! Make that sucker run! Just keep a close eye on BLM from get go and tune!

[JeepsAndGuns]

Check out the EFI Live Screen Shot. 2001 5.3 liter

EFI Live can be downloaded free: http://www.efilive.com/index.php?opt...=48&Itemid=124

The free version does not allow changes to be saved, but looking at injector voltage offsets would be free!!!

The ".tun" files can be found here: http://www.tunefiledepot.com/index.p...Type=P&Stock=Y

dave w

Interesting. So if I were to find and install a set of the above mentioned LS1 injectors, how would I find the factory applacation for them so I can look up the correct bin fine. And since the 7427 doesnt use a 3D table like the above picture, I would assume I would just use the 0 map row?

[dave w]

Interesting. So if I were to find and install a set of the above mentioned LS1 injectors, how would I find the factory applacation for them so I can look up the correct bin fine. And since the 7427 doesnt use a 3D table like the above picture, I would assume I would just use the 0 map row?

The LSx computer is different than the '7427 PCM. I think seeing the factory settings for the LS injector would, at best, be a "ball park" guideline to use in a '7427 PCM. The injector drivers of the LS computer are different than the '7427 PCM injector drivers. The LS computer is able to compensate for very low RPM's, needed for emission standards!

Basically, some homework is needed to cross reference between injector part numbers and actual vehicle applications. I don't know of any published cross reference to be able to cross reference between vehicle applications and injectors part numbers.

I have invested a considerable amount of time with the LS computer, it is the future, as soon as the software drops in price!

dave w

[EagleMark]

http://www.gearhead-efi.com/Fuel-Inj...ncy-Chart-Link

[JeepsAndGuns]

I didnt see the injectors I am using, or the LS1 injectors, but I did see a couple that are real close to the ones I am currently using. I may try a few diffrent setting this weekend while I search for some LS1 injectors.

The LSx computer is different than the '7427 PCM. I think seeing the factory settings for the LS injector would, at best, be a "ball park" guideline to use in a '7427 PCM. The injector drivers of the LS computer are different than the '7427 PCM injector drivers. The LS computer is able to compensate for very low RPM's, needed for emission standards

I suppose they wont be perfect, but I bet it would probably be a lot closer than running my current injectors with the tbi offsets?

[dave w]

I agree that the LS computer setting won't be perfect, but closer than the TBI settings.

dave w

[JeepsAndGuns]

http://www.gearhead-efi.com/Fuel-Inj...ncy-Chart-Link

Ok, going by the site in that link, there are two injectors on that list that are kinda close. They have the same ohms, and like a hair more flow. First one is the "civic 92-00 ex/si" witch according to them flow 240cc/min (vs mine 238cc/min) but at 45 psi, mine flow close to that. The other is the "vw passat 2000" Witch shows the same ohms and flow, but a hair diffrent offsets.
So if I wanted to try these offsets just to see if they do anything good or bad with my current injectors, how do I figure out what to put in my table? The offset voltages they list of corse dont match the voltages in the table in my bin. Also What are the values they list, they dont look the same at the uSec in the bin I have.


Also a little more google work, it appears the 0280155931 injectors are for the LS6/ZO6

[34blazer]

Ok, going by the site in that link, there are two injectors on that list that are kinda close. They have the same ohms, and like a hair more flow. First one is the "civic 92-00 ex/si" witch according to them flow 240cc/min (vs mine 238cc/min) but at 45 psi, mine flow close to that. The other is the "vw passat 2000" Witch shows the same ohms and flow, but a hair diffrent offsets.
So if I wanted to try these offsets just to see if they do anything good or bad with my current injectors, how do I figure out what to put in my table? The offset voltages they list of corse dont match the voltages in the table in my bin. Also What are the values they list, they dont look the same at the uSec in the bin I have.


Also a little more google work, it appears the 0280155931 injectors are for the LS6/ZO6

i posted a link to the TGO with the offset table for the LS6 injectors back on pg 2, that has the offsets you need for those

[JeepsAndGuns]

Well I made of of the most significant changes today to the way it runs......

I unhooked the vac line going to the fuel pressure regulator.
I just kept feeling like it was screwing around with things. The pcm/bin was made for constant fuel pressure, and I just couldnt keep from thinking that having the vac refrenced fpr was messing with the bpw's and blm's, seeing as how bpw is calculated from engine size and injector flow. But I kept it hooked up because of the reccomendations on here that I should have it with mpfi. But with the injectors flowing diffrently across the rpm/vac range than what the pcm is expecting, I just felt like it was causing a problem.
I started out the day trying that offset table dave w posted a picture of, just for the hell of it. Didnt work out all that great, ran worse, so I changed it back.
Next I did a run to check my blm's (I had tweeked the tables and burnt a new chip before I called it a night last weekend but didnt drive it), still in the high 130's to low 140's. I then unhooked the vac line from the fpr, that made a noticeable (good) change. I datalogged it and now all the sudden all my blm's are in the mid to high 120's!
Got a wild hair and for some reason decided to try that offset table posted by dave w again, and it made a slight but (good) noticeable change. Datalogged it and now in map areas 20-40, my blm's are in the 1teens ( A little rich for a change!) But map areas 50 on up were still in the mid to low 120's. Witch is ok, but map 90-100 are up to 99.6 in the fuel tables, and map 80 is mid 90's. So I think I still need bigger injectors.

But, I did finally sell my 454 tbi unit, and took that money and just bought a BRAND NEW set of the 0280155931 LS6 injectors. They are take outs from a crate engine. I dont think I would be able to find brand new set of these for 25 each anywhere, so I feel I did pretty good. Hopefully once they get here, I will be able to get my fuel maps into a more manageable range.

And if pigs ever learn to fly, and tuning software for the 12200411's ever come down, I can just use a ls6 man trans tune as my base, and wont have to worry about offsets. But pigs will never fly.

[RobertISaar]

FWIW: all factory MPFI installations use the vacuum referenced fuel pressure regulator to maintain a constant injector flowrate due to vacuum in the intake causing a different flowrate than if they were shooting into atmo like a TBI.

[gregs78cam]

I would just turn up your pressure a bit. I have read that more pressure = better atomization, and better running. Some guys over on TGO are running 80psi with good results.

[RobertISaar]

to some degree, better pressure will result in better spray, but there is a point of dimishing returns, as well as a point that will cause hydraulic locking of the injector. 80PSI is quite high for a PFI injector.... i think the most i would ever run is ~55PSI.

more pressure does allow for more power out of the same injectors though, since more pressure from the same nozzle = more flow. you'll need to make sure your pump can handle the fact that it will flow less volume at higher pressures though.

[JeepsAndGuns]

Not all factory mpfi has a vac refrenced fpr. The obd2 jeep 4.0 does not have one. It has a "dead head" fuel rail with no return line, just a feed, and has a constant 49 psi of fuel pressure. The fpr is built into the pump/sending unit in the tank. Other factory mpfi sysems might be that way too, I dont know. My 99 grand cherokee is the only obd2 vehicle I have worked on.
All I can say is it runs way better with the vac line unhooked and running a constant pressure all the time. I still think it has something to do with the pcm. I just wonder if there is not some hidden or undefined code in factory mpfi ecm's that have a vac refrenced fpr, that accounts for the change in flow rate according to vac/map and therefore takes that into account with bpw. And with the 7427 being a factory tbi ecm, made for constant fuel pressure, its programmed diffrently in the way it calculates bpw?
But I am just a noob thinking out loud, and I know nothing about computer code.

Dont really want to keep bumping up fuel pressure, like I said, I just ordered new injectors, so I am just waiting on them.

[PJG1173]

from what I've read the flow rate shouldn't change much. with the vac ref FP since at idle manifold vac helps draw fuel out of the injectors so less pressure is needed to provide the same amount of flow as higer pressure with lower vac (higher Kpa) signals.

[EagleMark]

Not all factory mpfi has a vac refrenced fpr. The obd2 jeep 4.0 does not have one. It has a "dead head" fuel rail with no return line, just a feed, and has a constant 49 psi of fuel pressure. The fpr is built into the pump/sending unit in the tank. Other factory mpfi sysems might be that way too, I dont know. My 99 grand cherokee is the only obd2 vehicle I have worked on.

He's talking about GM OBDI stuff we work with.

All I can say is it runs way better with the vac line unhooked and running a constant pressure all the time. I still think it has something to do with the pcm. I just wonder if there is not some hidden or undefined code in factory mpfi ecm's that have a vac refrenced fpr, that accounts for the change in flow rate according to vac/map and therefore takes that into account with bpw. And with the 7427 being a factory tbi ecm, made for constant fuel pressure, its programmed diffrently in the way it calculates bpw?

That is actually a good point!

But don't think theres any coding in MPFI ECM for this as it's handled by the regulater. The vacuum referenced FPR is lower at idle and high vacuum as vauum sucks fuel out, then when vacuum is not present or low like WOT it adds pressure to compensate. Keeping same deleivery of fuel across board.