Larger injectors without standalone/piggyback

[MazterDizazter]

I think this is probably a stupid question but I'm wondering if it'd be possible to use and get very-close-to-stock fuel pressure from Denso 440cc low-impedance injectors by using an adjustable fuel pressure regulator, and not touching the stock ECU. I would like to get standalone and a larger turbo eventually, but for now I need new injectors and rather than get new/rebuilt stock units I'd like to just put the $$ toward Supra injectors and billet fuel rail. I have an SX performance adjustable FPR already that I can use... I'd like to get ~max boost on the stock turbo if that is of any difference.

[MazterDizazter]

herrooooooo?

[CamH]

You could probably pull that off with some very low fuel pressure but it will be very difficult to get it running right, I'm sure.

[DevilZX]

um, seeaaarrrch?

 

I haven't posted much but I've read through pages and pages of information. I can tell you that this topic has been covered.

 

A little spoon feeding: You need to mess with the AFM and CamH is right. It is difficult to get it tuned right. Just wait for money/time to put in a standalone with all the supporting mods. This is what I am doing. It will save you time and headaches in the long run.

 

Good luck!

[MazterDizazter]

I tried searching; I'm not that stupid lol. I would think it'd be a matter of ratios or something. If you can throw a larger fuel pump in and keep the stock ECU then I don't see why injectors wouldn't be possible. I found this: http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=190359738362&ssPageName=STRK:MEWAX:IT

 

Looks like a solid kit at a really good price. If I could get it tuned properly I could easily upgrade to standalone and a larger turbo in the future... Hard is a very relative term for me... you'd have to be more specific.

[CamH]

Yeah, alright, basically what you'd have to do is stick those in and start it up, and lower the fuel pressure until it idles alright. Then, you'd need to hope that it's driveable at that setting.

[ktm]

I suggest doing some basic research (just for fun) about engines in general. A larger fuel pump has NO bearing whatsoever on how much fuel is supplied to the engine (assuming that everything is already sized correctly). A higher capacity fuel pump simply flows more at a given pressure than a smaller pump. The larger flow requirements for a pump are dictated by the engine.

 

The engine requires XX amount of fuel at peak torque, so you size the fuel injectors accordingly. The amount of fuel required at peak torque also determines the flow requirements of your fuel pump. Many people "upgrade" their pump on a stock L28ET just because. It does absolutely nothing for them in terms of performance.

 

The stock ECU has a set fuel table based on the stock injectors. The ECU tells the injectors to stay open a given amount of time based on the AFM and RPM (assuming this part here) based on the flow rating of the injectors. Now, if you increase the flow rate of the injectors by over 50%, the ECU does not know this. It will still tell the injectors to stay open for the same amount of time. In other words, you will be supplying 50% more fuel than you need.

 

This is why people tweak the AFM or lower the fuel pressure to compensate for larger injectors. These are all band aid fixes. The real solution is to use a stand-alone setup like MS.

[Tony D]

The band aid approach is just that... The AFM will only affect the ratios below 3500 rpms, after that it goes to a preprogrammed fueling curve and you are throwing 50% more fuel (to use KTM's example) starting at that point.

 

The AFM will only alter the delivered flow so much (say 30-35%) from the preprogrammed curve---so if your injectors are 50% oversized the most any tweaking would give you would be 35%, leaving you 20% overfueled.

 

Similarly with O2 correction... it is limited in most cases to 10%, after that the ECU defaults to a programmed 'limp home' curve which is pig rich to begin with... so you tweak your AFM to get the O2 to take you within 10%....then drop the fuel pressure so your fueling is correct....and you end up with the proper fuel curve for the engine without any breathing mods. Seems like a lot of work compared to just leaving it alone.

 

If you DO modify the engine, then the tweaks become even more detailed, or can involve grabbing parts from other vehicles, rewiring, etc etc etc...

 

FWIW Megasquirt is $400 assembled and shipped to your door. With that, a couple of keystrokes and you're set. With an ability to precisely tailor the engine AFR over 144 load points. Not three operating 'ranges' which are vague and not programmable.

 

That's the LONG answer. The SHORT answer to your original question is: "NO"!

[badjuju]

I suggest not doing this. I did it with my 280zx turbo, and it sucked. hard.

[MazterDizazter]

Thanks guys. I think I'm going to just have my stock injectors cleaned/flowtested for now and then get MSII as soon as possible, then run the 440's...or triple carbs...but that's another story.