So, I am now wondering what kind of miles to the tank guys with 370cc+ injectors are getting, or any FI maxima for that matter. Because although I have my tune to exactly 14.7 before boost (which is below 3k), I am not getting great mileage even when driving sanely. On an average I am getting about ~220miles/tank.

My fuel pressure is set to stock right now, which is why it makes me wonder where my fuel is going. Maintenance is up to date (filters, etc..)

Can it be that since they are larger injectors than stock, there is more fuel per pulse giving me a weaker consumption than with stock injectors?

 

I drive about 30% city and 70 hwy, and always get well over 300 miles per tank. Your "fuel per pulse" should yield a stoichiometric A/F ratio, regardless of what size injectors you are using. You should simply see a lower duty cycle with larger injectors.

I am not sure what you mean by "I have my tune to exactly 14.7 before boost ". Is that open or close loop? Do you have a wideband O2?

Your ECU should always be trying to trim fuel to get a stoichiometric ratio, except at WOT. If your fuel pressure is stock, then larger non-stock injectors may drop more fuel than your ECU can trim; resulting in a rich A/F ratio during part throttle and your poor mpg.

I am running a stock ECU, Z32, and 550 injectors. Of course, the only way to get it to idle reasonable stoichiometric is to really really drop the fuel pressure. Anything under 30psi is not recommended by RC or usually any fuel injector, but I chose to ignore that and run 20psi. It idles at about 12.5:1, but part throttle is stoichiometric resulting in more than fair MPG.

 

meximax, the man didnt specify. But he runs open-loop full time (o2s are not hooked up), and basically he's saying that under 3k (out of boost) he has it tuned (yes with an LC1 wideband and EB) to stoich.

 

I get normal gas mileage if I stay out of boost. The situation you're describing doesn't make any sense. If your AFR is around 14.7:1 that's right about what the stock AFR is at cruising, so you should get stock-like gas mileage.

 

Thanks 95blkmax for inside info....I am sure that this was known to the .org, is just don't frequent the forum as often as I should. Eitherway, I find the fuel consumption surprisingly low.

Could the slush box be the culprit of the low mpg?

 

meximax, i am running open loop (o2's disconnected) at all times, i tune below 3k/part throttle to 14.7.

I am going to fill up, and not even consider WOT for the entire tank (hard to do), and see what i actually get. Nealoc thats why i was asking, because if my a/f is at ~14.7, then i should be having normal gas mileage.

 

I'm running the same setup, however its 440 injectors. I currently have my fuel pressure at 39psi. Do you suggest I drop the fuel pressure? I am taking away alot of fuel on the VAFC-2 to stay around a 12.5 at WOT. (I'm putting the blower back on in 2 weeks)

 

Not trying to ***** up the thread but still quasi related.

98MaXeDouT, I would suggest that you lower you base fuel pressure to eliminate all negative correction on your AFC. Remember that (-) corrections increase timing, something I am sure you know is not recommended for a boosted setup.

On my NA 3.5 with stock injectors, I was running fuel pressure at 31 psi to attain a correction free 13.5:1 A/F ratio at WOT. You should only run higher fuel pressure if you purposely want to indirectly increase timing via negative corrections.

Your rather large negative corrections at WOT suggest that you are probably could be running rich at part-throttle all and possibly experiencing the same poor fuel economy performance that streetzlegend addresses in this thread.

 

You're also "adding" timing by pulling that much fuel.

EDIT: Damn you beat me to it while I was typing this.....

 

I just went to the car, hooked up one of the o2 sensors and removed all the corrections below 3k RPM. It seems that, a/f stays pretty close to stoich. one of the o2 sensors is bad so when it warms up, it throw's off the a/f big time causing the car to almost shut off. before it did that, I hooked up both of them, and a/f was perfect!!, then it got warm and died. i unplugged it, left one o2 running, a/f still fine slightly rich in low 14's. I am going to drive around for a while and monitor the a/f see how it goes and also check the fuel.

btw, my injector duty cycle at idle is at ~2.0% does that sound about right?

 

Hello,
This might be stupid question. I know you can use injectors from 300ZX for 1998 Maxima. Can anybody tell me which years 300ZX injectors would work ? Are they direct fit or do u have to modify them any way. If anybody can tell me I appreciate it .
Thank you !

 

Well I'll be staying NA for the next two weeks before I go boost again. I was just wondering what I can do in the meantime to correct the fuel issue. I have the 440's on currently with a walbro. Do you suggest I lower the fuel pressure for the time being?

 

95-96

 

hey streets I have no o2 sensor s either. my car is tunned to 14.1-15.1 under cruising and I get about 27-29 miles to the gallon.

 

Oh really, i didnt kno you had it set up like that as well. How are you tuning that? via MAF signal?

 

nah tunning from my pressure sensor!

 

So '92 z32 370ccs are different than the 95-96, and thus aren't direct drop?

 

correct

 

Kind of same question again, should've ask earlier where can you buy 440ccs injectors for 1998 Maxima if you're going for a Turbo application. I couldn't find them anywhere yet.

 

Deatschwerks.com and tell them you are an org member.

 

OK, back to topic!!!!

"my injector duty cycle at idle is at ~2.0% does that sound about right?" continue..

 

Thank you for that website really appreciate it. Anothere quick question. Does it matter how big you go on injectors like 440cc or 550cc be better or is it completely up to you depending upon how much horsepower you're running ?

 

BUMP for the original poster asking something regarding the topic of this thread

 

At least you arent at 95% duty cycle like i am

 

I don't have anything to measure duty cycle right now, but I will go by the shop and get you my 550cc idle duty cycle for you. I suspect its really really low.

 

So far, i have been driving with just one o2 sensor hooked up, with a couple of corrections, a/f's are almost perfect at 10-14.7 always, even under acceleration. So far, i am almost at 1/2 tank and I have traveld 150miles, I know its still not that great, but its alot better than before.

 

so do you think it has something to do with you not having the o2's hooked up

 

I think so dude, because something tells me that, even though i am tuning the a/f to be at 14.7 with o2's off. There is still something happening in the background, perhaps timing change, or other things. I'll see the how many miles this tank is going to take me.

 

My car has no O2 sensors on it whatsoever (besides the aftermarket wideband) and it gets normal mileage.

 

I dont see how the hell lol. How do you get normal mileage? you tune the 14.7 urself?

 

yeah just tuned it to that on emanage. i had bad O2 sensors on my N/A max too and that got normal gas mileage as well, without any tuning.

 

man!!!, you just have freak maxima's lol.

 

Not F/I but I ran with no O2's for over a month and didn't notice a difference in fuel or anything. Don't ask why I did this, it's a completely different topic.

 

i have o2's and get ****ty milage.