55psi on stock injectors...

[Liger]

Ok, first off, i do have 550cc's at my house but one of them does not flow correctly, one flows tooo much and i've already had them sent out to PTE and they say they are fine but obviously they aren't. So now i'm running my stock 450cc's on 55 psi base fuel pressure. I'm using dsmlink to tune so i am wondering, what would be the correct amount of global fuel to decrease by? Mine is set to 15 and it still runs quite rich. WOT is fine but i think further tuning can help it out a lot. Also, will i need to adjust the deadtime due to the added fuel pressure forcing the injector open longer? Brandon [VFRacing]

 

[GILZTSIAWD]

Just tune according to the dsmlink tuning guide and you should be fine. Get your fuel trims within the specified range.

 

[Liger]

well i've tried that but i'm having trouble with the formula actually. I did the calculations according to 50 psi and got negative 13% global fuel then i did it for 55 and got negative 11%. I did the calculations numerous times and i am baffled. I am thinking i should be around -17% on fuel trim and do you think i need to adjust my deadtime? Brandon [VFRacing]

 

[GILZTSIAWD]

I would set it to around -15% and do the 10 minute cruise 5 minute idle then see what the mid and lo is for the ltft. If it either number is -12.5 or 12.5 you are way off. Just read through that tuning guide though it tells you exactly how to do it and what needs to be adjusted which way depending on how those numbers come out.

 

[Liger]

Well, i did some tuning, sucker runs really rich and has a ton of carbon build up, got a lot out though by just crusing after some hard pulls. My MidLTFT was 7.7-9.2 and LoLTFT was 5.5. Looks like i'm gonna be setting global to about 16-17, see how both play out. Brandon [VFRacing]

 

[92GSXBaltimore]

i turned my base pressure up to 45psi on stockers and 2 of em sprung leaks. Prob not a good idea to increase the pressure that much on 13 year old injectors.

 

[Liger]

That could be the problem with them and the reason why my gasmileage is absolutely horrid. I get 15 average on highway and 10 or so on city streets i also did a lot of work with dsmlink this past night and day and the long term fuel trims haven't improved really at all, at -15% global fuel i was getting midLTFT 7.7 and loLTFT 5.2, now at -17% i was getting -12.5 and 10.3 and now with -14% i am getting 7.6 and 8.4. Do you think i should continue to lower the global fuel to let's say, -13%?

Also, i have the 550cc's, does anyone know what i can do to fix them or find out what the real problem is with them? One injector flows more by either staying open too long or doesn't seat all the way or what. But i had them flowtested and they checked out perfectly since they are brand new but they still have the same problem, and no it's not my car. i swapped the injectors around and it follows the cylinder with that injector.

 

[cdct99]

The formula for global fuel settings is {[old size]/[new size]/[sqrt(new pressure)/(base pressure)] - 1}. For your example we get 450/450/(sqrt(55/43.5) -1). The 450/450 equals 1, so we get (1/sqrt(1.2644) -1) or (1/1.12444 -1) or .88933 - 1, which is -.1106. Your global should be approximately -11%, so yes, you are on the right track by decreasing it. In closed loop, these changes will not affect how rich/lean your engine runs however, as the ECU is simply compensating for the changes you make. Dead times will be slightly higher with increased fuel pressure, just play with it until your lo and mid trims are equal to each other, then change global to zero them out. What makes you think you are running rich currently? If you are truly running rich in closed loop, I would suspect either boost leaks or a faulty O2 sensor.

Steve Parry

p.s. just read the part about horrid gas milage again... I would definately do a boost leak test if this is the case... dont even try tuning until you rule this out.

 

[Liger]

Yeah, i've done that equation numerous times. try it with 50 psi base fuel pressure and it comes out to .13xxx i believe. But i have done numerous boost leak tests and fixed any boost leaks and they are ruled out now. I setup dsmlink on gasemileage and it was still bad and for any of you who live in the sac area. I burn a quarter tank of gas going from colfax to roseville to colfax. That is roughly 62 miles round trip, all on I80. I notice that my gasemileage gets exponentially worse in city traffic or just driving a constant speed below 45. Gasemileage goes to about 10 or less. Brandon [VFRacing]