Compensating for a 2G MAF w/ fuel pressure

So I want to put my 2G MAF in. I don't have any sort of fuel controller except for an AFPR. The car has a stock ecu and 450's right now. Can I make everything play nice by turning up the fuel pressure? The way that I see it, is that the ecu has no way of knowing that the reason it's seeing a lower airflow signal is because a different MAF was installed. It just thinks the engine is requiring less air. The stock ecu also has no ability to monitor actual fuel pressure. I'd guess that if I was able proportionally increase the fuel pressure to match the decrease in airflow signal, it should work right?

Also, based on the assumption of fuel pressure rising 1:1 with boost pressure, if the airflow signal is reduced and fuel pressure increased as stated above, would this still be true? Or wouuld it need to be like 1.25:1? I wouldn't think so because boost pressure and airflow aren't directly related to each other, they're more like close cousins. And also because the fuel pressure rises 1:1 with boost regardless if the base pressure is 30 psi or 60 psi.

 

[Andy_S]

That will prove to be very inconsistent across a large boost range. Why wouldn't you want any tuning or fuel management on your car? A very simple way to compensate for the maf would be to toss in some 550cc injectors. Works out about perfect.

 

That's my point exactly though. 550's are only 550's at a certain fuel pressure, and the 450's can spray the same volume of fuel as those 550's, they just need more pressure to do it. The computer also doesn't know what size injectors you've installed either.

It is not that I don't WANT any fuel controller, in fact I have a keydiver ecu and chip that would allow me to run my 750's. I'm still fighting a knock issue so I'm not trying to crank the boost enough to need the big injectors yet. I'm more or less attempting to test a theory I have. I know that increasing pressure increases flow. I just don't know how much I need to increase the pressure by. I don't think that I'm off base here, I am hoping someone has done this before. Keydiver even compensates his chips based off of increases in fuel pressure.

 

[Andy_S]

Incorrect, the computer does know what size injectors. If it didn't, how would it even run correctly. You can try and run the fuel pressure higher, but you will most likely run out of pump. Your looking to pick up 20% abouts in flow. I'm not saying it won't work, I'm saying its crude and unnecessary considering the resources the dsm/vr4 community has available.

 

The computer runs on preset parameters based on factory installed equipment. The factory used a 1G maf with 450's and 37 psi of fuel pressure. If you put in a 2G maf and 550's the computer doesn't say "hey, this guy changed my maf and injectors", it is just the right combo of parts to still work well. The 550's add enough fuel to remove the lean condition the 2G maf creates. That is all.

 

Quoting Andy_S:
Incorrect, the computer does know what size injectors. If it didn't, how would it even run correctly. You can try and run the fuel pressure higher, but you will most likely run out of pump. Your looking to pick up 20% abouts in flow. I'm not saying it won't work, I'm saying its crude and unnecessary considering the resources the dsm/vr4 community has available.



What I'm doing right now is attempting to tap the resources of the dsm/vr4 community, looking for information.

Additionally, just throwing 550's on top of a 2G maf is crude. With adjustable fuel pressure I believe I can make the injectors into 550's, or 570's, or 540's. Fine tune so to speak.

 

[Barnes]

Why do you want to put the 2g maf on? If you have such limited fuel control capability, this sounds like a recipe for disaster. I kinda doubt you can bump your fuel pressure up enough to compensate. Plus, how do you even know if you've done it enough?

P.S. The computer has no idea what maf or injectors are attached to the car. It just sees and airflow signal and sends out the appropriate pulse width to the injector. That's why you can put a 2g maf on with 550cc injectors and have it roughly balance out. The 2g sensor will lean the system out, and the 550's will rich the system up.

My recommendation is that you hold off on putting this on until you get the proper tuning parts for this.

 

[SouthCaliVR4]

"Additionally, just throwing 550's on top of a 2G maf is crude." seriously?!? you want to crank up the psi to get "larger" injectors but using 550's is crude /ubbthreads/images/graemlins/idea.gif Ok it's your world we're just living in it right. If you have already made up your mind, just do what your gonna do.

 

I have a datalogger to monitor fuel trims and O2 voltage. I'm not going into this blind. Thank you barnes for at least verifying one of my points. I want to run the 2G because every 1G maf I have is hacked. None of my 2G mafs are hacked.

Explain to me why I need any additional tuning equipment. Seriously. I say this because the 2G maf sends a signal that is less than the 1G, but it is linear. A 25% reductionm. Always. It doesn't vary with rpm or tps input. It is always 25% less. Why wouldn't a proportional increase in fuel pressure work? It will also be a constant linear increase.

 

Quoting SouthCaliVR4:
"Additionally, just throwing 550's on top of a 2G maf is crude." seriously?!? you want to crank up the psi to get "larger" injectors but using 550's is crude /ubbthreads/images/graemlins/idea.gif Ok it's your world we're just living in it right. If you have already made up your mind, just do what your gonna do.



Sorry I was replying to barnes when you posted this southcali. It is crude because there is no real tuning in that. Whether or not anyone wants to admit it, adjusting fuel pressure is tuning. If everyone here who is running an AFPR is only doing so to gain return flow to the tank, you are greatly limiting the potential of the system. Besides, fuel spray patterns are better at higher pressures. Put your thumb over the outlet on your garden hose. It sprays better.

 

[SouthCaliVR4]

Yes varying fuel pressure is a tuning method, One I have used as well, but my goals where more in the ten percent or lower range & your talking twenty percent or higher. eventually your going to hit a wall where any increase in pressure will have to be exponential to gain more flow. That is where your linear increase theory will fail.

I was a fire fighter for several years, one of the things I had to learn was fluid friction & pressure/volume loss due to restrictions. In our case it was hose dia, in yours it will be injector size. to achieve 25% more flow from that injector (And I'm just theorizing out of my ass here) you may need to raise the pressure as high as fifty percent. Your thinking on paper, so to speak but other things will come into play, like fluid friction. can you do what your talking about, yes but a variable rate regulator will be needed to maintain your given percentage of flow, this is where your going to hit a wall. how are you going to vary fuel press in a nonlinear manor in order to maintain a linear flow rate at the injector. Honestly it's just not as straight forward as you are thinking it is.

I could explain this better if I wasn't brain dead tired.

 

[Andy_S]

You obviously don't want any advice. Why you posted this up beats me. Go crack the fuel pressure and see what happens. It is the newbie section after all /ubbthreads/images/graemlins/banghead.gif

BTW, when I said that the ecu knows injector size, I meant that it is programmed internally for the stock injector flow at stock fuel pressure. I didn't mean it has a learn feature, I apologize for the confusing wording. Also know that because of this programming, you will be approximately 20% lower on your maps. But you already knew that I'm sure.

 

Quoting SouthCaliVR4:
Yes varying fuel pressure is a tuning method, One I have used as well, but my goals where more in the ten percent or lower range & your talking twenty percent or higher. eventually your going to hit a wall where any increase in pressure will have to be exponential to gain more flow. That is where your linear increase theory will fail.

I was a fire fighter for several years, one of the things I had to learn was fluid friction & pressure/volume loss due to restrictions. In our case it was hose dia, in yours it will be injector size. to achieve 25% more flow from that injector (And I'm just theorizing out of my ass here) you may need to raise the pressure as high as fifty percent. Your thinking on paper, so to speak but other things will come into play, like fluid friction. can you do what your talking about, yes but a variable rate regulator will be needed to maintain your given percentage of flow, this is where your going to hit a wall. how are you going to vary fuel press in a nonlinear manor in order to maintain a linear flow rate at the injector. Honestly it's just not as straight forward as you are thinking it is.


I could explain this better if I wasn't brain dead tired.



Now that's information. Up until this point the only thing anyone told me is "you're wrong". Thank you southcali for taking more than two seconds to think about this. Now I have something viable to consider.

Andy_S, I'm sorry if this offends you, but you never even tried to answer my question, you just told me to go buy some injectors. And then you argued using information that is false. I understand what you meant, now that you worded it correctly, but its kind of hard to take advice someone who isn't even reading your question. I understand that you were and are trying to help, but beating your head against wall because you think I'm an idiot doesn't help me or anyone else on the forums. I'm not just going to lay over and trust all of the information here either. Once again, thank you southcali for actually considering and answering my question, for telling me why.

 

[Brunoboy]

FYI this info has been covered many times here and on dsmtuners, use search, itll render many post for you to read rather than waiting for responses that "doesnt" help you at all..
-shane

 

[Andy_S]

Quoting galant1517:


Now that's information. Up until this point the only thing anyone told me is "you're wrong". Thank you southcali for taking more than two seconds to think about this. Now I have something viable to consider.

Andy_S, I'm sorry if this offends you, but you never even tried to answer my question, you just told me to go buy some injectors. And then you argued using information that is false. I understand what you meant, now that you worded it correctly, but its kind of hard to take advice someone who isn't even reading your question. I understand that you were and are trying to help, but beating your head against wall because you think I'm an idiot doesn't help me or anyone else on the forums. I'm not just going to lay over and trust all of the information here either. Once again, thank you southcali for actually considering and answering my question, for telling me why.



Glad I could help. Good luck on your project.

 

You know Andy, it's all good, at least on my end. The discussion shifted off of my original topic for a bit there, and I got aggitated. I'll admit that, and I apologize for that. The information that you brought to the table is valid, I simply couldn't recognize that during what I thought was a moment of brilliance on my part.

And to shane, I would've searched, really, but I had no idea where to start. Besides, Andy said it best when he said that "it is the newbie section after all".