14b and 550s. Fuel pressure a main factor?

[MindBlowin03]

Just wondering how much of a factor fuel pressure will be with stock turbo and 550cc injectors. I know that adding pressure gives me more fuel from the injectors, but can also lead to fuel cut. Does fuel cut become a problem on the 1G MAS and higher fuel pressure with only 550s? Does anyone have any insight on this?

 

[ucancallmedebo]

I beleive fuel cut happens when the mass reads a certain point or maxes out. the ecu thinks fuel pressuis always what it is stock. If u upped the pressure and leaned out on the afc, you could delay fuel cut. In the same way if u lowered the pressure and increased on the afc to compensate u would hit fuel cut earlier. Only because the Ecu is seeing more or less air than is really flowing. If u upped fuel pressure under part throttle conditions with no adjustments the 02 sensor and the ecu will conpensate by leaning out. This is why my car still runs decent with 255 and no AFPR at idle. when it transitions into open loop it is a diffrent story My afpr is backorder.

 

[MindBlowin03]

Sorry to bring this back after a couple weeks, but I have another question on this subject.

I have a Walbro 190 pump and my base pressure is a bit high(~42psi). I know its not a great idea to have a whacked out fuel pressure. I was contiplating on buying the B&M regulator, but I read you can only raise pressure and not lower it. After doing some thinking I dont think I will ever need to lower my pressure.

So lets say I add the B&M unit and keep my pressure around 42psi or so. The good is that I will have higher pressure to get more power from my injectors, and that I would also be able to push back fuel cut some because of the leaning out on my AFC. Are there any negative affects on having higher fuel pressure?

 

[psychlow]

Sorry to bring this back after a couple weeks, but I have another question on this subject.
I have a Walbro 190 pump and my base pressure is a bit high(~42psi).[...] After doing some thinking I dont think I will ever need to lower my pressure.
So lets say I add the B&M unit and keep my pressure around 42psi or so. [...] Are there any negative affects on having higher fuel pressure?

Here's the problem - base fuel pressure doesn't mean the least amount of pressure the car needs.

42PSI is the minimum the FPR will allow right now. Adding the B&M unit just adds an adjustable top onto your stock FPR - which means it still won't flow less than 42PSI. If you add the B&M unit and set the base FP to 42PSI, it'll do the exact same thing it's already doing right now.

When your car is in vacuum, the ECU thinks the car will produce about 27PSI of fuel pressure (on a 1G). This is because the FPR should be decreasing 1 PSI of fuel pressure for every "negative PSI of vacuum" - which is about -10 at 20 inMg (stock vacuum).

Since your FPR can't flow less than 42PSI with your new pump, your fuel curve will be 42PSI from vacuum all the way until 5PSI of boost (stock fuel pressure is 37, 42-37=5) at which point it'll start increasing 1:1. In order to make your fuel curve linear, you'll have to set the base pressure (pressure without a vac/boost hose attached) at a minimum of 52PSI - this'll let the FPR adjust from 42-52PSI at 20 inHg vac to 0 inHg vac, and then rise 1:1 with boost.

You shouldn't have any problems running base pressure at 52PSI unless you plan on running over 25PSI of boost. At that point, I'd be worried about the fuel system (injectors mainly) handling over 80PSI. I'm not sure what the max they'll handle would be - if anyone has some data, please chime in.

 

[MindBlowin03]

Im still a bit confused, but I think I understand this a little better. You might have misunderstood one thing though. The 42psi was w/o vacuum on there. During idle it was floating around 32-34psi.

I understand the B&M unit cant lower the base, but it will still always be a 1:1 with boost correct? And unless Im not understanding this, it should be ok with pulling back pressure because of vacuum. Please correct me if Im wrong.

 

[psychlow]

Im still a bit confused, but I think I understand this a little better. You might have misunderstood one thing though. The 42psi was w/o vacuum on there. During idle it was floating around 32-34psi.

OK, then you're not too far off from stock. In fact, your case might be a little odd - your fuel curve seems to be pretty linear from that data, if in fact, you get 32-34PSI at idle with the vac hose connected and 42PSI with the vac hose off, it's rising and falling right about where it should, just about 5PSI higher than stock.

In fact, it's almost as if you have a 2G FPR and it's not overrunning at all.

So lets say I add the B&M unit and keep my pressure around 42psi or so. The good is that I will have higher pressure to get more power from my injectors, and that I would also be able to push back fuel cut some because of the leaning out on my AFC. Are there any negative affects on having higher fuel pressure?

As long as your injectors aren't exploding or being damaged, and the rest of the fuel system can handle it, increased timing is the only downside I can think of (due to leaning out the SAFC).

If you add a B&M unit and keep the FP at 42PSI, it will be exactly as if it weren't there at all.

 

[MindBlowin03]

One last question. Being that my stock FPR is being over-run, does it still work exactly as it should? As far as adjusting correctly with boost and vacuum?

 

[psychlow]

Yeah - as I mentioned, yours seems to be operating correctly, from what you posted - it's just 5 PSI higher than normal. If you lean out fuel in these ranges where needed, you would not need an AFPR.

To make sure, I would get a vacuum source and run the car, and while you apply vacuum, make sure it's a linear decrease of about 1 PSI per 2inHg. I would also do the same thing with a regulated pressure source, making sure it rises 1:1.