550's and high afc settings-do i need an afpr?

[OnABudget]

whatsup everyone,
my 92 awd has a 190lph pump, and 550's as far as fuel goes. i run 15 psi and find that im pretty much around +0 to +4 % on my afc from idle to 7k. i realize that my hacked-a*s maf may be a slight cause for this, but it doesnt seem normal at all. so i was thinking it might be that my fuel pressure is too low.
i havent done too much research yet with fuel pressure regulators, but is it possible that the stock regulator isnt at a high enough pressure? i was under the impression that with an aftermarket pump and stock regul. the pressure would rise hence why you may need an afpr?
thanks for any help!

 

[OnABudget]

can an aftermarket pump with stock regulator result in too low a fuel pressure, or is the pressure always going to rise? might my fuel pressure be too low?

 

[OnABudget]

sorry to keep adding, but i have checked base timing and i actually need to set it to 3* because of my higher compression. also, im as lean as i can get without knock, its pretty well tuned, i see as much ass 22* advance, but im practically maxing out my injectors with a pulse as high as 20 at just 15 psi on an 18g and rre frount mount.
thanks again.

 

[pneumo]

heh,, you've got a nice thread going all by yourself here. Mind if I cut in?

Your fpr will raise pressure along with boost, just like it should. Your fuel pump won't lower pressure. Stock 1G already runs slightly lower fuel pressure at 36 psi measured with the hose off, compared with 43 psi for the 2G. If you raise the fuel pressure, you will have to compensate by lowering the AFC settings by a few percent. That might not be such a bad idea since you are almost maxing out your 550's. If you raise the pressure you can get a little more flow out of them. I tried tuning 550's on my setup and they were maxed out with a 16G at about 18 psi. We both share the same cali 91 craptane gas, so you're pushing the limits of those injectors already. Time to upgrade!

Your current settings sound about right for a hacked maf, unless you have a boost leak somewhere on that old car. How hacked is you maf?

 

[OnABudget]

i hacked the maf by taking out the lower honey comb, then unscrewing the screw, then i hacked sawed off the plastic going through, thats it for now, my idle isnt worse, my cut is gone for now.
so i guess im wondering if an afpr only lets you lower pressure?
also, what was your max injector pulse on the 550's? were you fuel cutting?
how is it bad to run them at their "limits" other than just worse timing advance curve?
thanks man

 

[pneumo]

That's a moderate ammount of hacking. I'm sure you'll notice the low throttle settings on the AFC like to be set higher at the 1000 rpm point, and gradually lower as the rpms go up.

An adjustable FPR can lower pressure as well as raise it.

The highest duty cycle I saw with my 550's was 110%. I never saw fuel cut with them, even when I ran 25 psi of boost at the track. Of course I had race gas then, and I leaned out the AFC settings, which pushes the fuel cut threshold higher. Running over 100% won't give your engine any more fuel than running 100%. When the DC goes from 98%>99%>100% the injectors get confused and can make the engine misfire for a split second. It feels like a quicker, softer version of fuel cut, or mini fuel cut. If you're logging a run, check O2 volts and injector DC to see if there is a dip in the O2 volts about the same time you see DC go over 100%. Sometimes it shows up.