Any reason to not hook FPR up to boost only source?

[SebringLX]

Fuel system in a nutshell: 750cc (rated at 43.5psi) injectors, return line, BEGi adjustable FPR (can go from 1:1 to more than 1:1 rising rate), stock Walbro 190lph pump in the tank, external Walbro 255lph pump running in-series with that pump. Tons of fuel available.

Blocking off the vacuum/boost source to the FPR, leaving the FPR open to atmosphere to use it as a static regulator, it seems I was running out of fuel in the upper RPMs, the higher the boost, the lower in the RPM range it would go lean. Pressure was set at 60psi, idle and part throttle were perfect, just can't boost at all or it goes too lean up top. Seems like I should have more than enough fuel flow and injector at that pressure rate for this not to be a problem, but it's still a problem.

Hooking the FPR up the way it should be, vacuum/boost source from intake manifold hooked to the vacuum/boost reference port on the FPR. 1 way check valve hooked to the adjustable valve on the FPR to seal vacuum leak, but allow boost to bleed through the valve based on adjustment setting (instructions say to do this, and it came with the check valve). Idle and part throttle are complete crap, tried adjusting the tune to compensate, got it a little better, but nowhere near what it was before. WOT is now way too rich, but didn't get to the point of trying to pull fuel at WOT because I hated how bad the idle and part throttle were.

Now if I put the check valve between the IM and FPR so that the FPR does not see vacuum, but will see boost and increase pressure under boost... I can set the base fuel pressure to 60psi, idle and part throttle are absolutely perfect, car is a pleasure to drive around town, but WOT is too rich (again, didn't get to the point where I start pulling fuel out in the tune to compensate yet).

Is there any reason NOT to hook the FPR up to where it will never see vacuum and only see boost? It seems like it would be a lot easier to pull fuel from WOT in the tune, than to try and fix idle/part throttle AND pull WOT fuel in the tune with the FPR hooked up the "correct" way.

[contraption22]

I see no reason no to. Many of the SRT-4 guys that have converted are running their regulators with a boost-only reference.

[SebringLX]

I see no reason no to. Many of the SRT-4 guys that have converted are running their regulators with a boost-only reference.

I think I will try to continue down that path and see where it leads then. While I have borrowed a lot of info and techniques from the SRT-4 crowd for this build, it's hard to decide what is really worth listening to from them and what isn't.

[contraption22]

Since your car has a returnless fuel system with a static fuel pressure regulator from the factory, the OE computer should be able to map the fuel correctly for all situations except when in boost, so there is really no reason for you to have vacuum going to the regulator.

[SebringLX]

Since your car has a returnless fuel system with a static fuel pressure regulator from the factory, the OE computer should be able to map the fuel correctly for all situations except when in boost, so there is really no reason for you to have vacuum going to the regulator.

Makes sense... that is what I had been thinking but then got confused about reading various different things. It should actually be able to map fuel correctly while in boost, as I have flashed a turbo cal to it... I have an NGC1 PCM... I use a Mexican Turbo Stratus PCM part number with some SRT-4 Stage 2 and Stage 3 values on top of it, as a base, then flash that to my PCM. I have a Mopar 3BAR MAP sensor installed as well. Out in Montana last year I had everything running pretty good, but I don't remember exactly how I had the FPR setup. Starting from scratch in IL (3000' elevation drop). I was able to control fuel up until 4500-5500RPM depending on boost with the FPR running static 60psi, but no matter what I did in the tune, at the point where it would jump lean I could not richen it up. I could richen or lean it at any point lower than that. Full boost is reached in the 3400-3600rpm range, so boost had leveled out before the lean jump occurs. Hoping that going back to 1:1 rising rate will fix the issue, just have to play around with the tune to find out.

[contraption22]

Is it possible you are running out of fuel volume?

[Ondonti]

If you can only get your car to idle okay at 60psi base fuel you have some serious problems.
try getting your car to run at 40 something.

[SebringLX]

Is it possible you are running out of fuel volume?

Should not be, a 190lph pump AND a 255lph pump in series = lots of fuel volume. At 60psi and 12v the 190 would be flowing 32gph and the 255 would be flowing another 49gph on top of that.

If you can only get your car to idle okay at 60psi base fuel you have some serious problems.
try getting your car to run at 40 something.

I didn't mean that I couldn't, I meant it is a pain to do. I've gotten it to idle at even lower than 40psi before, it's just a pain in the butt (not to mention very time consuming) to try and re-write the entire idle to 3500rpm and vacuum to 0psi range of the fuel table for it. For 60psi (easier to set than 58psi with the fuel pressure gauge I have), all I have to do is scale the injectors and the idle/part throttle tune is perfect, since stock pressure is 58psi, very easy. I don't have to touch the idle/part throttle area of the VE table at all doing that, only have to worry about the WOT portion.

Even if I scale the injectors to what they would flow at 40psi in the tune, it's still too lean without increasing the VE table values in that range for more fuel. Huge pain, much easier to set it to the stock 58psi with the injectors scaled, like I said.

[contraption22]

Curious how you made out with this. Any updates?

[Aries_Turbo]

can inline pumps decrease volume?

in other systems, when you run things in series, it increases the pressure but decreases the flow.

Brian

[Ondonti]

Twin walbros, one intank and one inline flows near what twin intank walbros do and more around 100psi.
John Montgomery's 9.1 second talon 2 years ago (faster now) was running 1 intake and 1 inline walbro. Probably with the pressure reliefs defeated though........
That combo is sufficient for 800whp on gasoline.

You are gonna screw up your idle maps by not running the regulator properly so being lazy is not really an excuse to use a lower base fuel pressure. Either way you have to tune the car. Save the calibrations so you don't have to redo it.
60psi base really makes no sense unless you are purposely trying to ghetto rig your fuel and you want to tax your pumps more then they need to be taxed.

[SebringLX]

Well the FPR rebuild kit should arrive today. I'm hoping I will be able to get everything running properly after rebuilding the FPR.

I could not get the fuel pressure to drop lower than 50psi, and I have had it lower than that in the past, so I know the FPR isn't working properly. Also, when I hook it up the way it should be hooked up (vacuum/boost source), the fuel pressure drops almost 20psi. The car idles around -9psi vacuum, so there's no reason for the fuel pressure to drop that much.

If the weather is nice enough, I will test it out after I'm done rebuilding the FPR tonight.

[contraption22]

Just to clarify, what is your vacuum at idle? You said 9psi, do you mean 9 inches?

[SebringLX]

Just to clarify, what is your vacuum at idle? You said 9psi, do you mean 9 inches?

-9psi (Negative 9) is what the boost gauge shows at idle.... so that'd be atmosphere (14.7psi) - 9psi = 5.7psi = 11.6 inches of mercury? Not sure if that's the correct way to convert it.

[SebringLX]

FPR was definately part of the issue. I rebuilt it last night, it was in bad shape, here's a couple pics:




I didn't get a picture of it, but the spring was stuck in a compressed state in addition to the shims being destroyed and the diaphrams being deformed. Rebuild kit included new valves, new spring, new washers, new shims, and new diaphrams.

After cleaning everything up and rebuilding it with the new parts, it works the way it's supposed to now. I set the fuel to ~45psi, hooked it up to vacuum/boost source, and watched it fall to ~35psi like it should. Prior to the rebuild, fuel pressure would drop over 20psi when a vacuum source was connected. Also I think the rate of gain when going into boost was way off due to the FPR being so jacked up, not to mention that it probably wasn't holding pressure like it should either.

Unfortunately I discovered another problem after solving this one that is going to prevent me from tuning... It seems somewhere in the last couple days while I was messing around with everything, the top bolt that holds my O2 housing to the turbo vanished. So now I have an exhaust leak. Need to find a new gasket and a new bolt for that before I can try tuning again.