97superchgedz28

procharger ps1..so the car got dynoed again yesterday 485 at the wheels... trying to figure out why at the 1/4 mile track i get loss of power for a few seconds in 4th and 5th gear high rpm..about 106mph.. tuner says fuel pressure gauge at 80lbs then drops after 1/4 mile simulation on dyno.... air/fuel ratio qui kley rises on graph to 19 on 4th gearhe says fuel pump fine.. its a new 255 walbro.. he says maybe the stock fuel module (plastic tube that encompasses the pump) may be restricting??
ive got bigger fuel injectors too.. prochager fuel booster too.
could the ignition timing if off simulate this drop in fuel pressure?.. no msd ignition box.. tried to put one in but cldnt get it running smoothly on dyno and software..so unplugged for now

rwb

Have you ever changed the fuel filter?

97superchgedz28

ive recently changed that too

rwb

More than likely either you are losing voltage to the pump or you need more pump, from the sound of it. Others might have ideas also.

Alex94TAGT

To answer your question, no, spark timing will not make your fuel pressure drop.

Just to cover all bases, what size injectors do you have, and what is their duty cycle when this occurs? Are you using the FMU supplied with the procharger kit?

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As rwb stated, this problem is typically due to insufficient fuel volume being supplied to the rail.

1) First things first, that procharger inline pump supplied with the kit is probably serving more as a restriction than it is helping. If memory serves, it flows 43gph @70psi, whereas your in-tank walbro 255 supplies somewhere around 46~56gph @70psi depending on input voltage, from the graphs I've seen.

2) A fuel pump's output volume decreases at higher output pressure. In other words, you will have less physical fuel volume being supplied to the rail at 80psi than you otherwise would at 50-65psi, for instance. I'd try gradually decreasing the WOT fuel pressure and see what happens when you retune (though this may present limitations with your fuel injector duty cycles). If the issue gets better but doesn't fully resolve, then it may be time for a larger aftermarket pump or dual pump setup. (As you may be aware, most of us run dual in-tank 255HP walbros in parallel, with the second pump triggered via a hobbs switch.)

It seems a few guys on here have achieved higher horsepower levels on a single pump than what you're hitting, whereas others find 450~500rwhp to be about the limit, but I've no clue whether they were using the stock bucket or aftermarket lines or voltage boosters, etc. They most likely weren't using the procharger booster pump, however. Sometimes a fuel pump voltage booster helps, as well as upgraded wiring. The hoses in the tank might be leaking at high pressures. Just some other stuff to think about.

Alex94TAGT

Pulled this from the net -- no idea who originally created it:



Note that flow decreases and amperage draw increases at higher output pressure.

97superchgedz28

Thanks for the help guys, I appreciate it.
I've got 44lb aftermarket injectors.
So if I run 2 intank pumps hoseclamped together ditching the fuel bucket?
Hobbs switch I would have to manually turn it on under high boost? Is there a way to automatically turn it on instead of on the fly?
Do I need to do anything differently at the fuel rails to run parallel?
Other question I had was anything special in removing the procharger fmu? Or just remove it and tie the fuel lines back together?
And would I need to change out the stock fuel regulator?

97WS6SCharged

Those are probably on the small side for an intercooled setup. 60's would be a better fit IMO.

You could also run one of the newer 340 lph pumps if you want to keep the bucket. It should work well with a hotwire kit or a voltage booster.

The Hobbs switch would turn the 2nd pump on automatically once you hit the boost threshold (use the smaller 2 psi switch). I've also used a nitrous window switch to activate a second pump before with good results.

The only way to run the rails in parallel is to weld fittings onto each rail and tie them together at an aftermarket regulator. Your stock regulator wouldn't work anymore. The Aeromotive A1000 works well.

Alternatively you could weld up the cross over tube and add fittings on top of the rails to make a larger cross over tube out of braided line and AN fittings.

Either way the stock fuel lines shouldn't be a restriction at 500 hp.

Nope, just remove it and reconnect the stock line back to the regulator and plug the vacuum line that went to the FMU.

97superchgedz28

awesome..thanks for the info!..
so how bout running the 255walbro i have now in the bucket..band clamp a 2nd fuel pump next to the bucket?..sure the 2nd pump wldnt be in a bucket but at least the first one wld. then i cld run a hobbs or a window switch to it.

But how wld i tap the fuel lines too it? do i need just to T the main feed line?

if i run the 2 intank fuel pumps shld i still go with the aeromotive regulator?

DirtyDaveW

80psi? That sounds high. I put a fuel pressure guage from the scrhader(sp?) valve to my wiindshield, taping in there, then go for WOT blasts to see what happens to the pressure.

Though I have the 340 aeromotive/relay kit, they are still in the box. I'm been running the stock pump and a NOS inline for 5 years, trapping close to 130mph.

97superchgedz28

Yeah not sure why its 80psi before it drops at high rpm 4th gear.. maybe regulator?

So I cant fit a 2nd fuel pump and keep the 1st fuel pump in the bucket.. not enough room to drop in .. so I'd be forced to get rid of bucket and clamp together 2 pumps, but I'd have to figure out the lines.. Looks like 2 returns and 2 feeds? One feed is directly from the top of the pump, and it looks like the other feed taps in the fuel that's inside the bucket, but if bucket ditched I'd have to extend line to bottom to aspirate the fuel?

So has anyone had any luck with the Kenne Bell Boost a pump? looks like for $299 I can tap in the existing set up and add the boost a pump, and just keep the single 255 pump in the bucket in the tank. Looks like no bigger fuel lines needed with the kenne bell. Any thoughts on going that route?

Alex94TAGT

That was my purpose in bringing up the pump flow vs pressure graph, though I should have stated it more plainly: You could attain an extra ~10gph of fuel flow (not an inconsiderable amount) by merely dropping your WOT fuel pressure from that whopping 80psi down to 60psi, provided that your current injectors have enough duty cycle remaining to compensate. The drop in fuel pressure at the top of 4th gear is likely due to insufficient pump flow, whether it be due to running such high pressure and/or a drop in the fuel pump supply voltage. Could also be that FMU acting goofy -- most people ditch it for large injectors.

I'd still like to know the IDC immediately before this lean spot occurred, but I realize you may not have this information. 44# injectors rated at 43.5psi will behave like 60# injectors at 80psi, albeit the fuel pump flow takes a hit as previously explained. Upgrading injectors would probably be my next step, in addition to lowering fuel pressure -- see where that gets you.

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To answer your questions:

Simple answer: You can't.

The opening in the gas tank is only just wide enough to fit the bucket itself (...OR two pumps side-by-side in its place). You'd never get the sending unit into the gas tank with a second pump affixed to the outside of the bucket.

Just to be clear, the hobbs switch or window switch would not be directly powering the second pump. You use those switches to trigger a second automotive relay, which in turn supplies power to the second pump directly from the battery/alternator.

There's a plethora of information on dual pump assemblies if you run a search -- far more than I could type here.

To run two pumps into the stock feed line, yes, you'd obviously have to tee (or wye) their respective output hoses together before plumbing that into the stock feed line. Seems everyone accomplishes this in slightly different ways -- just have to be creative.

That new 340lph pump Kevin/Dave mentioned would be considerably simpler/easier to install in terms of both plumbing and wiring. I didn't know we had that option now.

The type of regulator you use has little to do with the pump arrangement, and everything to do with your fuel line arrangement -- ie, whether you run the two fuel rails in a series configuration (counter-clockwise circulating manner like stock) or a parallel configuration (weld on some fittings).

Alex94TAGT

I use an MSD voltage booster on my primary pump, which is effectively the same thing as the KB. It's boost-sensitive (and I believe the newer ones are even programmable). In general, it will increase voltage supplied to the pump based on boost sensed via a connected vacuum line. Mine simply has an adjustment screw to modify the gain.

I was told that these pumps can reliably handle upwards of 15~16 VDC over short periods of time, so that's how I set mine up. Seems to work fine -- never had a pump failure -- though I have enough fuel from the dual pumps to run without it.

97superchgedz28

tremendous help thanks.
ok heres my direction then:
keep the single 255 pump in the bucket intank, go with kenne bell boost a pump on a hobbs.. ditch the procharger fmu.. and get it back on dyno to decrease pressure from 80psi..then see if my fuel is good.
If not..next step is 60lb injectors from the 44lb.

i didnt do the procharger install.. so theres the feed and return into the procharger fmu.. do i just coupler those fittings?
then the vacuum line looks like its "T" off before fmu then to fmu..do i remove that line and simply take the T out and coupler that back?

97WS6SCharged

The Boost a pump is not a physical pump, it's a voltage booster and it's powered at all times (doesn't use a hobbs switch). It simply provides more current to the fuel pump when the engine is at higher load or RPM.

If I were at your level I would leave the 255 in place and install a hotwire kit from Racetronix then retune the car to use a set of 60 lb/hr Motron injectors and ditch the FMU. Leave the stock lines and regulator in place.