MarkDonzi

Hey Guys,

I was testing out my new to me outerlimits SV40. The boat has Merc 700SCI's with stage 3 Whipple kits. When I ran the boat above 5300-5400 rpm I got a "low fuel pressure" Code and guardian 75% power on my port motor. We changed the spin on and in line fuel filters ran the boat again and felt the power drop off but did not throw any codes. Ran out of time and now have boat home trying to figure out where to go next.

Any advice would be greatly appreciated.

Thanks, Mark

BUP

iTrader: (9)

Have to ask first and foremost - Whipple ??? is the complete fuel system OEM stock and is the PCM 03 stock tune itself ? Any recalibrations here ? Does the stock fuel pressure still apply currently ???

I would find all this out and my next course of action would be fuel pressure testing with a quality fuel pressure gauge and connections. Do not use HF testing gauges here nor Northern tool either.

Stock as I recall the 700 SCi fuel pressure at dead idle of 750 rpm's should be 59 to 61 psi

STOCK fuel pressure test with just key on / NO engine running should be 64 to 67 psi

Stock fuel pressure at 5200 rpms should be 68-72 psi

Stock max fuel system flow rate at 5200 rpms is 67 gallons per hour just an FYI that's a lot of gas.

Fuel system leak down testing 20 to 30 psi static leak down after 2 mins is normal.

That is where I would start plus take your fuel tank supply side out of the mix and further testing of using a new small remote gas tank with new fuel line hooked to incoming fuel engine side. You are making sure as to what side your problem is on fuel tank / fuel vent / fuel pick up / fittings / rubber fuel line / anti siphon valve (if equipped) side all taken out of the mix compared to engine side. If problem still exists then its on the engine side for your fuel problems. Then possible fuel pump(s) problem.

Also your overspeed / over rev limit comes in at 5400, just check to make sure you are not hitting that - your scan will tell you and how many times if so.

MarkDonzi

Thanks BUP for your insight.

FYI, the stage 3 whipple kits run the engines up to 6,000 rpm and bump the 700SCI horsepower to ~850. According to Dustin Whipple at WOT my fuel pressure should be between 65-68 psi. ECM Tune is proprietary from Whipple and fuel system is completely stock.

I like your idea of separating the fuel tank from the mix. Start with simple problems first.

Thanks again for you comments.

We had a simple scan tool on the motors when this problem occurred and cleared the codes unfortunately. Do you know if the ECM would still have the codes recorded. Plan on hooking up a laptop today to find out.

Kelly O

Once you have cleared the fault, it should no longer be listed as active but it should be in the history on the ECM.

Use the "freeze-frame" function of your scan tool to look at all the stored parameters for the engine for the exact time of when the code was set. That way you can make sure the low fuel psi code was set when you were running. Seems like I have seen that warning at ignition power-up if the lanyard safety switch is in the off position, which prevents the electric fuel pump from running.

After clearing your active codes, be sure you have 100% power available during scan before test running again.

Only de-rate I have seen which did not set any fault codes was due to a bad coil pack. One bad coil caused power reduction to 92%, ECM kept reducing power available without setting codes until the coil was identified and replaced.

MarkDonzi

Thanks for your information!!

BUP

iTrader: (9)

If you are saying your engine was at 75 % guardian then in your scan will not show 100 % available power. If your scan shows 100 % available power then your engine never went into a guardian mode. Its that simple about available power vs guardian mode.

My bad I missed it was a stage 3 from Whipple. FWIW is I just double checked the fuel pressure specs OEM stock for the 700 SCI and I was spot on in my post. You engine is now 850 hp and higher RPMS your fuel pressure according to Whipple is lower than stock ? Just asking why is it lower and can you monitored your AFR with 02 readings or have they been monitored in the past ? Just curious to.

I assume Lowered fuel pressure at WOT after recal stage 3 - Possible rich or too rich to begin with and the new recal ECM might be a tad on leaner side / fuel pressure lowered a tad to tone down rich conditions at WOT from stock tune .

I think you are saying all your fuel system is stock and HAVE YOU DONE any fuel pressure testing ?

If I recall correctly lanyard switch activated is a no guardian activated fault.

MarkDonzi

My Mechanic will be looking into it in the next few days, Thanks again for your input.I'll let you know what we find.

unispeed

Mark ,We are having the same issues any updates on your finding way back when
I know this is old
Mark

Shallow Minded

Bringing this back to the top as I'm having a similar issue on one of my 700's. Runs like a top until 4,500 RPM or so, then I get a low fuel pressure warning. Back off and it's fine. A buddy thinks maybe the high pressure fuel filter is the culprit? Appreciate any info that may be out there.

Hustlin

I know this is from a ways back but I'm having the exact same issue as you at 4500 rpm. When throttling past that the pressure drops to low 50s and goes into Guardian. If you solved the problem let me know what you found. I appreciate it.