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fuel pressure on 502 /w prochargers

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fuel pressure on 502 /w prochargers

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Old 06-25-2017, 08:15 AM
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Default fuel pressure on 502 /w prochargers

I bought this 35 fountain with two 502 /w prochargers, runs very bad , miss firing and stalling , I looked at the fuel pressures and they look too high , set at 65 psi, I read they should be at 35 psi does anybody know the correct fuel pressure with prochargers , thanks
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Old 06-25-2017, 08:51 AM
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a procharger doesn't care what fuel pressure. it is the type of efi you are running. some are rated at 9 to 11 psi. (extinct old TBI.) stock merc 502-415 hp (mag style) efi and the 500 and 525 efi are all rated 38 running 43 max. so if it is a stock merc system, I would look at the pressure regulator and the fuel return. some aftermarket systems run pressures that high. now your efi controller has to know if it is feeding a procharged engine, but it is changing pulse width, not fuel pressure.
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Old 06-25-2017, 09:07 AM
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Raising Fuel Pressure is one way to add more fuel to compensate for to small of an injector, a bandaid in my opinion. In some cases Procharger, Vortechs, Paxton use a rising rate regulator to raise FP under boost to add more fuel. Sometimes those stick closed and cause a high FP situation. Hard to tell what FP should be, it depends on how it was tuned. 65psi for a base pressure seems very high IMO.
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Old 06-25-2017, 09:18 AM
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that's what I say boat has black very bad from exhaust , engines where rebuilt sparkplugs fouled black , bought this boat from Canada and don't think it was running good at all , has502 bored out 509 factory injector system with M3 prochargers on it I will see if I can lower the fuel pressure at regulator , I am also waiting to hear from Procharger tomorrow !
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Old 06-25-2017, 09:36 AM
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ok, this efi? Mercruiser 454 502 MPI System Intake Manifold Plenum ECM wiring, Fuel pump EFI eBay most likely. not this one MERCRUISER 500EFI UPPER / LOWER INTAKE WITH INJECTOR RAILS or this one... MerCruiser PCM Crusader MPI 7.4 8.2 454 502 Intake Plenum V8 # 12553838 ALUMINUM eBay ok, the guy put prochargers on it. which efi controller, or don't you know? what year boat? do you have any idea whether the seller got the ecm's reprogrammed for running the prochargers? tyler crockett is one name I hae heard for tuning merc mefi systems. but the stock fuel pressure regulators should set this fuel pressure around 38 to 43. it is also possible seller put too-high pressure fuel pumps in it. starting from scratch with something non-stock that doesn't work right usually takes checking everything...

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Old 06-25-2017, 10:25 AM
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Originally Posted by dereknkathy View Post
a procharger doesn't care what fuel pressure. it is the type of efi you are running. some are rated at 9 to 11 psi. (extinct old TBI.) stock merc 502-415 hp (mag style) efi and the 500 and 525 efi are all rated 38 running 43 max. so if it is a stock merc system, I would look at the pressure regulator and the fuel return. some aftermarket systems run pressures that high. now your efi controller has to know if it is feeding a procharged engine, but it is changing pulse width, not fuel pressure.
Prochargers use a raising rate regulator referred to as a FMU. Some are 4:1. some 7:1 and some are more. It's an archaic system but that's what ATI uses.

Now, if a shop removed that and installed larger injectors and did the required programming (this isi the better way of course) then the previous owner will have to give that info....

so, either way I vote contacting the previous owner !
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Old 06-25-2017, 10:28 AM
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Originally Posted by petergrieco View Post
that's what I say boat has black very bad from exhaust , engines where rebuilt sparkplugs fouled black , bought this boat from Canada and don't think it was running good at all , has502 bored out 509 factory injector system with M3 prochargers on it I will see if I can lower the fuel pressure at regulator , I am also waiting to hear from Procharger tomorrow !
Don't expect too much from Procharger....unfortunately.

Where in the US are you Peter...maybe one of us can direct you to a shop that has experience with this. Please say Michigan or Louisiana
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Old 06-25-2017, 12:41 PM
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the prochargers were done at ocean performance and they sent the computers to Arizona speed and the engines are 1999 502 bored to 509 . I just lowered the fuel pressure to 35 psi at idle so I will see .
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Old 06-25-2017, 12:48 PM
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What does Ocean Performance say about where to set the base (idle) fuel psi and where at WOT ?
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Old 06-25-2017, 02:46 PM
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Originally Posted by petergrieco View Post
the prochargers were done at ocean performance and they sent the computers to Arizona speed and the engines are 1999 502 bored to 509 . I just lowered the fuel pressure to 35 psi at idle so I will see .
Be very careful doing this. You could be playing with fire. Find out what you have first.
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