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| 5.7L EFI Upgrade / Fuel Pressure Issue |
| Author |
Message |
    
Chris Mertz
New member
Username: mertzcr
Post Number: 3
Registered: 05-2008
| | Posted on Monday, May 12, 2008 - 10:26 am: | 
|
Recently installed MPFI on a 5.7L. I am having issues with getting enough fuel pressure. I think the original fuel pump and fuel/water separator is too restrictive. Can anyone recommend what fuel pump and fuel/water system I should install for fuel injection on this motor? Any clue what Mercruiser uses on their version of the 5.7L MPFI? Thanks! |
Rod Stewart
Senior Member
Username: rod_stewart
Post Number: 1287
Registered: 08-2006
| | Posted on Monday, May 12, 2008 - 02:10 pm: |
|
On my 6.2 MPI there are two fuel pumps.
The first is a booster pump right at the fuel filter cannister on the front side low stbd.
This pumps the fuel to a Gen II Coolfuel assembly on the lower port side. The fuel is cooled by the incoming cooling water, then pumped by an inline elec pump up to the fuel rail.
The required pressure at the fuel rail is about 40 psig for MPI. You will need an inline elec pump to get this. If you converted from carbed, and you are using the original elec pump, or a mechanical pump, you will not have anywhere near enough pressure. They are designed for about 4-6 psig.
Rod |
Chris Mertz
Member
Username: mertzcr
Post Number: 4
Registered: 05-2008
| | Posted on Monday, May 12, 2008 - 02:23 pm: |
|
I purchased the MPI from affordable-fuel-injection.com and they included an electric fuel pump, which goes into the stock water/fuel separator. We couldn't get above 3500 RPM's before it started choking. After a couple runs, the pump gave out completely.
From what you are saying... perhaps the one they included which mounts on stbd should remain, purchase the Merc GEN II Pump/Cooler Kit 861156A03, along with 861126A1 fuel pressure regulator (both show as EFI parts for the EFI 350 stock).
You mentioned another pump after the GEN2 kit? Or is the pump/cooler combokit (replaced the orig separated parts) the all-in-one solution?
Are you running the stock/basic Merc fuel/water separator still? What is the fuel flow layout for yours then? Fuel tank --> booster pump --> etc.
Thanks for your help!!! |
MistaHays
Advanced Member
Username: mistahays
Post Number: 682
Registered: 02-2006
| | Posted on Monday, May 12, 2008 - 02:31 pm: |
|
How do you know you are having pressure issues? You sound like you are way up the learning curve, but if the fuel calibration on the ECM doesn't quite match the engine's volumetric efficiency...(e.g. if your engine has a big cam) you would get the same result (i.e. underfueling or overfueling at various speed/load conditions). |
dave_n
Member
Username: dave_n
Post Number: 72
Registered: 11-2005
| | Posted on Monday, May 12, 2008 - 07:07 pm: |
|
Chris,
Keep on mind that the ECM is assuming a certain fuel pressure. Increasing or decreasing the pressure from what it expects will create problems with fuel mixture. Asssuming it's a marine EFI setup, you should stick to the components that came in the kit and diagnose the problem. Swapping components from other sources will just make it more difficult to figure out.
Are you monitoring fuel pressure and supply side vacuum? Your not using a calibration from an automotive application are you? |
Rod Stewart
Senior Member
Username: rod_stewart
Post Number: 1289
Registered: 08-2006
| | Posted on Monday, May 12, 2008 - 11:40 pm: |
|
Chris;
My fuel flow is:
Tank>booster pump>water sep/fuel filter>(fuel pump>fuel cooler)>fuel rail.
The parts in brackets are all part of the CoolFuel II module. There is also a bypass line running back from the CoolFuel to the fuel filter.
You should follow the instructions that came with your kit as far as what fuel supply components to use.
Rod |
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