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  #31  
Old 09-10-2021, 09:47 PM
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prostar205 prostar205 is offline
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Minor update.

Fuel pressure at key turn on (not engine turn over) is 60 psi and then it quickly (within 1-2 seconds) goes down to 18 psi. I'm guessing that is because the ECM shuts off the power to the fuel pump if the key isn't turned to the run position. Should it bleed off that fast and all the way down to 18 psi. If not, could that be a sign of several stuck open injectors?

Also, I could not find any sensor on the heads. I did find the below sensor on the engine water pump main line going to the thermostat housing. There is also a temp sensor on near the thermostat housing for the sends the engine temp to the MMDC for the dash gauge. I know that because I've had to put a new ring terminal on that wire to get the temp gauge to work.

The first picture is what I believe is the ECT sensor, the second picture is the dash gauge temp sensor and the third picture shows each sensor relative to each other.
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  #32  
Old 09-11-2021, 04:40 PM
jpwhit jpwhit is offline
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Quote:
Originally Posted by prostar205 View Post

Fuel pressure at key turn on (not engine turn over) is 60 psi and then it quickly (within 1-2 seconds) goes down to 18 psi. I'm guessing that is because the ECM shuts off the power to the fuel pump if the key isn't turned to the run position. Should it bleed off that fast and all the way down to 18 psi. If not, could that be a sign of several stuck open injectors?
No, it shouldn't bleed off that fast. When you turn on the key, the ECU runs the fuel pump for 15-20 seconds to pressurize the fuel rail then it cuts it back off. It turns the fuel pump back on again once the engine starts. After that initial pressurization, when the pump is off, and the engine isn't running the pressure shouldn't drop any faster than 1 psi per minute. There are multiple reasons the pressure will drop once the pump cycles off.
  • Bad pressure regulator that's not completely closing off the bleed valve
  • Leaking valve in the fuel pump
  • Pinhole in hose(s) in fuel module
  • Leaking Injector(s)

Leaking Injectors almost never leak down as quickly as you're seeing. So even if the injectors are leaking, I think it's likely you have one of the other issues as well.

The way I diagnose fuel system issues is with an auxiliary portable fuel system I assembled for diagnostics purposes. It's a 2-gallon outboard tank, a high-pressure fuel pump, and an adjustable regulator with a built in pressure gauge. I put that in the boat and set it to the appropriate pressure and connect it to the fuel rail. It has standard fuel line quick connectors on it. I also have fuel quick connectors to block off any fuel return lines. If the boat runs right on my test fuel system, then I know the issue is with the boat's fuel system. I know my test fuel system doesn't have a leak down issue itself, so if I see leak down then I know it's the injector or other leak in the fuel rail.
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  #33  
Old 09-12-2021, 09:52 AM
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Raylar Engineering are the 8.1 performance guys, they may be able to help you with your issues also.

https://www.raylarengineering.com/
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  #34  
Old 09-12-2021, 11:21 AM
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Raylar Engineering are the 8.1 performance guys, they may be able to help you with your issues also.

https://www.raylarengineering.com/
I'll contact them on Monday.
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  #35  
Old 09-12-2021, 11:25 AM
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More updates: Started the boat and have 52-54 psi of fuel pressure at idle. At 2,500 rpm, fuel pressure goes down slightly to 50-52 psi. The engine runs great but uses many more fuel than it should when we are at cruising around or surfing. I'm still leaning towards clogged (open) fuel injectors. Cylinders 1, 2, 4, 5 and 6 spark plugs are completely black and have soot around the perimeter and electrode. I'm running fuel injection cleaner in it now but I'm not holding out hope that will fit the problem.
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  #36  
Old 09-12-2021, 11:27 AM
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Quote:
Originally Posted by jpwhit View Post
Leaking Injectors almost never leak down as quickly as you're seeing. So even if the injectors are leaking, I think it's likely you have one of the other issues as well.
Would the fuel pressure leak off that fast if 5 of 8 injectors were clogged (open)?
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  #37  
Old 09-12-2021, 11:30 AM
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Quote:
Originally Posted by jpwhit View Post
  • Bad pressure regulator that's not completely closing off the bleed valve
  • Leaking valve in the fuel pump
  • Pinhole in hose(s) in fuel module
  • Leaking Injector(s)
Are you referring to the pressure regulator on top of the fuel pump or the one on the fuel rail? Both have been replaced with the last 6 months. If either were bad, would that lead to plug fouling within 5-7 hours of engine operation? My fuel pressure is within spec at just over 50 psi at all rpm ranges. I'm still thinking its clogged fuel injectors.
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  #38  
Old 09-13-2021, 10:24 AM
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I took from fuel pressure readings over the weekend. Here are the results.

• Key ON but engine not running: 60 psi then within 2 seconds it drops to 18 psi and holds there.
• Engine running at idle (800 rpm): steady reading at 54 psi
• Engine running at 2,500 rpm: steady ready at 52 psi

Does this indicate several stuck OPEN fuel injectors? Again, plugs in cylinders 1, 2, 3, 4 and 5 are completely black and “sooty” only after 5-7 hours of engine operation.

I’m running fuel injector cleaner in the fuel right now but not sure if that will cure the issue if they are really clogged.

Thoughts??
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  #39  
Old 09-15-2021, 10:10 AM
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Any more thoughts on my spark plug issues?
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  #40  
Old 09-15-2021, 11:45 AM
chrislandy chrislandy is offline
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did you check the temp sender?
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