Fuel pump needing replaced?

[tigemech]

have you checked the anti syphon valve? Does it have a spin on fuel filter? And i would maybe see if you could borrow another fuel gauge to makes sure you dont have a bad gauge.

[rjh171]

Anti siphon valve is in place and appears to be working properly. They are cheap enough I should just replace it.

Fuel filter / water separator was replaced this summer. Spin on type. In line filter was replaced earlier this spring.

Looks like a trip to Autozone for a new gauge!

Could an injector be stuck open leading to lower pressure?

Sent from my SM-G950U using Tapatalk

[rjh171]

Completed another round of troubleshooting. Here is a summary of everything completed thus far:
- Changed low pressure pump after realizing it was locked up --> no to minor improvement in fuel pressure
- Other maintenance completed included changing filters
- Changed high pressure pump and fuel pressure regulator; both were orginal; suspected ethanol fuel may have contributed to component failure --> no to minor improvement in fuel pressure
- Changed vacuum line at time of install of new fuel pressure regulator; suspected 15 year old line might be showing signs of dry rot
- Checked new low pressure pump powered direct to battery as well as by ignition --> good output of fuel; no noticeable change in pressure
- Checked new high pressure pump powered direct to batter as well as by ignition --> good output of fuel and pressure reached 30 psig
- Checked anti-siphon valve at fuel tank; opens and flows easily; no signs of sticking
- Started everything up, pulled vacuum line from fuel pressure regulator --> pressure when up to 30 psig

So I think the pumps and fuel pressure regulator check out good. Therefore, I'm guessing it looks like something is wrong in the vacuum system. Any thoughts or ideas? Bad MAP sensor? A bit confused as I'm not picking up any error codes with the code reader. I didn't get a chance to look at all of the vacuum hoses today. May be a loose hose somewhere in the system.

[dj2]

I just got everything installed in mine tonight, low pressure pump, high pressure pump and rebuilt injectors. Fired right up and running great on the hose. (Would barely idle and backfire when trying to throttle up previously)

I have not researched or been able to check my fuel pressure but I know those injectors are rated at 43.5 psi.

[Bud Wieser]

rjh171, I think 30 psig is what you need for your system. If you take it out on the lake use your fuel pressure gauge. If the pressure drops when the motor stalls I would think it is fuel related. One think you could try, use a portable fuel tank and tie it in where the fuel line enters the low pressure fuel pump. This would eliminate everything before that point. Along with the gummed up fuel pumps you may have an ignition issue. Ignition module assembly, distributor, rotor, wires, plugs...

[tigemech]

Completed another round of troubleshooting. Here is a summary of everything completed thus far:
- Changed low pressure pump after realizing it was locked up --> no to minor improvement in fuel pressure
- Other maintenance completed included changing filters
- Changed high pressure pump and fuel pressure regulator; both were orginal; suspected ethanol fuel may have contributed to component failure --> no to minor improvement in fuel pressure
- Changed vacuum line at time of install of new fuel pressure regulator; suspected 15 year old line might be showing signs of dry rot
- Checked new low pressure pump powered direct to battery as well as by ignition --> good output of fuel; no noticeable change in pressure
- Checked new high pressure pump powered direct to batter as well as by ignition --> good output of fuel and pressure reached 30 psig
- Checked anti-siphon valve at fuel tank; opens and flows easily; no signs of sticking
- Started everything up, pulled vacuum line from fuel pressure regulator --> pressure when up to 30 psig

So I think the pumps and fuel pressure regulator check out good. Therefore, I'm guessing it looks like something is wrong in the vacuum system. Any thoughts or ideas? Bad MAP sensor? A bit confused as I'm not picking up any error codes with the code reader. I didn't get a chance to look at all of the vacuum hoses today. May be a loose hose somewhere in the system.

so with everything plugged in you now get 30psi? or running its still at 22? Have you had it running again yet? and by code reader, what are you using excatly?

[rjh171]

Tigemech,

After all the changes, I still see about 22-24 psig. See notes below. By code reader, I'm using the CodeMate code reader for small troubleshooting items. The tool is not picking up any error codes stored in the computer.

http://www.rinda.com/marine/marine.htm

Bud Wieser,

I agree with you that 30 psig is definitely what is needed, but after seeing your post and Tigemech's post, I realize I need to clarify a few statements. I did remove the anti-siphon valve and in-line filter, dropped in a short piece of new fuel line, put it in a 5 gallon gas can and fired up the engine. Pressure was still at 22-24 psig with engine running and those items removed. Here is what I see along with clarifying some of the earlier statements.

After changing the low pressure pump, high pressure pump, fuel pressure regulator, and everything else mentioned earlier, when I place the ignition to on, I see about 24-25 psig on the gauge. When I crank the engine and startup, I see about 22-24 psig on the gauge with the engine running. I can remove the vacuum line from the fuel pressure pressure regulator, and I see about 30-31 psig at the rail. Reinstall the vacuum line connection to the fuel pressure regulator, and pressure drops back to 24-25 psig. Apply some throttle, and pressure drops to about 20-22 psig.

With the ignition off, I disconnected the power source for each pump. I ran a set of wires connected to the pump back to the boat battery. Doing a direct connection to the batter, the high pressure pump will reach 30-31 psig. I did the same for the low pressure pump, but there was no pressure registered on the gauge at the rail. Just for safe measure, I disconnected the output line from the low pressure pump, placed a can on the outlet, made the direct connection to the battery, and verified fuel volume was coming out of the low pressure pump. Volume appeared sufficient as the gallon can was filling quickly. Reconnected everything, fired it up, and still only 22-24 psig while running.

I haven't had a chance to get out on the water yet. Despite fixing the locked up low pressure pump, I still see low pressure and anticipate it will be a problem. Secondly, the weather south of Houston has not been too cooperative for me. Nice weather while I'm at work; not so nice weather when I have free time to wakeboard. Hoping to try to get out on Friday, but looks like we're going to have either a tropical storm or low level hurricane this weekend.

Despite the low fuel pressure, engine easily fires up. Only prolonged starts seem to be when I've cracked a fuel line and air is being purged from the system. I think my next step is to get a vacuum gauge to measure how much vacuum is being pulled by the intake. Vacuum appears to be too high leading to the lower pressure at the fuel rail. I think the fuel pressure regulator is functioning given that when powered directly to the batter, it pegs at about 30-31 psig.

I'm fearful there is an electrical issue as you have eluded to given battery power gets pressure up to 30-31 psig, but when powered through the ignition, it's only reaching 22-24 psig while running. Voltmeter connected to the alternator registered about 13.7V. Voltmeter connected to each fuel pump power source with the ignition on registered right at 12.5V.

Welcome any thoughts on the idea of too much vacuum or the idea of an electrical issue.

[tigemech]

try hooking up 12 volts directly to your high pressure fuel pump and running it, and seeing what you get for fuel pressure. I had a carb engine, that showed 12 volts at the connector for the fuel pump, but the oil pressure switch had high continuity causing the fuel pump to not be able to draw enough amps.

[rjh171]

tigemech,

Interesting you found an issue like that. See my post up above stating seeing 12.5 volts and the connector for the fuel pump. How'd you stumble upon the oil pressure switch issue? All the other sensors on the boat appear to be working properly (voltage, rpm, oil pressure, water temp, etc). Leaning more towards an electrical issue given direct power from the battery yields the right pressure, but when powered through the ignition system, see only about 22-24 when running.

Thanks,

Joe

[tigemech]

tigemech,

Interesting you found an issue like that. See my post up above stating seeing 12.5 volts and the connector for the fuel pump. How'd you stumble upon the oil pressure switch issue? All the other sensors on the boat appear to be working properly (voltage, rpm, oil pressure, water temp, etc). Leaning more towards an electrical issue given direct power from the battery yields the right pressure, but when powered through the ignition system, see only about 22-24 when running.

Thanks,

Joe

Hey Joe, im a little on the new side to the inboard world, so i havent had much experience with the scorpion motors. Do you have an engine serial number? That boat was a tks boat, and they use a oil pressure switch to turn on the fuel pump. The switch had high continuity when the motor was running, but mercury doesnt exactly have a spec for what it should be, there spec is it should have continuity when running and no continuity when off, that was the confusing part. So i just jumped the switch and test ran. Ordered a new switch and it was good to go. Again im unfamiliar with your exact motor though. I would have to look at a service manual and see what turns on the fuel pump.

[rjh171]

Engine serial number is 0L679439. Wiring diagrams from the manual I have are provided below. General troubleshooting points to electrical items to inspect test as ignition voltage output, intermittent opens or shorts in the ECT, MAP, or TPS circuits, or check for opens on the injector driver circuits 467/468. Looks like some troubleshooting with the multimeter!

Boat Starting Charging.JPGBoat Wiring.JPG

[tigemech]

I would try swapping out that fuel pump relay

[rjh171]

Had some spare relays, swapped out with no improvement.

[rjh171]

Work on this problem is postponed until Harvey passes through the area. Will hopefully have more to report next week.

[morrislynch]

Great thread for those who are new tigeowners.