Fuel pump needing replaced?

[rjh171]

I have an '02 23v with a Mercruiser 350 Black Scorpion that is experiencing power issues when under load. Engine starts and idles without any problem. Problems occur when trying to pull up a rider. I suspect it is a fuel pump, but I am trying to narrow down and consider any other troubleshooting to perform. Fuel filters have been replaced and gas is fresh. While on the trailer, placed a pressure gauge on the fuel rail, and I'm seeing about 22 psig. Manual says it should be 30 psig. Also, while on the trailer, placed a code reader on the data link, and it is not indicating any error codes. Is it likely the low pressure pump or the high pressure pump.

Other information: Spark plugs, wires, distributor cap have all been replaced. Battery is new. I am in the process of cleaning the IAC, throttle body, and flame arrestor as they are somewhat gunked up, but I don't suspect this as the issue given the engine does not run rough at idle.

Any other suggestions?

Thanks,

Joe

[Brosef]

if pressure is low, sounds like it could be the pump. it could also be vapor lock if the fuel lines are getting heat soaked from idling after hammering it. happens from time to time on my boat (although different motor).

[TeamAllen]

I wouldn't think it would idle or run at all at vapor lock. You have done all the usual things to check.
I think there is an Airtex replacement for it if needed. https://www.amazon.com/Airtex-E11004.../dp/B0076D5NVK

[bsreid]

We had a little screen in our fuel line that was clogged, causing the boat to shutdown when under higher loads. I'd definitely take a look for it.

[rjh171]

Thank you all for the feedback. A few other symptoms. After pushing down on the throttle, boat comes up on plane, but then starts to bog down, sputters a bit, might backfire (can be hit or miss). If I pull back on the throttle, it usually saves the engine from stalling completely, but sometimes it will shutoff completely. Turn key off for a second, and engine restarts without any issue. Go to push back down on the throttle, and the symptoms repeat.

I don't suspect vapor lock is the issue. I have not experienced any problems restarting the engine whether I turn it off or if it dies. Water appears to be circulating well through system. I've cracked open the drain plug on the fuel cooler, and clean water is running out from the drain. I'm not seeing any screens on the Merc manual schematics for either of the fuel pumps, but that doesn't mean they are not there. Guess I'll have to bite the bullet and pull the pumps. Not looking forward to this job especially for the high pressure pump with motor mount and the exhaust in the way of the pump! Is there a means to test the fuel pressure regulator?

[rjh171]

Spent the afternoon taking out both fuel pumps. Started with the high pressure pump, and did come across a small screen between the cool fuel assembly and the fuel pressure regulator. There was a minor amount of debris, but nothing that should have caused a lot of pressure drop. Moved to the low pressure pump, and once both pumps were out, put both on a power source and found what should be the culprit as a locked up low pressure pump. The high pressure pump hummed right a long. I could not find the rated pressure output of the low pressure pump, but have seen a few mentions around 7 psig which would explain the 22 psig at the rail when it is suppose to be operating at 30 psig at the rail. I would have thought with a dead low pressure pump, the engine likely would not have started at all. I guess with enough of a pull from the high pressure pump, it would operate fine at idle but could not pull enough fuel under load. Does this make sense? Just looking to validate before purchasing the low pressure pump and reinstalling everything.

Thanks,

Joe

[Bud Wieser]

I just went through a similar issue. My boat would stall if I throttled over 2500 RPM, but would catch and not die if I backed it off. Replaced the water fuel separator filter found next to the low pressure fuel pump. I added some Sea Foam thinking it may be bad gas. Rented a fuel gage from Autozone and took it back on the water. The fuel gage was missing the insert that pushed on the Schrader valve, so that didn't work. Ran the boat for awhile and it finally stalled and I got a tow back to the dock from an old 70s boat. My 2003 Tige 6.2L Merc. boat would not start at this point.

Here are some tips from reading hours of online stuff and spending hours with my boat:

The low fuel pressure pump located next to the water fuel separator runs on 12 volts DC and should run for a few seconds when the key is turned on. If you don't hear it then it could be dead or gummed up. If gummed up there are videos on how to fix this. The pressure should be around 9-10 PSI. One test I did was removing the exit line and using a 2 liter bottle put the end of the pump into the bottle to see if gas shoots out when turned on. I had zero gas come out but it did click slightly. I replaced the pump and gas was flowing well at this point, but the boat still wouldn't start. From the dealer this part cost me $320 with tax. You can buy on-line starting around $72.

I then moved on to the cool fuel unit and the high pressure fuel pump (should also run when key turned one click). From my understanding the pressure here should be 43 PSI for my motor, but there is also a 30 PSI such as yours. The fuel regulator on the cool fuel unit is located near the top and a return line flows back to the low pressure pump. You can't do the remove and turn on the pump to see if gas will flow as the high pressure side has a pressure fitting. It will only let gas through when the nipple is depressed. To test if the pump is working you'll need a fuel pressure gage attached to the Schrader valve near the injector rail on the top of the motor. If the pressure is zero you can pinch the fuel return line coming out of the fuel regulator. This in effect should raise the fuel pressure at the Schrader valve. Careful there is a upper limit you don't want to surpass, so if you don't have a gage you don't want to pinch this very long. If you have good pressure you probably have a good pump, and your fuel regulator is bad. The dealer wants $150 for the regulator and I bought the high pressure pump for $120 from an on-line vendor.

I replaced both the low and high pressure pumps, water separator (O'Reilly - $18), and in line OEM fuel filter ($70) going to low pressure pump. My boat will start and rev normally in my backyard. Hoping all will go well under load when I take it to the lake.

One other tip: if your boat isn't starting, you can poor gas down the air intake. If it runs, then it's probably not an ignition issue. Careful though, I always put the flame arrester back on before starting.

[rjh171]

Bud Wieser,

Thank you for the tips on troubleshooting. I have been soaking the pump in fuel and fuel treatment since yesterday. Will try to test pump on Thursday when I get back home. Hopefully it works, but if not, certainly have validated the problem.

No issues starting the engine, but will keep your list of troubleshooting items handy in the event it is needed.

Thanks,

Joe

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[rjh171]

Replaced the low pressure pump this weekend, but didn't get a chance to get the boat out on the water. Pressure at the fuel rail is showing 24 psig. Any thoughts as to why the pressure is not at 30 psig? Would the possibility of some air in the system result in a lower pressure. Won't be able to get the boat out until this weekend due to the 3rd consecutive week of business travel.....

The engine as a while sounds to be running smoother with the pump replaced. Just trying to troubleshoot in advance. High pressure pump going bad? Bad fuel regulator? Any other ideas?

Thanks,

Joe

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[UNSTUCK]

You can have low pressure for a few different reasons. Like what was said before, pinch off the return line just long enough to see fuel pressure start to rise. If it gets over 30, then you know the pump is good. If it doesn't, make sure your alternator is putting out good voltage (at least 12.5v but should be 14ish). If that's good I'd go after the regulator. If there is any air in the system it wont be there for long so it shouldn't be an issue. Just for fun though, shut the engine off and look for fuel leaks right after doing so. It could be that it is sucking air, but once the engine is shut down it would start leaking fuel at that point, at least until pressure drops.

[rjh171]

Thank for the feedback.* I tried pinching the line yesterday, but I was short an extra set of hands, so I couldn't get a good look at the pressure gauge.* I did work on bleeding air out of the system prior to starting the engine after replacing the fuel pump.* I was able to get the pressure up from 10 psig to about 24 psig by cycling the key thus engaging the pump and pushing the bleed valve on the pressure gauge.* After 3 or 4 cycles, the air appeared to be gone.* I did this also to look for leaks prior to reinstalling the exhaust given the ease of access of getting to the high pressure pump (note sarcasm).* Pressure dropped from around 24 psig to 20 psig.* There may be a slight leak somewhere, but I was not able to observe any leaks yesterday when testing, so I went forward with reassembling the exhaust for startup.

*

I'll try pinching the return line again with somebody to help.* The location of the return line is a bit difficult to access!* I'll through a voltmeter on the alternator as well.* Low voltage would certainly yield a lower pressure on an electric pump.

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[rjh171]

Finally was able to check the alternator output and fuel pressure return line.

Alternator output was around 13.7V at idle. Likely didn't have the greatest ground connection, but I don't believe the alternator to be the culprit.

Pinched the fuel return line and saw no change in pressure.

Engine appeared to be bit heavier on exhaust than normal. Guessing it is running rich on a failed fuel pressure regulator? Tested high pressure pump for operation prior to reinstalling, and functionality appeared to be correct.

So now on to replacing the fuel pressure regulator. Hoping this solves the issue as I am running out of ideas!

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[rjh171]

Changed the fuel pressure regulator and high pressure pump, and still only getting 22-24 psi. Checked voltage to each pump, and getting 12.5V at the pump power connection. Can disconnect the high pressure pump, and engine slowly comes to a stall and dies. Can disconnect the low pressure pump, and engine keeps running.

Still no codes thrown by the computer. Any other thoughts?

Not sure if I have a bad gauge, or if there is some other issue. Weather has not been cooperative to get out on the water, but will finally get out this weekend to test if the issue is resolved.

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[dj2]

If you can disconnect the low pressure pump and there is no change, then I think you may have found your problem. I am working backwards for the issue I am currently fixing but it looks like the low pressure pump went out which eventually caused the high pressure pump to fail. I was doing the same thing you had to do, letting pressure off the rail and cycling the key for a few trips before my high pressure pump went out. This also sent tiny pieces of brass from the high pressure pump bushing into the fuel rail and injectors. I am now replacing both pumps and having all 8 injectors rebuilt.

[rjh171]

Maybe I need to check the fuel rails for plugging. Low pressure pump was replaced earlier and functioning well. The old low pressure pump was seized up. Replaced the high pressure pump and fuel pressure regulator thinking they were both failing in line with what you described.

I'll check the low pressure again with direct power from the battery and see what pressure is generated. If that checks out, I guess my next step is to tear in to the fuel lines from the high pressure pump to the fuel rails.

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