496 Mag HO Fuel pressure issue

[25Outlawboy]

This may be a long post but I wanted to give as much information and be as accurate as possible in hopes that someone could help me.

2005 Baja 25 Outlaw w/ 496 mag HO 264 scanned engine hours. Having intermittent low to no fuel pressure issue. History of boat/issue. I purchased the boat about a month ago, prev. owner said only issue he had with boat was fuel pump problems so he replaced both pumps (Gen II cool fuel), verified and looks like both pumps are silver in color (new looking). I had put about 12 hours on engine and ran flawless, after that is when issues began. Went to start engine and started and stalled two times before staying running but then ran good (crusing at about 3500 rpm) for about 30 min. or so, then felt like some pulled back the throttle, went to about 3000 rpm than back to 3500. Odd... then a few minutes later engine cut back to about 1500 or so, I pulled the throttle back to idle and let the engine idle a bit with no issues. Throttled back up and headed back home (about another 40 minutes) it stumbled a few times but never quit. Researching the topic I see I am not the only one that has had issues with these motors. Merc. CDS shows no faults/codes.

Here is what I have done so far: Checked fuel for water. Replaced fuel water sep. filter. Pulled fuel tank pickup tube to look for debris/restriction on screen (no screen, no debris). Replaced ASV as check ball had a small piece of nylon filing (from when fuel tank was built) and check ball would not return to sealing position. Checked IAC valve and tested its operation.

Here is what I found so far. Fuel line going into first pump at hose barb (boost pump, starboard side of engine) had too large a barb fitting for the hose which caused the inner nylon lining of the hose to get pushed into a ball causing a restriction in fuel line. Replaced line with larger correct style and size. Sure looked like I had found the issue right? Test ran the boat with the pressure gauge connected at fuel rail showed 38 psi consistently. Ran it 3000-4500rpm for about 15 min. and ran WOT for a few min. also ran good up until headed back home than stumbled again and came back to life. Turned and went back out again and watched the pressure gauge go to "0" several times (the engine would cut right back, not die though) then pressure would come back to 38 psi and engine would (come back to the previous set rpm) and run fine for a bit longer. Idling back in at 1000 rpm, the pressure would go to 8 psi every now and then and the engine would almost stall (650 rpm) , but never quit.
Back at dock, isolated both fuel pumps by electrically disconnecting them and making sure relay would power them up. No relay issue. The boost pump (starboard side) seems nice and quiet when key is first turned on and running and produces 8 psi alone when the high pressure pump is electrically disconnected. The other pump (high pressure pump located on the port side in the cool fuel box) is very loud when running and producing 38 psi.

Is the high pressure pump normally much louder than the boost pump?
Remember both pumps had been replaced (per the previous owner), could that restriction I found in the hose have caused the high pressure pump to run hot (after the several hours I put on the boat) and weakened the pump?

I have ordered a new high pressure pump and hope to have it early next week but was hoping anybody seeing this post could shed some light and point me in the right direction. Without either pump or any other part just failing all together it's tough to know where the full issue really lies.

Any help would be greatly appreciated. Thank you

 

[Scott Danforth]

welcome aboard

post your engine serial number

38 psi is about 5-7 psi low.

 

[alldodge]

Is the high pressure pump normally much louder than the boost pump?

No, its should not be making loud noise. The pump either has a problem or there is an air leak or restriction feeding the pump.

If the low pressure pump is staying at 8 psi when the high pump goes low, then the feed components are good. If the low pressure also go low then could be a bad gas cap vent or other restriction

 

[25Outlawboy]

Thank you Scott Danforth
Engine serial number is 0W030271

 

[25Outlawboy]

Thank you AllDodge, Yes the High Pressure Pump is much louder than the Boost Pump. Fuel tank venting seems good and feed lines are good. As was stated by an earlier post from Scott Danforth and I agree with, the 38 psi is lower than the spec'd 43 psi I have seen in other test publications.

 

[Bt Doctur]

May have your answer from a simiiar problem boat . Run a test with a remote outboard tank first . Confirm there is no change in fuel pressure and post the results. Assuming you have changed/replaced/removed for testing the anti-syphon valve

 

[25Outlawboy]

Hi Bt Doctur. I do not have an outboard tank readily available but I did think along the same lines as your suggestion.(to confirm there was no issue with anything before the boost pump inlet), so I did
1. check the fuel quality
2. pull the pick up tube assy and look for any blockage
3. replace the ASV
4. replace a collapsed/restricted fuel line
5. replaced fuel/water separator filter

Is there another reason your thinking to use the remote outboard tank?

 

[Bt Doctur]

I did all those same things on this customers boat. When you pulled the pickup did you unscrew it from the 90 deg fitting .
I found a SS fine mesh screen that was plugging up with debris only when running at high speed/fuel flow. Once the motor stalled from lack of fuel the debris dropped down and all was normal until you tried a sustained high speed run.When testing with a gauge mounted at the carb fuel pressure would go from 6 psi to 1 psi during a sustained run. but on a remote tank it maintained the 6 psi no matter how long we ran it. Hooked back up to the main tank it would die in a sustained high speed run.
A quick test is to remove the A/F and try to slip a thin, flexible, wire, into the 90 fitting to see how far you can push it in.If no obstruction present it should go to the bottom of the tank. If it wont, remove the pickup and go from the bottom of the tube , Guessing you`ll find a 3 - 4 inch deiierence
Remove the inlet tube, unscrew the tube from the fitting and most likely you will find a fine mesh filter

 

[Bt Doctur]

heres where I found mine
click to enlarge

 

[QBhoy]

Does this engine also perhaps suffer from the cool fuel internal paint flaking issue ? Then it blocks the fuel system at the internals and regulator ?

 

[muc]

A couple of service bulletins that will help with troubleshooting and ordering the right parts.
MCM Bulletin No. 2004-01
MCM Bulletin No. 2004-05R1
Is it possible that the thermal transfer compound wasn’t used on the high pressure pump?
Recommend that you inspect and replace the filter that is under the fuel pressure regulator when you have this apart.

 

[alldodge]

Bul's found on line

View attachment Bul 2004-01 Fuel pump.pdf

View attachment Bul 2004-05R1 Fuel pump.pdf

 

[25Outlawboy]

Bt Doctur. Thanks for the additional information on the fuel pickup potential issue. Now you got me rethinking about the pickup and if I looked all the way up into the tube towards the 90 degree fitting. I thought I did but I'll do a double check today. I'll post my update once confirmed.

 

[25Outlawboy]

Does this engine also perhaps suffer from the cool fuel internal paint flaking issue ? Then it blocks the fuel system at the internals and regulator ?

Not sure about the flaking issue, I had heard about this problem but wasn't sure if it's contributing to my problem. I will have to check this in more depth. I did get a new HP pump and will be installing it tomorrow sometime, I will also check the regulator and internals. Thank you

 

[25Outlawboy]

A couple of service bulletins that will help with troubleshooting and ordering the right parts.
MCM Bulletin No. 2004-01
MCM Bulletin No. 2004-05R1
Is it possible that the thermal transfer compound wasn’t used on the high pressure pump?
Recommend that you inspect and replace the filter that is under the fuel pressure regulator when you have this apart.

Thank you for the information Muc. I will check and post any findings. What is the "thermal transfer compound" you mentioned?

 

[25Outlawboy]

Bul's found on line

Thank you AllDodge... That was my next question "Help locating those two Bulletins" You read my mind. Much appreciated.

 

[muc]

Thank you for the information Muc. I will check and post any findings. What is the "thermal transfer compound" you mentioned?

It’s use is explained in the service manual. The high pressure pump needs to be cooled, this paste allows that to happen.
It comes with the kits the S.B. listed, not sure if it’s included when you buy just the pump.
It’s white in color and makes a mess if you try to replace the pump while the cool fuel 2 is still on the engine.

Might be a good idea to read the manual before attempting the pump replacement, there is a bit more to this job than just the pump.

 

[25Outlawboy]

Bul's found on line

Thanks for this info AllDodge

 

[25Outlawboy]

I did all those same things on this customers boat. When you pulled the pickup did you unscrew it from the 90 deg fitting .
I found a SS fine mesh screen that was plugging up with debris only when running at high speed/fuel flow. Once the motor stalled from lack of fuel the debris dropped down and all was normal until you tried a sustained high speed run.When testing with a gauge mounted at the carb fuel pressure would go from 6 psi to 1 psi during a sustained run. but on a remote tank it maintained the 6 psi no matter how long we ran it. Hooked back up to the main tank it would die in a sustained high speed run.
A quick test is to remove the A/F and try to slip a thin, flexible, wire, into the 90 fitting to see how far you can push it in.If no obstruction present it should go to the bottom of the tank. If it wont, remove the pickup and go from the bottom of the tube , Guessing you`ll find a 3 - 4 inch deiierence
Remove the inlet tube, unscrew the tube from the fitting and most likely you will find a fine mesh filter

Took off pickup tube again to look for a screen and/or blockage. No screen and no blockage.

 

[Bt Doctur]

you cant physically see it unless you unscrew the tube from the fitting.
when you probed the tank end with a wire did it go all the way to the 90 fitting, Eg: 11 inch tube, 11 inches of wire