Engine putters out once up to temp

In need of some serious help!

My port engine (2021 repowered 6.2L Mercruiser MPI with ~75hrs):
-Starts fine when cold
-Maybe runs a little rough when in gear (not so much when running in neutral)
-Sputters to a stop once it reaches operating temp (160F-ish?) after running for 6-10min
-I can restart the engine but the time interval that it stays running gets shorter 2-3min

The engine has shut down on me at idle speeds, while up on plane, and in neutral while at the dock testing. One of these times the 50A breaker right behind the spark arrestor tripped but that's been the only "symptom" I've found so far.

So far I've: (1) replaced the starter slave solenoid (I was having intermittent starting issues for a long time prior to this issue), (2) checked all battery voltages - all good, (3) replaced the 50A breaker that tripped, (4) swapped the alternator from my other engine - made no difference.

I read of a somewhat similar situation on another forum and it turned out to be the ignition coil in that case. I may look there next.

Where else should I look?

I have a video of the engine sputtering to a stop that I will try to post a link to if I can figure out how to do that. The one thing I will say is notable is it continues to rotate and slowly soon down to a stop vs. the more abrupt stop you get when you turn the ignition switch off.

Welp, the saga continues....

I swapped the ignition coil + distributor cap + rotor from the good engine and get the same result.

I noticed that as the engine started to die giving it more throttle did nothing to bring the RPMs up. Maybe it's a fuel issue?

Does anyone know what type of gauge I need to read the fuel pressure at the rail and how to hook it up?

There is a lot of talk on this forum and others about the cool fuel module causing vapor lock issues. A couple posts claim there was a blockage in the cooling lines for the cool fuel module. Maybe I should look there next?

Thoughts?

You can borrow a fuel gauge kit from Autozone. Have you run it with the gas cap off?

scoflaw said:

You can borrow a fuel gauge kit from Autozone. Have you run it with the gas cap off?

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Ok, I will give this a try. Are the fuel gauge kits universal or do I need specific information to get the right one?

I'll try running with the gas cap off as well to see if that does anything.

Will report back with findings.

Thanks!

The parts in the kit will work for your app.

scoflaw said:

The parts in the kit will work for your app.

Click to expand...

UPDATE;
Fuel rail pressure rides between 35-40psi until the engine reaches temp (6-8min). Then the needle abruptly drops to about 30psi and it bleeds all the way down to about 5psi over 5 seconds until the engine cuts out. Thoughts?

Additional questions:
(1) Is the proper pressure range for normal operation?
(2) Based on feedback from FB I suspect this could be vapor lock due to insufficient cooling at the cool fuel module. If that's true I guess I will check the water flow at the cool fuel module. Not sure exactly how to go about this or where to look. Any suggestions?
(3) Another theory says there's a secondary oil pressure sensor that if faulty could shut off the fuel pump. Anyone know anything about this or how I would test this theory other than locating and swapping the sensor?

Thanks for the fuel pressure gauge tip!

Use the fuel tester release button to see if there's air or fuel coming out of the rail. Sure flush that cooler out and the lines. Your going to have to get creative to see if the pump is shutting down.

scoflaw said:

Use the fuel tester release button to see if there's air or fuel coming out of the rail. Sure flush that cooler out and the lines. Your going to have to get creative to see if the pump is shutting down.

Click to expand...

Thanks again for the reply here! I think I can confidently rule out the vapor lock theory at this point due to two factors: (1) Engine cuts out at high RPMs while up on plane (this has happened to me twice) and I'm told when the fuel is moving that fast it wouldn't have time to "boil", (2) I can restart the engine immediately and I'm told with vapor lock it would take 15-20min before restarting would be possible.

The new prevailing theory is either I've got bad fuel pump(s) or a bad fuel regulator. I've attached pictures of what these look like on my specific engine.

Any thoughts on how to test these parts before shelling out cash for brand new?

Your going to have to see if the pump is losing power. Relays are cheap, I'd put a new one on to start.

scoflaw said:

Your going to have to see if the pump is losing power. Relays are cheap, I'd put a new one on to start.

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UPDATE:
-Opened gas cap (in case suction was an issue)
-Replaced fuel pump relay
***No Change***

Additional Tests:
-After the fuel pressure bleeds down and the engine dies...when I attempt to restart the engine immediately the fuel pump(s) doesn't kick on when I engage the ignition. After about a 2-3min wait, when I engage the ignition switch the pump does kick on like usual....however the engine runs for a very short period (<30sec) after starting. If I wait longer between starts the engine will run longer (3-5min).
-I spoke to a local mechanic who told me the high pitch squeal that can be heard when the engine is struggling is the fuel pump(s). He also said that a fuel regulator is more likely to fail closed causing the fuel pressure to increase (rather than decrease if it were to fail open).
-Based on the mechanics advice I went hunting for the squeal....I "think" it's primarily coming from fuel pump on the upper starboard side of the engine (pictured). However when I unplug that fuel pump and start the engine there is still a squeal. When I unplug the other high pressure fuel pump the engine runs for less than 5 sec and there is also a (louder) squeal coming from the pump circled in the picture that's still plugged in.
-I've also learned that a squealing fuel pump is indicative of a starving fuel pump so here's my theory:

******
I believe the low pressure fuel pump is failing because there is a faint squeal all the time from that area and it gets louder as the engine stops (but I can't pinpoint that it's definitely coming from that pump). I believe the pump slowly heats up as it runs until the pump motor overheats causing a temporary open circuit. Engine starves and shuts down slowly.

I don't believe the high pressure pump is the culprit because when I unplug it and start the engine the engine shuts off faster than the normal failure. I also don't think that pump squealing while the other pump is unplugged tells me anything because it's downstream from the low pressure pump and therefore it's getting starved of fuel which causes it to squeal.
*******

There you have it. Let me know if I've made any glaring errors. I'm off to buy a low pressure fuel pump - and will be checking the upstream fuel line for potential restrictions. Thanks!

That's a cf2 , mine doesn't have a low pressure pump. Single pump.
Post up a pick of this lp pump

No lp pump in those pics

I think they're calling the fuel pump a boost pump, the out of focus pc. in the box looks like a secondary filter

This is a good pump for short money.
airtex e11004

scoflaw said:

This is a good pump for short money.
airtex e11004

Click to expand...

My understanding is that this is the "boost" / low pressure pump. It's first in line from the fuel tank and is mounted on the top starboard side of the engine.

sparkhill said:

My understanding is that this is the "boost" / low pressure pump. It's first in line from the fuel tank and is mounted on the top starboard side of the engine.

Click to expand...

My understanding is this is the high pressure pump. It resides inside the CF2 housing mounted on the bottom port side of the engine.

bingo

scoflaw said:

bingo

Click to expand...

Good news! I think the low pressure/boost pump replacement solved it! But... I say "think" because I've only tested it in neutral....but it ran good at various RPMs for 30min+. A sea trial under load will be the true test.

I will report back with the final/final. Thank you for helping me with this!

Just to confirm…. The air Tex e11004 is the direct replacement for the 5.7 tbi cf2 application?

I may a fuel pump going bad on one of the engines…

Thany you.