MP 340 hp - Apparent Fuel System Issue

[Jason AZ]

Hi all. Many thanks for the questions. I'll see if I can spell out where things stand for me:
- the boat in question is a 2007 22Ve with about 120 hours.
- maintenance has been religiously followed and impeller has been changed every year or two at most
- we bought the boat when new and have noticed with increasing frequency that when the boat is parked with the engine off for approx 30 minutes or so when it restarts there is a clear stumble feel and usually takes a couple minutes to sort itself out and run smoothly
- as of late we are now running into more basic idle problems in that the boat will only idle for about two minutes or so before it needs about 15 minutes of soaking before it will restart. Once the boat is running it will run great. It is simply that once it returns to idle that the problems return.
- based on the above I am guessing not the HP pump going and have spoken with tech support at marine power. They gave me some basic suggestions to look into but nothing that seems to be the root cause
- since old dude's post seems to line up completely with my issues I was hoping he might share details

If anyone else has suggestions I would greatly appreciate them. Thank you very much for your time.

Jason

[chpthril]

Sure sounds like vapor lock. This occurs when the fuel pressure drops off, lowering the boiling point, and fuel turns to vapor in the fuel rail. Goes away once cooler liquid fuel begins to circulate, forcing out the vaporized fuel or cooling it back down to the point it condenses again into liquid.

[Jason AZ]

Thanks for the note and we're definitely thinking along the same lines. Really would like to better understand the root cause and how to fix. Had hoped old dude could shed light on what worked for him, but looks like he has not been around the site for some time. Bummer.

[talltex360]

I have a 08 RZ4 340 MP. The boat runs great but when I go get it and try to start it , it takes a while on the starter to make it start. It seems like its not getting fuel or building up fuel pressure on a cold start. Its fine after the first start. This is my first inboard so I was wondering if this was normal? If it sits for a couple weeks , it takes a while to get it started. In the spring I have to make sure the batts are strong because it takes a long time to start. Is this the fuel pump? Is there a low and high pressure pump? Is this something I could change myself? I do the winterizing and have changed the fuel filter several times , so basic stuff doesn't scare me. Just wondering what you Sage's think about it. Thanks in advance for any info.

[dj2]

Borrow a fuel pressure tester you can hook to the fuel rail from the parts store. Check your fuel pressure when you turn the key on and then while cranking. Should point in the right direction if your problem is consistent and only at first startup.

[dakota4ce]

Don't some people squirt water from a squirt bottle down on the cooling coil looping around the fuel pump to cool the whole area down and reverse the vapor lock? I swear I read that somewhere. Or dreamed it?


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[UNSTUCK]

In a true vapor lock situation doing anything to cool the fuel rails will resolve the problem faster. So squirting them with a water gun/bottle, putting a bag of ice in top of the engine, etc will do the trick.

To help avoid the situation do not do a quick shut down after a hard, long load. Let the engine idle for 2-3 minutes to cool down.

[rhoadsdj]

My issues last year appeared to be a result of a bad tank of gas. Upon the next fill up, the problem went away entirely. During the issue, I would just leave the engine compartment cover up for about 10 min and it would be all good.

[Brianrzr]

If a engine just cranks and will not start, a Good rule of thumb to determine if it's a fuel delivery problem or spark, is to squirt some starting fluid into the intake. If it pops off and runs however poorly for a few seconds, it's fuel system. If it still just cranks, it's the ignition system.

[UNSTUCK]

FYI, NEVER squirt either into an engine when it's not cranking, unless you like to replace piston rings. Also, I'm not a fan of using either in spark ignition engines anyways due to predetonation. There are other easy ways to check for spark or fuel.

[JCP]

Could you explain how that would hurt the rings?

[dj2]

2 ways...
First, ether washes oil off the cylinder walls which is bad for your rings and cylinders.
Second, ether is much more volatile than gasoline and the impending detonation can break rings or ring lands... worst I have seen is a bent rod.

You may be fine, but when I weigh risk/reward there are better ways to check spark and fuel.

[JCP]

I have used and seen it used many of times with no issues. I guess proper use would be the key. A quick 1 second spray is all that is needed with the throttle slightly open. It is best to have an assistant crank the engine before and during the short spray but some times not possible. The only way you are going to wash down the rings would be by spraying way too much fluid.

[UNSTUCK]

I have used and seen it used many of times with no issues. I guess proper use would be the key. A quick 1 second spray is all that is needed with the throttle slightly open. It is best to have an assistant crank the engine before and during the short spray but some times not possible. The only way you are going to wash down the rings would be by spraying way too much fluid.

This is the correct procedure. For whatever reason, my equipment operators have a hard time figuring that out, and have cost us too many motors. It's too easy to put too much in and hydrolock a cylinder, among other issues noted above.

If you want to know if you have fuel, check fuel pressure. If you want to know if you have spark, look for a spark. Both very easy to do, and don't require storing a can of either on the boat.