2015 250 Pro XS no idle

[KGood]

Serial: 2B117805
2015 Mercury Pro XS 250HP TM2

Problem: The motor will crank and start but then quickly die.

Background: Ran the boat all over the lake the day before with no issues, start and idle were perfect with no misses or hesitation.
The next morning I went out and boat ran great just like it always does and about mid-day. I was heading to a spot and when I came down off plane to an idle it very sharply died, almost immediate when boat got off plane with boat still in gear. I tried to start it and it would start quickly like normal, but then die immediately - this is the first time ANYTHING seemed wrong, so the problem occurred so quickly. I fished that spot for a while and then when time to go it would start and then die again. So I gave it a little gas and I could get it to start and stay running at higher RPMS, but when I left off the gas to idle it died again. So I had to crank with giving it gas and then quickly slam into gear to get it to go. Once it was running past idle it ran totally normal. It felt a little bogged down during launch, but then mid and top end were completely fine turning over 5500 RPMS running 70mph down the lake. I had to start it and throw it into gear about 3 more times throughout the day. Every time it would run totally normal if I could get it past idle.

Troubleshooting: I thought it sounded like it was not getting correct fuel/air ratio only at idle so maybe it was the one of the tracker, air, or fuel diaphragm valves. I took all three out and inspected them. the tracker valve looked ok, with a pin hole sized hole (took me a minute to see) only on one side. I have had a tracker give me issues in the past but the boat actually idled, just at rough idle. and the tracker valve was torn much worse then.. so i didnt think it was the tracker valve. the fuel diaphragm looked great with no rips or holes at all. The air diagram valve looked to be in bad shape with rips and tears i could see, plus I could see a oily mixture on the outside of the valve. I bought the $300 diaphragm from a local shop and installed (Yes I bought the the tool to compress the spring after failing to compress the spring with just longer screws). I put old diapragms back in tracker and fuel since they looked ok. put everything back together and tried to start motor and it would quickly fire and then rough VERY rough for 1-2 seconds and then die... so no change.

I have the little square smart craft, i guess its the SC1000. I have not gotten no beeps or anything during this whole time. and when I start the boat it gives the single beep when you turn the key to signal everything is normal.

I do the annual service as recommended on this form, however in January I had a dealer do this for me... so my next step is the check spark plugs to ensure the correct spark plugs were used (IZFR6J) by dealer and that the gapping is correct at 0.043.

I run "Dons Cocktail" in just about every fill up and consciously try to conduct proper warm up and shut down procedures before and after each crank.

I have called around to dealers for service and they are all several weeks out, bad time of year with everyone getting their boat serviced.

Have you seen a similar problem in the past? what was root cause?

[EuropeanAM]

Of there are ANY tears, splits, or pin-holes in the diaphragm (whether or not they appear to go all the way through) it MUST, MUST, MUST be replaced.

At 108-110 psi I can assure you, fuel WILL find it's way through.

Replace that tracker valve, and then verify Air/Fuel Pressures on highly-accurate dual-pressure (glycerin-dampened) gauge set. Record results:

-At idle

-Under Acceleration

-5/10/15 seconds after shutdown (repeat for each time period).

[KGood]

Thanks for the reply Don!

Is there a thread on how to correctly verify air/fuel pressures?
do you have a link to purchase the correct gauge for this?

[KGood]

Replaced tracker valve and it did not fix the issue.

currently working to purchase an air/fuel pressure gauge to get the data you requested.

However, I dont think I will be able to get pressures at idle, because it wont idle - ill try to get a reading before it dies i guess?

[JOE54]

just fire it and watch gages look for rapid fall in either fuel or air psi

[KGood]

Ok. I am in the process of ordering a dual pressure gauge, but in the meantime I used a single fuel gauge I had in the garage. and here are the results:

Fuel Pressure: form the top of the starboard side rail.
At idle: 45
acceleration: 50 (would not stay running)
5 seconds after shut down: 21
10 seconds: 18
15 seconds: 18 (and would hold 18 for some time)

Air Pressures: from the middle of the port side rail
at idle: 36
acceleration: 40 (would not stay running)
5 seconds after shutdown: 11
10 seconds: 6
15 seconds: 0

While doing all of this I noticed a large amount of liquid in the lower cowl... It gas.
I had my wife turn the key and immediately saw gas spraying form the fuel regulator diaphragm on port side rail. I did not install correctly and pinched one side of the diaphragm.

so I will be going back to purchase another $300 valve. ugh!
hopefully this is my problem but will update after I replace.

What SHOULD fuel and air pressures be at those times (idle, acc, 5, 10, 15 sec)?

[JOE54]

my gage connections have slow leak but at 5 sec fuel psi is still above 90

[KGood]

Does this mean I need to replace high pressure fuel pump or low pressure?
how can I test the fuel pumps?

[EuropeanAM]

No... you need to start by locating and correcting the LEAKS.

Start with the leak you could visibly see.

Retest pressures with CORRECT tool (your readings are literally a mile off from where they should be).

[KGood]

Ok, I will get the correct dual air/fuel pressure gauge and re -test and send results.
When screwing on the fuel testing fitting, I noticed that the Schrader value was spinning freely, so it was difficult to get the fitting on tight enough to prevent leaking from the valve during test.
is it normal for the Schrader to valve spin like that? I noticed the air valve didnt do that.

[EuropeanAM]

No, that is not normal. They are usually quite snug in the bore of the rail.

[KGood]

Took it to a shop yesterday. Ended up being the reed plate. Replaced and idling fine now. $400 to replace and Im back running.
thanks for everyone's help and hope this thread will help someone else in the future.

[EuropeanAM]