2011 Mercury 300XS runs rough

[mthaler]

I have a 2011 300xs that seems to have a misfire, It started when i was running WOT and acted like I was out of fuel (gauge showed 1/4 tank ) I put fuel in started the motor and it was misfiring. Changed plugs, and fuel filters. I found at this time there was still fuel in the tank that i thought was empty. It seems the problem was not from running out of fuel. checked spark and compression ( had coils replaced 2-3 months ago ). No codes or faults on Smartcraft gauges. Im told could be air compressor failure. Engine has 75 hrs.
What are the symptoms of a failed air compressor? by the way it seems to be running rich. old plugs were black and cyl#2 was wet. lots of smoke when idling. pulled the electrical connector off of the #2 injector and made no change in the running. Engine will hardly idle and will stall. 22' Stoker 2007 MOD VP

[mthaler]

checked compressor and fuel pressure. Air compressor checked on Port side fuel rail shrader valve and is putting out 40 PSI as I understand it should be 80-90 PSI. Fuel I checked on Starboard side fuel rail reading 70 PSI but wondering if misfire and lack of RPM has anything to do with low readings.

[life is good]

Could be a an issue with the tracker valve if you have those readings on fuel and air pressure. I would ask Don over at bbcboards.com I seems very knowledgeable about these opti motors and he is very willing to help. I have had a compressor failure on a 250 xs and the motor would hardly run in my case

[davemvegas]

try a different gauge. air and fuel should both be about 100 psi. the tracker valve is what keeps the pressure within 10 to 15 psi of each other. I would think you should be able to cycle the key from off to on a few times. without starting motor and get about 95psi of fuel pressure if pump is good and filter is not clogged. I have cranked my motor over with coil harness unplugged and seen 95psi on the air side in about 4 revolutions.

[mthaler]

all coils replaced 2-3 months ago under warranty.

[TUNNEL T]

Just from experience , the tracker valve will also produce a hard start and will smoke a bit at start up, it's been a while so I could also be forgetting something but that's what comes to mind..... TUNNEL T

[Kcraft]

Very similar problems I am having with mine... Changed the rails and air injectors and tried a different DBR ecu... Same thing, starts for a second smokes like Willy Nelson and shuts her self down... Will not take any throttle too help keep her run... Another weekend without my boat sucks

[merctech5591]

If the motor will only build 30/40 psi of fuel on the top of the strb fuel rail I would first look at the vst grommet on top of the high pressure pump.. I have seen many split due to the corn

[Wayne Cammidge]

The fuel pressure is regulated by the air pressure plus a 10-15 PSI spring.
That is how the engine maintains the pressure difference.
The tracker valve is basically like a shock absorber to help smooth out the differences between the 2.
When the engine is running you should have a constant difference between the 2 rails and on the 300xs I think it is 95PSI air and 110 PSI fuel.
If you do not have that, there is a problem and you need to work out what it is.
Check fuel delivery, by free flowing fuel out the test valve, you should have a nice strong constant stream.
Then check that the fuel pump will deliver enough pressure by blocking the return pipe to the vapour separator, by pinching that pipe with a pair of pliers, pressure on the fuel should jump to 150PSI or beyond. If those work then the high pressure side of the fuel is okay.
Move onto the low pressure, or start here. There is a test shraeder value on the VST this is for the low pressure side. Again free flow it and then see what the pressure is like.
Should be about 25-30PSI.
Then move onto the air side, with the engine running try to bleed some air out the test port. Make sure that it is dry. If you have fuel in the air then either of fuel pressure regulator or tracker valves have a tear in them or one or more of the Direct injectors has stuck open. If Dry carry on.
Find the dump pipe for the air rail and block it with a pair of pliers, pressure should jump up significantly.
All of these tests should be done with the engine idling.
Depending where you find the problem will determine what you have to look at further.

This is all assuming that when you did a cylinder drop test, you did not find an issue, like faulty coil, coil wire, spark plug, or either of the injectors relating to a specific cylinder

[merctech5591]

Personally I would not pinch off the return line back to the vst.. The upper grommet will not hold the pressure and will for sure split.. When u crank the motor and try to start what are the fuel and air readings? Disconnect the crank sensor and just crank the motor and read max air/fuel.

[Wayne Cammidge]

Please don't believe me.
This is out the manual.

[Kcraft]

Wayne where can I get my hands on one of those service manuals/disks for the 300xs ? I still do not have my problem solved

Please don't believe me.
This is out the manual.

[Euroski]

Manual, call Mercury and give them your engine number. Ask the one for engine electrical and EFI diagnosis

[Big Steve 435]

Lots of good advice !

After running a dozen 300xs we have had a couple issues along the way.
1. Coil and plug
2. TPS switch
3. Tracker valve

We keep a replacements in our boats tool boxes

We use the Mercury engine tune cleaner and spray it down the air pump intake

Found a air pump pressure x-over hose had worn a pin hole in the line.
and bleeding off air pressure at low rpm and real rough running.

You must have fuel and air pressure !
Tracker valves have problems on early motors and the replacement valve is a different color. Cheep part or real expensive fix later FWIW