150 Optimax no start

[3-Liter]

Mercury 150 hp Optimax 2010 year, serial 1B809033. Started this morning but died everytime I put it in gear. Acted like out of gas, but had 1/2 tank. Switched to other tank, started and ran fine all day. Tried to start to put on trailer, cranks but no start. Fuel pump coming on when key is turned on. Spark at plugs with tester. Air pressure after 15 seconds cranking 79psi, BUT fuel pressure also at 79 psi. Service manual shows 89psi for fuel. Also noticed pulsing fuel instead of a solid stream coming from test gauge when dumping fuel while cranking. Retired marine tech, but worked mostly on OMC and Merc EFI motors. Any ideas?

[lpugh]

Check presures key on engine off and time the fuel pressure decay rates when the pumps stop running

[3-Liter]

Pressure with key on, no crank is less than 40 psi. Fuel pressure after 15 seconds cranking is 79 psi. Pressure drops very quickly when I stop cranking.

[lpugh]

be sure the vst is full of fuel, Pump the bulb till hard, Drain it it to verify quantity. Check low pressure at vst shrader valve 20-30 psi. Pinch the high pressure return line and retest fuel pressure , should be 110+ I believe. What you find at this point will narrow it down for further tests
It would be helpful to know if there is air in the fuel rail or fuel in the air as this could be a tracker valve which is very easy to pull for inspection and replacement
I would highly recommend you get a service Manuel for your motor by the serial number, as it will have exact specs and procedures to follow for you motor

[3-Liter]

Update. Fuel pressure with pinched return line 100psi+. Get this,,,,,,,,belt from compressor removed still have 70 psi air and 62psi fuel. No fuel in air test valve on port rail. Where can air pressure be coming from. Motor tries to run with compressor belt removed and gauge dump valve open so motor gets no air pressure.

[lpugh]

During cranking direct injectors are held open to rapidly build air pressure
If 40 psi open and holding 100 plus pinched I would think you have a bad fuel pressure regulator

[EuropeanAM]

1. Are you using a DUAL PRESSURE, Glycerin-Dampened Gauge Set that reads BOTH the Air and Fuel Pressures LIVE, at the SAME TIME without connecting or disconnecting?

2. Make sure there is actually fuel IN the VST. Pump bulb firm and check by draining VST as described in the Service Manual.

3. Pump bulb firm again. Relieve ALL PRESSURE from both sides. Make a recording of the gauges while cranking the engine, and post the recording on YouTube (put a link here).

[3-Liter]

Not able to get video to load on you tube. Mercury dual glycerine filled gauges, VST full, primer hard. Fuel climbs from 20 psi key on, up to 62psi and holds. Air climbs instantly to 74, then jumps from 74 to 78psi. NOTE, still have 62 psi fuel and 70 psi air with compressor belt removed.

[EuropeanAM]

Pressure readings with belt removed are useless. That is because the system relies on AIR pressure (Fuel pressure = Air Pressure + 10 psi).

Given limited means of observation, let's do a trial to prove what I suspect:

Unplug the HIGH PRESSURE fuel pump connector. This it the connector at the FRONT of the VST.

Crank the engine over and record the pressures (BELT ON THE COMPRESSOR, PLEASE). Still have about the same fuel pressure (62 psi)?

[3-Liter]

Performed test. Pumped primer bulb full, high pressure connector disconnected, cranked for 15 sec. Fuel pressure started at 2-4 psi then dropped to "0". Air fluctuated between 50 and 58 psi. Able to upload photos, but not video. opti-1.jpgopti-2.jpg

[lpugh]

Upload video to you tube or another and then insert a link to the videos in you post

[3-Liter]

Leon, my phone will not let me send a file that size.

[lpugh]

Could you hear the low presure run momentarily for a couple of seconds at key on?

[EuropeanAM]

Your air pressure isn't consistent- that's one item that should have been virtually identical each time (unless your battery is weak). Incidentally, a weak battery may be able to spin the engine, but NOT be able to keep the MPR contacts closed (and power the many electrical items required to run the engine).

Reconnect the HP fuel pump, fully charge that battery, and LOAD TEST it (most auto parts stores will do this for you in hopes of selling you a battery). Provide the test results for CCA (Cold Cranking Amps).

[3-Liter]

Sorry about slow responses. Called out of town for 4 days. Leon, low pressure pump runs for about 4 seconds when key first turned on. Don, 6 month old 1000mca battery with charger hooked up during each test. Will test battery today.

[3-Liter]

This morning fuel pressure while cranking 10 seconds steady at 62 psi. Air pressure fluctuating between 70 to 74 psi. Took battery to auto parts store, tested OK. Once in a while motor will 'pop' like it is trying to start. Never did that before. Fuel is always 10 psi below air, not above. Used different set of gauges, hoping bad gauge. Still same, air 10 psi more than fuel. opti-3.jpg

[EuropeanAM]

Do you have fuel in the air side (liquid fuel present if you relieve the air pressure)?

When you did your line-pinch test, are you CERTAIN you were reading FUEL pressure that spiked to 100+ (and not air)?

[3-Liter]

No fuel in air line. Yes sure fuel schrader valve is on top of port rail, air in in middle. Test was key on with fuel return line pinched, not cranking. Am I now at a point where I need to tear into the fuel pressure regulator and tracker valve and visually inspect diaphragms? Thanks for your patience with this unusual issue.

[EuropeanAM]

That- or the seal at the top of the HP fuel pump could be compromised.

[3-Liter]

Update. Bypassed low pressure pump by disconnecting wires, plugging low press pump output, and plugged VST top vent. Hooked fuel tank directly to the top hose removed from low pressure output. Motor starts and runs without even pumping primer bulb while running. . Fuel pressure 86psi, air 78-80psi. Then hooked fuel tank directly to bottom[input] side of low pressure pump, no start or run. Local auto parts store had China copy of Merc pump, no difference. Checked voltage into low pressure pump, and checked pump coming on. Any possibility other than $400+ low pressure pump from Merc?