Mercury 175 EFI Warm Start Issue

[bnt55]

2003 Mercury 175 EFI
Serial # 0T566138


Motor runs great, when cold it fires right up and idles beautifully. Run the boat down the river, stop to fish awhile go to start motor and it takes upwards of 5-6 times of turning the key while pushing in on the key choke before it will sluggishly come to life. Once it's started it runs great again, stop to fish and repeat the multiple key turns to start.

I have read everything I can on warm start issues, I level motor and pump primer bulb (99.9% of the time it's firm). I have not performed a fuel pressure test as I have no idea how to do that. The motor was recently gone through, fuel system cleaned, injectors sent off for balancing and cleaning, new plugs. This has cost me quite a few bucks, as I type this I think it was warm starting just fine after the service and it has progressively gotten worse to date. I would like to solve this issue myself if I can so I can at least learn about the fuel system on an EFI.

Here are some possible issues I read about:
1. Clogged final filter on VST hose
2. Fuel Pump needs rebuilt with fuel pump kit (don't have part number)
3. Inline fuel water separator causing fuel restriction?? Apparently Mercury does not recommend an additional filter
4. Corroded wire connections (I havent seen any so far)

Any advice/direction/help/stern reprimands would be appreciated

[leonreno]

I would hook up fuel pressure gauge to the schrader valve and check fuel pressure cold and hot. Also, not sure if EFI motors have the cold start enriched valve, but if so could be stuck open. It's a small fitting between the bottom two spark plugs on starboard head with an open fitting and a hose the the other fitting.

[cajunrgfm]

have you had the motor scanned ? this series of motors have way more electric issues than fuel,they are pretty efficient in the fuel injection system,if everything has been serviced as you state,that you have done,,,,,,,I have seen the pump inside the VST "stick" quite often,as in not fire up right away, when you turn on the key.,check to make sure that it is firing up on demand,and filling the vst. Also,make sure that your battery maintains 13+volts while cranking. the motorola box wont let it fire with low voltage,(almost like trying to start it with the kill switch deployed,it will turn over,but never fire)

[jarhead175]

You mentioned you "pump the primer bulb" is it soft? If it is you are losing fuel pressure. Been running a EFI since 2001 and no need to pump the bulb at all. Turn on the key and wait 4 sec for fuel pump then start anything else theirs a issue.

[bnt55]

Jarhead175, the fuel bulb is always hard. I have never turned the key on and let it set for the fuel pump to start...didn't know I had to. I usually turn the key while pressing the key in for the self choke? Next time I have the boat out I will let it sit for a 10 count while the key is on and see if that helps.

Cajunrgfm, I am pretty sure the battery drops well below 12 volts while cranking the big motor over, however I will put a tester on the leads and report back the numbers.

I am going to have to do some research on testing the fuel pressure, I have never done this before but it does sound pretty straight forward. I think Harbor Freight carries a schrader valve tester, might be good enough to get some basic numbers

[jarhead175]

I was told when I bought mine to turn the key on and it will beep to wait 4 sec for the fuel pump to pressure the system then start. If the bulb is firm it's not a fuel pressure loss issue.

[JOE54]

theres no choke on EFI,bulb being firm doesn't mean you have good psi at fuel rail

[leonreno]

Some auto parts stores have loaner fuel pressure gauges for free.

[bnt55]

OK, I am going to check the fuel pressure. I check at local parts store to see if they have a pressure gauge I can use. I will report back my findings

[EuropeanAM]

No choke on EFI.

Primer bulb shouldn't "always be hard". When you've pumped it- sure. Once you start the engine, fuel is being drawn through the bulb UNDER VACUUM. So... no longer "hard".

"FULL" is a better description.

Check your fuel pressure as suggested- verify the pressure regulator screen is CLEAN.

[bnt55]

Check your fuel pressure as suggested- verify the pressure regulator screen is CLEAN.

Do I need to take the VST apart to get to the regulator screen?

Another question...since the motor has a fuel/water separator next to the VST (which looks like it has never been replaced btw) do I need to use the additional one inline inside the boat?

[Rich Z]

The regulator is held by 2 screw at the back of vst so no need to take the vst appart.
The screen is pressed into the vst side. Remove and clean the screen and I would replace that water separator filter if never done before.

[EuropeanAM]

See the drawing below, and reference items #7 and #14.

#7 MAY or MAY NOT be present (if the brass fitting requires a 3/4" wrench, the filter SHOULD be there).

#14: Remove the Regulator, verify no debris UNDER it, and clean the screen on the bottom side of the regulator.

[bnt55]

I took the boat out last night and gained a few more clues into it's hot start problem.

1. Once the motor cools down after a hard run (approx 45 min) it will fire right up on first key turn

2. If the motor will NOT start due to it being hot, I can advance throttle to the midway point and it will start immediately. Once it starts revved up I have to coax it back to idle rpm range, if I chop the throttle it will die out.

I could be off base here, but this problem (at least to me) does not appear to be fuel related. From what I have gathered from talking with other people and researching is that the issue may lie in the stator or temp sensors?

[EuropeanAM]

Doubtful. No harm in checking them- but it's likely they are simply doing their job (and some other fuel system problem is resulting in a VERY rich condition when warm).

Fuel pressure readings at 15/30/60 seconds after engine shutdown (as well as at idle, and under acceleration) may prove helpful.

[fishingandhunting]

I took the boat out last night and gained a few more clues into it's hot start problem.

1. Once the motor cools down after a hard run (approx 45 min) it will fire right up on first key turn

2. If the motor will NOT start due to it being hot, I can advance throttle to the midway point and it will start immediately. Once it starts revved up I have to coax it back to idle rpm range, if I chop the throttle it will die out.

I could be off base here, but this problem (at least to me) does not appear to be fuel related. From what I have gathered from talking with other people and researching is that the issue may lie in the stator or temp sensors?

I have the same issue on my 2000 175 EFI I always have to give it just alittle bit of gas to crank up, but once it is running I can let off, also when I put it in gear it will die out, was thinking it was an idle issue, but it idles around 1000 rpms when in neutral and about 900 rpms when in gear.

[silverbullet02]

Another possibility could be a stator getting weak since it's more cantankerous when hot. Or a bad sensor.

[bnt55]

I am still planning on checking the fuel pressure tomorrow night, however it seems to me the motor is running pretty rich. I took a short video about 5 minutes after start up while idling and it does smoke alot. I am using quicksilver premium 2 stroke oil. Could one of the temp sensors cause the motor to run rich all the time? I believe they are only about 35 bucks each, might be worth a shot.

[silverbullet02]

Have you done a link n synch to make sure everything is where its supposed to be before you start throwing parts at it?

[EuropeanAM]

Have you done a link n synch to make sure everything is where its supposed to be before you start throwing parts at it?

+1... all of the settings MUST be correct if you want the engine to run properly.