'98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

Everytime i put the boat in for the first time for the day, i start motor, it starts then stumbles/dies. I end up having to start the motor on fast idle and let it sit there for a few minutes before i can return the throttle to neutral (true idle). Then when i go to shift to leave the dock the motor bogs down and dies. I then can restart again on fast idle, let it warm up even more, then it will go into gear, drive for a few more seconds, then die again. Restart on fast idle, then goose it a little then after 5 minutes or so of monkeying around lookin like an a-hole at the dock, its like the motor instantly starts running just fine, and will run like new the rest of the day including from rest to full throttle runs, full throttle, part throttle, everything, it runs flawless, i can even troll all day at idle without it missin a beat. it does this every time.

Just this year the motor has a brand new fuel/water separator (mercury brand), new quicksilver fuel primer bulb (installed the right way, triple checked), all new fuel line from tank nipple to fuel water separator in the motor, and i drained the whole tank, tested for water in a mason jar, no water. refilled with fresh gas, no improvement. I also tested all cylinders for spark, all had spark. Compression is 125 psi on all cylinders. Also has new spark plugs and spark plug wires this year...

the only thing that seems odd to me is that no matter how many times i prime the primer bulb, it never stiffens up like it does on the other outboards i've had, you can just keep squeezing it and it never stiffins up, which is why i replaced the bulb with a new one, and that didn't change it...its quit odd not sure thats normal but the only thing that seems odd to me, everything seemingly checks out. my gut instinct says the mechanical fuel pump in it is going out, as i tested the electric high pressure one and it runs just fine, and if it didn't the motor wouldn't run at all, i would imagine.

Thanks for help in advance guys...

Re: '98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

your needle seats are not sealing rebuild the carburetor this should fix the problem good luck

Re: '98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

The mechanical pump fills the VST tank and the electric one pressurizes the injectors. It could be one of several things:
1) mechanical fuel pump weak and VST runs out of fuel
2) sticky float in VST tank not allowing fuel in
3) air leak in fuel line from boat to engine
4) electric pump low on fuel pressure
5) debris in fuel strainer on bottom of fuel pump

Re: '98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

Additional info, i posted a similar problem on here before, long of the short i replaced all the parts originally mentioned and that made it better, but not cured, if anything the new parts might of just masked some of the issues...anyway what happened i was running back to the dock, when all of a sudden the motor literally turned off for one second, then kept going like nothing happened, got back to dock, seemed as if the engine wasn't idling 100%, and thats when my more severe problems started where i couldn't even get it to run at all. after replacing all the parts mentioned above, this is where im at, motor runs like crap for first 5-10 minutes then snaps out of it and runs like a champ rest of day.

maxz695 - The engine is an EFI engine, would it still have these needle seats you describe?

Faztbullet - I did a Fuel pressure test today again, may look familiar, did a different one months earlier when i had the more significant problems you helped with. Video 1 is of the fuel pressure guage. I primed the bulb, then turned key to on position. High pressure pump turned on, fuel pressure rose to ~35psi, then started the motor just fine, ran fine. I didn't tape any of that, rather the video starts when the motor starts running rough...not at one time did the fuel pressure change though, it stayed around the 34-36psi mark. So im thinking the fuel pumps are ok.

Now im wondering if this is ignition related if compression is good, and fuel pressure remains constant. Attached is a picture of the spark tester i had. I did a spark test back last year when i started having problems, i found spark on all cylinders, however some cylinders seemed stronger than others. Where on this guage should i consider minimum spark requirement? I found some cylinders needed to be at the "15" mark to get spark, while others sparked right away at like 30 or 25. (I started at 30 on a all cylinders and worked down till i got spark)


Side note, the video sound seems to pick up a clicking and makes it very pronounced, that clicking isn't nearly as pronounced in person. not sure that matters. it just sounds like fuel injectors to me in person.


Thanks

Robert

Re: '98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

maxz695 - The engine is an EFI engine, would it still have these needle seats you describe?

Click to expand...

No....

Where on this guage should i consider minimum spark requirement?

Click to expand...

Measure gap to 3/8 of inch ,if it has problems jumping this and is not a bright blue with a defined "snap" that cylinder/s is weak. Does the engine smoke more than normal when you first start it as the the plugs look rich. #1,2,3 & 6 look the worst, these are BU8H NGKs correct? Have you checked the tps voltage and timing when its acting screwy?

Re: '98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

where is the tps and timing marks? also im not sure which cylinder is #1 to get the timing off of , and where the timing marks are, on top of motor i'd assume but where to look?


Thanks Fazt

Re: '98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

Stop... Go here and print off the pages for timing/sync/adjusting and the 96 and up EFI design...
http://1manual.com/Mercury manuals/Service Manual PDFs/TwoStroke/824052r3/cover.pdf

Re: '98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

Faztbullet said:

Stop... Go here and print off the pages for timing/sync/adjusting and the 96 and up EFI design...
http://1manual.com/Mercury manuals/Service Manual PDFs/TwoStroke/824052r3/cover.pdf

Click to expand...

Great link! What part of the timing/sync/adjusting would you recomend i check? Tomorrow i will redo the spark test, setting gap to 3/8"

Thanks Fazt

Re: '98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

update: i read through the link posted above, and read that adjusting the TPS will change lean/rich condition somewhat. SO i ordered the mercury TPS voltage tester today, and also ordered the mercury spark gap tester. I'll check this out friday once the parts arrive. It does seem to be running either rich or a plug or two or three aren't firing well causing all that smoke. See updated video from today.

Anyone else have anything else i can try in the mean time till the mercury tools arrive?

Also when i bought the parts from the local dealer i asked how much they'd want to take a look at the motor and diagnose, they said 110 bucks an hour. i laughed thinking they were joking. nope. looked up and there's the sign....WOW.....what a joke..

Re: '98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

Man the idle is way low on that thing, is fuel comsumption up on it? If so you may have a injector/s flooding.

Re: '98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

Faztbullet said:

Man the idle is way low on that thing, is fuel consumption up on it? If so you may have a injector/s flooding.

Click to expand...

i haven't noticed anything on the fuel, i've only owned the boat a half year, when i bought ran mint, then one day acted up out of the blue and its like this now, how can you test for a bad injector(s) ??? im hoping to find something with the tools i ordered, if not im gonna loose my mind. Fuel side is confirmed good, fuel pressure is text book, compression is text book at 125 psi all around, but something electrical is causing this, or as you said, bad injector...we'll see Friday.

Re: '98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

Ok im getting to witts end here...

as feared, the quicksivler spark tester i picked up yielded nothing wrong with spark. All six cylinders yielded a consistant, white/blue spark the thickness of a piece of pencil lead, so that sure seems like cylinders are getting spark.

So next up was the TPS voltage tester, i had high hopes here after the spark test yielded no problems. Followed TPS voltage testing procedure per your link Fazt, and initial voltage was .18 without loosening any screws or adjusting it just to see what the tps was reading prior. So i followed the directions. It stated key on, temp sensor disconnected on port head, then turn the tps fully clockwise and it should read between .200-.300 but it read ZERO. It said if thats the case then adjust it to .240-.260. I landed on .250 and tightened her down, and rechecked before disconnecting. Yep .25 still. So i reconnected the stock harness, and temperature sensor, zero improvement or change, goose it some, still runs like complete crap.

I pull plugs, they look exactly like the pic above, small spot of fresh oil on each of them....

What the hell...so i have confirmed spark, confirmed fuel pressure, compression compression, and it still runs and dies !!!!

50 bucks to anyone that finds the problem. NO JOKE. Paypal'd once fixed.

Re: '98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

I stumped everyone eh...

Other notes gas(87 octane, 10% ethanol (only gas around)) is only about 3-4 weeks old and has quicksilver quickleen in it. Not sure thats old enough to cause issues...

Re: '98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

Pm me you address, I have a test ECU you can try...

Re: '98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

You said you have a poor running motor then instantly
a good running, it sounds like it's electrical or ignition.
I scanned this looking four ser # I'm not so good with
mercurys with year only I would clean and tighten all grounds
If you get good spark that might change under load?
The reason I was looking for ser#, do you have a idle stabilizer?
They are known for problems at idle.

Re: '98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

first of all i can't tell if you was running muffs to your motor if not not you'll damage the moter running it like that.

Re: '98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

Update: pumped out all the gas again, filled with fresh, non ethanol, 91 octane gas, motor runs ALOT better, then i changed plugs, motor ran even better, so i toke her to the lake and off the muffs, well as usual it bogged down when shifting into gear and died...but condition did improve which tells me theres something still wrong and the new plugs/fresh non ethanol gas helps cover it up...

Faztbullet - i sent you my address, let me know what shipping is i can paypal you to cover shipping. I really appreciated this!! My concern is that its almost down to the ECU, especially since this just started one day after motor cut out after running back to dock for 1 second then kept running but worse, really odd, not sure a loose battery wire at the time caused all this and friend something... (i had wing nuts on at time, now i use locking nuts)

Big flop im not sure if i have a idle stabilizer, would pix of motor help? let me know im all up for any ideas, something is still wrong with this motor.

04whitetb - yes muffs on always

Re: '98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

Since you have surface gap plugs, then I'm
thinking you have 2 switch boxes ?
Look up your motor on line parts & and you
will see the idle stabilizer , might be with The block
and end caps.
Normally on carb motors you un plug it and
Forget about it.
Can you please post ser #

Re: '98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

0g655679

Re: '98 Mariner 150 mag efi stumbles/dies for first 5 minutes then runs like champ

Coming off your switch boxes you have two short
wires one red and the other white. They should be
about 4inches long with bullet connectors on the ends,
they hook to red and white that go to inle control unit.
(idle stabilizer)
Unplug them and try it.