94 mercury efi 150xri fouling plugs with minimal idling

[Jeaton1985]

Hello this is my first post but I have followed the forum for years so thanks for all the good advice in the past my problem is I have a newly rebuilt 94 mercury 150 efi serial number 0g028731 only has 40hrs on it oil injection has been removed and I run 50:1 and quick clean in every tank it starts right up and runs good with a new set of plugs smokes pretty good when I first start it but will run like a scolded dog on plane my problem is after minimal idling through long no wake zones or doing a little graphing or idling waiting to blast off or load in a tournament it will than bog when nailing the throttle than after a brief bog will jump up and take off but will sometimes die coming off plane but will start right back up also when trying to load on the trailer that last little bit you have to goose it dies and slide back off over and over change plugs and it's good again for awhile until any idling over 5 min I have replaced the high and low pressure filters , fuel pressure at idle is 36 to 39 , TPS is within range according to manual compression is 120 psi on all cylinders I was running NGK bu8h have since tried NGK buz8h for the R.F.i
Blocking I have checked spark and all show a blue spark also replaced a few semi leaky fuel hoses coming from final filter any ideas would be greatly appreciated

[Okiefish70]

Jeaton I have been having similiar issues with my 2000 Model merc 200 EFI, I had recently replaced the spark plugs mercury spec and gapped correctly, thinking it would fire up and run great...but I couldnt even get it to fire so I took it to a local shop where they cleaned and tuned the injectors, rebuilt the fuel pump changed filters etc. but when i got it home i still had the same issue so i have been trying to debug and figure out what is going on with this thing, so heres what i found out yesterday, brand new plugs again and i crank the engine with the hotfoot held down all the way until it finally coughed and thought ok somethings happening here so i repeated this until the motor started and I feathered the throttle to keep it running (rough) but after a minute or two it cut loose and revved up and i let off and it idled perfectly so that when i touched/goosed the throttle I had the response that i was looking for. Not sure why but it was like it was flooding/fouling out the plugs right outta the gate just initially turning the key cranking (no throttle). Now that i know HOW to get it to start I can get it out on the lake to see if it will actually get on plane and keep running at higher rpm. and then just idle around as you were describing to see if it loads up and starts to bog down. It sounds like maybe the plugs arent burning hot enough to keep up with fuel delivery at low rpms? Very interesting I will follow this thread and offer any discoveries that i make.

[EuropeanAM]

Moving thread to the 2.0/2.4/2.5L Forum.

[Jeaton1985]

Very sorry your dealing with this problem too definitely the worst time of year for our boats to be having problems the difference with mine and yours is mine has no problem starting starts right up even after it dies sometimes coming off plane or dies trying to load it will start right back up and idle

[EuropeanAM]

If you've switched this engine to PREMIX, you're going to have to dial back on the "idling". Fuel system is designed with a Variable Ratio OIL INJECTION system, and you are now running it PREMIXED at the WOT ratio ALL the time.

This will cause fouling and loading-up if you do too much idling.

ANY abnormalities (not coming up to temp due to thermostat problems, too much oil being added, poor fuel quality, fouled plugs, improper SYNC-n-LINK settings, TPS setting incorrect, IAT reading erroneous, etc) will make this much worse.

[Jeaton1985]

Thank you for the reply the oil injection was removed before I bought it 10 years ago something about a gear being prone to stripping out on this make of mercury and it robbing the engine of oil and blowing them up im not sure that's just what I was told but the engine blew #2 piston last summer and was rebuilt during winter there were a few hiccups during break in period and had to go back a few times for adjustments one time it was dying coming off plane and it was the Tps needed adjusting and it was fine for awhile it would still foul out spark plugs every 3 to 4 weeks I'd change them and good to go again now it has 43 hours on the motor and just the last 3 weeks it's been doing this while coming off plane or loading even if I put in new spark plugs that day I checked the TPS I believe it was .233 if I remember correctly I get non ethanol gas at the same station always and always run quick care fuel stabilizer I replaced thermostats about 3 years ago I use a oil ratio jug I bought at Walmart that has a line to fill oil for so many gallons at 50:1 ratio so I hope that's accurate but who knows as far as the sync and link settings im not sure or the Iac valve where would that be located? And how do you test it? It's just weird how good this motor runs starts right up will idle all day runs great mid range and full throttle it's mainly the initial bog taking off and the constant bog and dying trying to load and all recently also now the dying if revved up in gear almost like the throttle plates are closing to much when the throttle is snapped back suddenly . Sorry for the long reply it's just driving me crazy over 4,000 in rebuilding this motor and it's still not right

[EuropeanAM]

There is no IAC on this engine.

I would get someone very knowledgeable in this engine series to go through the ENTIRE Sync-n-Link from using a dial indicator to set the timing pointer, cam/roller sync, Idle timing setting, WOT timing setting, TPS setting, Verify engine coming up to temp on both banks, and then set IDLE SPEED in FWD GEAR, in the water (using the screw on the UPPER throttle blade set that's hidden behind the VST).

While that's being done the IAT can be checked (it should match ambient temp before starting engine) and the MAP sensor values can be monitored.

Note: If the engine still has the Idle Stabilizer/Advance Module, this would be an opportune time to consider removing (BEFORE the Sync-n-Link).

[Jeaton1985]

Thank you so much for all your help , now the fun part is finding someone in my neck of the woods that is even half as knowledgeable as you on it engine and can do the steps you have here im in middle Tennessee if you have any recommendations please let me know if not I would not be against making the drive to your shop in the near future if you had time I would love to get this thing right I spend alot of time on the water

[JOE54]

1/4 mabe no 1/2s

[Jeaton1985]

Lol absolutely at this point I'd be happy with 1/4 lol but your right there aren't many probably within the country that gave 1/2 the knowledge Don does

[Jeaton1985]

Where you say if I still have the idle stabilizer it would be a good time to remove before set up does that mean do away with completely? I've heard mixed reviews on them

[JOE54]

take it off

[EuropeanAM]

+1... and place it in a trash receptacle at least 50' from the engine.

If it grows legs and re-installs itself, then maybe you could... NAH... throw it away again.

[Jeaton1985]

Haha ������ I will definitely check to see if it still has them do you just unplug them? And see if it changes anything ? Also I checked Air temp sensor today in a bowl of ice water as shown in Manuel resistance consistently climbed so I think I can rule that out I was going to attempt to check head temp sensor port side the same way but it's pretty stuck in there like the rubber has melted and expanded over time so im afraid to pry it out I've ordered a new one when it gets here I will be more forceful I guess 20200625_173758.jpg

[Jeaton1985]

Ok now I've really screwed up as per Manuel minus the actual tps test harness just pinned the back of the plug with port temp sensor unplugged key on tps was reading 7.45v which is full throttle voltage but the hot foot wasn't depressed when I would press down the hot foot the voltage would work its way down to 0.00v at full throttle my nephew loosened the screws and removed it to look at the inside and put it back on put it back on moved it back and fourth and couldn't get it lower than 5.4v so he put it back at the voltage it was before unscrewing it and now motor sounds a little worse and ran for a good minute to 2 minutes and it never started peeing through the telltale temp at thermostats housing with laser gun at its highest was 159.3 before I shut it down and im guessing was running real rich because the smoke was burning my eyes but now I'm really upset because I wish he had never messed with that sensor it always pees within a minute impeller was changed a month ago please help im worried I've screwed up bad

[Jeaton1985]

20200625_185740.jpg20200625_185805.jpg

[Jeaton1985]

Ok update on it peeing I ran a wire up telltale and shone mud came out after that started peeing but I believe bottom 2 cylinders are flooding there temp is 120 where top cylinders are 145 to 155

[lpugh]

Ok now I've really screwed up as per Manuel minus the actual tps test harness just pinned the back of the plug with port temp sensor unplugged key on tps was reading 7.45v which is full throttle voltage but the hot foot wasn't depressed when I would press down the hot foot the voltage would work its way down to 0.00v at full throttle my nephew loosened the screws and removed it to look at the inside and put it back on put it back on moved it back and fourth and couldn't get it lower than 5.4v so he put it back at the voltage it was before unscrewing it and now motor sounds a little worse and ran for a good minute to 2 minutes and it never started peeing through the telltale temp at thermostats housing with laser gun at its highest was 159.3 before I shut it down and im guessing was running real rich because the smoke was burning my eyes but now I'm really upset because I wish he had never messed with that sensor it always pees within a minute impeller was changed a month ago please help im worried I've screwed up bad

You must have the tps adaptor testing that way and a DVOM is not accurate enough, need a DSO or a scan tool. Automotive is somewhat different than marine, The reversed voltage is the way you are connected to the TPS
#91-859199 or an equivalent jumper harness for tps

[EuropeanAM]

A DVOM can be used for the TPS... instructions are included in the Factory Service Manual.

You were, indeed on the wrong wires, like Leon suggested. You'll know you're on the RIGHT ones because the idle position voltage will be LOW, and will INCREASE as the throttle is advanced.

[Jeaton1985]

Well that definitely explains why I was getting such a high reading I want to thank each and everyone of you for taking the time to help me with all your great information I finally threw my hands in the air and took it to a marine mechanic I heard was one of the best sound here we will see I guess. God willing he gets this thing figured out and i can report back what was causing my problem so i can pay it forward and help out the next guy thanks again i will report back soon.