Cold start rough idle 300 hpdi

[TerryS]

Motor runs great when its warmed up but it runs like crap when cold,Checked the thermosets were clean and working, filters are good VST and others just changed plugs any ideas

[boats.net]

It needs to be put on computer diagnostic system to check temp and air sensors.

[COJones]

I have 04 300 HPDIs doing the same thing, "cold start roughness" with multiple stalls and start attemps at times. If I start it and immediately put it in gear, the motor runs smooth and will not stall. The funny thing is that they are both doing the same thing off and on. Had the local tech check both engines on the computer and he could not find any problems. Engines run great otherwise. It seems to me that this first started happening when I started running the 10% ethonal blended fuel. If you discover a remedy please share and I will also. Thanks, David

[COJones]

I'm still having the same concerns:

" I have 04 300 HPDIs doing the same thing, "cold start roughness" with multiple stalls and start attemps at times. If I start it and immediately put it in gear, the motor runs smooth and will not stall. The funny thing is that they are both doing the same thing off and on. Had the local tech check both engines on the computer and he could not find any problems. Engines run great otherwise. It seems to me that this first started happening when I started running the 10% ethonal blended fuel."

and have failure to determine the root cause. I talked to the local Yamaha dealer, who did the original diagnoses of no problem found, and he said to bring it in again for a second look. Before I do this (rather involved talking the boat off the lift and onto a borrowed trailer), has anyone shared this concern and found a remedy? Any help would be appreciated.

[bigfish1229]

i have an 05 300 that was doing the same thing. for the longest time. finally talked to enough people and someone said to look at the prop size, i know it sounds weird but what happens is the computer puts out a certain voltage to the coils. if the motor is not proped exactly right, then the voltage output is thrown off thus slightly fouling the spark plugs, not bad enough though to cause a major problem.the reason it will run if you immediately put it in gear is because it is then firing on all 6 cyls. makins it run even. in my case we found that even though i was turning right at 5600 rpms at wot, the diameter of the prop was one 1/4 inch too small. by increasing the diameter that much it changed the voltage output of the computer and cured the problem. hope this helps

[COJones]

I had 780 hrs on this setup with out this concern (currently at 827hrs). However, motors are well broken-in and might have lower friction and hence lighter loads; combine that with 10% ethanol requiring an ever so slightly richer mix and I wonder if I'm really the only one with this problem. Still looking for ideas before wasting my time again at the dealer (sorry about that dealer comment, I'm just frustrated they didn't fix it the first time).

[COJones]

Bump. Still looking for advice. Have had both engines sync'ed and tps set to up spec .62 but still having the same cold start issues. Has anyone discovered a root cause? How many with 03 and newer 250 and 300 hpdi are having multiple cold start attempts before engine stays running?

[COJones]

i have an 05 300 that was doing the same thing. for the longest time. finally talked to enough people and someone said to look at the prop size, i know it sounds weird but what happens is the computer puts out a certain voltage to the coils. if the motor is not proped exactly right, then the voltage output is thrown off thus slightly fouling the spark plugs, not bad enough though to cause a major problem.the reason it will run if you immediately put it in gear is because it is then firing on all 6 cyls. makins it run even. in my case we found that even though i was turning right at 5600 rpms at wot, the diameter of the prop was one 1/4 inch too small. by increasing the diameter that much it changed the voltage output of the computer and cured the problem. hope this helps

Bigfish,
I must admit that I didn't understand your post until reading it again now. So what you are saying is that by running the engine lightly loaded it will slightly foul the plugs and cause the starting concerns I have been seeing. If I prop up and load the engine more I won't foul my plugs and hence not have the starting issues. Now that makes sense to me.

So what wot rpm have you had to prop to? I can currently spin to 5700 rpm. Your feedback would be greatly appreciated.

Also, could I take a survey on how everyone has their hpdi prop to at wot? This might also yield some fruit.

[mrv8outboard]

E10 is going to be an issue. If you have just started to use it and did nothing to prepare... Use "Starton" it will help but it is not a cure. E10 runs 3% leaner at the same jet size/injector duration. The fuel also has a much shorter shelf life. 2-3 weeks for 86 octane and 3-5 weeks for 92/93 octane. Two things happen the alcohol evaporates ( loosing octane and oxygenator) or it will absorb water and you will get phase separation. Remember ethanol can absorb 10% of water by its volume. 100 gallons of fuel means it can absorb 10 gallons of water.

[99yam40]

i have an 05 300 that was doing the same thing. for the longest time. finally talked to enough people and someone said to look at the prop size, i know it sounds weird but what happens is the computer puts out a certain voltage to the coils. if the motor is not proped exactly right, then the voltage output is thrown off thus slightly fouling the spark plugs, not bad enough though to cause a major problem.the reason it will run if you immediately put it in gear is because it is then firing on all 6 cyls. makins it run even. in my case we found that even though i was turning right at 5600 rpms at wot, the diameter of the prop was one 1/4 inch too small. by increasing the diameter that much it changed the voltage output of the computer and cured the problem. hope this helps

This sounds interesting. I have never heard about a computer adjusting the voltage to the plugs on an outboard before. I know it changes the timing and duration of the injectors firing, but how does it change the voltage?

[COJones]

I understand the effects of ethonal and that is why I'm asking for feedback on how many others are seeing a cold start concern. I have pretty simplely ruled out the higher load requirement for clean plugs. Just checked my plugs after +60 hours and they're very clean for a 2 stroke. What I have been noting is the engines starting quality with soak temperature. If the cold start temperature is below say 70F (I'll need to start keeping track of this more accurately), the engines starts and stays running like it should. However, if the cold start temperature is in the mid 80s, it could take anywhere from 2 to 4 starts before they'll stay running. Next time I see +80 cold start temperatures I'll hit it with some propane to see if it's truly a lean start. Anyone else seeing this? Once again, this started with the use of 10% ethonal for these motor. Other than this anoyance, the engines run great with tons of power and good economy.

[leebleeb]

I am having the same concern with my 300 hpdi stalls cold and smokes excessive at cold idle.

Fuel pressures within specs. Checked the shrader valve with gauge and have the high pressure displayed on my lowrance hds12.

I have changed the plugs and gapped them. I changed all filters. I changed the low pressure fuel pumps (one was leaking a little) concern still present.

I do not run ethanol fuels!!!!!

If I put the boat In gear runs fine but still smokes bad far a while.

I have changed the primer bulb but I still think that it is difficult to prime and takes to long. I also feel that the bulb does not stay as firm as it should.

I am out of ideas of things to check. Boat runs great at speed.

[Bilge Rat]

Check your poppet valve. If it is not seating a idle the motor will take longer to warm up.
Let the motor idle for a minute or 2 to warm at first start.

It is a big motor, lots of metal to get warm.

Does that motor run differently until it sees 113 deg. then go to the normal mode?
Try getting all the parts warm and happy.
Recheck the fuel system, anti siphon to the onboard filter gasket.
If the computer readout is good look at what it doesn't see.

Ethanol is bad, seen 2 F150s that after started would stall when put in gear one time. Restart then run fine. Went to real gas and issue went away.

A cold 2 stroke don't run good anyway, or any motor for that matter.

[madharchod]

faulty spark plugs