2006 Opti 150, idle troubles - what to attack first?

[leaky]

I've got a set of these w/ 900 hours on them. Starboard runs pretty much perfect, like a new car might almost, the port engine runs OK with the trouble being it might start then immediately stall a couple times before it stays idling and until it's run at speed for awhile it tends to idle with a little stumble in it. Occasionally like if I'm driving up the trailer or backing off the dock I may notice the port engine stalled out on me, during regular operation there is no noticeable issue.

In the past I've corrected the idle temporarily by replacing plugs - which I attempted to do this spring, and sure enough what I removed were all pretty fouled, maybe from waking up after winter (I do put a rich oil/fuel mix in the engines filter as part of winterizing), but whatever the case immediately upon replacing the plugs I did not see much, if any, change this time - so it's not just fouled plugs but it may be the root cause behind the plug fouling that's actually impacting the idle is my theory.

Last year in the starboard (perfect running) engine I had an air compressor go, was really worrying me that the same was due on the port so I just replaced that (with no change).. Got a couple minutes of break-in left (in break in mode to prime oil system post compressor swap) and then the engine will be back to normal oil mixture, at that point I'll decarb, maybe replace and/or clean the plugs, and re-check but my guess is no change.

I've been tinkering around with this for awhile, never really getting it 100% fixed. In the past have gone through compression and spark checks, resistance of injectors, pressures, never finding anything. I believe in that process though I've noted fuel mist in the air side of the rails during pressure checks. I feel like I should go after the Fuel Regulator (nice that you can buy these diaphragms now!) and/or Tracker valves, maybe the Air Regulator too, but not sure what might make sense as a place to start and what problems I'll run into. Is it easy enough to take these parts out and inspect/replace?

Thanks in advance!

Jon

[RSWORDS]

I've got a set of these w/ 900 hours on them. Starboard runs pretty much perfect, like a new car might almost, the port engine runs OK with the trouble being it might start then immediately stall a couple times before it stays idling and until it's run at speed for awhile it tends to idle with a little stumble in it. Occasionally like if I'm driving up the trailer or backing off the dock I may notice the port engine stalled out on me, during regular operation there is no noticeable issue.

In the past I've corrected the idle temporarily by replacing plugs - which I attempted to do this spring, and sure enough what I removed were all pretty fouled, maybe from waking up after winter (I do put a rich oil/fuel mix in the engines filter as part of winterizing), but whatever the case immediately upon replacing the plugs I did not see much, if any, change this time - so it's not just fouled plugs but it may be the root cause behind the plug fouling that's actually impacting the idle is my theory.

Last year in the starboard (perfect running) engine I had an air compressor go, was really worrying me that the same was due on the port so I just replaced that (with no change).. Got a couple minutes of break-in left (in break in mode to prime oil system post compressor swap) and then the engine will be back to normal oil mixture, at that point I'll decarb, maybe replace and/or clean the plugs, and re-check but my guess is no change.

I've been tinkering around with this for awhile, never really getting it 100% fixed. In the past have gone through compression and spark checks, resistance of injectors, pressures, never finding anything. I believe in that process though I've noted fuel mist in the air side of the rails during pressure checks. I feel like I should go after the Fuel Regulator (nice that you can buy these diaphragms now!) and/or Tracker valves, maybe the Air Regulator too, but not sure what might make sense as a place to start and what problems I'll run into. Is it easy enough to take these parts out and inspect/replace?

Thanks in advance!

Jon

You should see absolutely no fuel on the air side. A very small amount of water may show up from condensation but no fuel. There is a few places it may be getting fuel I to the air side. Pressurize the air side with show air regulated to 80psi and look/listen for leaks.

Shot in the dark educated guess? Tracker valve dia is bad. But I don't like to throw parts.

[leaky]

You should see absolutely no fuel on the air side. A very small amount and water may show up from condensation but no fuel. There is a few places it may be getting fuel I to the air side. Pressurize the air side with show air regulated to 80psi and look/listen for leaks.

Thanks! Man that seems like such a simple idea and I don't think it's anywhere in the Merc factory manual - basically just hook an air compressor up to it w/ 80 PSI in the tank, correct?

Also occasionally fires up with a jump in RPM like you wacked the throttle, which I've come to learn is a characteristic of fuel in there too.

Jon

[Wayne Cammidge]

O Rings on the fuel injectors could be an issue as well

[baja200merk]

Pressurize one of the rails and put a gauge on the other to see if they are talking to each other some where. All my optis that had those symptoms got worse and worse then ended up needing a tracker valve.

[leaky]

Thanks again guys! I plan to take a look at this Thursday night (during the week the girls hair/nails/pool nights are Tuesday and Thursday so that's when I work on boats mid week until midnight if I want ) and will report back what I see w/ the pressures. Hopefully I've got enough bits of rigging for this process, if not will get them.

This is really good stuff - like I said before makes tons of sense but never saw anything like this in my factory manual, all they have you doing is checking pressures w/ a running engine and I don't think that really does crap to detect small leaks from one place to another.

Jon

[RSWORDS]

Thanks! Man that seems like such a simple idea and I don't think it's anywhere in the Merc factory manual - basically just hook an air compressor up to it w/ 80 PSI in the tank, correct?

Also occasionally fires up with a jump in RPM like you wacked the throttle, which I've come to learn is a characteristic of fuel in there too.

Jon

Yep REGULATED 80psi is the trick.... Don't want it going all over the place.

[leaky]

Tonight I got the regulated 80 psi air hooked up and no luck. It was a little windy and noisy out so I couldn't get a good bearing but seemed to be holding the pressure and not leaking into the fuel side. Will try this again next time I'm there and it's quieter.

When I pressurized the system there didn't seem to be much loss if any, had a little in my air line connections but with my ear on the rails and feeling around couldn't detect anything. If I tapped the valve on the fuel test point (to open it) I would get one pulse of fuel, I assume from some diaphragm that is flexing that direction, then no pressure/leakage if I held it open with the air side pressurized, so it does not seem to be much of a leak in that direction.

Is there a way to similarly test the fuel->air side leakage? Like just kicking the pump on is enough or can I somehow inject pressure there?

If I can't find something this way, what do you figure I should do? When I smell the open end of the air test line I do detect gasoline, it's not real strong, kinda smells like stale gas, but in the past when cracking that valve after the engine was running I get a stronger fuel smell burst and I'm fairly certain fuel mist with it, I feel like it's it but maybe I'm just imagining this.

Whatever the case would be sweet if I could ever figure out what this idle issue is.

Thanks in advance!

Jon

[Wayne Cammidge]

Try doing a cylinder miss fire test, it may narrow down if the problem is specific to only one cylinder.
If you have no access to a computer or DDT, try disconnecting a fuel injector wiring plug, one at a time.
See if you have a cylinder that does not react the same as the others when you disconnect it.

[leaky]

Try doing a cylinder miss fire test, it may narrow down if the problem is specific to only one cylinder.
If you have no access to a computer or DDT, try disconnecting a fuel injector wiring plug, one at a time.
See if you have a cylinder that does not react the same as the others when you disconnect it.

Thanks!

I can get something checked via computer if I really need to, but I don't have one, one of those deals where I drop the boat off at shop I'm friendly with, when he gets a minute he plugs in for some specific check and lets me know what he found. Can't really sit and trouble-shoot with it though.

The symptoms are 5 to 10 seconds of stable idle, stumble/miss, 5 to 10 seconds of stable idle, so may be a little hard to isolate if I get a change on each cylinder for instance, but will give this a shot.

Jon

[Euroski]

Have the fuel and air injectors been cleaned yet? Last fall I noticed my 300xs(180hrs) on warm startup acted like "vapor lock" for about the first few minutes. Turns out I needed 2 air injectors beside the normal cleaning. If U have a scope what does the piston tops look like? Attached are a few photos of my piston tops. Cylinder #3 I thin was normal and the other 2 cylinder had dirty injectors.

[leaky]

Have the fuel and air injectors been cleaned yet? Last fall I noticed my 300xs(180hrs) on warm startup acted like "vapor lock" for about the first few minutes. Turns out I needed 2 air injectors beside the normal cleaning. If U have a scope what does the piston tops look like? Attached are a few photos of my piston tops. Cylinder #3 I thin was normal and the other 2 cylinder had dirty injectors.

Thanks but a scope is not a tool in my kit unfortunately. I'm not sure what vapor lock sounds like but what I get is that little stumble in the idle that is sorta on a defined cycle, which gets more minor upon warmup, however that engine just runs weaker.

I've never done anything as far as cleaning injectors on either engine, maybe been lucky to have gone ~900 hours without doing so. I did have one air injector go on the other engine, was obvious via resistance check, that's it.

Jon

[leaky]

Today I pulled all the clips, fired it up, and went through the fuel injector unplug test.

Any fuel injector I pull results in either the engine immediately stalling, or causes the engine to develop a little convulsion of sorts, little but obvious vibration, until the engine stalls or I plug it back in. I went around twice and same results, any one you pull makes a difference..

Thoughts on what to do next?

Thanks in advance!

Jon