Random Miss at Idle. HELP!!

[Hicktacular]

In my manual, I read about a way to ohm test the coils and injectors. I'll try to do those today, incase my injector guy missed something. If they do not ohm out like the manual says, is it guarantee that they are bad? Could a coil cause an intermittent issue that I am having? The manual says that staying between 4k and 5k can cause a rich fuel issue, and that is where I am at 90% of the time. Curious if being overproped is causing this whole issue. I have a lot of work to do, and appreciate all of y'alls helpl!

[EuropeanAM]

In my manual, I read about a way to ohm test the coils and injectors. I'll try to do those today, incase my injector guy missed something. If they do not ohm out like the manual says, is it guarantee that they are bad? Could a coil cause an intermittent issue that I am having? The manual says that staying between 4k and 5k can cause a rich fuel issue, and that is where I am at 90% of the time. Curious if being overproped is causing this whole issue. I have a lot of work to do, and appreciate all of y'alls helpl!

First- let's see what you come up with in your tests. Some variances are acceptable, but if you have one component that considerably differs from the others, that is often a good sign that you have a problem.

Not sure what you are referring to on the "manual says that staying between 4K and 5K can cause a rich fuel issue"... as the engine actually runs it's CLEANEST in the midrange (3800-4800 RPM's range).

And your question about overpropping brings up another important question: Has this engine, on this boat, with the current propeller EVER achieved 5500+ RPM's for you, personally?

[Hicktacular]

Don,
I put the current prop (23 pitch Tempest Plus) on about 1.5 years ago, after I put the original prop (21 pitch Laser 2) into the boat ramp concrete. With the 21 pitch, I could hit the RPM alarm fairly easy with only me in the boat. I did not know anything about "over prop" when I put the 23P on. The 23P has a better hole shot, better lift and drives much better than the Laser 2 did, so I did not worry about the RPMs. I recently borrowed as 21 P Temest prop, and can hit the rpm alarm with it. I am currently looking for a 22 pitch.

[Hicktacular]

Don,

I may have looked at that wrong. I'll see if I can find it. My manual shows 4 wires to the coil, but I have 5... Do you have something showing what wires to ohm on the coils for a 2008 150 optimax?

[EuropeanAM]

What part number Manual do you have? Proper testing is covered in the manual (specific to your engine's serial number).

[Hicktacular]

Has 90-855347R1 JANUARY 1999 at the bottom of the page.. so it is definitely not for a 2008 lol. I got a screen shot from a friend of the correct manual and started testing and gathering the data. I have a pretty basic ohm meter. One of the test is from the middle pin (pin C) to the secondary tower where the spark plug wire goes. The procedure calls for 2-8 megaohm.. is that something that I can do with a basic ohm meter?

[Hicktacular]

From what I read, megaohm is a million ohms, and that makes sense. The manual says 2-8 mega ohms from secondary tower, to pin C (middle of the 5). I have anywhere from 12.8 M to almost 25 M on my fluke meter, for those two points on all of my coils. I even have a new coil that test 24.97 M. I am making an assumption that the "M" on my fluke stands for Mega, so I am confused on why I am seeing 24.97 on the new one, when the spec is 2-8.. Does that make sense to anyone, or am I looking at this wrong...

[EuropeanAM]

Correct on Mega-ohms.

What is the PART NUMBER from the box for that "other coil" (there are different coils and test results on pin "C" will be different).

[Hicktacular]

I am listing the coils as 1 through 6, but that is not necessarily the cylinder that I took them off of. I realize now that I probably should have done that. I will also post screen shots of the data that I got off of each coil or CDM.
Coil 1-6 part number is 8M0042381. The new coil was purchased 3 weeks ago, and is part number 8M0047457. I was told this was the newest coil for this engine. All show to be Rev A

[Hicktacular]

Attachment 402484Attachment 402485Attachment 402486Attachment 402487Attachment 402488Attachment 402489Attachment 402490

[Hicktacular]

COIL 1
	Secondary tower	EST Pin A	EST Low Pin B	EST Low Pin C	Primary Ground D	Battery + Pin E
Secondary tower	X	n	n	26.70 M	n	n
EST Pin A	n	X	10.05 k	n	36.1 k	16.02 k
EST Low Pin B	n	10.05	X	n	46.6 k	25.92 k
EST Low Pin C	n	n	n	X	n	n
Primary Ground D	n	36.5 k	46.6 k	n	X	17.49 k
Battery + Pin E	n	15.52 k	25.63 k	n	21.24 k	X

COIL 2
	Secondary tower	EST Pin A	EST Low Pin B	EST Low Pin C	Primary Ground D	Battery + Pin E
Secondary tower	X	n	n	23.12 M	n	n
EST Pin A	n	X	10.00 k	n	35.3 k	15.99 k
EST Low Pin B	n	10.00 k	X	n	45.3 k	25.86 k
EST Low Pin C	n	n	n	X	n	n
Primary Ground D	n	35.3 k	45.3 k	n	X	16.73 k
Battery + Pin E	n	15.48 k	25.59 k	n	19.68 k	X

COIL 3
	Secondary tower	EST Pin A	EST Low Pin B	EST Low Pin C	Primary Ground D	Battery + Pin E
Secondary tower	X	n	n	23.56 M	n	n
EST Pin A	n	X	9.97 k	n	35.1 k	16.05 k
EST Low Pin B	n	9.98 k	X	n	45.1 k	25.89 k
EST Low Pin C	n	n	n	X	n	n
Primary Ground D	n	20.68 k	44.8 k	n	X	16.44
Battery + Pin E	n	15.40 k	25.50 k	n	19.45	X

COIL 4
	Secondary tower	EST Pin A	EST Low Pin B	EST Low Pin C	Primary Ground D	Battery + Pin E
Secondary tower	X	n	n	14.61 M	n	n
EST Pin A	n	X	9.99 k	n	33.9 k	15.99 k
EST Low Pin B	n	9.99 k	X	n	43.9 k	25.94 k
EST Low Pin C	n	n	n	X	n	n
Primary Ground D	n	21.52 k	43.8 k	n	X	16.15
Battery + Pin E	n	15.50 k	25.53 k	n	18.33 k	X

COIL 5
	Secondary tower	EST Pin A	EST Low Pin B	EST Low Pin C	Primary Ground D	Battery + Pin E
Secondary tower	X	n	n	23.05 M	n	n
EST Pin A	n	X	9.57 k	n	35.3 k	15.99 k
EST Low Pin B	n	9.57 k	X	n	44.7 k	25.50 k
EST Low Pin C	n	n	n	X	n	n
Primary Ground D	n	21.40 k	44.7 k	n	X	16.65 k
Battery + Pin E	n	15.42 k	25.09 k	n	19.68 k	X

COIL 6
	Secondary tower	EST Pin A	EST Low Pin B	EST Low Pin C	Primary Ground D	Battery + Pin E
Secondary tower	X	n	n	17.62 M	n	n
EST Pin A	n	X	9.97 k	n	35.7 k	15.99 k
EST Low Pin B	n	9.97 k	X	n	45.6 k	25.91 k
EST Low Pin C	n	n	n	X	n	n
Primary Ground D	n	21.71	45.7 k	n	X	16.89
Battery + Pin E	n	15.50 k	25.58 k	n	20.06 k	X

COIL New
	Secondary tower	EST Pin A	EST Low Pin B	EST Low Pin C	Primary Ground D	Battery + Pin E
Secondary tower	X	n	n	25.64 M	n	n
EST Pin A	n	X	10.05 k	n	36.2 k	16.02 k
EST Low Pin B	n	10.05 k	X	n	46.3 k	25.99 k
EST Low Pin C	n	n	n	X	n	n
Primary Ground D	n	36.2 k	46.3 k	n	X	17.13
Battery + Pin E	n	15.54 k	25.69 k	n	20.55 k	X

[Hicktacular]

Coil 4 and 6 are much lower than the rest on the test between the secondary tower and pin C. I bought the new coil to have one to switch around to see if I could find a bad one. This data make me wonder if I have two bad coils, and explains why I could not make the issue go away with only replacing one while swapping them around... The rest of the points appear to be in spec (as good as I can tell).

[JOE54]

Coil 4 and 6 are much lower than the rest on the test between the secondary tower and pin C. I bought the new coil to have one to switch around to see if I could find a bad one. This data make me wonder if I have two bad coils, and explains why I could not make the issue go away with only replacing one while swapping them around... The rest of the points appear to be in spec (as good as I can tell).

very very possible

[Hicktacular]

I replaced coil #4 with the new one that I already had.
If that helps, I'll replace #6 tomorrow.
Spark plugs are at 32.
I lapped the cages. All reeds are extremely flat.

The good news is: My plugs look really good. The past year, they would foul really fast. I recently found a broken air hose out of the compressor. It must have gotten broken a year ago when I had the compressor replaced. Part of the reason I do my own work now.

I hope to put it in the water tomorrow. I'll report back the results. Fingers crossed!

[JOE54]

how recent on air hose , reason for comp replace, were di injectors cleaned and tested for debri

[Hicktacular]

Air compressor started making a squeaking noise, so I replaced it about a year ago. All 12 injectors and rails were recently cleaned and tested. I found the broken air hose about 2 months ago, and replaced it.

[Hicktacular]

I ran it in the water today. Although it still has a stumble, it seems much better. The things that I did yesterday:
1. Replace #4 Coil
2. Check all connections and use a dielectric grease on connections.
3. gap plugs back to .032
4. lap reed cages and assure a closed valve.
5 ohm'd all injectors. All are within tolerance.

What I will do next:
Replace #6 Coil.. and cross my fingers.

[JOE54]

id have to observ flash pattern on timming light first looking for misfire , something just tells me coil not yo problem , but ive been wrong before and prob will be some more

[Riccochet]

My '14 150 ProXS does the same thing at idle, mostly when warm. Has done it since new. It's been back to the dealer numerous times for it. They never found anything wrong. My buddy I fish with is a Mercury tech, even he said it's odd. And he's checked the motor three times over, never found anything. It hasn't gotten worse or better in 6 years, and the motor still runs perfect at anything over idle. So I just chalked it up to a nature of the beast.

I hope you find your answer, as I'm genuinely curious.

[Hicktacular]

Riccochet You would think a fuel inject engine would run smoothly. At least smoother than the 1984 carb engine next to me, while mine is spit'n and sputter'n lol. I believe the coils are going to fix my issue. The reeds are easy to check on the engines by the way. I had mine apart in about 30 minutes. There isn't much you can mess up either. Just don't disconnect any of the oil lines from the oil pump if you do it yourself. I think once disconnect, you have to re-prime them with a computer.

I plan to pickup another coil today to replace the other bad one. I'll post updates to whatever the fix ends up being. I hate digging in a thread, and not getting what fixed it in the end.