'94 70hp cuts on wot and rough sea

[TownsendsFJR1300]

How can i check that all 3 cylinders work correctly when idling? Removing plugs from cyl 1&3 didnt produce much bogging as when i removed cyl 2 plug...

A compression check on all three cyclinders (with the throttle wide open) would give you an idea as to the health of the engine.

Spark plug color/ carbon build up would also give a good idea as to whats happening in the combustion chamber.

[papadakn]

A compression check on all three cyclinders (with the throttle wide open) would give you an idea as to the health of the engine.

Spark plug color/ carbon build up would also give a good idea as to whats happening in the combustion chamber.

Compression is good (115-118-115 psi). Is there any guide regarding spark plug color?

[TownsendsFJR1300]

Compression is good (115-118-115 psi). Is there any guide regarding spark plug color?

Yes there is.

After the below picture is open , double click again and it'll enlarge it.

The optimum color on the tip should be a tanish brown (first picture).


I have to agree there's likely a bad electrical connection somewhere, battery switch, ground wire, etc. Don't just look at it, pull it off, visually check it, re-assemble with dilectric grease to prevent any future corrosion. My moneys on something simple, battery switch, ground wire, etc...The bumping is making/braking the electrical connection...

If you could get either get the engine on rabbit ears (or better yet a container with the lower unit immersed in water). Duplicate the running conditions on land/trailer and then start pulling(gently) tapping on harness's, etc until the problem surfaces. A slightly corroded main terminal, (even a small terminal with corrosion) can easily cause issues..

For safety reasons, if using a water tank, pull the prop off. You can run the engine on dry land easily and safely.

Also, If you have access to a timing light, simply clipping it over each spark plug wire while the engine is running will confirm IF you have spark coming from that coil. The spark plug cap should also be checked for tightness.

Good luck and please post your results/fix...

[papadakn]

Update: i tried to run the engine on muffs. Cyl #2 does not seem to participate. Running only on cyl#1 or #3 the engine bogs but works. When trying to do the same for the second one, it stalls and does not re ignite. Should this be normal? How can i check if it's fuel starvation or something electrical?

[TownsendsFJR1300]

Update: i tried to run the engine on muffs. Cyl #2 does not seem to participate. Running only on cyl#1 or #3 the engine bogs but works. When trying to do the same for the second one, it stalls and does not re ignite. Should this be normal? How can i check if it's fuel starvation or something electrical?

If you have a timing light simply clipping it over the ignition wire to the spark plug will let you know if its firing. If not see below.

Looking at the #2 spark plug should tell you something. If its wet with fuel, it's not firing and getting fuel. If its bone dry and the below steps show spark, its in the fuel system.

Pull the #2 spark plug, insert it in the cap as normal, ground it and spin the engine over (on muffs in case is starts). You should see a healthy blueish spark in-between the electrodes.

If none, start with swapping plugs, coils, again, checking electrical connections.

[papadakn]

The more i try to isolate the issue, the more mixed up i get. So, the latest update is:

- Cyl.#2 has no spark.
- Spark plug of cyl#2 seems to be reasonably "wet". Then again, when i connect a pipe from cylinders 1 or 3 to cyl. 2, the engine does not "pick-up", it continues to bog just like when only one functional cylinder (1 or 3) is working.
-When idling, the engine sounds pretty good even though only 2 of the 3 cylinders work. If i hadn't tested it in the sea two weeks ago, i wouldn't be able to hear the malfunction just by running the engine on muffs.

So, my current guess is that the engine has 2 issues: One electrical (no spark) and one fuel (??) related. How can i can continue narrowing it down?


Thanks a lot for the ongoing support.

[TownsendsFJR1300]

The more i try to isolate the issue, the more mixed up i get. So, the latest update is:

- Cyl.#2 has no spark.
- Spark plug of cyl#2 seems to be reasonably "wet". Then again, when i connect a pipe from cylinders 1 or 3 to cyl. 2, the engine does not "pick-up", it continues to bog just like when only one functional cylinder (1 or 3) is working.
-When idling, the engine sounds pretty good even though only 2 of the 3 cylinders work. If i hadn't tested it in the sea two weeks ago, i wouldn't be able to hear the malfunction just by running the engine on muffs.

So, my current guess is that the engine has 2 issues: One electrical (no spark) and one fuel (??) related. How can i can continue narrowing it down?


Thanks a lot for the ongoing support.

If you've confirmed there's NO spark from cylinder #2, the spark plug is wet (its getting fuel but not burning it) you need to focus on that part of the ignition system.

IF, you can swap coils from one cylinder to another and the #2 cylinder NOW FIRES, you apparently have a bad coil(the present #2 coil).

You can also put the #2 coil on another cylinder and see if it fires ruling it out(its good if it fires).

Again, check the grounds, all wires going to #2, nothing pinched, loose, etc.

Good luck

[papadakn]

If you've confirmed there's NO spark from cylinder #2, the spark plug is wet (its getting fuel but not burning it) you need to focus on that part of the ignition system.

IF, you can swap coils from one cylinder to another and the #2 cylinder NOW FIRES, you apparently have a bad coil(the present #2 coil).

You can also put the #2 coil on another cylinder and see if it fires ruling it out(its good if it fires).

Again, check the grounds, all wires going to #2, nothing pinched, loose, etc.

Good luck

When coil #3 is put on cyl #2, still the cylinder does not work. When i put coil #2 to cyl#3, this cylinder also stops working.

[TownsendsFJR1300]

When coil #3 is put on cyl #2, still the cylinder does not work. When i put coil #2 to cyl#3, this cylinder also stops working.

Thats with swapping the main wires to each coil too? (IE, coil on cylinder #3, the harness wires go to that coil, for #3)

[papadakn]

I went to a mechanic. He replaced the crank position sensor and cyl#2 coil. In addition he cleaned the carbs (i had already bought the carb repair kit) and now the engine works perfectly.

I am not 100% sure that the coil was bad, i would guess that just the sensor should suffice. Anyway, issue seems to be solved.

Thanks again for your help!

[papadakn]

Unfortunately the mechanic was wrong. I took the boat out for a ride today and although not heavy loaded, it wouldn't accelerate above 2000rpm. The boat never came to plane. I called my mechanic and he told me to try to unscrew the 3 pilot screws one more turn because the engine does not take enough air. At the moment the screws are set to 1 1/2 turns (factory service manual says 1 1/4 +-1/4).

I am afraid that turning the 3 screws will not solve anything. Any suggestions?

[papadakn]

After some further checks, still there is no spark in cyl #2 even though crank position sensor and plug coil have been replaced. What could i check now?

[robert graham]

I had some gauges and tachometer that were erratic when I crossed a wake or rough water.....so while we were running on smooth water I reached under my console/dashboard and jiggled those wires by hand and guess what!...I reproduced my erratic gauge problem!....turned out to be a bit of corrosion on the tips of some in-line fuses.....maybe your problem is loose/corroded or otherwise compromised electrical connections. I think the very damp marine environment plus the vibration and pounding of normal operation plays havoc with all those electrical connections. May want to remove/inspect/clean/grease and tighten each one, because you can't really tell just by looking at them if they're good or not....good luck!

[99yam40]

how about going back to what I said before and check peak voltages with the proper test equipment. That will tell you what is working properly and in spec and what is not