Force 125HP misfiring, running rough...

[fmt2bx]

Bad day!!!
Motor has been running great and suddenly, running rough seems more like misfiring than fuel starvation.

At idle, runs a bit rough but not too noticeable. RPM at 900 to 1000 today (neutral), usually 1100RPM.

When opening throttle, seems ok at first then motor starts to run rough, vibration. Then smooths out but I could hear a slight "bang" noise.
After stopping engine for 20 min, engines runs ok all the way to WOT, then as it warms up it starts to run rough again.
Very erratic though.
When motor runs ok I only get about 4200 4400 RPM, usually getting 4800.

What I did so far:
-Changed spark plugs.
- Fuel pump ok, (in line filter more than 3/4 full). Fuel filter clean.
- Cleaned and Checked grounding from Coils and ignition box.
-Checked spark plugs wires seemed ok

How should I proceed from here? Any suggestion ?

Thank you.

Cheers.

 

[jerryjerry05]

Year???
Compression/ spark test.
The 125 came with a couple of different style of ignitions.
The early ones had the plug in type connectors, the later the screw down.
Try the trigger wires, they sometimes break under the shrink wrap, look good but make it miss.

Outboard ignition.com test procedures for your motor.

 

[fmt2bx]

Thanks for reply. Year is 1986, lots of plugs in there, i guess it is the plug-in type.

 

[fmt2bx]

1986 Force 125hp

 

[fmt2bx]

BTW:

The motor is a 1986. MDEL: 1251X6A // SN:2607

I was looking on the iBoat forum for the Ignition switch box. The site has this model part for 1986-1988:
http://www.iboats.com/mall/partfind...gd_poid=334618&gd_row=44&session_id=263292466

However the ignition box on my engine looks more like the 1985 model:
http://www.iboats.com/mall/partfind...gd_poid=334619&gd_row=43&session_id=263292466

I cannot find a part/model number on my ignition box, so I can't match it with the info on the site.

What do you think?
Thanks

 

[fmt2bx]

Year???
Compression/ spark test.
The 125 came with a couple of different style of ignitions.
The early ones had the plug in type connectors, the later the screw down.
Try the trigger wires, they sometimes break under the shrink wrap, look good but make it miss.

Outboard ignition.com test procedures for your motor.

Jerry,

Thanks.
Where are the trigger wires? Are they the wires connected to the CDI box?
I'll post the compression test number as soon as I have them.
Will also do another spark test but was ok yesterday.
Thanks

 

[fmt2bx]

Update:

I checked all the wires off the switch box, all appeared good.
I ran the primary and secondary test on the coils. 2 Coils were showing 0 on secondary test, turn out to be the spark plug connectors inside boot, completely corroded. Replaced and checked ok.
Verified,and cleaned all electrical connections. Some showing a bit of corrosion but overall pretty good.

After fixing the spark plug connectors off the 2 coils, went for test run.

Better but still acting up.

Getting 4600 RPM max at WOT, no misfire passed idle but idle is rough. I took some videos.
If I run the engine hard for a few minutes and go to idle (neutral), I read 1100/1200RPM, if I let it there, the RPM goes down to 900 after a few minutes and I can definitively hear now and then the engine "quit" for a split sec then back on.
I had one instance where the motor didn't recover from the misfire and simply quit.
Sometimes the motor runs just perfectly for 10 20 minutes then the issue starts all over again and it can last for a while.

I am reading the maintenance manual right now and I was wondering, how does the engine shuts down normally? Is there a shut-off wire somewhere that I should check?


Questions:

1)- Can a coil be erratic?
2)- Can a switch box be erratic ?



The following videos show the sudden drop of RPM then recovery.

-Erratic idle:

https://youtu.be/1BGoDa3DjB0



-Sudden 250rpm drop then recovery

https://youtu.be/2liIyXmcr2Y



-At 2 sec and at 36 sec. Sudden drop.

https://youtu.be/3G5ueM4RrcM




Thanks

 

[Jiggz]

Inconsistent misfire like yours are very hard to diagnose. Usually, the only method I use is through process of elimination starting with the easy ones. Electrical in this case is easy by simply using a timing light. connect the timing light to one of the plug wires and then bounce it off a dark colored paper while idling. Watch the bounced off light for consistency and move on to the next spark plug until you've seen all four. Take note which plug wire gave you the inconsistencies with reference to the tone of the motor while idling and then troubleshoot from there.

If all plug wires shows consistency of sparks, then the next diagnosis will be mechanical. You will need to open and inspect the reeds to see if they are still closing properly. Any petal not closing with tolerance, you have the initial option of reversing those petals and then test ran it again. If the motor idle and performance improves, you have the final option of replacing those reeds (by sets).

If reeds are in perfect condition, the next diagnosis should be on fuel. Again start with the fuel air mixture first by setting them all at 1 turn out from lightly seated. This setting is the initial setting from the manufacturer and YOU SHOULD NEVER SET LOWER THAN THIS. Use the official method of opening the screw one at a time until the engine starts to bog down due to very rich mixture and then start closing it in until it starts to bog down due to a very lean mixture. Mark both extreme settings and set the screw right in the middle. After you set it in the middle verify how many turn is the screw from lightly seated. IT SHOULD NOT BE LESS THAN ONE TURN OUT FROM LIGHTLY SEATED!!! If it is then open the screw to one turn to 1 1/8 turn out from lightly seated. Do the same for the other remaining carb.

If problem persists, the next diagnosis will be the fuel recirc system. You will need to disconnect all the hoses to the fuel recirc system and make sure none is clogged. You need to be careful as these are very old hoses and usually easily breaks. You need to check your manual for details on this system works.

As for how the system is turned off, there is a wire (usually white in color) on each CDM that connects to the ignition switch through the terminal board in the engine cowling that when the ignition sw is turn off, it connects these wires to ground (M terminals on the switch) thus shunting the CDM to discharge to ground instead of the ignition coil and spark plugs, thus shutting off the motor.

 

[fmt2bx]

Ok thanks, I'll start with the timing light and plug wires.

 

[Glastron_V210]

I'm just finishing fixing up the ignition on my bottom two clyinders with the same ignition system. I found that when cold, the stator output coils would generate the required output, but when warm, one of the stator coils would go open circuit, killing the power supply to one of the cdi packs responsible for the bottom 2 cylinders. the sytem is Prestolite CDI and parts are available for it still.

I'm not saying this is your issue, but it certainly could be.

You're going to have to get it in the state where it misfires, and then check the spark at that time. The easiest way is to warm it up cruising around the bay, then get it back on the trailer when it misfires. Pull the spark plugs out of the head, then reconnect the high tension wires to the plugs and wrap the spark plugs in the threaded section with a bare wire, then to ground.

Have a helper turn the engine over and see what is going on. If one cylinder is dead, try swapping the spark plugs. If the same cylinder is still dead (IE not the plugs), try swapping ignition coils. If the same one is still dead (IE, not the coil), then you're looking at trigger or CDI pack. You can swap triggers next.

Through all of this, DO NOT mix up where the connectors originally were. In fact, maybe mark them before you start all this stuff. The colours are repeated.

If two plugs on the same CDI pack are dead, it's likely the stator, although it could be the CDI pack, or the shorting wire (White) on the CDI shorted out somewhere.

There are other tests you can do with a meter, and a DVA, but start there and get a general idea of what is going on.

You may have a weak spark that fails to ignite the cylinder from time to time.

After watching the videos it almost seems like preignition/backfire. That would be very unusual though. Check timing as suggested.



Chay

 

[fmt2bx]

I'm just finishing fixing up the ignition on my bottom two clyinders with the same ignition system. I found that when cold, the stator output coils would generate the required output, but when warm, one of the stator coils would go open circuit, killing the power supply to one of the cdi packs responsible for the bottom 2 cylinders. the sytem is Prestolite CDI and parts are available for it still.

I'm not saying this is your issue, but it certainly could be.

You're going to have to get it in the state where it misfires, and then check the spark at that time. The easiest way is to warm it up cruising around the bay, then get it back on the trailer when it misfires. Pull the spark plugs out of the head, then reconnect the high tension wires to the plugs and wrap the spark plugs in the threaded section with a bare wire, then to ground.

Have a helper turn the engine over and see what is going on. If one cylinder is dead, try swapping the spark plugs. If the same cylinder is still dead (IE not the plugs), try swapping ignition coils. If the same one is still dead (IE, not the coil), then you're looking at trigger or CDI pack. You can swap triggers next.

Through all of this, DO NOT mix up where the connectors originally were. In fact, maybe mark them before you start all this stuff. The colours are repeated.

If two plugs on the same CDI pack are dead, it's likely the stator, although it could be the CDI pack, or the shorting wire (White) on the CDI shorted out somewhere.

There are other tests you can do with a meter, and a DVA, but start there and get a general idea of what is going on.

You may have a weak spark that fails to ignite the cylinder from time to time.

After watching the videos it almost seems like preignition/backfire. That would be very unusual though. Check timing as suggested.



Chay

Chay,

Thanks so much for all the great info. At this stage, you are right, I can't ignore any possibility. I just wish that the engine would quit instead of being so erratic.It makes it so hard to diagnose the issue or issues.
Thanks again.
Fmt

 

[fmt2bx]

Update 07/16/15:

Did a compression test and I am getting 125, 125, 124,125.

Something strange happened though. I got this boat 6 weeks ago, at first the idle speed was good, right around 1000RPM (neutral), after using the boat for few weeks, the idle speed decreased to about 800RPM in neutral and the motor would stall quite often when engaging forward gear. I adjusted the idle speed back to about 1000 to 1100 RPM, that mostly solved the problem. Then after a week I noticed that the idle speed was decreasing slightly every day. Note, that sometimes it came back to 1100RPM.

So this afternoon, I had the boat in the driveway on a very slight slope, bow pointing down. After doing the compression test, I rigged the timing light to follow Jigzz instruction and stated the motor. At first I had some difficulties starting, which by the way, is very unusual, this motor always started easily in the past (even with recent issue).
Once started, the idle was very rough oscillating between 600 and 1000 rpm and all of a sudden it went to 1400RPM and stayed there!!!! Actually, it sounded very good, too high but still sounded great.
I re-adjusted the idle speed to get 1000RPM.

Also, the other day when the motor started to act up, I remembered that while on the water, I tried to trim the motor and it seemed to make the problem worse.

Seems like the angle of the motor has an influence on the way it runs. Could this be a possible carburetor/float/needle issue? I dont see what else could make a difference. Fuel recirc system perhaps!?!

It is highly probable that there might be more than one issue here, maybe an electric issue and a fuel issue. I might have had the fuel issue for some time now and something else compounded the problem.

Anyway, it is overwhelming at time.

Tomorrow I'll do the timing light test on the spark plugs and see what I get.

Thanks guys for all the great info.

Cheers.

FMT

 

[SkiDad]

just a shot in the dark but I noticed your top spark plug wire has tape on it - have you checked the plug wire where it goes into the coil. - i picked up a whole ignition of eBay last year CHEAP for parts - the power packs were in good shape the wire coming out of 2 or 3 of the coils where loose feeling to me - i pulled one apart and the insulation inside the wiring was dry and easily cracked - i just keep the good coil and power packs for a spare. But I'm wondering if one of the wires is dancing and loosing a little contact when you are running. maybe with gloves you could see if gently moving it does anything

 

[Jiggz]

Great observation. However, process of elimination is still the way to go just to make sure you do not miss anything and end up doing more. Eliminate the electrical part with the spark consistency diagnosis. You can also eliminate the fuel by monitoring that clear fuel filter making sure it at least stays 3/4 full. As for the engine running better at an angle, the only thing that changes when the angle of the boat changes as far as the engine is concern should only be the fuel level in the carb's bowls. Now this can affect the position of the float hence the inlet needle valve. The other thing that could also get affected is the flow of unburned fuel in the crankshaft casing which will tend to pool towards the reed's instead of getting sucked in to the intake port and finally into the fuel recirc system. Maybe you should remove the air covers for the carbs (while diagnosing) so you can have more visual if there is too much blowback of fuel coming from the carbs.

 

[Glastron_V210]

You know, I was thinking about this some more.

It's possible you have a load of crappy gas.

One way to diagnose this is to get a kicker tank, fill it with known good gas, then take it out and try it. You could very well be hitting a patch of water once in a while.

If you have water in the carb bowl this could explain the tilt changing things too.

If you try this, first pull the carb bowl drains and try to capture the fuel in there, then inspect it for water. Purge the system with good fuel as best as you can and run the known fuel source.


Chay

 

[Glastron_V210]

I thought about this some more...you could have a load of crappy gas in there and be hitting some water from time to time.

Water in the carb bowls could be the cause of changing with trim as well.

I'd try purging the system (drain carbs...collect and check fuel for water etc), the use a kicker tank with known good ags and see what happens. It's rare, I know, but will send you into these type of gyrations trying to find the issue.

Chay

 

[jreyn006]

Is that a crack on the lower right hand corner of the lower coil?

 

[fmt2bx]

just a shot in the dark but I noticed your top spark plug wire has tape on it - have you checked the plug wire where it goes into the coil. - i picked up a whole ignition of eBay last year CHEAP for parts - the power packs were in good shape the wire coming out of 2 or 3 of the coils where loose feeling to me - i pulled one apart and the insulation inside the wiring was dry and easily cracked - i just keep the good coil and power packs for a spare. But I'm wondering if one of the wires is dancing and loosing a little contact when you are running. maybe with gloves you could see if gently moving it does anything

Good point. I have noticed when changing the plug connectors in boots that the wires seemed pretty dry. Continuity test was ok, however I agree, it could use some new wires. Seems like the wires come with the coil tho. Right?
Thanks

 

[fmt2bx]

You know, I was thinking about this some more.

It's possible you have a load of crappy gas.

One way to diagnose this is to get a kicker tank, fill it with known good gas, then take it out and try it. You could very well be hitting a patch of water once in a while.

If you have water in the carb bowl this could explain the tilt changing things too.

If you try this, first pull the carb bowl drains and try to capture the fuel in there, then inspect it for water. Purge the system with good fuel as best as you can and run the known fuel source.


Chay

Thanks Chay, I removed the carb bowls and didn't see any presence of water but that's a good point. I seriously believe that I might have more than one issue here.

 

[fmt2bx]

Is that a crack on the lower right hand corner of the lower coil?

No crack on coils but thanks.
Cheers