#3 cylinder, good spark - no fire

[bogginyota]

I have a 1997 Force 120hp. The third cylinder down has no fire; however, there is spark. I've checked the coil and the plugs. The #3 plug appears to be a lot cleaner than the others. I'm not sure if it has water or just unburnt fuel on it.

I've read other threads that suggest exhaust plate/gasket or head gasket and even the reed pedals. I'm at a loss and need some suggestions/advice. Is there a way to check if it's the reed without taking it all apart? How can I diagnose the exact piece I need to replace?

The one thing that struck me as odd, is that while the motor is running, I can touch the spark plug boots for 1, 2, and 4, but touching the spark plug for boot 3 gives me a tremendous shock. I traded the number 3 spark plug with the other plugs and the #3 boot still shocked me. I recently changed the stator, the regulator, and bought a new 1000amp battery.

 

[pnwboat]

Re: #3 cylinder, good spark - no fire

Before you start taking anything apart, the first thing you should do is to perform a compression check on all the cylinders and let us know what the reading are.

 

[Frank Acampora]

Re: #3 cylinder, good spark - no fire

It is a possibility that with a shorting boot, you are losing spark under compression. Try swapping (if possible) the boot or even the coil and wire onto another cylinder and see if the problem moves to it. If it does, replace the boot or even the coil and wire (I believe the wires are not replaceable and the whole coil/wire assembly must be replaced)

 

[bogginyota]

Re: #3 cylinder, good spark - no fire

The compression on all 4 cylinders is right at 120psi. While investigating the problem I rearranged the coils and the spark plugs multiple times, however no matter which coil or spark plug was on the #3 cylinder the problem stayed on that cylinder. I tested the coils by unplugging the trigger at the coil and plugging them back in one at a time while the engine was running. Unplugging #1 and #2 I couldn't clearly tell if they were working until I plugged them back in. When plugging them back in the motor burned the extra fuel (faint pop and puff of smoke) that accumulated while unplugged, and gained some RPMs. #3 did not respond in any way no matter what coil or plug I had on that cylinder. When I unplugged #4 the motor died every time. While using a spark tester i could clearly see spark from all 4 plug wires, plus I touched the boot on #3 while the engine was running, big big big shock.

Will a spark plug still spark if it has some water on it? After reading other treads it seems like they do and that in turn steam cleans the cylinder. I looked in to the spark plug hole and it is equally dirty to the others.

 

[pnwboat]

Re: #3 cylinder, good spark - no fire

Sounds like you may have a bad plug wire/boot on #3 cylinder, but from what you are describing (re-arranging coils), not so sure that it's causing a problem. How does the motor run? A really clean plug usually indicates that it is not firing the way it should. You should see some carbon deposits on it

If you have the Mercury style CDM ignition system with the 4 pin modular connectors on the wiring harness that attach to the coil/CD packs, the spark plug wires are replaceable. The wires "screw" into the coils. The hole in the coil where the wire goes has a threaded stud in the middle of it. To remove the wires, just twist the wire counter clock-wise. To install the wire, stick it into the hole and twist it clock-wise until it you feel it get hard to turn. This indicates that the wire has bottomed out and you're good to go. Most of the wires that I've seen on the CDM ignition are solid core wires, not the spiral wound carbon core RF suppression type used on most ignition systems nowadays.

If enough water is getting into a cylinder to affect the way it runs, then you can usually see very small water droplets on the end of the plug itself. It's normal to see some oil on the end of the plug, but if water is present, you can see the small beads of water too, since the water doesn't mix with the oil. Depending on how long the motor has been running in this condition and how extensive the carbon deposits are, the piston may or may not show signs of being "steam cleaned". Usually you see that affect on the head itself which is difficult to see from looking into the spark plug hole.

Like you mentioned, water in the cylinder is usually a bad head gasket, which is relatively cheap and easy to change or, the exhaust cover gasket leaking, or a small crack in the stainless steel exhaust cover baffle plate.

 

[bogginyota]

Re: #3 cylinder, good spark - no fire

Thank for you advice pnwboat. All the testing I did with the coils and plugs give me the impression that the coils, plugs, and wires are in good working order. In a different thread some time ago you helped out a guy with the same problem. In the end hes said he had broken a reed, but he never said why he checked them. If its a reed like he says it was how does that explain the water in his #3 cylinder?

This is the link to the post.

http://forums.iboats.com/force-chry...r-not-working-543780.html?highlight=onthechip

 

[bogginyota]

Re: #3 cylinder, good spark - no fire

Sorry I forgot to answer your question. The motor run ok, it misses from time to time. As fare as the plugs #s 1, 2, and 4 have some build up and are slightly gooey. Which I believe is typical. #3 comes out clean with fuel and maybe a few very tiny specks of water. I'm going to try and put up a picture of #3s plug.

 

[bogginyota]

Re: #3 cylinder, good spark - no fire

View attachment 223992

 

[pnwboat]

Re: #3 cylinder, good spark - no fire

I looked at that old post. I vaguely remember that one. That one was kind of unusual. The difference is that he was seeing milky residue on his plugs. I also remember that the only motors that I've ever seen with broken or cracked reed petals are the 1995 and later motors. Not saying that the earlier ones don't break or crack, I've just never seen or heard of one breaking. Having re-read the link to the old post, I guess you could inspect the reed petals, but to do that, you have to remove the carburetors and carburetor adapters. If you're really careful, you might be able to get away with re-using the old gaskets. Just be really careful removing the carburetor adapters and reed block assemblies.

I guess the bottom line is that you have several directions to go. My own person preference would be to check the reed petals first. Not that hard to do, and if you're careful, won't cost anything if you can re-use the gaskets. You do have to make sure the carbs are all "sync'ed" up after re-installing them, but again, not a difficult task.

If the reed valves are OK, then it's a coin toss as to whether I look at the head gasket or exhaust cover gasket. Either one has some risk involved. The risk is corrosion causing a bolt to seize. Easy to break one off. The head bolts are larger in diameter, so they're a little harder to break off, but still possible. The exhaust cover is known for seized bolts and just my opinion would be the most likely culprit for a water leak, but you never can tell 100% for sure. You know how "opinions" are LOL! I hope this helps give you some idea as to which direction you feel you should go.

NOTE: Can't open your attachment.

 

[bogginyota]

Re: #3 cylinder, good spark - no fire

Would a broken or cracked reed pedal result in water in the cylinder? If so why? Wouldn't I see water it in both cylinders associated with the faulty reed?

Is it normal for my 97 120hp to cut off only when I unplug the trigger from #4 coil but keep running while I have others unplugged? (1 at a time of course)

 

[pnwboat]

Re: #3 cylinder, good spark - no fire

A broken reed would not allow water from the cooling system to enter the cylinder.

The older post indicated milky residue which is usually water or moisture mixed with oil. I suspect that there must have been some type of atmospheric conditions, either outside temperature, or something like that, combined with blow back that was causing moisture in the air itself to collect in the crank case and cause the milky residue. What ever it was, it was unique and not the norm. There is one reed block assy. for each cylinder, four in total. Two reed block assemblies sit under the top carb, and two sit under the bottom carb. In all the cases that I've seen with leaky head gasket or exhaust cover problem, there was no milky residue, you could actually see very small water droplets on the plugs.

Here is a picture of a complete set of reed valve blocks for a 1995 - 1998 120HP motor.



This is what they look like from the top. If you look at the hole in the carburetor adapter on the right, you can kind of see the reed valve block sitting down in there.


Normally.... killing the spark for one cylinder should not stall the motor. Remember that #3 doesn't seem to be working like it should. When you kill the spark for #4 it's too much for the motor to overcome. Why it does not kill the motor when you kill #1 or #2 cylinders, I don't know. Maybe it has something to do with the fact that #3 and #4 cylinders are fed by the same carburetor.

 

[Jiggz]

Re: #3 cylinder, good spark - no fire

Reeds are individualized to each cylinder. In your case, you have 4 cylinders hence should have 4 reeds, one for each cylinder even though you only have two carbs. With a broken petal on a reed, usually this can be indicated with a slight decrease in compression, which sometimes is hard to determine depending on the gauge used. You can check the reeds on 3 & 4 cylinders following PNW's lead.

Personally, I would conduct another test before doing so. Remove the plug on #3 cylinder, activate the kill switch to prevent the engine from starting and then get a clean cotton rag and ball it up to a size of a tennis ball. Hold the ball of rag in front of the #3 plug hole about 1/2 inch away and then had someone crank the motor for a second or two. Look into the rag and you should see some fuel wetting resulting from the fuel-air mixture blowing from the cylinder, assuming the reed is operating properly.

In fact, there should be a strong smell of fuel from the rag. If not, then the reed is faulty. Just make sure you wear your face or eye protection if you have to do this. If you cannot tell if there is strong smell of fuel or wetting, try doing the same on a known working cylinder and then compare the results.

 

[bogginyota]

Re: #3 cylinder, good spark - no fire

Thanks for the clarification on the reeds pnwboat. Jiggz, that's a great idea. If i get equal amounts form all the cylinders tested that tells me the reeds are fine, correct? Should I do the reed test with the water off?

I am leaning more towards the exhaust plate to be my culprit. After I do the reed test Ill tell you the results. Thanks for everyone's input, it is greatly appreciated!

 

[Jiggz]

Re: #3 cylinder, good spark - no fire

With a broken reed, a cylinder will have a free flow of air from and two the crankcase and carb. In short, when the piston goes up it creates low pressure in the crankcase allowing air/fuel mixture to come in from the carb. With a good working reed, when the piston comes down, this air-fuel mix gets compressed a little bit until the piston clears the intake ports, which then makes the compressed mixture to rush into the cylinder.

However, if the reed is broken, during downward stroke of the piston instead of compressing the air-fuel mix in the crankcase, it blows back out of the carburetor. Even after the piston clears the intake ports, very little of the fresh air-fuel mix goes into the cylinders instead some of the exhaust gases stays in the cylinder. This is the reason the affected cylinder never fires.

 

[oldboat1]

Re: #3 cylinder, good spark - no fire

Can you switch out the #3 plug with a known good one? The issue doesn't seem to be a leaking boot (#3), as you are getting shocked at #3 whatever wire is used. Just for grins, though, you might run the engine in a darkened area or at night and see if you see any leakage in any of the wires or boots.

note: see in #1 that you already tried switching plugs, so guess that test is moot. sorry.

 

[bogginyota]

Re: #3 cylinder, good spark - no fire



This is a picture of the #3 plug. The plug was wiped clean and run for about 5 minutes.

This is the attachment from an earlier post that wouldn't open.

 

[pnwboat]

Re: #3 cylinder, good spark - no fire

Hard to tell but looks like some oil residue which is normal, but it also looks like some water drops may be sitting on the end too.

 

[bogginyota]

Re: #3 cylinder, good spark - no fire

I too think it's got a bit of water on the plug. my compression test 120-123 on all cylinders. Are those numbers within spec?

 

[pnwboat]

Re: #3 cylinder, good spark - no fire

120-123 on all cylinders is a little lower than average for a 1997 motor. You should see around 140. 120 is not something that I would worry about. Keep in mind that there is a wide variation on the accuracy of some of the standard compression gauges. I have two gauges. One is a KD brand mechanical gauge that I've had for at least 20 years which reads 130 PSI on my motor. I have another newer Mityvac calibrated electronic gauge that reads 155 PSI. As long as the readings are within 10% of each other and in the 120ish range, I wouldn't worry about it.

 

[Jiggz]

Re: #3 cylinder, good spark - no fire

I maybe looking at the plug differently, although I agree it has oil and trace of water in it, there is also no indication of spark. Usually, when a plug produces spark especially with this gapless style, there will be carbon trace of spark in the ceramic between the anode and cathode. Unless the plug shown is a very new one that was just installed. Of course, there is a very easy way to verify if it really sparks by uninstalling the plug connecting the plug wire and grounding it to the motor. Start the motor and you should see spark right there in the center anode arcing over to the cathode.