115 4 stroke loosing RPM and misfire

[glfolts@gmail.com]

Hi all,

I am new to the forum and have a 2002 Yam 115 EFI 4 stroke on a 02 hurricane 19 ft deck boat. I have had the boat for about 4 years and it has never idled quite right (stalls when coming off high RPM)

Recently it began to loose RPM and surge. It has gotten worse and will no longer plane out and sounds like it is missing at high RPM, under load. Out of the water, It idles at start up fine and sounds a little rough but mostly OK . Under load it runs very rough and sounds like it is missing

I do not think I have a fuel delivery problem:
Add new high octane fuel
Checked:
Tried squeezing the fuel bulb when running rough- no change
VST filter (tank and filter were clean no build up)
Fuel pressure at Rail (37-40#, no drop at any speed or while running rough)
All injectors are spraying (tested before reassembling Throttle body) and click when running

I think Compression is not a problem:
Compression (all reach 150-155# and hold)

I have some concern about spark:
All plugs deliver spark
The spark is more yellow with some blue, hard to see
Plugs 1 was pretty fouled (black) and 3 somewhat fouled
Load balance test did not show any cylinder that was not firing (out of water, not under true load)- when injectors are unplugged, one at a time, all drop the RPM a bit as expected

All ECM input sensors seem to be working:
Tested TPS (.75-79 volts at idle- resistance went from .880k closed to 4333 ohms WOT ), WTS (1.67K ohms cold), IAT (22.5K ohm slightly warm engine), and Neutral switch- all seem within spec
Hooked up a test light to the computer (l/wh and r/b wires)- no fault codes blink (I tested to be sure I was getting feedback from the computer by pulling the water temp sensor. The light blinked a 15 code, so I know it is working)
They could be out of adjustment, but none are flat out broke

Air- I have concern with the air and throttle adjustments, but do not know why it would have changed
I pulled the Idle speed control today and made sure the filter on it was clean. I found some carbon build up on the end of the stepper motor, filter seemed ok. When I put it back together at first it would not start- I found that it was being starved of air and would start fine, if I cracked open the throttle valves a bit. I think, at least at this point, the ISC is not opening to allow bypass air at idle. Maybe the ISC is mess up and is allowing air to by pass and mess up the air fuel mix.. Any ideas on how to test this??? I

I noticed that the throttle linkage( small bent rod with snap on ball joints) had the lock nut backed out. When I had it disconnected it might have turned, but the basic symptoms are still the same. Are any components in the linkage or throttle subject to failure?

At this point I think it is either spark or air. Any thoughts or hints would be a great help.

Thanks

[Sparkieboat]

at over $100 a piece I can see why you are hesitant to replace the coils..I know that the air is real important..I have read some post by Rod that mention the crucial importance that the air is set right. I have a 2003 F115 and am just getting familiar with EFI motors...
your post indicates that you have a decent knowledge...how did you test the spark?? I usually use a spark gap tester at 7/16 gap..I noticed that my yammy 4 stroke seemed to have a skinnyer less powerful spark than my carbbed motors...maybe I have a coil problem if I do it is both coils....not sure yet..I have to get my ECU tested as I suspect it to be bad.
I am sure Rod will post a great suggestion for you soon...good luck

[rodbolt17]

if the shutters adjustments have been dinked with you will have to use a 4 channel manometer to reset them.
your describing a classic ISC valve failure.
using the laptop in dynamic test mode cycle the ISC about 5 times while monitoring the valve temp with a temp gun.
if it goes above 200*f its failed.
another quick test???
after the engine runs and immediatly on shut down, listen for the ISC valve to rattle.
this rattle is the stepper motor resetting the valve to 100% opn in anticipation for the next start cycle.
typically after the valve fails it takes the ECU circuits out with it.
that is a waste spark TCI ign.
doesnt give much problems but typically if you pull a plug wire it takes two cylinders out with it.

[glfolts@gmail.com]

F115

Thanks Guys!

I will listen for the stepper motor later this week. And see if I can cycle the stepper. I do not have the YDS, so I can't manually cycle. Would it be a similar test to start the motor and actuate the ISC that way (then check temp)??? Can I pull the ISC stepper out and watch it cycle?

Rob, Are the "classic signs of an ISC problem" the poor running engine or the won't start with throttles closed, or both?

I checked the spark with an actron spark tester. It has an adjustable screw to set a gap for the spark to jump. I am not completely sure how to use it, I got the spark to jump a small gap like a spark plug gap, but screw adjusts out to about 1.5 inches. you mentioned 7/16 in your post. do you actually get a spark to jump that far??? Sounds like a scene from Dr. Frankenstein



Summary:
Any tips on testing with out the YDS
Any tips on the spark gap tool

[rodbolt17]

without YDS there is no way cycle the ISC with the engine running.
what happens is the ISC sticks mechanically and the ECU overcurrents trying to move it.
this leads to overheating the ISC and to much current draw that then overheats the ECU.
while I wont say its common it can happen to anything that uses an ISC or IAC valve.
yes that ign system can jump a 7/16th gap.
but its a 12V setup, waste spark.
anytime cyl 1 fires so does cyl 4,anytime cyl 2 fires so does cyl 3.
on the TCI ign system the ign coil primaries have 12V anytime the key is on, the ECU has some transistors that toggle the ground path,think of it as electronic points.
if the ECU circuits are overheated due to a bad ISC(stuck) then the ECU can do funny things.
on the F225 I have seen it melt the ign coils.

[99yam40]

If the ISC is sticking, seems to me the more you cycle it the more chance you have of hurting the ECU circuit.
But you have to find the problem, so what else can you do.
Maybe you need to take it to a shop that does have the YDS
Just my thoughts

7/16ths is what I have always read for the testing, if it will not jump that then it is weak and maynot spark properly under compression.

[glfolts@gmail.com]

Ok guys thanks for the tips!!!

I will open my gap tool to 7/16 inch and see if it can jump. I am almost positive it wont jump that far...... I have it set at more like 1/8th inch at this point and barely see the spark. SOUNDS TOO WEAK.

I am also going to try and pull the ISC motor (three screws on top) and cycle it out of the valve body. That should let me know if it is working or bunt out.

[rodbolt17]

on this type ign coil and TCI system you cant use a single lead spark tester.
you need to use a tester that hooks to at least both ign coil secondaries.

[glfolts@gmail.com]

Where, pray tell, do I get such a beast????

Does it connect between both plug wires and then to ground?

[Sparkieboat]

can you use 2 single testers????

[rodbolt17]

yes you can use two single testers.
you can also use the stevens s-48 or make a spark tester.

do a google search on homemade spark tester.

[glfolts@gmail.com]

Thanks, Do I both testers to ground or connect them in series somehow???

From what I see online, they fire in series. The current passes from the coil wire for cylinder 1, through cylinder 1 plug, uses ground to complete the path to the cylinder 4 plug, back through cylinder 4 coil wire to complete the circuit.

It would seem that when the tester replaces plug 1 the circuit is complete. How is two testers different than one tester and the other plug still in the cylinder????

[Sparkieboat]

I have been checking out injector stuff and found that just because they have an even spray pattern does not mean that they have even flow..so unless you have had your injectors flow tested you can not rule them out...here is a DIY injector cleaner video I found..I would be curious for Rods opinion of it.
YouTube - DIY Fuel injectors cleaning

[glfolts@gmail.com]

Thanks for the reply! I saw some video on line that showed the injectors filling test tubes and while they all fired, the were filling at different rates. After cleaning they were all filling at the same rate.

I agree, I have not ruled out the injectors. I am currently checking the spark and ISC function, because I think I have fairly quick tests that will eliminate them as probabilities, I have not found an easy test for the injectors, except to confirm they are spraying. I may at some point send them off for cleaning and testing.

[glfolts@gmail.com]

I checked out the spark more closely this week end. My coils read withing the specified range with an ohm meter. (1-4= 24.3K and 2-3=23.7k).

With new plugs installed, I can jump > 7/16 with the plug wire hooked to the spark lead for Coil 4 (C4) and ground. As I understand it, this would run the current from C4 coil wire, through my tester (jump the 7/16 gap), through the engine block to C1 plug and wire (still connected in the engine) to C1 side of the coil. When do the same test on C1 to ground (C4 still connected to the engine) I GET A REALLY CRAPPY SPARK. It will not jump but about a quarter inch). I get the same thing on 2 (good) and 3 (bad). I know you are supposed to test from coil to coil, but I see know reason I should get a different result on the two coils with this test unless my spark plug, wire, or connection is bad on the plug still in the motor. Also the motor runs (fairly rough) with coil 4 out for test, but will barely run when C1 is out for test. Same for 2 and 3.

Summary of test:
C4 to ground Runs fair, good spark jump, plug was wet and fowled when pulled
C3 to ground Runs like crap, will not jump 7/16, plug was in fair shape when pulled (a bit carbonized, but not wet)
C2 to ground Runs fair, Jumps 7/16, plug fowl and wet
C1 to ground Runs like crap, will not jump 7/16, plug looks very good

So it seems that plugs 2 and 4 are not firing, due to bad connector or wire, and I should buy new coils (it seems like the only way to change the wires and connectors is with new coils)

Any thoughts or other suggestions before I spend 200+ on new coils?