Motor jumps around wildly, misfiring

[archcycle]

1990 Johnson 140

http://www.youtube.com/watch?v=CYJ3RzD0-yQ
I'm aware of what's written on the cowling

It runs smoothly up to about 2300, then starts to miss badly until it hits a brick wall at 2800. Occasionally it will act like its going to take off, smoothing out and pulling for a moment,then drop back to 2800ish. It's missing really hard.

This started last fall which was when I last used it. Took it out and half way through the day this started so I limped home. Sparks checked good, cleaned the carbs. Went out the next weekend and it ran awesome for the whole day, starting and stopping until time to go home. Fired up to go home and it started this again. Limped home, where it sat untouched during hunting season until this weekend.

I replaced every last fuel line on the motor and going to the motor, thoroughly cleaned the carbs until they were like new inside and out, cleaned out the fuel tanks and filled up with fresh gas and ethanol treatment thinking fuel had been the issue last time. So it's not fuel it's an intermittent ignition issue. Fuel flow through the bulb is great.

Since this weekend I haven't had a chance to go step by step through the ignition troubleshooting in my OMC manual. All cylinders have spark, but the lower starboard doesn't respond much to the cylinder drop test however it does respond.

Does anyone see an obvious problem or tell tale symptom here? I guess maybe timer base with it missing like this?

Good compression, brand new suppression plugs, and ignition components tested good last year but I'll test again as soon as I can.

 

[Chriswalden]

Re: Motor jumps around wildly, misfiring

without knowing too much about that ignition system, keep it simple. Check all your grounds and then see how strong your spark is. See if it will still jump a 1/4" gap with a strong blue spark, no yellow or red.

 

[WernerF]

Re: Motor jumps around wildly, misfiring

Looks like the power pack is in overtemp rpm limit mode (2500 rpm) for some reason.

 

[Chinewalker]

Re: Motor jumps around wildly, misfiring

Almost sounds to me like the carbs might be fouled. That motor has four separate carburetors. If any one of them is gunked up, it could lose power like that, particularly if it's a high speed jet, which really doesn't do much until you get into the throttle a bit. Don't run anymore until you can either eliminate them as a cause or get them cleaned as you can blow the motor due to lack of lubrication on the associated cylinder(s).

 

[daselbee]

Re: Motor jumps around wildly, misfiring

Looks like the power pack is in overtemp rpm limit mode (2500 rpm) for some reason.

Sounds like SLOW mode to me too. Check head temps with palm of hand (2-3 secs) or digital temp gun.
If not truly overheating, unplug the temp sensors, and see if the problem goes away.

 

[boobie]

Re: Motor jumps around wildly, misfiring

Me Too. SLOW mode. If you don't have an overheat you could have something else puttinng it into SLOW.

 

[archcycle]

Re: Motor jumps around wildly, misfiring

It's not spark, all spark tests were all great with hot blue sparks.
It's not compression, all four tested at 130-140 in a straight cold test.
It's not air/fuel, as I've done a thorough job of cleaning the carbs and jets and passages, replaced every fuel line frpm the tanks to the carb feeders, replaced the fuel/water separating filter, and cleaned out the tanks and verified fuel flow while running.

So moving on to all of those SLOW recommendations. First off both of my temp sensors each have just one tan lead coming out of them. I was under the impression one ought to have another lead but I think that's just for quickstart anyway. It's always worked without it.

It's not overheating. I can touch all over the heads without getting burned and the telltale is lukewarm.

Can't test the temp sensor grounds until I can get back to the water, but here's what I got on the power pack SLOW tests:

ohmmeter set to 200K. OMC manual says set it to Rx100 scale but mine has a 20K and then a 200K. Seemed like an ok choice.

disconnected power pack orange and orange/black leads from the terminal strip

PP O to ground - 9.7
PP O/Bl to ground - no continuity
PP O to O/Bl - no continuity

The OMC manual is a bit unclear. Is that O to ground bad?

 

[laderwell]

Re: Motor jumps around wildly, misfiring

I had that happen to me when I was out. I had a spare 6 gallon tank which i hooked up and the problem went away. The final problem was my anti siphon valve and pick up tube screen.

hope that helps

 

[archcycle]

Re: Motor jumps around wildly, misfiring

It can't be anti siphon because my boat uses a pair of 12 gallon plastic tanks in the center console. I've cleaned them both and neither has an anti siphon.

 

[99yam40]

Re: Motor jumps around wildly, misfiring

Think about it, if you have good compression, that does not come and go that I have ever seen.

So that leaves spark or fuel/ air mix that can cause a cylinder to miss fire.

Spark is easy to see with an induction timing light on the different plug wires while problem is happening, and will also show if timing is in spec.

If all is good then you are left with fuel.
spraying a fuel/oil mix into the throats of individual carbs while problem is happening will help show if a cylinder is running too lean to fire properly.
A lot harder to test for too rich in cylinder, but maybe pinching off the fuel line to different carbs if you can get to them

Simple way of eliminating what you can test and then work on what you cannot test

 

[archcycle]

Re: Motor jumps around wildly, misfiring

I appreciate all of the suggestions everyone please keep them coming

spraying premix - last october, before parking it for the season, I did spray premix into each cylinder and they all bogged. now with them even cleaner it should still be ok but I might as well do it again. Not like there's any shortage of available premix since I filled both tanks on Saturday as a way of insisting to myself that it was fixed before putting it on the water. Will post new results from that when I get home.

timing - last year I checked the #1 timing before parking it and it was correct, assuming quickstart was working which I have my doubts about, but did not mark off and test 2/3/4 and test them. With the timing being a static setting it's hard to imagine it being the issue since the problem started out as intermittent and I haven't changed the timing since before or after it started. Will do those and post new results tonight.

The intermittency when it first started does scream ignition.. I should mention that the coils are only about a year old.

But how about the SLOW system power pack results? Can anyone tell me if the reading I got on the ohmmeter says bad power pack?

 

[99yam40]

Re: Motor jumps around wildly, misfiring

See if you can find the info you need on this http://issuu.com/cdielectronics/docs/troubleshootingguide/124?mode=a_p Page 43-46 may help and 105 charts

 

[daselbee]

Re: Motor jumps around wildly, misfiring

Dude...why not just do as I suggest and simply disconnect the tan leads? Run it. You are making it more difficult that it has to be.

Brush up on the operation of the temp sensors, too. The "temp sensor grounds" is the case of the sensor itself, which is in contact with the hole in the head that it is mounted in, and if that was corroded to the point that no electrical connection could be made, the sensor would never trigger an overheat nor would it trigger SLOW. It would be like it was always open electrically.

 

[archcycle]

Re: Motor jumps around wildly, misfiring

you can bet i will drop it in the water and test without those sensors the first chance i get. weather issues here. since it's been intermittent and sometimes it will start to take off then decide not to, it seems reasonable to me to pursue other possibilities in the mean time.

 

[daselbee]

Re: Motor jumps around wildly, misfiring

Lots of times using resistance measurements to do a GO-NO GO test on an electronic component is a waste of time.

The reason is that due to various meter qualities, in specific, various BIAS current supplied by the meter, will result in just plain weird
readings. Nothing like the book says it should be. Ever notice that the service manual specifies EXACTLY which meter they used to take the readings?

I have three meters. One el-cheapo, one Simpson analog, and one BK Precision digital. When testing timerbases, I get different readings from all three on the same TB. And to make matters worse, try to do peak voltage readings (DVA) with three different meters, (some using the home built adapter, some using the internal circuits). It will just make you shake your head.

Personally, I would never trust just a resistance measurement to determine a bad part. Well, a fuse maybe!!! In fact, to me, it so unreliable, that I will not even do the test, unless I knew exactly what to expect.

Now excuse me, I have to go out and check a box of fuses to make sure thay are not shorted....

 

[archcycle]

Re: Motor jumps around wildly, misfiring

hence why i ask if my resistance measurement is ok, considering that the measurement scale on my multimeter does not even match the format of the manual

i hate the idea that the solution has to wait for a chance to get on the water but that's probably the case. forecasts for the 32563 have more downpours every day into the weekend right now. as soon as there's an evening where i can take it out ill post some updates on how it likes no temp sensors.

 

[99yam40]

Re: Motor jumps around wildly, misfiring

If you do not want to use the proper equipment or get the manual to tell you what the specs or proper equipment to use then just flip and coin and hope as you replace parts

 

[archcycle]

Re: Motor jumps around wildly, misfiring

If you do not want to use the proper equipment or get the manual to tell you what the specs or proper equipment to use then just flip and coin and hope as you replace parts

99yam40 do you have a multimeter that reads in Rx100? Maybe you do, I don't know, but I went to home depot, lowes, and two pawn shops yesterday and every multimeter i found measured in K just like mine. Did you read where i said my OMC service manual (yes, factory) says if at Rx100 you get 96+/- 10ohms on this SLOW test that the powerpack was bad? Did you read the part where I got a reading on that test and just asked about whether the 200k scale is comparable to Rx100 scale? Conversions? If you knew enough about electrical tests to answer the question you probably would have so I'm going to assume you don't. If that's the case then you have no reason to talk trash in this thread. If you have something real too add though, please do, otherwise don't get sarcastic when someone asks a troubleshooting question on a troubleshooting forum.

 

[archcycle]

Re: Motor jumps around wildly, misfiring

thanks daselbee that gives me some hope for my ohmmeter result.

That said.. after some googling it's my understanding the Rx100 scale will apply to analog meters, and a k = 100 so 95*100=9500 ohms and therefore a scale that reads near that on a multimeter is the corresponding setting. a K=1000 so 20K on the multimeter = readings between 0 and 20,000 so the answer was 20K is the correct setting to look for the 9500 reading that the manual was looking for at 95+/-10 at Rx100, or 1k*9.5 (where I got 9.7 and allow for some margin of error from my tool vs. their tool). an analog meter would be measuring in how many 100s, but my multimeter measures in 1000s so you have an x10 conversion to get what my 1000 scale would show on a 100 scale. someone please correct me if i've misunderstood that.

but no matter. i'll let the on the water test be the judge of it like you said. i really hope i'm wrong about the power pack because i had to replace it 18 months ago and if it's bad again then there is a larger problem.

 

[daselbee]

Re: Motor jumps around wildly, misfiring

Arch:

"ohmmeter set to 200K. OMC manual says set it to Rx100 scale but mine has a 20K and then a 200K. Seemed like an ok choice.

disconnected power pack orange and orange/black leads from the terminal strip

PP O to ground - 9.7
PP O/Bl to ground - no continuity
PP O to O/Bl - no continuity"

First reading....9.7....now taking what you posted, 200k scale, that means that the meter will read up to 200 thousand ohms and no more before going off scale. A reading of 9.7 on a 200k scale is 9,700 ohms.

Your next scale down, 20k, will give virtually the same reading, but with added decimal places...like 9.754....which is 9,754 ohms.
More accuracy.

The Rx100 deal is for analog meters, where the needle swings to the resistance value being measured. Set on Rx100, if the needle swings to 1/2 of the scale, it will be on a 5, and the resistance would be 5x100=500 ohms. So you see, that the book wants you to use an analog meter, and they have a higher bias current source than a digital multimeter. Your choice should have been to set the DMM to the 200 scale (or possibly the 2k scale ) when trying for an equivalent setting against a Rx100 requirement.

You never posted what value the book calls for on the three measurements you took. Basically, you have 9.7k, open and open. What does the book say they should be?

If the book says you should have a specific resistance range on either of the two opens, then likely your meter will not supply enough bias to "turn on" the circuit internally to the pack, and therefore read open.

It is tricky. Your readings could very well change simply be reversing the polarity of the leads themselves.

My opinion, you are pi**ing into the wind trying to measure a PP for a GO/NOGO determination. Best to measure the operating voltages instead of passive resistance.