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Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 14306
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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I have a 2004 90 that runs poorly and dies when warm at idle

Customer Question

Hi Dave, I have a 2004 johnson 90 that runs poorly and dies when warm at idle and low rpms. it sounds like its down a cylinder or two. when and if you can get it up in the rpms you can feel it kick in and take off. It runs well on the top end. I've changed fuel, drained the carbs no change. I replaced the optical and the engine ran much much better with a slight stumble at idle I could tell all cylinders were firing as i brought up the rpms. I ran it for about an hour or two, it ran good then the same thing started to happen when when I was going slow in the 5mph zone. It wanted to stall. you could hear it wasn't firing on all cylinders. the engine starts right up but will die after a few seconds. the problem seems even worse now. I put the old optical sensor in and it ran the same. I did notice at one point the tach stopped working. I turned the engine on and off a couple times and it started working. I didn't notice any difference. I disconnected the quick start at idle and the rpms
Submitted: 1 year ago.
Category: Boat
Customer: replied 1 year ago.
when i disconnected the quick start the rpms went up and it stayed running
Expert:  Jason replied 1 year ago.

Hello my name is ***** ***** am I speaking with?

What you are describing is that of a failing coil or a bad powerpack. Do you have a timing light so that you can check for spark on each cylinder? Also, what is the model number on the engine?

Customer: replied 1 year ago.
Hi Jason, My name is***** could get a light. I'm not sure of the model the engine isn't here now, it's out on the mooring. the serial # ***** ***** if that helps.
Expert:  Jason replied 1 year ago.

Hi Tom. This is pretty simple to do. What you want to do is hook up the light and see which cylinders show spark and which do not. If the light flashes there is spark present, no flash means no spark. After that, take the ignition coil that is sparking and swap it for the one that isn't. If the lack of spark follows the coil, it is a bad coil. If the lack of spark stays on the same cylinder, it is a bad powerpack. Does that make sense?

Customer: replied 1 year ago.
ok, I have a light I can use. How would I test it? Thanks, Tom.
Expert:  Jason replied 1 year ago.

I don't understand, are you asking how to use a timing light? Did you see my last reply?

Customer: replied 1 year ago.
the last time i used a timing light was on a car 20 years ago. I guess if you could talk me through where to hook it up and what to look for that would be great. I have an inline spark tester light also if need be. thanks
Customer: replied 1 year ago.
sorry, just saw your answer. thanks, ***** ***** it a try and get back to you.
Expert:  Jason replied 1 year ago.

Unless yours is self powered you would hook up the timing light to the battery first to power up the light. After that it is as simple as hooking up the sensor lead to each plug wire one at a time, hitting the button, and seeing if the light flashes or not. DOes that make sense?

Expert:  Jason replied 1 year ago.

Are you still with me?

Customer: replied 1 year ago.
I'm still here. I'm getting ready to go down to the boat. sometimes it runs ok when cold. when it's warm it won't stay running. how will I check the spark if i can't keep it running? will it still work if I throttle up to keep it running?
Expert:  Jason replied 1 year ago.

Have a helper turn the key just to crank the engine over. If there is spark it would spark regardless if the engine was running, or cranking.

Customer: replied 1 year ago.
ok, Thanks
Expert:  Jason replied 1 year ago.

You are most welcome.

I think that should do it. But I work for tips so I do want to make sure you are happy with my service before you go. If you had a further question on the issue by all means feel free to ask. If not, Just in case you do not understand the way the website works (and some folks do not). You do have to put forth a positive rating in order for it to credit me for helping you. When ratings are not done, the website simply keeps your deposit and they will not credit me. The ratings box is located at the top of the screen. To rate, you must select the start and also confirm it. Please let me know if you run into any problems or errors when trying to do it. If you do have a problem, or if you can not see the ratings box which is at the top of the screen. Please reply back "I rate Jason's service _______" and fill in the blank.

Questions do not close out, so if you have to come back later on with follow up questions to the issue you still can even after doing a rating.

Thank you
Jason

Customer: replied 1 year ago.
Hi Jason,
Why do you think it ran better right away with the new optical sensor then, after an hour or so was running the same as it was. is there a way to check the resistance of the coil also? Are there any other things I could check with a meter? is there a way to check the power pack?
I'm very happy with the quick response. How much time do I have to rate you?
Expert:  Jason replied 1 year ago.

It was more than likely just a fluke with the new optical sensor. When electrical parts go bad they will work when cold, fail when hot, and work when cold again. But there is no time frame in between cold and hot.

As far as the testing goes. It all takes special equipment that you won't have, so thats whey when we do this we try to do it by symptoms. To test the optical sensor takes an oscilliscope. To test the power pack takes a high quality meter such as as a Fluke, as well as a special adapter for that meter called a "Direct Voltage Adaptor", or DVA for short.

Expert:  Jason replied 1 year ago.
Was there anything else?
Customer: replied 1 year ago.
Hi Jason, few more things before i go. I forgot to mention, the engine stays running if I disconnect the quick start. also on the piece the optical sensor is connected to it has a hi lo adjustment on the other side. someone set it on high. what is that tool called to loosen the screw? it's like a torx with a pin in the middle. someone has obviously been through the electronics as screws are missing and some holes are stripped.
Expert:  Jason replied 1 year ago.

The tool is called a tamper proof torx bit/screwdriver.

The symptoms still point to the powerpack. Perform the aforementioned testing and that will tell you if it is a bad coil, or in fact the powerpack.

Expert:  Jason replied 1 year ago.
Hello. Just checking in. Any progress?
Customer: replied 1 year ago.
Hi Jason, I tested the coils with the timing light. they were all firing. I put in an OMC power pack. At first it didn't make a difference then, after a few revs it stayed running. still a little rough. I ran it for a half hour, It seems ok but does not want to stay running at idle speed when warm. I disconnected the quick start to see if it would run different, there was no change. Before the power pack when I disconnected it the rpms would bump up.
Expert:  Jason replied 1 year ago.

Did you replace it with a brand new powerpack, and if yes, was the powerpack the correct part number for that engine? Some have quickstart and others do not.

Customer: replied 1 year ago.
Brand new OMC power pack from the dealer.
Expert:  Jason replied 1 year ago.

Hi Tom,

Did you ever check spark with the timing light to see if any of the cylinders were actually dropping spark?

Customer: replied 1 year ago.
I did use the timing light. all cylinders were firing
Expert:  Jason replied 1 year ago.

If all cylinders were firing then it is not an ignition issue. Have the carbs ever been professionaly gone through on this engine?

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