1999 Mercury 150 XR6 misfiring during idle and stalling

KDUB10

Cadet
Joined
May 16, 2010
Messages
14
Ok my I just got the boat and motor a couple of months ago and have been having this problem that it keeps stalling at idle. It happens almost every time i go to load the boat back onto the trailer, i will slowly idle and coast onto the trailer and it dies and starts up hard. It is hard to start the motor unless you activate the throttle only, not engaging the prop, however even once it gets going using the throttle only it will stall when put back into neutral. I ran it in my driveway today with the muffs on it and it seemed to start ok, then would start to run rough and would backfire or misfire then would stall. I have replaced the fuel line from the tank to the motor including the primer bulb, replaced all of the spark plugs, cleaned the bottom carbeurator completely disassembling it spraying carb cleaner in all the jets and blowing them out with an air compressor, as well as cleaning the inside of the jets with a piece of small wire. I put a water seperating fuel filter on the fuel line. I put seafoam in the gas, ive tried so many things and now its backfiring. I have a vacation on friday in which im taking the boat so any help is appreciated very much.

thank you
kyle whitcomb
 

kmkeeney

Recruit
Joined
Feb 4, 2011
Messages
2
Re: 1999 Mercury 150 XR6 misfiring during idle and stalling

Kyle,

Did you ever figure out what was causing this problem? It sounds eerily similar to what my engine has been doing lately and I'm about out of ideas.

Kevin
 

1nebel0

Chief Petty Officer
Joined
Nov 28, 2005
Messages
512
Re: 1999 Mercury 150 XR6 misfiring during idle and stalling

This is what I would do... You have to start with a compression test to insure that all cylinders are with 15% of each other. Then you need to do a spark test on all 6 cylinders to insure a good strong blue spark. If that is all good you need to have a DVA meter to start testing the entire electrical system..Time consuming but well worth the time given the cost of a trigger, stator, and two switch boxes not to mention coils. Switch boxes for Mercury are the usual culprit and then stators with coils and triggers failing the least but don't assume anything. Stators are $300 or so...Swith boxes are to replaced in pairs....$400 for two if your lucky...You get the idea...You need a DVA meter and also a peak voltage adapter to capture the readings. Without that you are wasting your time..let me know if you have any other questions...you can get the spec's on the above all over the internet...Good Luck..Just realized this is a real old post...oh well hope this helps someone.....
 

powrguy

Petty Officer 2nd Class
Joined
Aug 7, 2009
Messages
180
Re: 1999 Mercury 150 XR6 misfiring during idle and stalling

Ok my I just got the boat and motor a couple of months ago and have been having this problem that it keeps stalling at idle. It happens almost every time i go to load the boat back onto the trailer, i will slowly idle and coast onto the trailer and it dies and starts up hard. It is hard to start the motor unless you activate the throttle only, not engaging the prop, however even once it gets going using the throttle only it will stall when put back into neutral. I ran it in my driveway today with the muffs on it and it seemed to start ok, then would start to run rough and would backfire or misfire then would stall. I have replaced the fuel line from the tank to the motor including the primer bulb, replaced all of the spark plugs, cleaned the bottom carbeurator completely disassembling it spraying carb cleaner in all the jets and blowing them out with an air compressor, as well as cleaning the inside of the jets with a piece of small wire. I put a water seperating fuel filter on the fuel line. I put seafoam in the gas, ive tried so many things and now its backfiring. I have a vacation on friday in which im taking the boat so any help is appreciated very much.

thank you
kyle whitcomb

I had similar symptoms on my 1988 2.0L Mariner. Turned out that at idle, one switchbox was not firing and I was running (at idle only) on 3 cylinders. Af WOT, it was fine, and even didn't hesitate on acceleration. I changed out both switchboxes and it's fine now.
 

j_martin

Admiral
Joined
Sep 22, 2006
Messages
7,474
Re: 1999 Mercury 150 XR6 misfiring during idle and stalling

I had similar symptoms on my 1988 2.0L Mariner. Turned out that at idle, one switchbox was not firing and I was running (at idle only) on 3 cylinders. Af WOT, it was fine, and even didn't hesitate on acceleration. I changed out both switchboxes and it's fine now.

OR...... it could be a fuel problem. The quickest and least expensive route to a repair is proper diagnostics. Start with compression, etc.

hope it helps
john
 
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