Intermittent Engine Stall

P

Phil Chieco

Member
Member
Joined
Jun 25, 2001
RO Number
5084
Messages
67
I have a 2002 4.3 L MerCruiser with thunderbolt ignition and non EFI carburetor that I have been getting an intermittent stall either during a slow cruise or while in neutral. The engine just stops and almost appears like I flipped the kill switch. After a few minutes of trying to start the engine it would eventually start again and run fine. Two years ago the distributor, distributor cap rotor and sensor were all replaced as I cracked the distributer while putting in a new sensor due to no spark. This year I Replaced fuel seperator and plugs and still having issues. I was planning on replacing the coil next. Any assistance would be appreciated.

Thank you for your responses. Is there any documentation someone can provide that would show me how to either test the neutral start switch or the lanyard switch to determine if it could possibly be the problem?
 
That does sound electrical but why replace the coil before you've tested it with an ohmmeter?

The "Mechanical How-To" forum on the boatered website is a wealth of valuable info.
"Posted - Feb 26 2004 : 21:30:04 Show Profile
Ignition Coils

Measuring Internal Coil Resistance If you suspect a malfunctioning ignition coil, check the resistance of primary and secondary windings. Do this when the coil is hot, and again when it is cold. Also measure from the case to each connector.
The primary windings should have a very low resistance, typically from a few tenths of an ohm to a few ohms. The secondary windings have a higher resistance, typically in the 10,000 to 13,000 ohm range. To get the actual figures for a specific coil, check the manufacturer's specs. But as a rule of thumb, primary windings range from a few tenths of an ohm to a few ohms, and secondary winding may be 10 ohms or more.

George Van Parys, http://www.boatfix.com "

I believe that forum has manuals for diagnosing Thunderbolt problems too.

I would strongly suggest turning on the motor at the dock and giving all on-engine harness wires and those around the ign switch , kill switch and battery The Serious Wiggle Test to see if it cuts out. If so, you are "getting warm".

Also , since it doesn't take much reduction in fuel flow to stall out at engine running at low rpm, when it stalls you might just quickly remove the flame arrestor and look down the carb throat while you press the throttle lever , to confirm a good shot of gas comes out , and that it smells strong & fresh.
 
If this is an I/O could the shift cut out be an issue?
 
quote:
Originally posted by boatbum

If this is an I/O could the shift cut out be an issue?

Click to expand...


Bingo. 4.3 w/ an Alpha One, first place I'd go is shift interrupt switch. Been almost twenty years since I worked with Mercs for a living, but those switches were "fast-mover" parts.

It's really just a little microswitch, they crack and break easily. Not much to be done in the way of adjustment, but easy enough to troubleshoot.
 
quote:
Originally posted by Radioactive

Check the safety lanyard switch...

Click to expand...


Only failure mode I’ve ever seen there is human error. Since he mentioned it in his post, I kind of ruled it out, but you’re correct - it’s a possibility. I’m still seeing textbook shift interrupt switch failure, though. Past life I worked at a Mercruiser distributor - those switches were on the same shelf as water pump kits and lower unit seal kits and bellows. Fast-movers, right at the top of the stairs in a three story warehouse. (I was in damned good shape by the time I left that job! Heavy stuff like manifolds and heads that didn’t move as fast was all the way upstairs. Different story now that I sit in a chair for a living.)
 
quote:
Originally posted by Sandy

That does sound electrical but why replace the coil before you've tested it with an ohmmeter?

The "Mechanical How-To" forum on the boatered website is a wealth of valuable info.
"Posted - Feb 26 2004 : 21:30:04 Show Profile
Ignition Coils

Measuring Internal Coil Resistance If you suspect a malfunctioning ignition coil, check the resistance of primary and secondary windings. Do this when the coil is hot, and again when it is cold. Also measure from the case to each connector.
The primary windings should have a very low resistance, typically from a few tenths of an ohm to a few ohms. The secondary windings have a higher resistance, typically in the 10,000 to 13,000 ohm range. To get the actual figures for a specific coil, check the manufacturer's specs. But as a rule of thumb, primary windings range from a few tenths of an ohm to a few ohms, and secondary winding may be 10 ohms or more.

George Van Parys, http://www.boatfix.com "

I believe that forum has manuals for diagnosing Thunderbolt problems too.

I would strongly suggest turning on the motor at the dock and giving all on-engine harness wires and those around the ign switch , kill switch and battery The Serious Wiggle Test to see if it cuts out. If so, you are "getting warm".

Also , since it doesn't take much reduction in fuel flow to stall out at engine running at low rpm, when it stalls you might just quickly remove the flame arrestor and look down the carb throat while you press the throttle lever , to confirm a good shot of gas comes out , and that it smells strong & fresh.

Click to expand...


You need an anchor to view those posts.
 
It's not a good idea to bypass the switch. What it does is cut the engine out briefly when you shift so as to protect the gears in the outdrive. It's supposed to be a brief cut out. I think what I might do is look it over carefully. Look for loose mounting or other insecure mechanicals associated with the assembly. Perhaps stick an ohm meter on it while tapping it lightly. Maybe NC has a better approach. It could be cheap enough to swap out and hope for the best.
 
Ok. The boat acted up today and now will not start at all. I pulled a spark plug and grounded it while I turned over the engine and I did get a spark. I also pulled the flame arrester and checked to see if I was getting fuel in the carb. That checked out when I tried to start it I saw a mist of fuel. So now I am starting to think its either the kill switch or the shift interrupter switch. I have a MPC 4000 series mechanical panel control but not quite sure on how to get at either of the switches without removing the entire panel. Does anyone have a step by step instructions to troubleshoot this. Thank you
 
If it will not start ensure it is in neutral and apropriately jumper the switches one at a time?
 
Well I finally figured it out. One of the leads to the ignition switch was barely attached and when the boat vibrated came detached. I realized this when the engine would crank but I had no power at the dash.
 
That's simply awesome! Congrats on the fix.

I recently found an interesting one...while on plane, my port engine would "dive" in RPMS once in a while. Then while at dock, the radio cut in and out...yep, bad battery, it was piping hot! I guess under full load the coil needs more than the alternator can handle. Plus I had to use parallel to start the engine. But the RPMs dropping was a weird symptom.
 
I would think the alternator could handle the full load of the engine and then some. When you get the battery in check the voltage at the battery and compare it with the gauge on the dash. It should be floating at 13.6 or there abouts when fully charged.
 
You must log in or register to reply here.
Back
Top