Mercruiser V6 4.3 Thunderbolt V Ignition Problems?

[watrski4ever]

Hi folks, I have a 1997 V6, 2 bbl carburetor, (engine SN OKO282235) MCM 4.3 LX Gen+, that is giving me some, what I can only assume, are ignition problems. I'll be running along, smoothly cruising 4000-4300 rpm when the engine will quit - like someone turned off the ignition switch, no warning, no spitting and sputtering just stop. After I pull her back into neutral, she'll fire right back up and off we go again...for ten minutes or so then it does it again. So far, it has always started right back up - with no problem. Before I go throwing parts at this thing does anyone have any ideas as to what this might be?

 

[zealer]

What happens if you let it idle? Does it still cut off after 10 minutes, does it take longer? Are you getting good oil pressure? Do any alarms go off? Could be a lot of things I suppose. Faulty ignition switch or wiring, deadman switch/wiring.

 

[NHGuy]

Any chance you could run with the motor box open? If so you could eye the shift interrupt and see if it pulls it out of the V where it's supposed to stay.
You could also just run the motor and start wiggling wires at the dock.

 

[watrski4ever]

What happens if you let it idle? Does it still cut off after 10 minutes, does it take longer? Are you getting good oil pressure? Do any alarms go off? Could be a lot of things I suppose. Faulty ignition switch or wiring, deadman switch/wiring.

I haven't tried just letting it idle to see if it will have the same symptoms. After I started having problems, I pulled it out of the water and brought it home. Oil pressure has been good, no alarms, no deadman switch on this boat.

 

[watrski4ever]

Any chance you could run with the motor box open? If so you could eye the shift interrupt and see if it pulls it out of the V where it's supposed to stay.
You could also just run the motor and start wiggling wires at the dock.

I should be able to pull the engine cover off and run it with ears on in the driveway. Which other wires do you think I should be "wiggling" besides the shift interrupt?
Thanks

 

[alldodge]

Check the pickup inside the distributer, it may be loose. Also may need to run a ground wire from the distributer case to the engine block .

 

[Bondo]

I should be able to pull the engine cover off and run it with ears on in the driveway. Which other wires do you think I should be "wiggling" besides the shift interrupt?
Thanks

Ayuh,..... Welcome Aboard,....... All of the wires of the Ignition circuit, from the battery, to the coil's (+) terminal,.....

 

[watrski4ever]

I Finally got around to working on this problem. I ran it in the driveway and it behaved the same way; ran perfectly then stopped; restarted it and repeated the same thing. I wiggled every wire I could find and got no reaction. The I pulled the distributor cap off to check for anything loose inside as suggested by AllDodge. Nothing was loose but the pick-up looked really corroded. I have ordered a new one and of course am hoping it does the trick. You can see in the picture below how bad the old pick-up looks. I will update when I get the new parts. Thanks for all of your insight so far!

 

[watrski4ever]

Sorry about the multiple uploads! I kept getting an error message that it wasn't uploading so I retried it... a few times LOL

 

[watrski4ever]

Rather than waiting for a new pick-up sensor, I decided to try cleaning off the rust on the pick-up sensor with a small file and it all came off without too much effort. I put it all back together and started her up and I believe that was the problem! She ran perfectly without any issues. I appreciate all the assistance.

 

[Bondo]

Sorry about the multiple uploads! I kept getting an error message that it wasn't uploading so I retried it... a few times LOL

Ayuh,.... Use yer "Refresh" button,......... Alot, Anytime yer in doubt,......

 

[Bowboss]

Hi folks, I have a 1997 V6, 2 bbl carburetor, (engine SN OKO282235) MCM 4.3 LX Gen+, that is giving me some, what I can only assume, are ignition problems. I'll be running along, smoothly cruising 4000-4300 rpm when the engine will quit - like someone turned off the ignition switch, no warning, no spitting and sputtering just stop. After I pull her back into neutral, she'll fire right back up and off we go again...for ten minutes or so then it does it again. So far, it has always started right back up - with no problem. Before I go throwing parts at this thing does anyone have any ideas as to what this might be?

WOW. Just WOW! that year range 96-97 EVEN on VOLVOS had that same problem!! and i have been scouring the internet forums everywhere for MONTHS to try to find a way to fix it!

I finally solved mine. First things first
Change your ignition control module located inside the distributor. It's pretty much toast

Forget about genuine mercruiser parts. These charge almost double for the same thing you can get a really well made one at autozone (made in the U.S.A by wells) for like 45 bucks and it has a lifetime warranty.

Second step. The alternator wiring must be changed.

You problem must be that you alternator is pumping too much voltage in turn which is killing the HEI module. it's likely pumping 15-16 volts which is way too high. They must of wired the purple ignition wire to the EXcite and sense terminals on the alternator. Whoever did the harness style in those years must of really screwed it all up. But volvo and merc wont admit it.

The correct way is to bridge the sense terminal with the BATTERY main terminal on the alternator. THIS ALONE sould drop the voltage to 14.2 or 14.5 (basically acceptable limits to not do any harm to the HEI module)

I take it that you must have a vbelt driven alternator. If so this should be your problem that could potentially give you a heartache. You'd think it would be a faulty voltage regulator but it's actually the sense wire detecting the current flow wrong since my theory is that the excite terminal draws current close to the sense terminal so the sense terminal is thinking that there is a deficiency in voltage so it must tell the regulator to kick up that to such a high amount.

Give this a shot and tell me how it goes.

Mike.

 

[Bowboss]

oh and I almost forgot. Heres the backview of what i had to go through on my alternator.

basically where it says +12 volts switched and +12 volts sensed. Those two should NOT share the same wire. Instead the sense terminal should share with the positive main charging wire. That's a much better place for the regulator to sense voltage since that wire goes straight to the battery.

 

[alldodge]

Bowboss, Don't see the OP having the same issue as your discussing. If the problem the OP had does come back, then further testing will need to be done to verify if an over voltage issue exist.

 

[Bowboss]

Bowboss, Don't see the OP having the same issue as your discussing. If the problem the OP had does come back, then further testing will need to be done to verify if an over voltage issue exist.

His issue is almost IDENTICAL to the issue i've had. 3k to 4500 rpm is perfect for the alternator to pump far too much voltage. Eventually it gets to the point where the engine does not start back up because the HEI module gets too hot or fried.

They are mostly all the same in that year. My boat is a 97 as well with the SAME engine and SAME displacement. It's likely his is carbureted as well. 2 bbl holley carb.

 

[watrski4ever]

I finally got this thing back in the water and discovered my "fix" had nothing to do with my problem. Bowboss, I'm intrigued by your overcharging the system theory but need to clarify my problem. I am going to change the HEI module to see if that fixes the problem. But I discovered today that the problem has gotten much more frequent and rpm's have nothing to do with the problem. I could be idling or cruising at 4000 rpms. It quits, sometimes after 10-15 seconds, sometimes it takes a few minutes. It restarts right away without any hesitation. I changed the coil today, but that wasn't it. Module next. I'll post my results.

 

[achris]

Merc ignitions systems and Volvo ignition systems are COMPLETELY different. The only things the same are the base block from GM...

Watrski. Have you established where it's an ignition (spark) problem or fuel? If it's becoming more frequent, it may be worth putting a timing light on one of the spark leads and watching it....

Chris.......

 

[watrski4ever]

I haven't positively confirmed it's an ignition issue, but I have confirmed there is gas in the carb when it quits. The way it behaves seems more like a spark issue I think; no sputtering or bucking or rough running, just stops running. Using a timing light is a good idea to positively confirm loss of spark though. I ordered a new HEI module and will install it and run it. If that doesn't take care of the problem, I will use your timing light idea. Thanks.

 

[watrski4ever]

I changed the HEI module today and there was no change. Still runs perfectly for a few minutes and then dies. Starts back up, runs a few more minutes and dies. I am going to try achris' idea and try to track down a timing light and watch to see if it is in fact an ignition issue. Any other suggestions would be greatly appreciated.

 

[Watermann]

Throwing expensive parts at a ghost intermittent problem really is frustrating. GM and their 90's distributor pick up sensors cause that exact problem until one day it just won't start back up again. This happens in the GM vehicles as well.