Help.....Cutting Out

[EricG]

My Boat has developed a bit of a gremlin that I need some help diagnosing.

Basically, when running over approximately 3000 it cuts out (quits for just a second and backfires) and then keeps running fine. It started doing it only when taking a big hit, but now it seems to do it randomly. As long as I keep the boat running conservatively, it runs fine, but if I try to get on it - it starts again. I originally thought it was a short, because it seemed like the dash was going dead, but I was actually just catching the Tach and Oil Pressure going down for a brief second, the other gauges seem to keep their power fine.

It's a 1988 350 Magnum - Qjet Carb, Merc Thunderbolt IV, Alpha.

Anybody ever have a similar problem, or have any suggestions? Thanks,

EG

[Moody Blu']

umm intake leak? vaccum leak?

[rong]

This was a good one. When I first got my boat, it was running well for the first couple of times out. Then all of a sudden it would do what your talking about. Eventually it would quit altogether. I would leave it alone for 10 minutes and off again. I would fool with the points thinking I fixed it. What it eventually came to be is the coil. It was mounted horizontally with an aftermarket bracket and one mounting bolt to the intake. During the run the casing of the coil was bouncing off the intake denting the coil case. Eventually the thing quit altogether which allowed me to properly troubleshoot it. Intermittient problems are always a guess unless you can catch it doing the problem. Well maybe something you can check. Seeing the power go from the gauges is interesting. Do you have a Main Plug Connect to the engine. These sometimes come loose or corrode.

[Formula Jr]

THE BaCK FIRE TO ME POINTS TO a PROBLEM WITH YOUR PLUG WIRING HaRNESS. CHECK aLL THE WIRES FOR CROSS FIRE. I heaRD you had a little SaLT waTER IN THE BOaT aT SOUTH SOUND...

IS THIS a MISS OR a COMPLETE SHUT DOWN OF aLL THE PLUGS? If a miss its probably the secondary (coil to engine ground strap.) If a complete momentary loss of firing, then it is either the primary (everything before the +/- terminals of the coil, the coil) or a float adjustment. Coil is easy to check. run it in ice. then run it hot.

[Stix Magill]

Eric,
My Minx with a 1997 350 mag has a very similar problem. Every now and then it will abruptly shut down, usually while planing. 3K RPMs sounds about right. I don't have a backfire though. One time before this happened and I tightened the battery terminal connection and it didn't do it again for months. Coincidence? I will let you know if I figure mine out.

[Surfer]

This is a timely question, am having the same problem right about 3000. But the problem is only under a load, will run fine in neutral. Novice gear head that I am, I've been thinking fuel starvation, changing filters ect. could somebody
elaborate on the coil test. Thanks

[Formula Jr]

*=a

Coils *re very e*sy to repl*ce *nyw*y. *ny V8 *uto coil will do *s * known good. *g*in the only re*l difference being the m*teri*ls the termin*ls *re m*de from *nd the housing co*ting. If your re*lly che*p *nd w*nt to check for he*t rel*ted opens in the coil, then run it with *n ice p*d *round the coil once its hot *nd the f*ult is h*ppening. See if the f*ult stops.

the a is a terrible key to lose...... :D

[Jamesbon]

Had the same problem a couple years ago, turned out to be a bad coil.

[EricG]

Wow Owen....That makes for interesting reading!!

Anyway, I'm not positive, but it sure seems like a total shut-down for a brief second as opposed to just a miss. It doesn't backfire every time, but probably 50% of the "cough's" include a backfire....I seems to do that when it catches again. I was thinking Coil/ignition too. I think I'll start with the Coil, Cap and Wires (since I've never replaced any of them since I've owned the boat :rolleyes: ).

Thanks for your input everyone, I'll keep you all posted.

[CnV & Family]

Eric,

We had a similar problem when we first acquired our 16. Turned out that the plug wires were very worn and arcing was occurring in rough water. I pulled and replaced the wires and have had no problems since. We would get sputtering and cutouts, even had the engine die but never a backfire. Never observed any issues with the gauges... probably because I was always looking back expecting the worst.

I've been busy and didn't realize how close our problem was to yours until a second read on this topic. Would have posted sooner!

-C

[Surfer]

thanks for the coil info, after I get out my decoder ring I will go to work on the boat...Sorry to hear about the AAAAAAAAAAAA

[Bryan Tuvell 33ZX]

Good luck fixing her!

Formula Jr... that a=* killed me, I read the entire email before seeing the above key!
Whew, thank goodness for 1800 or I might not have figured it out sober eek!
r/Bryan

[RickR]

3000rpm=<advance@>rpm
Check the simple things also, like moisture in the distributor cap. :rolleyes:

[Tidbart]

You want simple? Check the ignition switch for loose connections. The rivets come loose from all the jarring. Then they make and break contact as you are driving. The engine will cutout and then turn back on immediately. It happened to my eighteen and drove me nuts. The bouncing of the wiring and the key with chain on it eventually does a job on the $18 part. I would start there.
I found my problem accidently. As I was sitting in the boat and listening to music with boat off, I bumped the key and saw the voltmeter drop 6 volts and then come up again. Found my 8 month old problem, that 3 Merc mechanics couldn't.
Good luck.
Bob

[Formula Jr]

RickR is right on. Th@t's where @dv@nce st@rts. Excellent Point..|||||||||||||

-excl@m@tion point is gone too.... :D

[RickR]

Formula
Total advance should be "all in" around 3000rpms.

[olredalert]

Geez,

------This sounds so similar to what Ive been going thru this week.Changed the points,rotor,cap,and condensor out and seemed to have an intrmittent miss.Nothing seemed wrong when I took the cap off and as I kept thinking about it I remembered that I also had put in twenty bucks worth of 93 octane just before launch.Pulled the Merc fuel-filter,dumped it and found it had a load of water.93 octane has been really bad up here for the last couple of weeks at least.Even different stations!Put the heavy duty "heat" in the tank,and it was OK today,along with a new fuel filter............gassy......ol red!

[oldLenny]

...From another post it seems you fixed it...If so, what was it. I want to know. It was interesting. If the water was too rough and you only got to 3K on Lake Washington, then it should have bailed out on you,..unless you fixed it?

Was someone right?...

Was it something different?...

Can you tell us?.. :rolleyes:

[EricG]

I haven't totally fixed it....but the water was sooooo crappy that I didn't get a great test...here's where I'm at:

Last week, Just getting on a plane caused it to sputter and backfire once I got going a little bit, it would run fine below 3000, but if I went above that 3000 number, it started the intermittent cut-out.

This weekend I replaced the Cap (had lots of build-up on the contacts), the Rotor, the Wires, the Plugs, the In Carb filter (some gunk in there, but not totally plugged), and the H20/fuel seperator (no noticable water in there when I dumped it into a jar).
Now it planes fine, and wasn't cutting out near as bad (in fact, I didn't think the problem was there for the first part of the day), at one point I got it up to about 3600 for a mile or so, and it was running fine. Then, during the last part of the trip, at about 3000, every time I took a bad hit (and they were bad hits eek! ) it would do it again.

I bought a new coil but didn't put it in yet, because I wanted to see if the other stuff fixed it.

So, to make a short story even longer.....it's better - but not quite 100% yet.

-EG

[PaulO]

One more thing to check as I have had this recently: On an alpha drive, if the shift adjustment is getting out of whack, pressure on the throttle lever can kick in the cut-out switch during acceleration. Disconnect the micro switch on the shift linkage to test. Do not shift much without the switch connected though. Just enough to determine if that is the cause.
PaulO

[rong]

The ignition switch sounds more like it, if the gauges are still dropping out during the misfire.
FYI, on the coil. I researched and found a HI-Vibration coil made by Accel. It's in an epoxy case that's compact, with no oil and is working great on both my 302 's. It's somewhat hard to find, requires browsing on the Accel site. It's uses the street/strip coil makeup.

[EricG]

I was wondering about the Shift interupter. As I have Zero Effort controls, I don't think it's the pressure on the throttle knocking the shift mechanism (different lever), but, is it possible that when taking a big hit, it could engage the "cut-out" mechanism?

As far as the dash going dead...I think I was wrong when I initially thought that was happening. Now the dash keeps it's power throughout.

Thanks again to everyone for the ideas...I'll let you know what happens next time out (which may be awhile...damn non boating committments wink )

EG

[Formula Jr]

If you've tr@ced it down to the l2 volt side there's four pl@ces to check thru.

l. Shift interupt.
This is @ mirco switch mounted to the top of the re@r of your engine. There is @ little tunning fork looking swing @rm th@t moment@rily compresses the switch to ground out your ignition. Very difficult to @djust. @nd not @ likely c@ndid@te if it is working well right now.

2. Kill Switch. Depending on the type you h@ve, check to m@ke sure the cont@cts @re held completely open by the Pl@stic key.

3. In Ge@r St@rt s@fty switch. This is intern@l to your shifter housing. Not @ likely c@ndid@te @lso @s this just disconnects your St@rted Selinode.

4. Ignition switch. If you h@ve @ l@rge key Fob these C@n go B@d @nd its the g@ngling of the Keys th@t bre@k the cont@ct. Try using just THE key t@ped in Pl@ce.

Since your entire engine is being shut off monent@r@ly, but you still H@ve D@sh power, the Gremlin is living somewhere on the plus side of your Coil. Purple Wire #5 on the H@rness. Some where @long the line this is being Shorted to Ground or It is losing cont@ct thru @ b@d crimp or termin@l. Tr@ce this wire's cont@ct @ll the w@y b@ck to the B@ttery's plus termin@l. If its @ll good, then look @t the Neg@tive side of the Coil. I @m @ssuming you H@ve ruled out the Coil by now WITH @ KNOWN GOOD. We do know th@t the f@lure is Shock rel@ted - @s opposed to he@t or run time. So its wires @nd cont@cts moving @round th@t set the problem off. The problem should then be tr@c@ble @t idle on the muffs if you st@rt b@nging @round the bo@t. Like T@ke @ soft H@mmer @nd give the B@ttery @ good t@p @nd see Wh@t H@ppens. Or just giggle things @round while On the Muffs @t idle. Good Hunting

[Surfer]

After reading all of the above, I went at it, and found loose electrical connections everywhere. Tightend up the entire boat and she runs great. Sometimes it is that simple.

[Forrest]

I know exactly what it is. You need a new keyboard - - - dude!!

[RickR]

You can bypass all the interupters and switches by installing a jumper (wire w/alligator clips ) directly from the battery to the + side on coilDon't forget to remove it when you're done testing. :rolleyes: