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Schizoid engine behavior

timbo59

New member
"Hi there,
Ple


"Hi there,
Please bear with me, as I have a rather confusing problem to try and solve.

We own a 1995 Sea Ray 230 DA powered by a 5.0 Mercruiser that we purchased about a year or so ago. One of the reasons we purchased the boat is that it came with a refurbished engine that had been dropped in 3 years ago, plus new manifolds that were little more than 8 months old when we purchased the boat. Being a complete moron where engines are concerned I was happy with the purchase, as the engine had less than 100 hours on it at the time of purchase and thus seemed a good investment for someone who barely knows how to tinker with the mechanical side of things – ask me to install a kitchen, rewire a house, tile a floor, reconfigure the plumbing, whatever, I can do it quite happily – stick an engine in front of me and I’m lost! I know the theory, but not much on the practical side of things.

As luck would have it though the engine has recently started giving us problems, and it’s driving both me and my mechanic crazy. At the end of last autumn it began developing a problem where it began choking and coughing at higher speeds but would settle back down once the throttle was eased back to cruising speed, but once you tried upping it again back would come the spluttering. I was told at the time that it could be something as simple as the fuel filter, but I pulled it off, checked that all was okay by pouring the fuel into a bottle and checking the contents for any sign of water or debris, and then placed a new filter back on.

The new summer came around this year and we decided to take the boat out. I did the smart thing and gave the engine a good run the night before we went out and all seemed fine. Started up almost first time, purred away nicely as I revved it up. Beautiful. Next day we got down to the St. Johns here in Florida, put it in the water, and the SOB wouldn’t start. I eventually coaxed it to life, got it up to 2000 RPM for a few minutes to warm it up and shake the cobwebs out, then tried to ease it down to put it in gear. I wasn’t anywhere near neutral when it conked out on me, and no matter what I did I couldn’t get it started. I ended up running the batteries down trying to do so.

I called in a reputable mechanic to take a look at it for us here at our home, and he gave it a really good going over but could find nothing wrong. The damn thing started up straight away for him, ran beautifully for him at both high rpm’s and at idle, and had no trouble running nicely when put in gear. He suggested that perhaps the fuel was a little stale, told me to top the tank up with some 93 octane gas, and maybe throw in some fuel cleaner as well.

Back we went to the St. Johns last weekend, kids all cock-a-hoop that we were finally going to make it out, and the damn thing gave me a repeat performance of the previous occasion. It refused to start up after I’d pumped the throttle, came to life after I’d let it sit for 10 minutes, then died on me as I eased it back towards neutral after a warm up. Trying to start up again proved a fruitless exercise – it would just turn over and over. A five or ten minute wait though yielded results, as up it would start again, only to die once I eased it back under 1000rpm. I felt like giving the boat the last rites and putting a hole in the bottom of it! In my driveway the damn thing ran just fine, but put it in the water and it threw a hissy fit! Off we went home again!

The mechanic was determined to get to the root of the problem and offered to come out free of charge to the boat ramp the next day to see if he could nut out the problem. So off we went. And what happened once I got the boat in the water? It started up like a charm first time for him, revved up beautifully, and came back to neutral like it had never had a problem in its life! Did a feel like a fool – YES! I was sitting there going “but…but…but” trying to convince the guy I wasn’t the local village idiot, and he suggested we go out for a run to really check it out.

Off we went, and the boat ran perfectly, leaving me feeling even more foolish as he got it up to the kind of speeds that had caused problems last year. Then, thankfully (if one can be thankful under such circumstances) the engine commenced to show its true qualities by spluttering and slowly dying back until we came to an absolute standstill. All attempts to restart failed, and I was left joyfully muttering “There see, that’s what it’s been doing all this time! Now you see I wasn’t crazy!” He pulled off the carb, used some engine spray to get us restarted, and off we went – for about a hundred yards. Then it died again. This kept up for about 15 minutes, by which time the engine refused to start up at all. All the indicators seemed to suggest that there was something wrong with the carburetor, particularly in the way one had to wait a while before it would kick back to life – like it was getting flooded and needed a while to dry out. Yet the mechanic said that the way the engine was popping and backfiring as it was dying indicated that it was running lean. When it wouldn’t restart at all he pulled out his tester and checked to see if it was sparking at all, and discovered that it wasn’t. The mystery deepened. Finally we had to resort to hailing down another boat to tow us in the half-mile or so to the ramp.

With the boat out of the water he ran a compression test and found everything was okay (thankfully – I was sweating on that one), saw that the spark plugs were in reasonable shape, then checked the distributor, which seemed visually okay – clean, no rust, etc. We then put the boat back in the water on the trailer, watched it start up first time, and then go on to exhibit its Jeckyl and Hyde character for the next half hour. It would run perfectly for a few minutes, in neutral or even in gear with some revs behind it, then suddenly kick over into its nasty side and splutter/backfire its way to a full stop. It would lose spark one minute, then suddenly give it back. Most times after it died he’d have to wait a few minutes before it would purr back to life again, on the odd occasion it went the other way and started up in sweet mode straight after coughing painfully to a halt. It was simply very frustrating and bewildering to watch.

The mechanic is starting to thing that the distributor (at least that thing that’s inside once you pull off the cap) may be overheating and cutting out, and that’s going to be his first line of attack when he comes back on the weekend. But if that’s the case and it explains why the engine seemed to need a rest before it would start again, why did we have a few instances where it started up straight away running perfectly after having died off? My own little theory was that something might have been floating around inside the carburetor that eventually floated up into a key area and cut off the fuel supply, only to fall back down once the engine was dead and start the whole process again. But then if that, or anything else was wrong with the carb, why should it affect the sparking? On the other hand, if it’s the electrics, why does it seem to be affecting the carb by making it run lean and backfire? Has anyone ever come across this Jeckyl and Hyde behavior before?

The mechanic stayed out there with me for nigh on four hours, and didn’t charge me a cent for his time as he felt he’d underestimated the problem in the first place – can’t blame him, given how perfectly it ran in my driveway. He’ll start with the coil and distributor first, and if that doesn’t work he won’t charge me for the parts and will move on to working on the carb. If that doesn’t work I’ll pull out the pump action and put the boat out of my misery!

Just for my own interest I’d really appreciate it if anyone can share their own thoughts or experiences on the matter. Just seems like I have a landlubber of a boat that doesn’t like getting its feet wet!

Apologies for the long-winded nature of my post. I just really wanted to spell it all out so that readers could really comprehend the problems we’ve been having. Just seems I’ve landed one of those idiosyncratic engines that wants to make life difficult as far as diagnosis is concerned."
 
Sure sounds like an ignition c

Sure sounds like an ignition coil to me...
 
"Had a similar problem albeit

"Had a similar problem albeit not as severe, Dizzy cap came off 3 times and was declared fine, boat felt like it was running lean. Eventually replaced the cap and all 8 leads....now runs perfect!"
 
"Mechanic thinks it might be t

"Mechanic thinks it might be the sensor in the ignition module - does that make sense? He's ordered one in, but we'll have to wait a few days to find out.

Thing that beats me is that he feels it's heat related. On two separate days, as I mentioned before, I tried starting the engine in the mornings when I wanted to go out in the boat with my family. The engine was stone cold and gave me grief from the very beginning. Yet the day he came down to check it out, again when it was cold, it started straight up and idled perfectly.

It's this inconsistent behavior, cold or hot, low or high rpms, that is puzzling me. It runs like a champion one minute, dies in the petoot on the other, coughing and backfiring the whole way. Very weird.

Until I'm 100% certain this thing is gone I don't feel safe taking my family out. I'm just nervous all will seem okay, and 20 miles from home the thing will suddenly conk out on me again. It's going to get a damn good run before I let the wife and kids come out on it for a trip.

Lastly, I should also have added that we did check the fuel pump and lines to be sure that everything was fine from that end, and all was a-okay.

Thanks for the feedback so far."
 
"The first line is to perform

"The first line is to perform a full tune up.
especially if true history is not known. Also keep a log of services performed to help keep track of hours of operation and time for service intervals.
Spark plugs, cap, rotor, ignition cables, and a coil as they are cheap. I keep a spare coil on board as well. Once we know it is tuned up, then the diagnostics can commence if the concern shows its ugly face again. Also, I don't know what rpm's you were hitting on the muffs, but 1500 rpm's is the recommended limit on muffs or neutral, as per mercruiser. Also check fuel tank vent is clear and also check carb inlet screen is clean.

Kurt"
 
"Tim:

The first thing I wou


"Tim:

The first thing I would check, since it's an intermittant problem, would be ALL related electrical connections. Remove the ground wire on the ignition module and clean the connector and the contact surface w/400 grit sand paper; reattach and coat w/white grease.

Remove the dist. cap and the rotor and inspect the optic trigger sensor for rust. If you find rust on it, that may be part of the problem. I would consider replacing it for $50.

Disconnect each elec. component plug and inspect for corrosion and clean as needed. Make sure to inspect the main engine barrel plug.

Clean the coil connections the same as above and leave the gray tach. wire disconnected and taped. Wipe the the coil upper half clean w/a clean cloth and WD-40 to remove finite dirt.

Start the engine on muffs to see if the problem reappears. If it does not, take it to the lake and run it w/in a close proximity of the ramp. If you can not duplicate the problem, leave the tach. disconnected for a few boat trips to be sure the problem is gone.

If the problem rears it's ugly head again, reconnect the tach."
 
"Hi Guy,
Sorry to take


"Hi Guy,
Sorry to take a few days to get back to this. Been very busy looking after kids while my wife was visiting relatives in Ohio.

I think the mechanic is on the same page as you, Guy. He did inspect the sensor and said it looked fine, but he's bringing out another next time we take the boat to the ramp just in case. We were supposed to go today, but it's taken longer than expected for a new ignition module to come in from his supplier, so we hope to be in the water by Thursday. He's also bringing down a new coil. Hopefully between the three parts he should be able to isolate where the problem lies, and I will update this post once everything is hopefully fixed in order to pass on the details to anyone else who may encounter this little mechanical/electrical conundrum."
 
"tim: try these tests when it

"tim: try these tests when it fails

Tests for Thunderbolt Ignition:
W/ignition key on AND BILGE WELL VENTILATED OF GAS FUMES!!!

#1 - Connect your voltmeter neg. lead to the engine ground and pos. lead to the white/red wire terminal at the dist. It should read 12 volts.

#2 - If 12 volts is present, remove the coil spark wire from the distributor and connect it to a spark gap tester to ground. Remove the white/green lead from the dist. terminal. Turn the ign. key to on and strike the white/green lead to ground. If there is spark, replace the ignition sensor in the dist.

#3 - If there is no spark, substitute a new coil and repeat test #2. Now if you get spark, install a new coil. NO SPARK, replace ign. amp.

#4 - In #2, if there is No voltage present, disconnect the white/red wire and check it again for 12 volts. If 12 volts is present, replace the ignition sensor inside the dist. cap. If no 12 volts present w/it disconnected--ignition amplifier is shot and must be replaced."
 
I had a very similar sitution

I had a very similar sitution and it turned out to be the ignition module. Acted ok one time and the next it would back fire thru carb and then not run at all untill cool. Repplace mine and also used some 3/8"nuts behind bracket to keep it off riser and create a cooler area for it.
 
The bracket is a heat sink for

The bracket is a heat sink for the module; put some heat sink compound on the module first before bolting it on the plate.
 
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