warm restart issues, low speed stall

[mckavity]

Hi all

Boat is: 1991 Startcraft Eurosport Mercruiser 5.0L (LX) V8 (19") bowrider.

Last summer i bought the boat at auction. It had sat for 3 years. I replaced the starter, fuel pump and alternator and had a decent working boat all last summer (60+ hours). The only 'issue' I was having was I would stall occasionally (more than not) when going from idle (850-900) to 1100 rpm. This only happened when the boat was warm, and never happened when cold.

This summer boat was on the water for 6 weeks (weekends that is, I got to work too), blasting all over the lake. I would still get that stall problem, that now seemed more chronic. All my buddies were saying it's 'flooding' or is O2 starved or what ever. I lived with the problem since you can get it to go by revving it in neutral and then engaging the forward gear quickly. Sometimes took a few tries, but would always eventually go. Not so safe if in wind or stormy though, I will admit.

2 weeks ago I had a minor overheating episode. I had weeds on the skeg and didn't notice the temp gauge rocketing up. Once I noticed, I put boat in idle and waited till the temp came back down and weeds fell off. 5-10 minutes later, temp moved back to 160 I was on my way. Baoted for 4-6 hours more that day without issue (except the stall thing). The next weekend boat was fine until after spending 5hrs on achor, I went to go home and had no power and could not rev past 3200rpm, Temp was about 200 (usually 160). I limped home at 2200rpm.

We tried changing the coil with no luck. So I pulled the boat and we did a compression test. Cyl 8 was 0 (zero). This past weekend we (my mechanic buddy with awesome shop) replaced the head and manifold gaskets. Boat started up and ran fine on Sunday (record time I might add). I did probably 10 restarts on the driveway on the hose without a problem. Once in the water, the boat blasted (and I mean blasted) along at 3500-4500 rpm without issue. Best it's ever ran.

After 10 minutes of driving, water temp 155, oil pres good, I slowed and then idled, then boat stalled. Boat would not restart. No spark.Towed in to dock and parked it for 3 hours. Boat started fine after cooling down, but after 3-5 minutes idling, it stalled and would not re-start. I am about to do the ignition spark test as recommend Mercruiser, but wanted to get some opinions. I will test it tomorrow night and let you all know the result

Ignition Sensor vs Ignition Amplifier (ICM) - boat has Thunderbird IV (V8-22) module. Could this be the sensor or module ?

Tim

 

[mckavity]

I forgot to mention, the reason it would not start was due to no spark. In fact, even with a brand new coil, both terminals would read 12v positive. I'm really leaning towards the ICM amp being dead/failing at warmer temp, but wanted to solicit opinions.

 

[60sboater]

Post this in the Mercruiser forum.

 

[GA_Boater]

Moved this from the Merc OB section. Maybe some of the M/C guys will see it now.

 

[Bondo]

Ignition Sensor vs Ignition Amplifier (ICM) - boat has Thunderbird IV (V8-22) module. Could this be the sensor or module ?

Ayuh,..... Welcome Aboard,..... There's a diagnostic flow chart up in Don'S Adults Only section, at the top of this forum, that'll lead you to which part is bad, 'n what's still workin' properly,....

 

[mckavity]

Hi all, thanks for link to the Adults Only section. This is a very informative site.

Back to my story....went back to the boat that evening to find it started up with out issue. I did approx 15 restarts in a 45 minutes period, in neutral. Boat has never run so smoothly. During that period, I would rev it a bit, leave it at 1600rpm for 5 minutes etc. Temp was 150F the whole time. Could not reproduce the 'no spark' thing.

Not having a rescue boat handy at the time, we decided to secure the boat to the dock and run it in reverse, to create a load. Did this at 1200-1400rpm for about 15 minutes, with about 5-7 restarts. Nothing, boats started fine each time. Then, after about 15 minutes, tied to the dock (simulating a load), we turned off the key and then tried to start it. Wamo, no crank and no solenoid click. Nothing coming to the main solenoid lead (used a lead tester). The ACC power was fine (blower and lights working). We then moved to the key switch, but by the time we got ready to test those terminals (maybe 5-8 minutes), we tried the key again and it started!

Now, after about 1 minute running, the temp gauge began to climb rapidly. Shut it off, restarted ok, but again, starting to heat up. Remember early in the story I had an overheating episode. Now having it again, this time no weeds. At this point in time, we just shut it off and went home (it was late, we were there at night over an hour recreating the issue), so I never really checked the water pump (by disconnecting the main hose). The decision was that we needed to pull the boat out and get the water pump and whole lower unit checked out. This had not been done since I bought the boat, so I don't really know the condition. That is where I am today. Since I did not feel this (lower unit reseal) was a DIY job, I took it to a well known local shop. Boat will be ready tomorrow for pick up.

The plan is to repeat the tests at the dock (or on bunny ears on the driveway) once we know the waterpump/lower unit is good. The funny thing is, the 'no spark to starter' problem seemed to happen before the boat had heated up. Even if the boat did heat up, can that we a cause of loosing spark to the starter (starter is brand new last season). temp never went above 200F. I guess we need to check the thermostat too.