Hi all. New here. I've read as much as I could get my eyes onto trying to solve this problem. I'm admitting partial defeat posting here as I pride myself at solving difficult problems. However, I don't know everything...
This is longwinded, but thought I?d get as much info out as I can at once.
Boat is a restored 1957 Chris Craft Constellation, about 40 ft. Was beautifully restored and re-engined early 2000's with 2 Mercruiser 5.7l's of 1998 vintage. Supposedly, these were new crate engines at the time and have adjacent serial numbers, 0Kxxxxxx. 4bbl Weber carbs with thunderbolt V knock sensor ignition and fresh water cooled manifolds. There's about 300 hours on these engines and have been maintained with Mercruiser parts.
Boat itself is gorgeous and well protected. It sits in salt water full time in a boat house in Puget Sound, but the boat isn't the issue. It's the engines.
Symptoms: Engines always start/run great. After 30-120 minutes up on plane around 3800 rpm, an engine will pop/backfire once out of the blue. Usually a single event, but once this begins, it will become more frequent to the point of rough running forcing us to run at 1200-1500 rpm to keep the stumbling under control. This has occurred for many seasons and randomly to the point of not trusting the boat for any kind of extended trip.
I got involved with this almost 2 seasons ago, and have systematically improved and fixed many things, but no conclusive luck with the bad behavior I described.
Here's what's been done:
#1 Compression is good. All cylinders are 165-175, with one outlier at 155.
#2 Exhaust elbows were serviced and confirmed no water going where it shouldn?t go.
#3 No water in the oil. No coolant leaks.
#4 Initially, suspected the fuel system. Inserted (temporary) clear gas lines at the fuel filter inlets to watch for bubbles and crud. Inserted gauges at the filter inlet and pump outlet (both engines) while underway. These are mechanical fuel pumps and everything looks great, even when the bad behavior begins. We always use ethanol free fuel. We inspected all fuel lines and vents. Took bottom of tank samples, looked inside tanks for rust/crud. Checked carbs for sinking floats, carb filters, all the normal stuff. Concluded we don't have a fuel problem.
#5 Full electrical tune up in the past 2 months both engines: Plugs, wires, rotor, cap, ignition sensors. Used Mercruiser parts and set the TB V base timing, idle and carb mixtures using the proper TB V procedure. These engines run sweet.
Recently, have been able to perform sea trials attempting to exacerbate this problem. Sure enough, starboard engine now consistently acts up after extended running. Engine temps do not run hot, however. In fact, I was finally able to reproduce this behavior after extended 2000 rpm idle episodes in the boat house. Great, I thought. Now I can figure this out. Nice thing about 2 identical engines, is ease of swapping parts. I swapped all of this stuff port to starboard one at a time and was still able to recreate the bad behavior on the port engine:
Coil, ICU, ignition coil, carb. Oh yeah, unhooked the tach wire too.
Starboard engine still stumbles and runs horribly after all of these swaps.
Then, two breakthroughs? First, I had the timing light connected during these episodes and watched ignition timing while the stumbling occurred. Indeed timing jumped around, but I was loosing spark (flashes) synchronized to the engine stumbling.
Next, I connected voltmeters at the coil + connection, and another to the +12V wire into the ICU. These voltmeters can capture min/max DC so I ran another test. No issues there, rock solid DC with no fluctuations. Checked the notorious Cannon connector and was fine. Cleaned it up a bit anyhow for due diligence.
More timing light tests; I don?t believe I?m seeing enough advance. But I swapped the ICU?s, how can this be?
Next another sea trial, mainly because it was a nice day. This time, we were a bit more aggressive when the starboard engine problem occurred. That is, we didn?t the port engine way down as we would normally do on the water. We let the starboard engine continue to stumble as I went below looking for more symptoms while continuing to cruise on port power. After a few more minutes of this, the port engine began stumbling exactly the same way. This is this first time we realized either engine exhibited this behavior. Mr. Captain was not happy as we were 10 miles out with 2 sick engines. I knew we could let things cool a while and be fine again. And, we?re on to something.
This is where I?m at:
This is an electrical problem. Spark drop out. Timing goes crazy and advance is messed up, I believe.
It?s temperature related.
Both engines have exactly the same behavior.
Now, the previous swapping proves nothing. Could I have 2 bad coils, or 2 bad ICU?s? I think that is highly unlikely, but I?m stumped and don?t want to spend $500+ for an ICU science experiment.
I?m inclined to consider something was fundamentally wired wrong when the engines were installed way back when. I haven?t found anything wrong, yet?
Any and all suggestions are welcome,
?bill
This is longwinded, but thought I?d get as much info out as I can at once.
Boat is a restored 1957 Chris Craft Constellation, about 40 ft. Was beautifully restored and re-engined early 2000's with 2 Mercruiser 5.7l's of 1998 vintage. Supposedly, these were new crate engines at the time and have adjacent serial numbers, 0Kxxxxxx. 4bbl Weber carbs with thunderbolt V knock sensor ignition and fresh water cooled manifolds. There's about 300 hours on these engines and have been maintained with Mercruiser parts.
Boat itself is gorgeous and well protected. It sits in salt water full time in a boat house in Puget Sound, but the boat isn't the issue. It's the engines.
Symptoms: Engines always start/run great. After 30-120 minutes up on plane around 3800 rpm, an engine will pop/backfire once out of the blue. Usually a single event, but once this begins, it will become more frequent to the point of rough running forcing us to run at 1200-1500 rpm to keep the stumbling under control. This has occurred for many seasons and randomly to the point of not trusting the boat for any kind of extended trip.
I got involved with this almost 2 seasons ago, and have systematically improved and fixed many things, but no conclusive luck with the bad behavior I described.
Here's what's been done:
#1 Compression is good. All cylinders are 165-175, with one outlier at 155.
#2 Exhaust elbows were serviced and confirmed no water going where it shouldn?t go.
#3 No water in the oil. No coolant leaks.
#4 Initially, suspected the fuel system. Inserted (temporary) clear gas lines at the fuel filter inlets to watch for bubbles and crud. Inserted gauges at the filter inlet and pump outlet (both engines) while underway. These are mechanical fuel pumps and everything looks great, even when the bad behavior begins. We always use ethanol free fuel. We inspected all fuel lines and vents. Took bottom of tank samples, looked inside tanks for rust/crud. Checked carbs for sinking floats, carb filters, all the normal stuff. Concluded we don't have a fuel problem.
#5 Full electrical tune up in the past 2 months both engines: Plugs, wires, rotor, cap, ignition sensors. Used Mercruiser parts and set the TB V base timing, idle and carb mixtures using the proper TB V procedure. These engines run sweet.
Recently, have been able to perform sea trials attempting to exacerbate this problem. Sure enough, starboard engine now consistently acts up after extended running. Engine temps do not run hot, however. In fact, I was finally able to reproduce this behavior after extended 2000 rpm idle episodes in the boat house. Great, I thought. Now I can figure this out. Nice thing about 2 identical engines, is ease of swapping parts. I swapped all of this stuff port to starboard one at a time and was still able to recreate the bad behavior on the port engine:
Coil, ICU, ignition coil, carb. Oh yeah, unhooked the tach wire too.
Starboard engine still stumbles and runs horribly after all of these swaps.
Then, two breakthroughs? First, I had the timing light connected during these episodes and watched ignition timing while the stumbling occurred. Indeed timing jumped around, but I was loosing spark (flashes) synchronized to the engine stumbling.
Next, I connected voltmeters at the coil + connection, and another to the +12V wire into the ICU. These voltmeters can capture min/max DC so I ran another test. No issues there, rock solid DC with no fluctuations. Checked the notorious Cannon connector and was fine. Cleaned it up a bit anyhow for due diligence.
More timing light tests; I don?t believe I?m seeing enough advance. But I swapped the ICU?s, how can this be?
Next another sea trial, mainly because it was a nice day. This time, we were a bit more aggressive when the starboard engine problem occurred. That is, we didn?t the port engine way down as we would normally do on the water. We let the starboard engine continue to stumble as I went below looking for more symptoms while continuing to cruise on port power. After a few more minutes of this, the port engine began stumbling exactly the same way. This is this first time we realized either engine exhibited this behavior. Mr. Captain was not happy as we were 10 miles out with 2 sick engines. I knew we could let things cool a while and be fine again. And, we?re on to something.
This is where I?m at:
This is an electrical problem. Spark drop out. Timing goes crazy and advance is messed up, I believe.
It?s temperature related.
Both engines have exactly the same behavior.
Now, the previous swapping proves nothing. Could I have 2 bad coils, or 2 bad ICU?s? I think that is highly unlikely, but I?m stumped and don?t want to spend $500+ for an ICU science experiment.
I?m inclined to consider something was fundamentally wired wrong when the engines were installed way back when. I haven?t found anything wrong, yet?
Any and all suggestions are welcome,
?bill
