Hi all, I'm hoping that someone can point me in the right direction.
I have a mercruiser repower 357 alpha 4v. Which is just a standard carbed 350 with the thunderbolt v ignition.
Before about three weeks ago it had been running great. On the way back to the ramp on Lake George. I was cruising along on plane at about 3500 rpm. Life was good, All of a sudden it died out of no where. I restarted a couple of times and it would startup immediately, like normal, idle fine but as soon as I gave it any power it would cut out.
I opened the engine cover and the bilge was pretty full of water, maybe up to the bottom of the oil pan and spraying out of the starboard side exhaust manifold feed hose. Apparently the hose clamp broke. I stole a clamp from somewhere else and fixed that issue. The bilge pump did its job and I thought we would be back in business. to be clear the hose stayed on the nipple so most of the water was still going through the exhaust on that side. The starter , knock sensor, plugs and wires on that side were getting sprayed with fresh water, but the rest of the engine was still nice and dry, maybe humid, but not wet. Earlier in the day I noticed that the water coming from the bilge pump was hot, but I thought it was from the heat in the engine compartment. So in retrospect I think it had been leaking that way for a short while before the engine quit. Keeping that in mind the water spray may be unrelated to the actual issue.
Anyway I found that if I ran anything over 1200rpm it would eventually cut out. 1400 rpm it took maybe 7 or 8 min. 3000 rpm maybe a min. 4800 rpm almost immediately.
I tried opening the gas cap, possible vent issue, no issue there, pulled the spark arrestor in case it was plugged nope, good bat voltage, 13.9, 14.5 at 1400 rpm. No issue there. I measured at the coil and it has the full 13.9 to 14.5 volts at the coil
So we idled back to the ramp, which sucked, but ok.
Back at the house I checked for fuel. Ran it til it cut out and then after it died "revved" the throttle, plenty of gas visible in the carb, so fuel isn't the issue, but after a lot of back and forth I also rebuilt the edelbrock carb, with no change in the issue. I changed the fuel filter, spin on type, and checked for water, looks good, no water in the fuel, I have almost a full tank of fresh non ethanol fuel. I inspected the anti siphon valve, looks great ball moves freely. I also tried to pull the pickup tube, but the pickup is bigger than the hole, so I couldn't inspect it. I did blow through it though and it didn't feel restricted.
On the ignition side I Pulled the distributor cleaned the contacts. Seems ok, I'll probably replace it since I'm running out of ideas, but I haven't yet. I pulled the plugs, they all look good, nice sandy color. New plugs, properly gapped were installed about two months ago. No more than 10-15 running hours ago. I inspected the plug wires, no visible abrasions, and I felt them while running. I didn't get zapped so I don't think they are shorting anywhere.
I followed the ignition system troubleshooting guide in the manual, everything looks good. Nice blue spark. I checked the resistance of the ignition sensor, it is at 6.7Megaohms. Manual says to replace if it is less than 100 ohms, so that seems good. I've read about coils failing at high RPM's so I swapped in a brand new coil, but there were no change in the symptoms. The issue doesn't seem to be heat related as it will happen when cold or hot, and always restarts and idles fine. If I cut the throttle as soon as it happens it will sputter a bit and then idle fine again.
I also performed the knock sensor and Knock module tests in the manual, That system seems to be working perfectly.
After three weeks of trying to isolate the issue I still have basically no idea what is going on. Before it failed I had no issue running at WOT, although honestly I only do that to get on plane, and then I always back it off to 3500 to 3800. Now if I rev to 4k it immediately starts cutting out. If I push harder it dies, if I let off it returns to a perfect idle. I do limit this to very short revs since I'm no the trailer.
I'm planning a water test this weekend.
My thought is to place a vacuum gauge in the fuel line between the tank and the mechanical pump to see if there is a restriction.
Other than that though I'm not sure what else to test. I've run through everything I can think of, and I still don't know whether this is a fuel or a fire issue.
thanks for the input guys!
I have a mercruiser repower 357 alpha 4v. Which is just a standard carbed 350 with the thunderbolt v ignition.
Before about three weeks ago it had been running great. On the way back to the ramp on Lake George. I was cruising along on plane at about 3500 rpm. Life was good, All of a sudden it died out of no where. I restarted a couple of times and it would startup immediately, like normal, idle fine but as soon as I gave it any power it would cut out.
I opened the engine cover and the bilge was pretty full of water, maybe up to the bottom of the oil pan and spraying out of the starboard side exhaust manifold feed hose. Apparently the hose clamp broke. I stole a clamp from somewhere else and fixed that issue. The bilge pump did its job and I thought we would be back in business. to be clear the hose stayed on the nipple so most of the water was still going through the exhaust on that side. The starter , knock sensor, plugs and wires on that side were getting sprayed with fresh water, but the rest of the engine was still nice and dry, maybe humid, but not wet. Earlier in the day I noticed that the water coming from the bilge pump was hot, but I thought it was from the heat in the engine compartment. So in retrospect I think it had been leaking that way for a short while before the engine quit. Keeping that in mind the water spray may be unrelated to the actual issue.
Anyway I found that if I ran anything over 1200rpm it would eventually cut out. 1400 rpm it took maybe 7 or 8 min. 3000 rpm maybe a min. 4800 rpm almost immediately.
I tried opening the gas cap, possible vent issue, no issue there, pulled the spark arrestor in case it was plugged nope, good bat voltage, 13.9, 14.5 at 1400 rpm. No issue there. I measured at the coil and it has the full 13.9 to 14.5 volts at the coil
So we idled back to the ramp, which sucked, but ok.
Back at the house I checked for fuel. Ran it til it cut out and then after it died "revved" the throttle, plenty of gas visible in the carb, so fuel isn't the issue, but after a lot of back and forth I also rebuilt the edelbrock carb, with no change in the issue. I changed the fuel filter, spin on type, and checked for water, looks good, no water in the fuel, I have almost a full tank of fresh non ethanol fuel. I inspected the anti siphon valve, looks great ball moves freely. I also tried to pull the pickup tube, but the pickup is bigger than the hole, so I couldn't inspect it. I did blow through it though and it didn't feel restricted.
On the ignition side I Pulled the distributor cleaned the contacts. Seems ok, I'll probably replace it since I'm running out of ideas, but I haven't yet. I pulled the plugs, they all look good, nice sandy color. New plugs, properly gapped were installed about two months ago. No more than 10-15 running hours ago. I inspected the plug wires, no visible abrasions, and I felt them while running. I didn't get zapped so I don't think they are shorting anywhere.
I followed the ignition system troubleshooting guide in the manual, everything looks good. Nice blue spark. I checked the resistance of the ignition sensor, it is at 6.7Megaohms. Manual says to replace if it is less than 100 ohms, so that seems good. I've read about coils failing at high RPM's so I swapped in a brand new coil, but there were no change in the symptoms. The issue doesn't seem to be heat related as it will happen when cold or hot, and always restarts and idles fine. If I cut the throttle as soon as it happens it will sputter a bit and then idle fine again.
I also performed the knock sensor and Knock module tests in the manual, That system seems to be working perfectly.
After three weeks of trying to isolate the issue I still have basically no idea what is going on. Before it failed I had no issue running at WOT, although honestly I only do that to get on plane, and then I always back it off to 3500 to 3800. Now if I rev to 4k it immediately starts cutting out. If I push harder it dies, if I let off it returns to a perfect idle. I do limit this to very short revs since I'm no the trailer.
I'm planning a water test this weekend.
My thought is to place a vacuum gauge in the fuel line between the tank and the mechanical pump to see if there is a restriction.
Other than that though I'm not sure what else to test. I've run through everything I can think of, and I still don't know whether this is a fuel or a fire issue.
thanks for the input guys!
