My dad’s boat has a Mercruiser 5.7L 350 MAG MPI Horizon MIE engine manufactured in 2006. The serial number is 0W398110. We have a no start issue with a very long back story. I’m not sure how much is relevant so I’m throwing the whole story out there. I have lurked on boating forums for years and solved many different issues that way, but the time has come to make my first post and ask for help.
The boat was running flawlessly on about 5 different outings this year up until about 2 months ago. Then things took a turn. On the day the boat died, we had used it for about 1.5 hours with at least 30 minutes of WOT, no issues. We pulled up to the dock so we could wash the boat and organize some stuff, that took maybe another 1.5 hours. My dad backed the boat off the dock, into the lake, while I dropped in the trailer so we could pull the boat out for the day. A few short minutes after he pulled the boat off the dock, it died. He cranked it a few times, but it would not start. Another person on the lake towed him in.
Fast forward a few hours later. I am diagnosing what happened to the boat. I discover the fuel pumps are not kicking on like they should when you turn the key. I verified 12v at the power plug going into the module. I decide to check the fuel relay, and some of the plastic on the pin it draws from had melted. Clearly there was an issue with fuel delivery. I pulled the cool fuel module (Gen III) off the boat and opened it up on the work bench. To my horror, there were paint flakes everywhere inside the cavity with the 2 fuel pumps. I looked it up on google and sure enough it is a known problem.
Next, I weighed all my different options but ultimately decided to fix it myself. I painstakingly removed all the paint delamination inside the module until it was all gone. Then I replaced both fuel pumps and the regulator and reassembled it. I also put in a new fuel filter in the module and a new water fuel separator on my boat. I made sure everything was filled with gas while assembling and then I primed the system to also help get air out. I also replaced the fuel module relay in case it was damaged. From, reading the above forum. I knew that the injectors being clogged could be a very real and likely probability, but I decided to wait to see if that was a problem. My logic was that, since there were no signs or symptoms of issues before the incident, maybe I got lucky and caught it before it got to the injectors.
Well, after all that work, I turned the key and the boat started. It ran pretty rough on idle for about 2-3 minutes and then cleared up. By rough, I mean RPM’s dropping to like 400 and then going back up to the usual 700 RPMs. After it cleared up, I let it idle for 20 minutes with the hose hook up and it had no issues. I took it on the lake the next day with my dad but the same thing occurred, rough idle on cold start for about 2-3 minutes and then it was good. We idled around the lake and eased into acceleration, watching all the gauges. Everything was good, we then went around on WOT for at least 40 minutes. Every 5 minutes or so we did a visual inspection of the engine compartment to make sure everything was good.
We thought the rough idle on cold start was odd but that maybe we just needed to burn through some gunk. We took it out one more time but this time in the ocean. Same thing rough idle on cold start for about 2-3 minutes. We were out all day, stopping at islands for a bit with the engine being shut off for as long as like 2 hours. Absolutely no issues all day expect for the rough idle when we dropped in at the start of the day.
Following our gunked up theory, we decided to add injector cleaner to the fuel this time. (So as a quick recap, the boat has worked on 3 occasions, once on the trailer for 20 minutes and then 2 times on the water) We dropped it in the water and tried to start it. It started but idled like horribly rough for about 30 seconds and then died. It would not start up again. We pulled it out and took it home. One thing to note here, there was now a second beep from the on-board computer. The first one was the standard beep when you turn the key halfway, the other beep occurred when cranking.
Some google searching revealed the idle air controller was a possible reason for the rough idle and maybe even the no-start. I replaced the IAC and it’s muffler and then performed the reset procedure mentioned in the service manual. The second beep that was occurring during cranking was now gone but the boat did not want to start. It would have a nice initial combustion and then no follow up.
Knowing what we knew, we decided it was time to pull the fuel rail and injectors. We were quoted $50 per injector to clean them. Instead we decided to buy new bosch injectors. I pulled the fuel rail and it was full of paint flakes. There was literally paint sticking out of one of the injectors too. After soaking and blasting the fuel rail like crazy, the paint flakes seemed to be all gone, I reinstalled it with the brand new injectors. I crossed my fingers, hoping the no start issue was gone but the boat would still not start.
I verified the fuel pumps are still engaging. I don’t have a fuel pressure gauge to hook up to the schrader valve but I poked it with a flat blade and it squirted a lot of fuel (I was wearing safety googles
). There is definitely fuel pressure but obviously without a fuel pressure gauge, I don’t know if its within spec. I decided to table fuel for now and maybe come back to that later with a fuel pressure gauge. I am confident that with all the work I put into the fuel system, that it should be working great.
Next I tested spark on one of the sparks plugs with a cheap little spark plug tester and it only lights up like 5 or 6 times while cranking for a couple seconds. That did not seem right to me. (My only other time using this tester was on a jet ski and that lit up much more frequently and faster) So now I think my no start issue has to do with the ignition system. I tested power at the ignition coil and it was getting 12.9v with the key turned half way. I consulted the internet and discovered there are a bunch of sensors that could cause the computer to shut off the fuel system and cause a no start. Stuff like the ECT sensor, oil pressure sensor, manifold air pressure and temperature sensor, camshaft positions sensor, etc.
The only two sensors I could figure out how to sort of test was the ECT and the manifold air pressure and temperature sensor. The ECT measured 2.35k ohms which as far as I could tell was within spec. The service manual states that if you disconnect the manifold air pressure and temperature sensor, the computer will use the last known good configuration, so I unplugged it and cranked the engine. This time, the engine seemed to have sputtered for 2-3 seconds after that initial combustion. (Unless I’m just going crazy) I tried to crank again but it was the same one-off combustion no start.
At this point, I need help. There are a few more diagnostic steps I could do, like test for compression and buy a fuel pressure gauge, but I’m going a little crazy and need to take a step back for now. If anyone here can point me into some direction that would be much appreciated. If not, I will probably be calling around for a mechanic with a diagnostic computer.
The boat was running flawlessly on about 5 different outings this year up until about 2 months ago. Then things took a turn. On the day the boat died, we had used it for about 1.5 hours with at least 30 minutes of WOT, no issues. We pulled up to the dock so we could wash the boat and organize some stuff, that took maybe another 1.5 hours. My dad backed the boat off the dock, into the lake, while I dropped in the trailer so we could pull the boat out for the day. A few short minutes after he pulled the boat off the dock, it died. He cranked it a few times, but it would not start. Another person on the lake towed him in.
Fast forward a few hours later. I am diagnosing what happened to the boat. I discover the fuel pumps are not kicking on like they should when you turn the key. I verified 12v at the power plug going into the module. I decide to check the fuel relay, and some of the plastic on the pin it draws from had melted. Clearly there was an issue with fuel delivery. I pulled the cool fuel module (Gen III) off the boat and opened it up on the work bench. To my horror, there were paint flakes everywhere inside the cavity with the 2 fuel pumps. I looked it up on google and sure enough it is a known problem.
Next, I weighed all my different options but ultimately decided to fix it myself. I painstakingly removed all the paint delamination inside the module until it was all gone. Then I replaced both fuel pumps and the regulator and reassembled it. I also put in a new fuel filter in the module and a new water fuel separator on my boat. I made sure everything was filled with gas while assembling and then I primed the system to also help get air out. I also replaced the fuel module relay in case it was damaged. From, reading the above forum. I knew that the injectors being clogged could be a very real and likely probability, but I decided to wait to see if that was a problem. My logic was that, since there were no signs or symptoms of issues before the incident, maybe I got lucky and caught it before it got to the injectors.
Well, after all that work, I turned the key and the boat started. It ran pretty rough on idle for about 2-3 minutes and then cleared up. By rough, I mean RPM’s dropping to like 400 and then going back up to the usual 700 RPMs. After it cleared up, I let it idle for 20 minutes with the hose hook up and it had no issues. I took it on the lake the next day with my dad but the same thing occurred, rough idle on cold start for about 2-3 minutes and then it was good. We idled around the lake and eased into acceleration, watching all the gauges. Everything was good, we then went around on WOT for at least 40 minutes. Every 5 minutes or so we did a visual inspection of the engine compartment to make sure everything was good.
We thought the rough idle on cold start was odd but that maybe we just needed to burn through some gunk. We took it out one more time but this time in the ocean. Same thing rough idle on cold start for about 2-3 minutes. We were out all day, stopping at islands for a bit with the engine being shut off for as long as like 2 hours. Absolutely no issues all day expect for the rough idle when we dropped in at the start of the day.
Following our gunked up theory, we decided to add injector cleaner to the fuel this time. (So as a quick recap, the boat has worked on 3 occasions, once on the trailer for 20 minutes and then 2 times on the water) We dropped it in the water and tried to start it. It started but idled like horribly rough for about 30 seconds and then died. It would not start up again. We pulled it out and took it home. One thing to note here, there was now a second beep from the on-board computer. The first one was the standard beep when you turn the key halfway, the other beep occurred when cranking.
Some google searching revealed the idle air controller was a possible reason for the rough idle and maybe even the no-start. I replaced the IAC and it’s muffler and then performed the reset procedure mentioned in the service manual. The second beep that was occurring during cranking was now gone but the boat did not want to start. It would have a nice initial combustion and then no follow up.
Knowing what we knew, we decided it was time to pull the fuel rail and injectors. We were quoted $50 per injector to clean them. Instead we decided to buy new bosch injectors. I pulled the fuel rail and it was full of paint flakes. There was literally paint sticking out of one of the injectors too. After soaking and blasting the fuel rail like crazy, the paint flakes seemed to be all gone, I reinstalled it with the brand new injectors. I crossed my fingers, hoping the no start issue was gone but the boat would still not start.
I verified the fuel pumps are still engaging. I don’t have a fuel pressure gauge to hook up to the schrader valve but I poked it with a flat blade and it squirted a lot of fuel (I was wearing safety googles
). There is definitely fuel pressure but obviously without a fuel pressure gauge, I don’t know if its within spec. I decided to table fuel for now and maybe come back to that later with a fuel pressure gauge. I am confident that with all the work I put into the fuel system, that it should be working great.Next I tested spark on one of the sparks plugs with a cheap little spark plug tester and it only lights up like 5 or 6 times while cranking for a couple seconds. That did not seem right to me. (My only other time using this tester was on a jet ski and that lit up much more frequently and faster) So now I think my no start issue has to do with the ignition system. I tested power at the ignition coil and it was getting 12.9v with the key turned half way. I consulted the internet and discovered there are a bunch of sensors that could cause the computer to shut off the fuel system and cause a no start. Stuff like the ECT sensor, oil pressure sensor, manifold air pressure and temperature sensor, camshaft positions sensor, etc.
The only two sensors I could figure out how to sort of test was the ECT and the manifold air pressure and temperature sensor. The ECT measured 2.35k ohms which as far as I could tell was within spec. The service manual states that if you disconnect the manifold air pressure and temperature sensor, the computer will use the last known good configuration, so I unplugged it and cranked the engine. This time, the engine seemed to have sputtered for 2-3 seconds after that initial combustion. (Unless I’m just going crazy) I tried to crank again but it was the same one-off combustion no start.
At this point, I need help. There are a few more diagnostic steps I could do, like test for compression and buy a fuel pressure gauge, but I’m going a little crazy and need to take a step back for now. If anyone here can point me into some direction that would be much appreciated. If not, I will probably be calling around for a mechanic with a diagnostic computer.
. And if you don't have a problem with the cap, and at the moment it doesn't sound like you have, leave it alone!
