2003 Chaparral 200SSi

N

nauty dog

New member
Looking for some help diagnosing a problem on my mercruiser 5.0 mpi. I trailer it to the lake and it has been running fine all year. Last week, I took it out for about an hour, medium speed, ran great. Brought it back to dock, shut off and went to back trailer down ramp. Engine was off for maybe 10 minutes. It started right up and while idling it died maybe 10 seconds after starting. Repeated attempts, it would idle for a second and die. Put it back on trailer and went home. Changed out the water/fuel seperater, put the water muffs and and it started right up and sounded good at idle and with gas. Took it back out, it ran good. But I didn't shut it off until it was loaded.
Yesterday went to a concert on the water, it ran great, no problems, took about 1/2 hour from dock to show. Shut it off for about 1/2 hour and when I went to start it, exact same scenerio. Had to do the tow of shame. About 1/2 way thru our 45 minute tow, engine temp had gone down to about 100 and it started. I sut it off and continued the two to the dock.
This am, I put the muffs back on and it started and sounded normal.
So, I'm thinking it is some kind of vapor lock, Yesterday when it would not start, I opened the gas tank and got no "rush" of pressurized air. It also would not start with the cap removed. Also, when I removed the old seperator, it was full and all gas. So, I am stymied.
Thank you.

also, when it doesn't start, I also try it with throttle open it at different openings. No start, just sounds like it is out of fuel.
 
How many times have you tried to start the engine [but it wouldn't] with the temp above 100 vs how many times when the temp was at or below 100?
 
We’ll I haven’t done a series of start tests, but it only will not start after I’ve run it and brought it up to temp and then shut it off and it’s sits for approx 10 minutes. Run temperature is a steady 160’. I am thinking I will take it out today and test it some more at the dock. I don’t feel comfortable getting it up to full temp in the driveway with the water muffs. Also not interested in paying for another tow. 😂
Thanks. I will post back.
 
So todays test was a series of runs near the boat ramp.
1. boats starts right up at ramp dock. Warm it up and ran it in the cove area near the dock. Runs flawless, all rpm's.
2. Take it back to dock and shut it down. Wait 10 minutes, starts right up, shut off. wait another 10 minutes, starts right up.
3. Back out to cove where it runs flawless .

Did this three times, all the same results, temp guage at 160'. Started and ran good every time.

After the 3rd time, I didn't see the point of continuing, so I put the bimini away and went and backed trailer down ramp. Wouldn't you know, it started, ran rough for two seconds and died. Temp still at 160'. Tried to start again and ran for a second and died. So I waited for the engine to cool and check temps. After temp went down to 120', it started for 4 seconds, would not take throttle and died. Waited until temp was around 100 (guessing as gauge does not read below 120'. Same result, runs for several seconds and dies.

Put it on the trailer and brought it home., Hooked up the hose muffs and the motor fired ran up and revved properly.

So, it is temperature related, but I don't know enough about fuel injection to know if it is a solenoid, temp sensor or where to begin.
 
If it was me, I would start at the basics. I would replace cap and rotor as a first step, Than Wires and plugs. There too cheap not to try, but I would base my suggestion on "when was the last time they were replaced". Than look at other places or take it to a mechanic.

Years ago I learned to replace the cap and rotor every 2 years. Moisture would get into the cap and create problems.
 
I hooked up a fuel pressure gauge and ran a seres of tests. Key on fuel pump runs for two seconds and holds 40psi. Start up engine and gauge at steady 38 psi. Run about 6 runs out the cove and back. Engine restarts evertime and pressure holding 38 psi. The 7th time the pump runs longer than normal and engine starts and dies after 2 seconds. Fuel pressure at 10 psi. After an hour of cool down, pressure goes up to 40 and engine starts right up. So I need to replace the pump.
 
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