2003 Merc 5.0 MPI no start, intermittent spark

Jimmi007

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Jun 1, 2021
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I’m at a loss. Unrelated, port motor just got new fuel injectors and a tmap sensor. Took boat out and ran mint. Next week, go to take it out, Stbd dies 1000’ away from dock. Won’t restart.
Open cap and rotor. Very slight corrosion. Ok Replace. No start. Checked the 3 fuses and the relay. All good. Replaced fuel pump as it would cycle on and off with key on. Like if it was priming for the first time. Checked spark at coil and plug 5. Good spark. Still no start. Checked coil again and this time no spark. After a few times of on and off, I get spark and then no spark. Changed fuel filter and fuel water separator filter, Changed relays Changed crank position sensor. Also did ignition module, put a new coil on, even went as far as swapping PCM. Still no start. All parts that were put on, worked on Port motor. Wires and plugs are a year old. Any ideas?? Thanks so much.
 
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alldodge

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How about your kill switch?
Check for 12V at the coil with key ON and see if it stays there when cranking
 

Jimmi007

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Jun 1, 2021
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No kill switch, it’s a Searay Sundancer 300, but will check for 12V at the coil!
 

Jimmi007

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Just an update, I had a loose ground on the back port side of the motor. Took off the leads, cleaned them and retightened. Motor started and ran for an hour. Storm blew in, decided to take out the next day, Motor started and ran. As I left dock, motor died. Won’t restart. Got my buddys Rinda cpu, had my 5V system low
Code 133. Unplugged each 5v sensor till my 2.99 V went back to 5V. Found the temp sensor on the cooler to be bad.
Have to purchase on Monday and hopefully the. Gremlins have moved to another boat!
 

alldodge

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5V low will be one of the 5V sensors. With key ON disconnect them one at a time until you find the one pulling it down.
 

dubs283

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5V low will be one of the 5V sensors. With key ON disconnect them one at a time until you find the one pulling it down.
Um.....OP did that test with a rinda

Guessing they found a transmission temp sensor at fault based on provided info?
 

Jimmi007

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Um.....OP did that test with a rinda

Guessing they found a transmission temp sensor at fault based on provided info?
Water pressure sensor on the steering cooler went bad. The loose ground caused my intermittent spark. Once tightened, the code 133 showed.
 
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