Engine wouldn't start after warmed up

boater2065

boater2065

Active Member
Jul 30, 2018
222
Everett, WA
Boat Info
Searay
Engines
merc
Hi all, hope everyone is enjoying the summer heat.

Hoping someone can shed some light on an issue i ran into the other day. Fired up the boat before heading out and it started up fine (when cold it cranks for a few seconds before it fires up, and that is normal to me since i've had it). I cruised around about 25mph for maybe 10 minutes or so, then putted along slowly for another 10 or 15 minutes, then shut of the engine to drift. After about 30 minutes i attempted to start the engine and it just cranked over and over and wouldn't start. I tried this a couple times, with maybe 20 or 30 seconds in between each attempt. Next, I decided to give it some throttle, it cranked and cranked like before then finally fired up and i pulled back on the throttle. Due to time constrictions i headed back to the dock and left. The engine sounded fine on the way back.

Is there any reason something like this may happen? Am i over reacting? Anything i can try or look for? Any advice would be great.

The engine is an MCM 5.7L EFI in a 2002 Sundancer.
 
IAC most likely..... simple swap out.
 

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From what i'm reading, a bad IAC would cause stalling and overall poor idle performance. I do not seem to have any of that. The only thing i have noticed is it's hard to start when the engine is hot.
 
Jeff Fabiani said:
Hi all, hope everyone is enjoying the summer heat.

Hoping someone can shed some light on an issue i ran into the other day. Fired up the boat before heading out and it started up fine (when cold it cranks for a few seconds before it fires up, and that is normal to me since i've had it). I cruised around about 25mph for maybe 10 minutes or so, then putted along slowly for another 10 or 15 minutes, then shut of the engine to drift. After about 30 minutes i attempted to start the engine and it just cranked over and over and wouldn't start. I tried this a couple times, with maybe 20 or 30 seconds in between each attempt. Next, I decided to give it some throttle, it cranked and cranked like before then finally fired up and i pulled back on the throttle. Due to time constrictions i headed back to the dock and left. The engine sounded fine on the way back.

Is there any reason something like this may happen? Am i over reacting? Anything i can try or look for? Any advice would be great.

The engine is an MCM 5.7L EFI in a 2002 Sundancer.
Click to expand...
Jeff Fabiani said:
Hi all, hope everyone is enjoying the summer heat.

Hoping someone can shed some light on an issue i ran into the other day. Fired up the boat before heading out and it started up fine (when cold it cranks for a few seconds before it fires up, and that is normal to me since i've had it). I cruised around about 25mph for maybe 10 minutes or so, then putted along slowly for another 10 or 15 minutes, then shut of the engine to drift. After about 30 minutes i attempted to start the engine and it just cranked over and over and wouldn't start. I tried this a couple times, with maybe 20 or 30 seconds in between each attempt. Next, I decided to give it some throttle, it cranked and cranked like before then finally fired up and i pulled back on the throttle. Due to time constrictions i headed back to the dock and left. The engine sounded fine on the way back.

Is there any reason something like this may happen? Am i over reacting? Anything i can try or look for? Any advice would be great.

The engine is an MCM 5.7L EFI in a 2002 Sundancer.
Click to expand...
I had a 7.4 EFI with a bravo 3 2000 270 sundancer with a similar problem only mine would not restart , the next day after the motor cooled down it would start. after checking batteries , removed starter and had it checked , replace sensors I bought a new starter and when it wouldnt start after it was hot I replaced the starter and never had a no start problem again
 
@dodge 403 Thanks for that info. I wondered about starter myself, but after reading about bad starter symptoms, it didn't sound at all like what i had going on. Of course, it could be early stages of dying i suppose.

Another thing i've read about is vapor lock. Don't know much about that or how/why it happens.
 
IAC and Throttle Position Sensor are the two most likely culprits. You should have one of each as spares.
 
Have you thought about a fuel problem. My 350 MPI did the same thing. I changed out everything everybody said to change and then read an article that Mercury was have problems with fuel vapor lock when the engine was shut down. It was mostly found in ethanol fuel due to the heat in the engine compartment. They suggested 2 fixes. #1 change to non ethanol fuel. If that did not work #2 was a check valve for the cooling water for the fuel pump.
 
Sounds mostly like vapor lock if it was iac valve it would start but not stay running and if it was the throttle position sensor it would not start if you advanced the throttle to make it catch The reason why the symptom completely disappears by the next day is strictly from vapor lock
 
Southern Pirate said:
Have you thought about a fuel problem. My 350 MPI did the same thing. I changed out everything everybody said to change and then read an article that Mercury was have problems with fuel vapor lock when the engine was shut down. It was mostly found in ethanol fuel due to the heat in the engine compartment. They suggested 2 fixes. #1 change to non ethanol fuel. If that did not work #2 was a check valve for the cooling water for the fuel pump.
Click to expand...
I strictly put ethanol free into the engine, i will look into your other suggestion. Thanks
 
joeyleggz said:
Sounds mostly like vapor lock if it was iac valve it would start but not stay running and if it was the throttle position sensor it would not start if you advanced the throttle to make it catch The reason why the symptom completely disappears by the next day is strictly from vapor lock
Click to expand...
This is what seems most likely to me, from everything i have read.
 
I had been chasing this problem for several months (on my 350 Mag MPI). For me it ended up being the IAC valve. The valve seemed to get stuck closed, but after starting the engine there must have been enough vacuum pull to get it to open as it would idle and run just fine. I installed a fuel pressure gauge on the rail and confirmed that when it wouldn't start hot I still had ~ 42psi of fuel pressure at the injector rail (presumably ruling out the frequently mentioned and dreaded vapor lock problem). I even purchased an engine code reader to see if there was a trouble code in the ECM (there wasn't). The final clue for me was that I could start the engine hot if I first advanced the throttle to about 3/4 and then started the motor. After catching I would pull the throttle back to idle. After figuring this out, it seems that with the IAC valve stuck closed, the engine was becoming flooded while trying to start hot. If I let the motor cool down for 30-40 minutes it would start as normal. The tricky part of the diagnosis is that for me, the motor performed perfectly while running (no stalling, rough idle or anything), it just wouldn't start after running on the lake for about 10-15 minutes. Also could not reproduce in the driveway. Anyway, changing the IAC is pretty simple. If you buy the Mercruiser part it is about $180. I did a lot of research and quite a few posts mention that Mercruiser used the exact same part from a 2002 Ford Windstar V6 3.8L (Motocraft CX1766) which runs about $50 mainly because the GM part needed 4 wires and the Ford part only used 2 and they were down to only 2 outputs available on the 555 ECM. Anyway, I went a different route and ordered a 3rd party part from Amazon and haven't had any issues with it so far (this was before I found out the Motocraft part is the same as the Mercrusier OEM part).
 
Earl Bryner said:
I had been chasing this problem for several months (on my 350 Mag MPI). For me it ended up being the IAC valve. The valve seemed to get stuck closed, but after starting the engine there must have been enough vacuum pull to get it to open as it would idle and run just fine. I installed a fuel pressure gauge on the rail and confirmed that when it wouldn't start hot I still had ~ 42psi of fuel pressure at the injector rail (presumably ruling out the frequently mentioned and dreaded vapor lock problem). I even purchased an engine code reader to see if there was a trouble code in the ECM (there wasn't). The final clue for me was that I could start the engine hot if I first advanced the throttle to about 3/4 and then started the motor. After catching I would pull the throttle back to idle. After figuring this out, it seems that with the IAC valve stuck closed, the engine was becoming flooded while trying to start hot. If I let the motor cool down for 30-40 minutes it would start as normal. The tricky part of the diagnosis is that for me, the motor performed perfectly while running (no stalling, rough idle or anything), it just wouldn't start after running on the lake for about 10-15 minutes. Also could not reproduce in the driveway. Anyway, changing the IAC is pretty simple. If you buy the Mercruiser part it is about $180. I did a lot of research and quite a few posts mention that Mercruiser used the exact same part from a 2002 Ford Windstar V6 3.8L (Motocraft CX1766) which runs about $50 mainly because the GM part needed 4 wires and the Ford part only used 2 and they were down to only 2 outputs available on the 555 ECM. Anyway, I went a different route and ordered a 3rd party part from Amazon and haven't had any issues with it so far (this was before I found out the Motocraft part is the same as the Mercrusier OEM part).
Click to expand...
Thank you so much for the detailed response. Your issue sound identical to mine, aside from the engine model. I'll be pulling the boat soon to replace the manifolds so I'll pick up the IAC and replace that as well
 
Don't believe the OP has a 555 ECM. If he has the MEfI, those IAC's rarely fail. Sounds like vapor lock to me.
 
Earl Bryner said:
I had been chasing this problem for several months (on my 350 Mag MPI). For me it ended up being the IAC valve. The valve seemed to get stuck closed, but after starting the engine there must have been enough vacuum pull to get it to open as it would idle and run just fine. I installed a fuel pressure gauge on the rail and confirmed that when it wouldn't start hot I still had ~ 42psi of fuel pressure at the injector rail (presumably ruling out the frequently mentioned and dreaded vapor lock problem). I even purchased an engine code reader to see if there was a trouble code in the ECM (there wasn't). The final clue for me was that I could start the engine hot if I first advanced the throttle to about 3/4 and then started the motor. After catching I would pull the throttle back to idle. After figuring this out, it seems that with the IAC valve stuck closed, the engine was becoming flooded while trying to start hot. If I let the motor cool down for 30-40 minutes it would start as normal. The tricky part of the diagnosis is that for me, the motor performed perfectly while running (no stalling, rough idle or anything), it just wouldn't start after running on the lake for about 10-15 minutes. Also could not reproduce in the driveway. Anyway, changing the IAC is pretty simple. If you buy the Mercruiser part it is about $180. I did a lot of research and quite a few posts mention that Mercruiser used the exact same part from a 2002 Ford Windstar V6 3.8L (Motocraft CX1766) which runs about $50 mainly because the GM part needed 4 wires and the Ford part only used 2 and they were down to only 2 outputs available on the 555 ECM. Anyway, I went a different route and ordered a 3rd party part from Amazon and haven't had any issues with it so far (this was before I found out the Motocraft part is the same as the Mercrusier OEM part).
Click to expand...

not sure about the iac part, but many of the sensors and the injectors on the intake are bosch parts with bosch numbers.
if you get the black paint off with a wire wheel you can see the numbers.

volvo uses the same manifold with injectors and sensors. their iac is different.
 
when you put the throttle past about half way or 2/3 the ecu will shut the injectors off untill rpm's reach a certain speed.

i had a similar symptoms once and i believe it was a leaking injector that was not closing all the way.

holding the throttle open helped it clear out the extra fuel.
put a fuel pressure guage on the fuel rail and see how long the fuel pressure holds at about 40 psi after you shut it off.
 
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