Juan

Engine running rough and not starting unless accelerated.

13 posts in this topic

I have a 2002 Chaparral Signature 260 with a Mercruiser 350 MAG MPI. Since I bought it that I felt it was not giving me all the power it could. Now, it's been acting up even more. It does not start unless you accelerate it and it smokes quite a bit. A mechanic that happened to be at the marina stopped by and connected his laptop to it. No error was found. He said he did not have all the tools he needed, but his next step would have been checking fuel pressure. 

Any suggestions would be highly appreciated. The engine has 520 hours. 

Thank you!

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Rough idle and needing to advance the throttle to start scream IAC valve. Quick and easy fix. Now the smoking exhaust might be something else.

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2 hours ago, cyclops2 said:

What year did you buy it & how many hours have you put on it ?

I bought it in October of 2016 and started using it after the winter in June '17. I did tune up and everything that was recommended by the Marina before I put it in the water. I put about 20-25 hours on it.

Thanks!

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What things did you replace ?  List them all if you can remember them.

Did the boat run worse after the parts change ? 

Can you remove, look at each spark plug white, center, insulator, record the color & if covered with black soot. Then put it back in. Make a note if 2 sparkplugs next to each other are   BOTH  odd  colored.  Do that with   each sparkplug. Post the results.  Make sure both ends of sparkplug wires are fully seated.

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I would put a fuel pressure on it and check running and rest pressure on it. Sounds just like leaky injectors and would also run some Techron through it.

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On 8/10/2017 at 10:07 PM, Juan said:

I have a 2002 Chaparral Signature 260 with a Mercruiser 350 MAG MPI. Since I bought it that I felt it was not giving me all the power it could. Now, it's been acting up even more. It does not start unless you accelerate it and it smokes quite a bit. A mechanic that happened to be at the marina stopped by and connected his laptop to it. No error was found. He said he did not have all the tools he needed, but his next step would have been checking fuel pressure. 

Any suggestions would be highly appreciated. The engine has 520 hours. 

Thank you!

Sure sounds like a faulty IAC valve for the hard starting with fuel advanced required. As for the smoking and rough running, that sounds like a faulty fuel pressure regulator causing too much fuel pressure, or faulty fuel pump perhaps causing too little fuel pressure.

Mercury / Quicksilver part # 862998 for the IAC valve, and 863112 for the IAC gasket, and 863829 for the IAC muffler inside the throttle body. Items # 16, 15, and # 6 in the top picture. Use some intake and throttle body cleaner spray to clean out the plenum (item # 14 in the bottom picture) under the IAC valve as it is probably in need of a good cleaning.

http://www.marinepartsplus.com/catalog/mercruiser/serial/350_MAG_MPI_ALPHA-BRAVO/884712/7585-80

10195.GIF

http://www.marinepartsplus.com/catalog/mercruiser/serial/350_MAG_MPI_ALPHA-BRAVO/884712/7585-50

Regulator is part # 13 in the picture below.

18618.GIF

 

 

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Thanks! It turned out to be the cylinder head being CRACKED! It has been a nightmare. Now that's fixed and it's mechanically sound. We kept having electrical issues so we replaced the wiring harness and coil. Now it does not want to stay on...it beeps and it shuts off and then it does not start again. My mechanic thinks it's the computer that may have been fried due to high temperature. Any idea of how to tell if the computer has to be replaced? It's a non-returnable part of $1800 I would not like to buy if it won't fix the problem....

 

 

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On 8/11/2017 at 9:12 AM, soldier4402 said:

anybody pull any plugs and look at them?  Check all electrical connections.

Thanks! It turned out to be the cylinder head being CRACKED! It has been a nightmare. Now that's fixed and it's mechanically sound. We kept having electrical issues so we replaced the wiring harness and coil. Now it does not want to stay on...it beeps and it shuts off and then it does not start again. My mechanic thinks it's the computer that may have been fried due to high temperature. Any idea of how to tell if the computer has to be replaced? It's a non-returnable part of $1800 I would not like to buy if it won't fix the problem....

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+1

Don't trust a mechanic that recommends replacing an $1800 part on a hunch.  You need a mechanic that has the experience, tools, and software to properly diagnose this.  Its hard to believe the computer was ruined by an overheating engine.  

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