Hard starting, 350MAG MPI

[Toddavid]

07 Chaparral 254 Sunesta.

My random hard start continues, even after replacing the IAC with a brand new OE unit. In fact, it may be a tad worse.

I have to crank the starter a few seconds to get the engine to fully fire. If I release the key early, on the next turn the engine will crank and crank and intermittently fire a cylinder or two but not stay running. I then have to push the neutral button and crack the throttle to get it to fully fire.

Recently put in new plugs, fuel filter parts, neither improved the situation. Runs 100% smooth otherwise, runs 50mph on GPS. Being going on for last 30 hrs or so, 197hrs on it now. Can happen when cold or hot.

Throttle body issue? Vac leak somewhere?

Thanks.

 

[alldodge]

07 Chaparral 254 Sunesta.

My random hard start continues, even after replacing the IAC with a brand new OE unit. In fact, it may be a tad worse.

I have to crank the starter a few seconds to get the engine to fully fire. If I release the key early, on the next turn the engine will crank and crank and intermittently fire a cylinder or two but not stay running. I then have to push the neutral button and crack the throttle to get it to fully fire.

Recently put in new plugs, fuel filter parts, neither improved the situation. Runs 100% smooth otherwise, runs 50mph on GPS. Being going on for last 30 hrs or so, 197hrs on it now. Can happen when cold or hot.

Throttle body issue? Vac leak somewhere?

Thanks.

It could be a vacuum leak issue, but this in most cases it would run rough all the time.

Could use an engine serial number to make sure we are work on your setup. Have you cleaned the IAC muffler (piece of foam rubber in the throat of the throttle body)? What about fuel pressure, has it been checked?

 

[Toddavid]

Thanks for the response. Engine serial is in my sig: 0W635474

I have not cleaned the IAC muffler, is that part number 8 in this diagram?

https://www.mercruiserparts.com/Sho...1681&bnbr=100&bdesc=Throttle+Body(Mechanical)

Since there's no issues with part or full load running, I have not checked fuel pressures. If it were a check valve bleed down problem on the return line (not sure if this engine even has that), the symptoms should be the opposite, no? Only will start after cranking for a while to build pressure?

 

[Fun Times]

The IAC muffler is item number 6 not 8. It's inside the throttle body not out.

Try thoroughly cleaning the inside of the throttle body along with both sides of the butterfly plates and the hole where the IAC Muffler resides.

Also what type of battery do you have? Is it a starting battery or deep cycle battery? Should be a starting battery. The cold cranking amps have to be a minimum of 750 CCA. preferably 800+ is better.

If your CCA's are low then starting your MPI engine will be difficult. Owning a tool like this is very helpful for all your battery needs to avoid a problem ahead of time.http://www.harborfreight.com/digital-automotive-battery-analyzer-66892.html