496 mag issue. 2005

scoflaw

Well-Known Member
Aug 10, 2011
6,395
cape cod mass, cape coral fl
Boat Info
1999 Powerquest legend 260 sx 502 mag
2005 Baja 242 islander 496
Engines
502 mpi Bravo 1
496 mag B1
So I just bought this boat a couple days ago and my Rinda scanner won't be here until Wednesday. So the problem is it won't start hot or cold unless fuel is sprayed into it. Once it catches it idles perfectly for as long as I let it, throttle up and down nice. Figured it was a bad boost pump but fuel pressure is spot on while cranking.

Any ideas ?
 
You prob have the paint issue with the Cool fuel... There's a recall on it... But you have to bring it to a dealer you pay labor they supply parts sometimes...
 
So I just bought this boat a couple days ago and my Rinda scanner won't be here until Wednesday. So the problem is it won't start hot or cold unless fuel is sprayed into it. Once it catches it idles perfectly for as long as I let it, throttle up and down nice. Figured it was a bad boost pump but fuel pressure is spot on while cranking.

Any ideas ?
Scoflaw is stumped??

8.1’s eat plugs. Maybe worn Or even incorrect plugs are the issue?

Have you run it at anything above idle? Does it reach WOT rpm?
 
2005 with a 160 hours on it. In my driveway and hasn't seen the water. Agent of the PO sold it to me and I have no history. Once it catches it idles rock steady . Syphoned some gas off the bottom of the tank, looked clean, smelled good. Changed out the fuel filter nice and clean as well. Got to be a fuel problem if spraying fuel to it starts it.
 
Pull the Fuel Regular on the cool fuel module, and see if there is paint on it....Or open it up and change the filters in there and see if there's pieces of paint in it...
 
As you mentioned, fuel delivery issue. I vote for clogged injectors (common on the 496) or weak high pressure pump inside the CF module.
 
Yes I was going to pull the FPR next. Changed out filters and they were clean
As you mentioned, fuel delivery issue. I vote for clogged injectors (common on the 496) or weak high pressure pump inside the CF module.
If you have good pressure at the rail, we are basically down to the injectors or their control.
CKP and CMP signals can effect their control immensely. TPS signal among other things shouldn't be ignored either. All of which can be tested with a good DVOM.
 
You prob have the paint issue with the Cool fuel... There's a recall on it... But you have to bring it to a dealer you pay labor they supply parts sometimes...
When I was at the boat show in New York the Mercruiser guy told me that offer is long gone. Did you have this done recently?
 
When I was at the boat show in New York the Mercruiser guy told me that offer is long gone. Did you have this done recently?

Had it done about 3 years ago...
 
When I was at the boat show in New York the Mercruiser guy told me that offer is long gone. Did you have this done recently?
I stand corrected- just off the phone with mercruiser directly and he said the dealers will still do this work if I pay for labor. Obviously the guy in the merc booth was a local repairman and provided me mis-leading info. Hence trust but verify.
He did mention that the parts were on back order till the end of summer……
 
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To close this out, it turned out to be an excessive voltage draw from the starter or the 90 amp fuse that wouldn't let the pcm fire the coils. Normally this would be the first place to look but no way was a normal size person getting to this starter.

I was lucky enough to find a mechanic with a talented 14 year old son to get in there . Took him 2 1/2 hours to do the R and R but it got done.
 
When I was at the boat show in New York the Mercruiser guy told me that offer is long gone. Did you have this done recently?
The Mercruiser Cool Fuel Offer is ALIVE AND WELL. Merc authorized service shop just needs to contact Merc with engine serial numbers and jump through a few hoops. Pics of regulator, cool fuel unit (be sure to include top cap close-up), a download on the engines, I thing it was a W3 ??? - not sure. Merc supplies the part, you pay the labor to have it all removed and installed. Sometimes you get everything as I did. Includes 2 new cool fuel units to include pumps and everything afterwards. Other times you will only get a unit and you will use your existing pumps. Our 340 is having this done either next eek or the week after. All parts are in with exception of injectors which are on the way.
 
The Mercruiser Cool Fuel Offer is ALIVE AND WELL. Merc authorized service shop just needs to contact Merc with engine serial numbers and jump through a few hoops. Pics of regulator, cool fuel unit (be sure to include top cap close-up), a download on the engines, I thing it was a W3 ??? - not sure. Merc supplies the part, you pay the labor to have it all removed and installed. Sometimes you get everything as I did. Includes 2 new cool fuel units to include pumps and everything afterwards. Other times you will only get a unit and you will use your existing pumps. Our 340 is having this done either next eek or the week after. All parts are in with exception of injectors which are on the way.
Hopefully the parts are at the dealer. The guy I talked to at Mercury looked up the engine s/n history for me to confirm the offer was available. He then said unfortunalty the "caps" and "injectors" we're on back order. He mentioned that in some cases they will authorize dealer to send injectors out to be cleaned and pulse tested and reused. I hope all goes well with your replacement. He said the dealers usually charge 4 hrs labor. Does that seem right ?
 
Hopefully the parts are at the dealer. The guy I talked to at Mercury looked up the engine s/n history for me to confirm the offer was available. He then said unfortunalty the "caps" and "injectors" we're on back order. He mentioned that in some cases they will authorize dealer to send injectors out to be cleaned and pulse tested and reused. I hope all goes well with your replacement. He said the dealers usually charge 4 hrs labor. Does that seem right ?
Yes it does - I was advised about 5 hours for both motors. I am thinking it will take longer. Either way, has to be done.
 
Plugs

Gap .060

NGK iridium tr55ix 7164

Best plugs. Change them every 3 years and still look good.
 

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