Hard Start Problem

2000 Scarab w/ twin 350 Mag MPI

I've got a hard start problem when the boat warms up. Both engines are experiencing the same issue. Engines start right off when cold, but just turn over when hot. In order to get them to start I have to turn the key on and off numerous times and throttle up all the way when cranking and it might start, along with some backfiring and then it takes a few minutes before it will idle correctly.

What I've tried:
Replaced temp sensor for computer
Swapped in known working IAC, no change so went back to original
Installed Holley in line booster pump (thinking vapor lock and this is a known possible solution) Pump is a 7psi pump.
Changed fuel filters
Filled up at different gas stations, including an ethanol free station.

I'm at a loss here and out of ideas, I really thought the booster pump would work. Any ideas are welcome.

Re: Hard Start Problem

Anyone think this could be ignition related? Got to thinking when the boat is warmed up is is smoking just a tad like its running rich. Also already changed the plugs but nothing else on the ignition side.

Re: Hard Start Problem

Think I might have found the issue. Fuel pressure is 30psi at best at the end of the rail, tested with two different testers and same result. Even after engines crank and are running. Shouldn't this be ~43 psi? They hold the pressure for a while so I wouldn't think pressure reg, maybe bad pumps?

Re: Hard Start Problem

Nobody has had a similar issue? Would at least like some opinions before I spend the $$$ on pumps.

Re: Hard Start Problem

Have you hooked it up to a scan tool to see what is going on?

Re: Hard Start Problem

Don S said:

Have you hooked it up to a scan tool to see what is going on?

Click to expand...

Unfortunately no I do not have one or have access to one.

Re: Hard Start Problem

You can't check EFI engines without the proper equipment (Tools) and manuals. Without them, you are just guessing at what might be wrong and swapping parts and hoping you hit on the problem. Which is what you are doing, and it's not working.

Without a serial number, I will guess that it's a 2000 or 1999 and this would be the manual you need. http://www.4shared.com/office/JOT2vS2W/24__GM_V8_50-57_98-01.html? of course, if the engine is a 2001 (very possible) it's the wrong manual.

You should also do some fuel pump pressure tests before buying pumps. I really doubt you have need for a pump.