Baja 278

+3

I had the same problem with an older boat. Just open the hatch right before you dock and let the engines idle for a minute or 2 before shutting them down. That allows the cool fuel to do it's job a little better before restarting them.

Uncle Dave

If you are idling in and out of a marina prior to power down something sounds wrong

The Merc 700's have a history of the following problems

PCM /IAC driver,
fuel pump never on - or always on,
coil driver failure
boost control valve failure

IF its not heating up, and its not a fuel vent problem its likely on of the above.

good luck!

Uncle Dave

fossil fuel

I have 2 700's in a 382. I have had the same problem. I had merc reflash the computer to run 89. It helped alot. It is simply vapor lock. The fuel rails get hot, you stop, fuel boils, no restart. Engine hatch open when stopped and flashlite reprogram. Really helped

Raylar

I've been studying the Mercury Racing drawings for the fuel rail, regulator, fuel cooler and pumps on the 600-700sci engines versus the plumbing they use on the 850sci for example. If the fuel in the rail, lines and regulator are getting heat soaked more in the 700sci than the 600sci which kinda makes sense due to lesser horsepower makes lesser BTU's of heat, I've got what may be a simple test fix for your hard starting. If there is enough room below the current spin on fuel water separator that's threaded on under the regulator, try and spin on a deeper Wix fuel water separator with the same thread size. The larger size separator if its two or three inches taller may hold enough extra fuel so that the heat soak and overall fuel temperature may be lower and stop fuel boil-vapor lock. From the fuel line diagrams on these engines Mercury choose to route the fuel rail side to side crossovers thru the intake manifold/intercooler and this is probably where the fuel is being extra heated versus just normal returning past the fuel pressure regulator-a mistake in my thoughts. Just some ideas and observation here with my experience in EFI fuel plumbing and cooling.
If there is room its a quick easy test and possible easy fix!

By the way, I am scratching my head to understand how re-programming the ECM for 89 octane helped cure this problem??

Best Regards,
Ray @ Raylar

PremierPOWER

Thank you everyone for the help!

Just ran yesterday for an hour or so and I opened the engine hatch after docking. Seems like a lot of heat under the hood! I waited about an hour and tried starting. They started a lot better, but still required cranking and a little sputtering. I purchase the Diagnostic Manual and it just arrived. Fuel pump is supposed to run 3 seconds and build 64-67 PSI at key on position. It does this, but the pressure should not drop immediately, which it does drop to 0 in a second or so. The only check recommended is to verify that there is no fuel in the pressure sensing line to the intake manifold. Otherwise could be a faulty regulator or injector bleeding off the pressure.

I am considering buying a replacement regulator and one set of injectors. Change up one engine and then I will send in the injectors in for evaluation and go from there. I got real worried about fuel in the oil from another post about a Mercury Racing engine dumping fuel in the oil. I will keep a real close eye on the oil level.

I will also change the fuel filter. I do think whatever is wrong is being highlighted by heat soak, but I have to check these other possibilities. Now I am more concerned about doing severe damaged than hard starting problems.

Thanks again,

Andy

TWIN-SPINS

if its dropping on all three engines,,to zero,,,ill stick with the problem at the manifold fuel transfer valve,,dont think fuel vapor would cause it to go to zero that quick

PremierPOWER

I have to agree, I have always been worried about the fuel transfer system. I did exercise the valves the last time out. It is unusual that they start up so much easier first thing. I would think that if the transfer valve and manifold is getting air in it that it would be worse over time.
The boat sat in a warehouse for over a year before I bought it. I removed as much of the gas as I could syphon out, replaced the fuel / water separator, replaced the small fuel rail filter, put in fresh gas, and added Lucas fuel treatment. I have filled up four times since I have owned it and I put Stabol at the end of each run when I flush the engines. After the News Years run, I replaced the fuel filters again. Both times that I replaced the filters, I dumped the separator and inspected the small fuel filter and I did not notice anything unusual. Something in the gas that was left in the tank could have fouled the regulators or injectors. Maybe the Lucos treatment damaged the diaphragms in the regulators?

Raylar

If you are measuring the fuel pressure at the Mercury pressure sensor, that fuel pressure would be at the injectors in the fuel rail plumbing system location and should stay up without dropping that quickly. That pressure is controlled by the fuel pressure regulator. The fuel transfer system is on the intake side of the fuel pump and regulator and would not be the problem for the pressure dropping at the injectors and fuel rail. Sounds like the quick fuel pressure drop might be the main problem. You might want to discuss this issue also with the technical department people at Mercury Racing and see what their comments or finding are.

Best Regards,
Ray @ Raylar

fossil fuel

The therory is that lower octane boils at higher temp, Higher octane boils easier. I was running 93 in the keys and the restarts were tough without opening the hatch. After the flashlite reflash I ran Rec 90 in the keys. It is a non ethanol marine fuel available everywhere in florida. Easy restarts even with the hatch closed.

39 Unlimited

Did you ever get this this problem solved? I just took delivery of a 2011 39 Top Gun w/700's and had a difficult time starting after an hour or so of sit time. Very frustrating!