Hi,
Thought I ran out of fuel while cruising the other day and, because engine wouldn't re-start after refueling, I thought I had air in my fuel lines which needed to be bled out. Mechanic showed me how to do this - but the problem turned out to be fuel vapour lock due to a problem with early model Gen III "Cool Fuel" Module (in production between 2004-2009).
I posted this elsewhere in the forum - but thought I'd put it here in case it helps anyone else suffering similar problems... (apologies if this is old news).
Cheers - Ric
Raft61 wrote:
A mechanic showed me how to bleed the fuel line to the injectors.
There's a small valve under the Flame arrestor on the top of the engine (Schrader Valve). It's a bit like a tyre valve with a centre pin in it. Pressing the centre pin releases fuel allowing it to be "bled" of any air (obviously this shouldn’t be done on a hot engine and care should be taken not to squirt fuel everywhere)
The mechanic had a clear PVC tube which screwed onto the valve (so that fuel doesn't squirt out all over the engine) and allowed the released fuel to be collected in a bucket/container. The tube also had a pressure gauge on it so when the flow out of the tube was blocked it would read the fuel pump pressure.
When the ignition is turned on (engine not cranked) the fuel pump runs for about 5 sec. By doing this while the Schrader valve is open, fuel runs out through the clear tube. Lots of air/bubbles were present. After doing this 4 or 5 times, the bubbled disappeared. He then checked that the fuel pressure was about 40 psi. All seemed good. (It’s worth noting that the fuel pump made a slightly different sound when air was present in the line and when it wasn’t)
Unfortunately when out on the water the next day, after about 3hrs of running (starting, stopping, cruising, pulling a tube etc) the engine died while under power at about 3400 rpm and wouldn't re-start again. Had to be towed back home by Volunteer Marine Rescue.
Long story short - further checks revealed I was getting a (not un-common) problem of “hot fuel vapour lock”. The cause - early model Gen III cool fuel fuel pump module in my Mercruiser. “Gen III Cool Fuel Modules” were introduced by Mercruiser in 2004, where a seawater cooled fuel pump block assembly was introduced to stop the fuel from getting too hot and causing a vapour lock http://www.marinemechanic.com/merc/distributors/mercurymarine/sterndrive/gen3fuelmoduletesting.PDF On mine, the seawater cooling lines were corroded and completely blocked. Unfortunately the unit isn't made to be field serviceable. Seawater cooling hoses on these early units are factory press-fit rather than clamp-on hoses. If they have a problem the entire unit needs to be replaced. On top of that it’s difficult to access because it's at the bottom of the starboard side of the motor – hence an expensive replacement.
The unit houses the low pressure (booster) fuel pump, the high pressure (injector fuel line) fuel pump, and an additional fuel filter/water separator. Two other problems were found after the entire module was pulled out. The low pressure pump was marginal on pressure, and there was lots of dirt/grit in the fuel chambers. Apparently the dirt/grit is caused by paint delaminating off the inside of the Cool Fuel module. It can then get into the fuel pumps, pressure regulators and ultimately into the fuel lines/injectors (hopefully mine are OK).
Mercruiser knows about all these potential problems and released a newer version Gen III Cool Fuel module in about 2009. These have clamp-on cooling water hoses, different fittings which aren't as prone to corrosion and hence cooling blockage, and they don't have painted components inside the unit anymore. Mercruiser replace the older units for free if they failed while still under warranty (not many of these still in warranty these days given they newer modules were introduced in 2009). For the rest of us with these early Gen III modules - we have to wait until we have a failure and pay for the replacement ourselves.
I've found there are lots comments/complaints on-line about the issue. There is no direct announcement by Mercruiser to owners about the potential problem, but there was a tech bulletin provided to Mercruiser service personnel http://www.mercruiserparts.com/bulletins/001/04/2009/EN_01.PDF
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2005 Sundowner 205
5.0L MPI Mercruiser, Bravo1, 3 blade Mirage SS prop
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