Resolving Vapor Lock Issue-2007 DF200

[Lostsoul58]

Why don't you take a temp gun out with you the next time you get a hot day, and when it plays up stop and take the cowl off and shoot some temps on the vst cyl heads exhaust and so on. Or if you don't want to do that take the boat to a Suzuki dealer and get all the data pids read and check the cyl temp, and exhaust temp, it will give you the temp and voltage for each one and a heap of other information that might shed some light. Has your engine got a water cooled fuel rail and a water cooled vst.

That would take some of the mystery out of the equation to know the actual temps I'm dealing with. Maybe vapor lock isn't the correct term here but after running 5 miles at 6k rpm before shutdown I'd bet you a Fosters that the VST is full of fuel. It disapates while sitting during the hot soak. Vapor lock? I dunno but the summer temps is when it shows up. If I were a smart man I would create a lower cowl vent so the heated air in the cowl would rise and exit while drawing in cooler air. My vent system on my home roof has a ridge vent and soffit vents that create the same effect. Waterproofing is the challenge with the cowl though.

[redlowrey]

Well, as Tonto said to the Lone Ranger, " I have the information, kimosabe"

Spoke to one of my Suzuki gurus at the show. He has been in the Suzuki game simce before the 4 strokes were introduced. He knew straight away about the issue, immediately said it wasn't a vapour lock issue, and remarked that he had only ever seen barely a small handful of cases years ago, mostly from motors pre-2008.

I will try as best I can to describe the cause as he explained it to me.

He said it is more boat related than it is an engine issue.

The issue is to do with the duty cycle of the low pressure fuel pump when the engine is at idle or low revs, up to about 3000rpm. The ecu cycles the pump on and off in a preset sequence at these revs. Once the engine hits 3000revs (or thereabouts) the ecu then makes the pump run constantly.

The low pressure pump provides fuel to the VSR chamber.

On a very small number of boats, due to the fuel tank placement, combined with things including the length between tank and motor, how the fuel lines are run, filters, fuel restrictions, and primer bulb placement, at low revs, the duty cycle does not keep up with the fuel being used and/or some fuel runs back towards the tank.

This causes the fuel level in the VSR to drop below a sustainable level and when the throttle is opened, there is insufficient fuel to feed the hp fuel pump and the engine starves. He recalled one boat where the owner lived on a canal so had a 10 minute trip at idle speed from his pontoon to the canal entrance where he could then open up the throttle - a perfect scenario for this issue to occur.

So it isn't actually a vapour lock issue at all!!!

The fundamental cause is insufficient fuel getting to the low pressure fuel pump, the pump not being able to suck enough fuel and/or fuel draining back thru the lines.

He said Suzuki, in later models, changed the low pressure fuel pump duty cycle settings to provide a longer running sequence at lower revs and that is why this issue doesn't occur with later engines. Unfortunately the LPP duty cycle is hard coded in the ecu and cant be changed in these early motors.

So we then had a chat about how to solve the issue.

- I mentioned the fuel rail change someone had suggested earlier as being the solution, but he said that was nothing to do with this issue.

- I mentioned the use of the small inline electric fuel pump - he said - yes, you can do that, but in his view it is a very last resort solution because it is treating the symptoms, not the cause.

So we had a further discussion about what to do to address the root cause, being insufficient fuel getting to the low pressure fuel pump. In other words, the boat's fuel system.

He said he would start at the tank and work forwards to the motor and to do everything possible to improve fuel flow to the engine, as follows:

1. remove the anti-syphon valve. It takes some initial "sucking" to crack open these valves and that can add to the load on th LP pump.
2. Replace all fuel lines between the tank and engine, and using one size larger hose wouldn't hurt. Make sure there are no kinks or restrictions in the line, lay it as straight as possible, and avoid it going downhill and uphill again on its path to the fuel filter.
3. Be certain to place the primer bulb between the fuel filter and the engine, NOT between the tank and the filter.
4. Replace the fuel filter element with a new high quality one and replace it regularly.
5. Use a new top quality primer bulb - he likes the new Suzuki ones, but also said the new Yamaha ones are very good too. These have good internal valves and can prevent fuel flowing back away from the engine.
6. Make 100% certain that the primer bulb is placed so it is vertical, with the arrow pointing upwards.
7. At every point in the system where the fuel line is connected to something (eg the filter, primer bulb etc) use an appropriate sealant on the join to minimise any chance of air leaks. And obviously make sure all hose clamps are fitted tight.
8. Replace the tank breather lines or at the least, make certain they are clear and unobstructed so the tank can breathe really freely. If in any doubt, add extra breathers. Check for mud wasps!

And last resort if you've done all that and it still happens, the small electric fuel pump put line as discussed previously.

Hope that advice from the expert helps.

'''I think you are getting confused with the high pressure fuel pump, it defiantly is duty cycled, and the low pressure pump has a full ground on it when the engine is running. It's only function is to supply the vst with fuel, the float and needle and seat keep the supply regulated. As I keep saying you must use gauges and check the pressure, don't assume.

[Moonlighter]

As I said, i was attempting to explain as best I could what I have been told by a master level certified Suzuki tech during the hustle and bustle of the boat show.

The gist of it was that the duty cycle was insufficient to keep the VST supplied with enough fuel. I probably didnt get it technically right. So thanks for correcting me. But if you think he is wrong would you like his details so you can raise it with him yourself? You may even have met him at a Suzuki technical school/event.

[Lostsoul58]

Many thanks to you boys down under. Y'all have more helpful to me than even the repair shops here. I reckon it's winter there but if you can ever get to South Carolina I'll buy you a Budwiser or 6.