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Has anyone noticed that HPDIs get horrible fuel economy at slow speeds? It really doesn't matter what boat you look at because at idle speed there is so little HP used at 3-5 mph speed yet the 250/300 are significantly more thirsty than the 200 HPDI whereas in the Bomb and Opti line up the 200 or 250 engines burn almost the same at 1000 rpms on all tests. These are pretty typical numbers:
Rude 200 thru 250 @ 1000 rpms= always under 1 gph no matter what boat.
Optis 200 or 225 @1000 rpms= always under 1gph no matter what boat
I wonder if the gas guzzling (almost 2X compared to the other DFIs) combined with a mechanical oil linkage is one of the base problems with these engines? At idle speeds you are burning 2X the fuel thus requiring the engine to supply about 2X the oil. Both the excess oil (even with the oil rod set right) and the excess fuel must surely be contributing to spark plug fouling, carbon build-up etc. Why is the HPDI system so innefficient at idle speed compared to the Rude and Opti systems? It's rare to see a Yamaha performance bulletin showing fuel burn at 750 rpms but Rude shows them down to 650rpms where they burn .40 gph which is amazing. To add more to the theory the 200 HPDI has had far less problems and burns significantly less fuel than the 250/350. As a long time Yami owner and fan I feel for you guys with the 250/350 HPDI problems and thought I would throw this one on the table as it has been nagging me for a while.
Sleeper....if your stats are right and the rudes get better gph at idle than the Yamaha's.....the rudes also do it on all 6 cylinders, where as I have heard Yamaha cuts out 2 cylinders.
I am sorry but I just wouldnt buy a motor that cuts cylinders at idle. I really dont understand the theory behind cutting cylinders at idle as you cannot disconnect those pistons from the crank. If those pistons dont fire at idle then if you cut off the fuel and oil to those cylinders they will burn up. If you still have gas and oil to those cylinders and they dont fire then the oil and gas flow out to the enviroment and then how does the engine pass epa???
I have posted that ? before on THT but really never got an answer.
I have heard the 300HP does it. But if it does infact cut cylinders I would think all hpdi would do it. And if they do drop 2 cylinders at idle what is really gained by this? Fuel economy??? Fuel economy at idle is not an issue.....fuel economy at speed is an issue. I just dont get the drop 2 cylinder thing with Yamaha.
Your comments just fuel the fire My 300 runs perfect There are about 5 guys on the board posting with all the problems! Mercury ran into the same bashing with Optis which I own one of also and have NO problems with! I know a guy who knows a guy that has a buddy that has a problem .Give me a break.There is so much here say I cant take it anymore! the FACTS are that a 300 hp engine is going to use a lot of GAS! And most problems are coming from dealers that have NO CLUE! One of them recommended mixing oil with the gas for break in on a Hpdi ! NO CLUE!
I'm an Opti guy - got no dog in this hunt...neighbor just went hunting to replace his old merc efi's - 2 Yam dealers in the area told him not to even look at the 300's - something clearly is going on...not just a few guys on this board stirring up trouble....
Easy now. I am NOT trying to fuel any fires. I do believe there is a problem with the 250/300 HPDI if you really don't that's OK just ignore the post. I can assure you the problems with these engines is not just a few guys spreading internet folklore. They are the hottest topic on every marine forum you go to. The big question is why are some reported to be running perfectly? What makes those engines different?
Yamahas, not just HPDI'sm have been dropping cylinders at idle for years.
OK, if they are designed to drop cylinders at idle for fuel economy reasons then why do those engines have such horrible idle economy? They average twice the fuel burn at 1000 rpms and under compared to other DI engines. I really think the engines are getting loaded up right from when you start them. If you warm up your engine, which I believe in before taking off or launch in an area that requires you to go slow for a while that is a sinificant amount of extra gas/oil. The extra gas they burn is not needed to make idle power as proved by the Bomb and Optis so what happens to it? I really believe that right from the break-in period while slow running these engines are building up carbon and oil very quickly.
At the very least Yamaha needs to freeze the sales of 250/300's until they get a handle on this problem. Stop shipping to the dealers and institute a fix at the port. Call all customers and get them in for the fix while reimbursing them at least*one lease payment.
If they really wanted to wow people, offer them a $$$ voucher to change over a 4 stroke if no fix is avail.
And Yes, Yamaha is a big enuf company to get this done.
Sleeper You have an excellent question about whether or not the dropped cylinders are getting fuel. If they are, where is the fuel going? If they are not, how are they being oiled? Any Yammie techs out there that can shed any light on this?
Sleeper stop selling the motors until they resolve the problems?????? Man are you trying to take all the fun out of buying a Yamaha right now...LOL!!! Hell all that would do is cost Yamaha more money and make more people have more faith in their product and it would be like Yamaha admitting there is a real problem! Now I ask you why would they be honest with the public and take a chance with loosing more money. Once you bought these motors they got your money!!!!
The big block HPDIs do drop two cylinders at low speed. DFIs don't mix the oil and gas, so the dropped cylinders can get lube, witohut getting fuel. Do they still get fuel? I don't really know, they do get lubed though. My understanding was that it had to do with emissions ratings, not fuel economy. I really can't verify the fuel consumption at idle, ... just isn't that important as I do zero trolling. At cruise speeds (4000 RPM) I think the HPDI is in line with other DFI motors. Mine gets 3.5 MPG (actual mileage) on a 80 gal tank of fuel, ... not bad for 24.5 ft boat.
There is a big problem with the basic premise of this thread. At least for Yamaha, the fuel consumption numbers on their performance bulletins are taken from a Yamaha Fuel Management gauge. As with all fuel flow meters that rely on a sensor in the fuel line, they are notoriously inaccurate at very low flow rates. This is especially true with a direct injection system such as the HPDIs. In other words, the fuel consumption numbers on those tables at very low rpms are almost meaningless, random numbers that bear little relationship to the actual fuel burn. Only a system that draws on the engine computer is able to give reasonable accuracy at low rpms. I believe that Mercury smartcraft gauges do just that, so perhaps their numbers are correct.
From looking at my service manual, there are two important points about HPDIs dropping cylinders at idle: 1) it only happens in neutral. When engaged in gear (as in trolling), all six cylinders are firing even at idle rpms; and 2) the spark and the signal to the fuel injectors is cut off, so there is no gas being injected into the two dropped cylinders.
So much for the various theories. I've noted this before, but from the experience I have wuith my pair of HPDIs and the the ones run by friends, if the 250s are set up right, adjusted right, and run with clean fuel, they will go 100 hours or more without fouling plugs even with lots of trolling, they burn 50:1 or less oil, and they deliver at least 10-15% better fuel economy than the old OX66 Yamahas, and even better than that as you approach WOT. Mine had 400 hours when I lhauled my boat for the season last week and have been trouble free. That being said, if the 250 four strokes had been available when I bought the boat, that's what I would have hung on there.
Back to the original question.
Since day one, I've never been impressed with the slow speed economy of my 200 HPDI's.
They've always run OK at all RPM's, but at displacement speeds, I get at best 1.4 MPG.
At planing speed, I'm averaging 2.0-2.2 MPG.
Interesting HPDI numbers
To add more to the theory the 200 HPDI has had far less problems and burns significantly less fuel than the 250/350. As a long time Yami owner and fan I feel for you guys with the 250/350 HPDI problems and thought I would throw this one on the table as it has been nagging me for a while. 
