250 HPDI...what causes wide fluctuations in idle RPM?

[scott-hydra24]

captritter I've been thinking about doing that for two reasons. 1 I've read more and more about fuel lines in general, and having it set up the way Hydrasports does is kind of "not good" marginal at best. The 3/8 line runs from under the deck, up about 2' to the racor, then back down and around the bilge, then up again and out through the bilge where it meets the bulb, is converted from 3/8's to the smaller motor tubing. I've suspected the Racor off and on.

I think one way to know for sure whether or not it has a leak is to put a pastic bag over it below the seals and pump the bulb, fire the motor. If the air is sucked out of the bag, I found the problem.

I think Glen E was right two weeks ago, the motor just didn't blow up by chance, something else let loose as well. Yamaha did refer me to a local dealer here on Cape Cod that just does service work, so there is some hope. Ocean House is very good, but I can't keep driving it back and forth for tuneups once a month, it's 250 miles total trip.

[physicistkev]

Scott,

I get mine back on tuesday next week. Took longer due to me not being able to get away from work.

To answer one question you have had I too noticed that upon starting, the under cowling fuel filter fuel level drops to a lower level then maintains. I always wondered about this but since there is another fuel "tank" (VST) before the fuel gets to the combustion chamber, I would't be to concerned about this. Saying that, as I posted before I have seen that my fuel vacume pressure, the amount of effort that the engine uses to pull fuel from the onboard tank, was at the upper limit. My mechanic will be testing a larger Racor and if the numbers don't improve we will bypass it for the 250 and continue to use it for the 15hp kicker.

I don't believe this is the overall cause for the HPDI #2 piston melting. Since this would have been going on from the getgo and affecting all cylinders, I find it unlikly that this is the cause of the problems. I tend to think its in the throttle bodies or reed blocks. Regardless, I think the problem is very local to cylinder #2, and is not geographically located far from the piston. I will update when I get mine back with what my mechanic says and what I see when I run the new motor.

I don't think I am going to worry to much about the motor, I have a kicker that will get me to 7 mph and get me home. If it goes it goes. No sense in worrying about it. I will take a new motor each year for the next 4 years, eventually, I think Yamaha will offer something else in replacement. But for now, I am just going to enjoy the way it runs at the moment.

[scott-hydra24]

physicist note also you have another Genmar boat with an HPDI problem. I did a ton of work on the boat today after talking to Ocean House. Here is what I found. I took a plastic bag and elastics and put it up and over the Racor, I figured this was the only sure way to figure out if it was sucking air. Nothing, so it's sealed fine. I did take some soapy water and tried each connection, all seemed fine again. After squeezing the primer bulb hard I did note the whiff of fuel. I believe I've traced the singular leak to the downside of the fuel filter. There is a kink in the hose there as the line comes up to it, and I think there must be a tiny hole. I replaced the entire length with hose this afternoon, and it now "appears" to be holding prime finally. I still think I will have the dealer run the compression checks though.
2nd, I took a good look at all cables running from the motor forward. What I found was a slightly loose connection in the bilge for the main motor that then ran forward to the batteries. I took that connection off, cleaned it and used some nylock nuts to tighten it down. I did the same in the battery compartment cleaning each connection. I upgraded the existing negative between the two batteries to 1 gauge from the 4, I did this because the other negatives were 1 gauge and every book I've read says use the same. I took my limited knowledge and figured I might as well test the cabling between the bolting in the bilge and the batteries. I ended up replacing a wire that looked beat at best and probably wasn't helping the situation.

I fired the motor over and interesting enough it's idling about 100-200 rpms higher than before, up around 8-9 which is out of spec. The TPS readings are up now too, likely because it's running a bit higher at "idle". I can't ever be sure which one of these things it was, but chances are it was a combination. One thing I noticed which makes me think it was the bad wire running from the bilge to the batteries was the fact that even with two new batteries the gauge would only read about 12.4 or so with the switch set. After replacing the cable it's up to 12.8, and now clears through 14.0 for the first time I can ever remember while at idle. Seeing as the bilge pump cables were damaged during the install, I'm guessing this cable was also knicked and slowly corroded, probably creating greater resistance and eventually it got to the point that it was too much.

It's raining out so I couldn't take it for another ride, but it looks like I'll bring it back to the dealer Tuesday, at which point they'll make the needed adjustments. It seems to have picked up a few hundred RPM now through the spectrum likely from a combination of new Racor, new bulb, some new fuel hose, new batteries, new cabling etc. Frankly who the hell knows....but I'm assuming it's found it's lost power. Now with a few tweaks post break-in and post fixes, it should be purring.

I wonder how many other HPDI issues are the result of decreased fuel flow, or reserve power getting to the motor.

[Bullshipper]

Good work and good post Scott

[ljpcar]

Just to add a little fuel to this fire! I purchased a 2004 Yamaha Z250 TURC Februrary 2005. I followed the suggested break-in running on the engine. At 10 hours, I contacted the dealer that sold me the motor and was told to wait until it had 20 to 30 hours on it before getting the service done. At 23 hours on the motor, I had replaced 3 sets of plugs$$. I brought it in for service - after 3 weeks - nothing was done. The selling dealer told me that the parts were on backorder for the required service bulletin. I contacted Yamaha - parts were sent to the dealer a week or so later. Then when the day came to supposedly have the motor ready to go. A phone call was placed to see if it was ready - I am told that the service was done but while testing the engine it lost compression on Cylinder #6! It needs a new powerhead! This is with 23 hours on a brand new - out of the crate engine! Ran only Yamalube, Had 2 - 850 max amp batteries, completely wired and set up by dealer! The $$ notes on the new motor will have to be paid for the next 30 or so months but Yamaha has no buy back or trade in solutions only parts replacement! Sure that will keep the dealer busy - fixin it! What is the buyer supposed to do?

[scott-hydra24]

If the dealer blew the motor up when it was in their possession, they own it JMHO. There is no excuse for that happening and almost no chance it was not the result of something they screwed up.