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

[scott-hydra24]

One nagging problem with the motor since it has come back. I went over to the marina and turned it over tonight with the YDS hooked up. I had felt that the motor was all over the place RPM wise at idle, and the YDS confirms fluctuations as high as 800 and as low as 650 with similar wide fluctuations in fuel pressure that seem to be in sync with the changes in RPM. EVERYTHING else checks out within spec, and this is without the #2 and #3 firing. If I put it in neutral and rev it up to 1500 rpms the fluctuations continue.

One other thing I am noticing that I do not recall before. I squeeze the primer ball 3 or 4 times versus 1 or 2 before and at that point the on motor fuel filter fills with fuel. I noticed again tonight as soon as I shut off the motor the level in the fuel filter drops about 1/4 exposing the top of the filter with air. I do not remember this happening pre-rebuild.

Should fuel pressure be varying this much at idle and also the RPMs? It's literally swinging by as much as 150 rpms within a second or two. New plugs, ring free and a mix of last years 87 octane stabalized, and this years 91 octane.

I'm concerned that there might be a fuel feed problem. Glen E I think was the one that mentioned the cylinder that went looked "lean". I'm just wondering now if the cylinder going was a symptom.

Incidentally, do Yamaha techs come out on site up here in New England? I refuse to drive another 4 hours to get this looked at, and would much prefer to speak to a tech on site.

[Bullshipper]

Retighten all fuel hose clamps for air leaks first, then the linkage to to the throttle to eliminate any possible slop if it still persists.

[scott-hydra24]

Bullshipper, thanks.

I slept on it last night, I'm just about positive something has gone amiss. It was literally ranging up to 200 rpm, just doesn't seem right.

It's sucking air somewhere. Will start with the racor and work back.

I'll let you know what I find. I think it's from the fuel filter forward, as I said I'm definately getting air introduced in there somewhere.

[Bullshipper]

Since you replaced the powerhead, I also think that your problem is more likely to be found under the motor cowling from the filter going forward to the second filter to the fuel pump. The small motor filter bodies will sometimes leak air too if defective.
But Check the seperator too as the oring seal on the external Racor needs a little oil and the exact spin tight + 3/4 of a turn tension more to make a good seal on clean surfaces. It should not drop in level on a airtight system IMO.

[OBMD]

This motor probably needs to have the throttle plates sync'd.
The Yamaha reps usually work through and at dlrshps, but there are always exceptions. Contact Yamaha CR and ask for help.

[iron banks]

Scott, man I hate to tell ya but I would sell the entire rig and start over. I have followed your threads for the past year and this rig would make me give up fishing or become a heavy drinker. Good luck with your rig.

[scott-hydra24]

Iron Banks, providing a miracle happens, this thing is history shortly. Truthfully, I'd probably never consider another Hydrasport after this fiasco. I love the boat, it's a mean ride, but this is just silly. I'm still patient for now, if this doesn't get worked out this week it's going to get ugly fast. Enough's enough, I've been very patient. I'm confident this problem can get worked out by the servicing dealer and Yamaha. I'm fairly confident this is just something out of adjustment. Heck that's why they have the 10 hour checkup. Aside of the surging, the motor sounds and looks great, no smoke etc.

Here is what I know, hope you all can continue to add to it.

1. I replaced the Racor today. The bowl had no water, but did have some debris. Set the seal properly I believe. Fired up the motor. Immediately the engine filter goes from full, down to the bottom 1/3. Sometimes pumping the ball will fill it back up, sometimes not. IMO, when it isn't filling it up, that's tell me there is air in the system and that it is actually air tight? How the heck do you bleed air out of this thing? Here is what is odd. After running it for maybe 5-7 minutes one time, it suddenly shot some fuel into the filter so it ended up about 1/2 full and never varied from that.

2. The fuel PSI does not vary much at all. It's within spec at idle and up through about 2k rpms. I didn't run faster than that.

3. TPS settings might be a bit high at idle. I'll have to take another look, data posted below.

4. At idle, and through trolling speed up through 1500 rpms, the engine will vary RPMS per the dash gauge by up to 100-200 RPM and by the YDS by up to 250 rpms. This just isn't right, and you can hear the motor surging up and down. I swear it didn't do this the other day after a long run with it, if that is any clue.

Can anyone tell me for sure that the onboard fuel cup should be full? Can a defective ball be causing this?

What I'm most curious about is the typical cause for fluctations of RPM, and what is actually considered normal? I assume 200 rpm variations (20%) at idle is not normal?

Thanks again.

[scott-hydra24]

Data posted beow from today after running for 20 minutes. Note the fuel pressure (6.76 to 6.61) is within spec, voltage is within spec 14.xx, tps is technically within spec, and water temperature seems fine. I'm going to use the YDS to drop cylinders later and see if I can isolate the problem to a particular cylinder and hope it's a bad cap. Incidentally pumping the bulb really doesn't seem to do much for evening out the engine....so I'm not sure if that's just a red herring. note RPM fluctations from 600 to 800 without me doing a thing, no electronics on etc. The 1150 was me playing with the throttle

[r/min] (7.0±1.5)[MPa] (12-16)[V](0.5-4.5)[V] (below 90)[°C]
20 min 1150 6.76 14.14 0.74 52.3
19 min 750 6.66 14.21 0.57 52.3
18 min 700 6.61 14.21 0.57 52.3
17 min 750 6.61 14.21 0.57 47
16 min 650 6.61 14.14 0.57 51
15 min 800 6.66 14.14 0.57 42.5
14 min 650 6.66 14.21 0.57 50.5
13 min 600 6.61 14.21 0.57 52

[Bullshipper]

Scott,
Thinking out loud.

Low gas level in filter
Air is getting into the water seperator after you fill it with gas.
If the engine is sucking fuel, the entire system is under negative pressure.
For air to reach the Racor it has to be coming into PRIOR to the filter or around its seal.
The bulb and the antisiphon valve should keep the gas from draining back to the tank, edspecially with the motor running.

[scott-hydra24]

Bullshipper....when you drain the Racor I assume that leaves air in it? Or does this not occur because of negative pressure within the line?

[SIM]

Scott,

You really should not have to be messing with this.......I would suggest you get your powerhead rigging dealer to send a regional tech to your boat and have them figure it out. Insist on it. Those guys are really good at what they do.

Potential fuel delivery issue troubleshooting........connect the engine to a portable tank right to the engine mounted filter. Test run and see what you get. If the problem goes away then its an issue with boat side of the fuel system.

If the problem is still present then I would hook up a fuel pressure gauge and see what psi you have at the VST tank pump......idle and underway. Should maintain 36psi consistently. Without checking I don't think this is a YDS feature on that engine. If thats good you have to start looking else where.

Whether your issue is even fuel delievery related....... I could not even guess.

Andy

[scott-hydra24]

SIM, I already left a message asking for a call Tuesday. The dealer has been great, no complaints as they got me back out on the water fast. I'm really not messing with it, more curious than anything. I did the basic stuff today, changed the Racor out, checked for loose fittings starting at the fuel tank and working to the Racor, through the Fuel Management, then replaced the bulb, and did the best I could checking fuel lines through the rest of the system. Let's face it, this is a cursory check and I have no test equipment to do anything further. The YDS is interesting only in that it shows the fuel pressure within the range, but I do note it's on the extreme low end of acceptable.

I've ruled out now the Racor by replacing it, a loose connection, water in the fuel (there has been ZERO), replaced the primer bulb and then gave everything a once over. I did check the plugs, they are all fine. It was doing this on the first set of plugs which were fine, I changed them anyway just in case I had a bad plug, same difference. They are nice and clean.

I took some video today of the motor fuel filter losing fuel. I frankly don't understand how it's happening, or if that is the actual design of this system. The bulb is primed and is rock solid, the onboard fuel filter is filled. Turn the motor over, and the fuel quickly begins to drain from the onboard filter until it's about 2/3 gone, then it stabilizes. I've never seen it fill back up partially like it did earlier today, and I sat there watching it for quite some time.

One thing I did notice goofing around watching the engine monitor with it warming up, when the timing jumps from 9 to 10, that seems to correlate PERFECTLY with the fluctuations in rpm. ATDC 9 smooth, bounces to 10 motor hicuups, back to 9 smooth for a second or so etc. Constantly the timing flips between 9 and 10 when at idle. Could just be a result of the problem or a problem in itself.

I believe the motor is fine at this point, I'm just being cautious because 1 I don't want to get stuck, and 2 I don't want to replace another powerhead. I'd have loved to have gotten out over the holiday, this is now two fourth of July's in a row I was in dry dock, but what can you do. Anyone have idea how fast a Yamaha tech can get on scene?

I really know nothing about the timing, nor do I want to, but I wonder if it is as simple as that.

I have a tough time thinking it's a fuel delivery issue, only way to know for sure is for another HPDI owner to run the motor for a few minutes with the cowling off. Just doesn't seem like the primer bulb should be going flat.

[Bullshipper]

scott-hydra24 - 7/3/2005 2:11 PM

Bullshipper....when you drain the Racor I assume that leaves air in it? Or does this not occur because of negative pressure within the line?

The negative pressure stops with the motor off, and I have never drained one with the motor on. But if the Racor is losing its gas level, I can only asume that the antisiphon valve is adjusted for too much pressure, and that the air is replacing the gas through some fitting.

Bulbs come with different sized fittings, and if one side is too small for its hose, it´s very hard to get a tight fit.

[scott-hydra24]

Bullshipper, the second time I removed the Racor in totality it was totally full. IE, right to the top. I think the problem is upstream of it.

One other thing I was contemplating this morning watching the news. At idle the motor is burning almost no fuel. Could it be simply that further upstream really isn't pulling much fuel, so there isn't a need for the motor to be "sucking" much? That might explain why I did see it partially fill once, as I had it up to maybe 1500 rpms. Heck even at 1 gallon per hour, it's barely going to be moving fuel.

With most all possibilities ruled out, and incidentally I had to replace the Racor anyway so I'm glad I did, and the bulb was an easy replacement too, I wonder if the varying RPMs is totally unrelated to the fuel issue in terms of lines, Racor, fuel filter etc. The fact that the ATDC output on the YDS bounces from 9 to 10 at idle and this perfectly correlates to the variation in RPMS makes me wonder if it's another problem up the line.

I'm very sure this motor is VERY close to being perfect, but being so delicate, I figure a few days waiting is better than blowing up another one. My bet is, either a plug wire is shot or losing it's ability, the timing is slightly off, or the throttle valves are a little off. Let's face it, really everything comes down to the one throttle stopper screw, and if the valves weren't synced perfectly everything else is moot.

If any of you have an HPDI and can give this a check...pump the ball, run the motor while you warm it up and check the ball again...is it firm? That would answer most of the questions.

You guys have been great. Seeing as Hot Rod had a similar problem last year, I'll continue to post back on this thread. I really want a Yamaha guy out to the motor who I can keep on the boat until it works fine

[scott-hydra24]

I spent the day cleaning up the boat top to bottom, doing some replacement caulking and other things I never got to last year like cleaning drain lines etc.

I fired the motor over later in the day. Ran like a champ. I really don't get it. In both reverse and in trolling gear it was slightly "rough" but didn't seem to be hunting as much as the day before. Only difference today was the weather.

Will wait on the dealer Tuesday. My fear is it's burning lean, I don't want to toast another motor if that is the case.

Boat looks "pissah" at the slip though...!

[John_Madison CT]

Scott-Hydra24: All I can say is I'm sorry to read your concerns. You gave Hydra/Yamaha many opportunities to do you right, but here you are again, concerned about your engine.

Yamaha has lost alot of respect in my book. I'm still a Yamaha lover, but the problems with the 250's and 300's is just ridiculous.

John

[scott-hydra24]

It all started where I bought the boat no doubt, but JMHO what Yamaha does right now in replacing only the powerhead is idiotic. They should be shipping out new, entirely dressed powerheads in case it is indeed something else on the motor. This would save the dealers a ton of wasted time.

If I do have a lean condition, and it's obvious I have something wrong when the motor cannot hold RPMs even at 1-2k rpms, all replacing a powerhead did was delay the next failure.

In about 10 minutes I'm going to start letting rip with Yamaha. You are right, this is ridiculous.

For all the jokes about Optibombs, I met a guy last night at the marina that bought one of the 2000 or 2001 models. He fouled a ton of plugs, and the motor ran like crap. Mercury tried once or twice to fix it, then shipped an ENTIRELY new motor, which he has had for 4 years now without problems. I've been struggling with this for two years.

Who knows if things would have been different if Hydrasports had rigged the boat correctly, I'll never know now.

[scott-hydra24]

Spoke to Yamaha direct this morning. No dice, but they did give me the name of a servicing dealer where I bought the boat Very helpful. Two of the other dealers they mentioned don't even sell Yamaha's that I'm aware of at this point.

They apparently don't send technicians out this way, they flat out refused that. So, I'm either making another 250 mile round trip, or I just tick by on the clock waiting for it to blow up again.

[Greg Manning]

Sounds like my experience......do like I did...bite the bullet and jettison the POS before you waste any more money on it. Yamaha can't fix these motors that are "the bad ones"...they don't know why some are good and others seem to blow up repeatedly and they don't know how to fix them. Think of the money this motor is continuing to cost you....that's what made me decide to get rid of mine, lose money or not. Yamaha won't see a dime from me ever again. Greg

[captritter]

Hey Hydra 24,

I have an 03 250 hpdi and my mechanic made me take off my external raycor filter. He said that they have caused a lot of fuel issues for the HPDI's. They have very sensitive fuel draw and external filters have caused problems. Your internal filter SHOULD NOT be doing that. I am very fimiliar with my internal filter and drain it alot, due to an old tank in my boat. I have found insects, debris and water in my internal filter since I switched to HPDI 3 months ago. My old engine did not care about those things, but this HPDI is very sensitive!!! Try bypassing your external filter and see what happens. Just a thought. Sorry for your troubles