300 HPDI rpms up/down and alarms/safemode

[islandbooty]

can anyone offer some help please....it may take awhile but I'll do my best to give a thorough description of the current situation. I have a pair of 2004 300 hpdi's, one has problem for couple weeks i've been tinkering with myself. Yesterday I put in new spark plugs, a new waterpump kit, new racor, fuel filter element, checked thermostats open at correct temp range, verified oil level in both tanks, verified consistent compression at 115-120, and then took for test spin. It starts, idles and gets on plane without hesitation. It's appears to be cooling fine, P'ing and blowing exhaust just like the other motor. After getting on plane and setting both at a steady rpm, it'll run perfect for a minute or two, then I can hear rpm loss and watch port tach loose about 200 rpm. After 15-20 seconds or so it'll pick rpms back up. Then usually within another minute or two, I hear the steady audible alarm and both engines go into safe mode dropping rpm's but not dying...I pull back on the throttles to neutral and the alarm clears, then I can put back in gear and take right back off again(neither engine ever dies). The same cycle happened 3 or 4 times yesterday before I quit. Did the same thing whether I was holding steady at 3500, 4500 or 5500(wot) rpms. I pulled the plugs this morning and see 5 of the 6 look exactly like they should, except the #1cyl is very dry black sooty. After hours of research some of the things I should probably do that I haven't yet is check/clean filter in the VST, change mid-pressure filter, maybe change filter at remote oil tank. From this info can anyone possibly pin-point the most likely problem or make additional suggestions to help me out here? Should I try to take apart the VST before I do anything else? Maybe a bad coil or plug wire/cap? Thanks

 

[islandbooty]

Re: 300 HPDI rpms up/down and alarms/safemode

Update - still looking for any suggestions. I still don't have her fixed. I disassembled the VST, screen didn't look that bad to me but cleaned it up and got it back together. Did couple other misc things like new filter on remote oil tank. This is a new powerhead Yamaha warranteed last February still with really low hours, out of warranty now and I really don't want to have it blow. Seems suspicious to me the one plug looking so different from all the others. What would be scenerios for 1 of 6 plugs to look so different? Does that rule out things like fuel pumps/filters? I've been trying to read and learn, maybe an individual injector problem? I've read these don't have O2 sensors, is there another sensor that could be bad and making the alarm at higher RPM? Thanks for any input.

 

[99yam40]

Re: 300 HPDI rpms up/down and alarms/safemode

monitor both high and medium fuel pressures at the same time when problem is occurring to see if pressures are dropping.

Hook it up to a computer to see if codes are showing up.

If you do not have the proper test equipment and a service manual you may want to take to a Yamaha shop that does before you cause some damage.

 

[rodbolt]

Re: 300 HPDI rpms up/down and alarms/safemode

would it be to hard to look at the digital tach and see what the visual indicate is showing when it alarms?
on that motor water detect,low engine oil tank,low battery voltage and overtemp can set the audible. nothing fuel or remote oil tank will ever set the alarm.
I am thinking your fighting 2 issues.

 

[islandbooty]

Re: 300 HPDI rpms up/down and alarms/safemode

rodbolt -looks like you are exactly right, I'm fighting two issues.

The alarm problem was overheat. I always have known to maintain waterpumps and thermostats, but never pressure relief valves. What a mistake. I'm embarrased and should be crucified, but I'll say it out loud hoping others learn from my mistake, check your poppet valves! Mine was stuck closed on port motor, the salt/oxidation so bad I had to chisel and pry out the spring and plastic valve. It was 100% blocked and frozen up. Only about $30 for 'all' new parts, did it myself as it's very easy. After a 1hr test spin today, that fixed the overheat problem I was having at higher RPMs! No more alarm. Yes I put all new parts in the stbd engine too!

But now to problem #2. At higher rpms I still have an intermittant +/-200rpm drop and then regain. Pulled all 6 plugs just now and #1 looks like crap same as before, other 5 are perfect. #1 is dry black fouled looking, except for one sizable white patch on one side. re: looks at the plug from one side and its 100% black fouled looking...spin it 180 degrees and the other side is 80% good looking like the other plugs. Still wanting to learn and fix, what's going on in there?

Thanks for the help so far! Anyone knows answer to my problem #2 please help.

 

[rodbolt]

Re: 300 HPDI rpms up/down and alarms/safemode

your describing a classic fuel issue, keep monkying and you will describe the cost of a Z300 powerhead.
you must monitor both the medium and high pressure fuel rails at the same time at the problem RPM and load.

 

[islandbooty]

Re: 300 HPDI rpms up/down and alarms/safemode

ok - i really really really don't want to have to describe the cost of a 300 powerhead, really can't afford to. I'll read and figure out how to monitor these pressures, and do it per your suggestion. I've gone thru the VST, didn't replace the screen but cleaned it. The good fairy sent me a box in the mail today with a new screen (and o-ring) for the VST, along with that expensive round metal fuel filter and clamp after the medium pressure pump. It hasn't been changed in the 3+ years I've owned them. Would it be considered monkeying to install those and and try her again before going to the pressure monitoring stage? I'm no mindreader and don't proclaim to have ESP, but I probably know the answer. But thought I'd risk another few teeth being knocked out to hear the answer from an expert. Sorry dad if your listening.

 

[rodbolt]

Re: 300 HPDI rpms up/down and alarms/safemode

you can but if it acts up throttle back and quit.
the high pressure rail can be monitored with a digital multimeter.