200 HPDI fouling plugs

[bweaver]

I have twin 2003 200 hpdis. They've run great. At 190 hours one engine started running rough. It got worse until it would only get up to 1800 rpm. Several plugs were fouled. Changed plugs and great again for 2 hours then the same thing. My Yamaha mechanic adjusted down the oil flow but they quickly fouled again. They've checked the engine with the computer- it says no problem.<br /><br />So now with new plugs it will be great- for 2 hours!<br /><br />I've read most of the posts. Lots of mention of O2 sensors affecting fuel flow and mix. Could this be a cause of the problem? Any suggestions or other ideas?<br /><br />Unfortunately I am confident it will happen again when I use the boat this weekend.

 

[rodbolt]

Re: 200 HPDI fouling plugs

if you have not corrected the fouling problem I am confident they will foul again too. running well plug fouling was an issue on the 200 hpdi.<br /> how did they adjust down the oil? if it as set up correctly ya really cant adjust it down without misadjusting it. now that the 10 min laptop laughter is done ya know whats not broke so concentrate on areas that may be, test the O2 sensor output as per the two test methods in the tech bullitens, one test is running normal at 3-4K RPM and the other is at an idle with airbox removed. test the red plug caps, check the fuel pump diaphrams, remove and inspect the t-stats for debris and proper operation. check the recirc valve nipples and inspect the oil pump drive shaft seal for leakage, normally a leaking pump shaft seal will be noticed as one engine will use lot more oil than the other.<br />my experience with that motor didctates an O2 sensor cleaning about every 75 hours if much low speed operation is done.<br /> ring free seems to help some but wont cure a running defect. flagship marine can test the injectors if a leaking one is suspected.<br /> but I would guess its time to check the linkage syncronization and the TPS setting as per the tech bulliten and make sure the ign coils have gray connectors not black. there is a tech bulliten on that as well. fouling plugs is an indication of poor combustion or ignition. time to go chase the cause. computers are rather stupid and wont detect an in range failure or bogus reading. sounds like your techs need to spend an hour or so reading the 03,04,05 and 06 marine technical guides.<br />there is a reason yamaha prints them other than to take up room in the tech library.