'03 250 HPDI rough idling ??

Hey guys, Last tourney my rig had a hard time idling both in and out of gear. If I give it just a little throttle, like maybe 800 rpm she's fine. Also she runs fine all the way to WOT at 5900 rpm. I decarbonized the engine thoroughly with little or no improvement. Installed new plugs and again little or no improvement. The plugs weren't bad at all. Did notice the bottom left plug was a little darker than the others but no buildup. I'm thinking next step is to replace some filters. After reading all the posts there are more than I thought. Give me some ideas or a Been There Done That. Thanks.

At times summer heat/hot water with humidity can affect idle...at least that was what I read a time or two...along with bad gas...

I have an 04 300 hpdi that was having a problem with a rough idle. I also decarboned mine and installed new plugs. After doing that is when I started getting a rough idle. I got to thinking that when I put the plugs in I didnt check the gaps on the plugs because I couldnt find my gap checker and I was going to do it later, but forgot about it http://www.bassboatcentral.com/smileys/doh.gif Well the other day I remembered and stopped by and bought some gap checkers and pulled the plugs. My gaps are supposed to be 1.5 to 1.6mm. None of the plugs I had in were over 1.2mm http://www.bassboatcentral.com/smileys/mad.gif . I also indexed my plugs, I know thats a matter of debate but I figured it wouldnt hurt. It all seemed to help.

Scott, have you ever had the low pressure fuel pumps rebuilt/replaced? If you're cleaning and replacing filters, you might as well rebuild these lift pumps.

Oh, is it idling within spec, or do you have to give it gas?

Jerry, Nope. Not unless involved in those early problems I was having back in '04. But even then that was 6 yrs. ago. I belive the rpm's at idle are the same but it's idling so rough it's hard to tell. Any thoughts about shocking it with a high dose of Sea Foam? Thanks.

Check your email, Scott.

Well I replaced my fuel pumps today. Took her out and ran her before dark but there was no improvement on the rough idling. I did notice however that once I got any air out of the lines the primer ball stayed firm where it has been going soft for the last couple years. Still runs fine idling @ 800 rpm or above and stays smooth right on through WOT. One thing I did notice was When I disconnected the first fuel line below the bottom pump, I let it drain into a small plastic container. I did catch a very small amount of very fine sand, A couple real small black particles, And a little bit of a sort of cottony slime. I guess replacing the filters comes next. Still open to any suggestions. http://www.bassboatcentral.com/smileys/ohwell.gif

Check and if necessary adjust the voltage at the throttle position sensor. It affects the idle. That is what was wrong with mine, same problem, same engine.

Did you change that filter with the funny release coupler? I thought you were going to order it when you did the fuel pumps.

Jerry, that's next. I'm ordering that filter as welll as the one that goes in the VST tank. I think I also need to clean out the small water seperator thats before the first fuel pumps too since I found that fine sand when draining the fuel pumps. Will post results next week.

My filters were delivered late this afternoon & I installled the VST filter screen and the high pressure filter. Took me about an hour and a half. Did not get a chance to run yet and won't have another day off till next wednesday. But here are a couple observations. Make sure you have a little of the RTV silicone handy. I would have never been able tokeep the main tank gasket in place without it. I had 2 small black flakes in my VST tank and that was all. There were a couple small particle on the filter screen itself but the thing I noticed was the new screen I could see through. The old one I could not. Only if I held the top of it to the light could I see through it. Might not mean anything. Also When changing the high pressue filter I noticed the old one was noticably heavier than the new one , even after draining the fuel out and letting it evaporate dry. Again, might not mean anything. The fuel injector clamp worked great on the high pressure fitting & that fancy fitting on the other end was no problem. Almost makes me wonder if it will hold it was so easy to remove and re-install. Will post results next week. http://www.bassboatcentral.com/smileys/praying.gif

Good luck, Scott. I'm sure you'll let us know how it does. You'll have to give me a call once you run it, I have a few questions for you.

I was able to take my rig out this evening and try it out but was greatly dissappointed. The rough idle and cutting off remained below 750 rpm. It is trying to idle @ 600 to 650 rpm. Is this the proper range? I ran her easy up to about 5000 rpm & then sat her down to idle and she still did the same thing. I then ran her hard back to the ramp & I was only able to get 5200 rpm! Ouch. After changing the fuel pumps but before changing the filters I was still getting5800 to 5900 in this summer heat. After changing the Vst filter and the high press. filter & cleaning out the separator filter on the outboard I have lost 400 to 500 rpm. BUT I made another run and it held @ 5200 & all of a sudden went to 5350 rpm and held there. but that was it. Any ideas what I could have botched up? What should I try next? I appreciate any and all help. http://www.bassboatcentral.com/smileys/doh.gif

Coil acting up but not completely failing??? A friend of mine just went thru that with a Merc and it was a coil that was working when it wanted to.

Have you checked the compression? If not please do, low on one cylinder would sure cause the problems you describe.

Charlie 206, you are dead on. Just got a call from the shop. Compression is down on 1 cylinder. Looks like I'll be the proud owner of a new power head. http://www.bassboatcentral.com/smileys/crying.gif

You have to buy it or did you have an extended warranty??

Sorry to hear that but I was sure suspecting as much. Just got thru rebuilding mine after it blew July 4 weekend. After it went south it would still run 5400 rpm with no noise - that Royal Purple oil is slick - but the idle was crap.

RangerGuy, I had an extended 5 yr. warranty but it ended 2 yrs. ago. The shop called Yamaha to see if they would offer any assistance or maybe ship a complete head with all injectors ready to bolt on, but they only do that for factory warranty repairs. I'm afraid this one is on me, but at least I'll get a series II head. Guess I'll be taking lunch to work for a while. http://www.bassboatcentral.com/smileys/ohwell.gif

Either flow test all injectors, or at a minimum flow test or replace the injector on the cylinder that went bad.