En­gine smok­ing af­ter cold start

Canal Boat - - BACK CABIN -

QI have an Isuzu 35hp en­gine in my nar­row boat that has only done 900 hours. It gives off white smoke when first start­ing up cold that goes af­ter 1 to 2 min­utes. When hot it starts up with­out smoke. Do you think it has fuel in­jec­tor prob­lems on one cylin­der? I have re­placed all the pre-heaters. BARRY CAMP

ATONY REPLIES: In the­ory it should not smoke but white smoke on cold start­ing is not par­tic­u­larly un­com­mon. The smoke is nor­mally just va­por­ised fuel that has not ig­nited on the first com­pres­sion stroke. There can be sev­eral rea­sons but at this time of year it might be low am­bi­ent tem­per­a­ture or a poor qual­ity fuel prob­lem. It seems in­ci­dents of smoke from poor fuel are in­creas­ing.

Have you mea­sured the volt­age at the glow plugs when they are op­er­at­ing? If it’s lower than 12V then there is prob­a­bly some sort of elec­tri­cal re­sis­tance on the glow plug cir­cuit that is pre­vent­ing them get­ting hot enough to start on the first cy­cle. In no par­tic­u­lar or­der, this could be un­der­sized ca­bles, dirty or loose con­nec­tion (of­ten in the big multi-plug that is in the main har­ness), or re­sis­tive ig­ni­tion switch or glow plug re­lay if a re­lay is used.

Once you are sure the glow plugs can get hot enough I would change the fuel fil­ters then drain and cut the old ones open to see what they have caught - if any­thing. That may give the first in­di­ca­tion of a fuel qual­ity or con­tam­i­na­tion prob­lem.

If the com­pres­sions were com­pro­mised you would get this sort of symp­tom but at 900 hours in­ter­nal wear is un­likely; how­ever a valve clear­ance may have closed up so check the valve clear­ances.

Af­ter do­ing the above I would give the tank a good dose of in­jec­tor cleaner from a mo­tor fac­tors or Hal­fords type out­lets and let it work through the sys­tem. Then see what hap­pens at the next refuelling. If the prob­lem goes away it is likely to be poor qual­ity fuel be­ing more dif­fi­cult to ig­nite or dirty in­jec­tors but at a true 900 hours I do not think an in­jec­tor prob­lem is likely, but who knows.

Any­thing that makes the fuel more dif­fi­cult to ig­nite can cause this symp­tom. So if an in­jec­tor is not clos­ing prop­erly or streak­ing rather than atom­is­ing the fuel it will cause un­burned fuel to lay in the cylin­ders and ex­haust at cold start, hence the white smoke.

If the in­jec­tor pump rack is a lit­tle sticky it may not rest at max­i­mum fuel, which is the cold start po­si­tion so try start­ing it with full throt­tle, but slow down as it fires.

Air might be get­ting into the fuel sys­tem some­where so if your en­gine has an elec­tric lift pump turn the ig­ni­tion off for a minute or so be­fore us­ing the starter. That should purge any air. If it’s a me­chan­i­cal lift pump try spin­ning the en­gine with the stop con­trol in the stop po­si­tion. That should do some­thing sim­i­lar. These are di­ag­nos­tic tests rather than reg­u­lar start­ing pro­ce­dures.

If all else fails you may have to get the in­jec­tors ser­viced but at 900 hours that seems un­likely un­less you have had wa­ter in the fuel prob­lems.

You may even find the prob­lem goes away once the am­bi­ent tem­per­a­ture rises a bit.

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