Stop­ping the urge to surge

Canal Boat - - Back Cabin -

QI have a nar­row­boat fit­ted with a Ve­tus P4.19 en­gine (a marinised Peugeot/Citroen XUD9 1.9 nor­mally as­pi­rated lump). The en­gine has now clocked up nearly 7,000 trou­ble-free hours.

How­ever, re­cently the en­gine speed ‘surges’. It does not ‘run-away’ as such, as you can close the throt­tle and it falls back to idle speed, but some­times you set the en­gine revs to say 1200 revs and it will, quite by it­self, in­crease revs to 2000 or so.

My ques­tions are: Is it dirty fuel/ wa­ter in fuel or sim­i­lar. Or (as the en­gine is quite high­ish hours) is this the first sign of un­burned fuel get­ting into the crank­case and be­gin­ning to de­velop “diesel en­gine run­away”

I usu­ally put diesel con­di­tioner in the tank twice a year (cer­tainly be­fore win­ter) and I usu­ally have the tank full (cer­tainly be­fore win­ter), but I have never had the tank cleaned.

The en­gine has started to smoke re­cently, al­though not badly. It hardly burns any oil and starts eas­ily, so I be­lieve the com­pres­sion is good, al­though I’ve never had it tested. KEITH HAMSHIRE

ATONY REPLIES: Af­ter a bit of Googling I found that en­gine ei­ther has a Bosch or Ro­todiesel ro­tary in­jec­tion pump. The Bosch pump is me­chan­i­cally gov­erned so un­less dirty fuel is, in ef­fect, caus­ing a weak, faster burn­ing mix­ture, which is very un­likely in a diesel, the prob­lem could be a sticky gover­nor inside the pump. I am not fa­mil­iar with the Ro­todiesel pump but from what I can see it looks like a CAV DPA clone. The illustrations I found show a me­chan­i­cally gov­erned ver­sion but CAV also made hy­drauli­cally gov­erned ver­sions that ex­hibit your ex­act symp­toms when suf­fer­ing fuel star­va­tion. The me­chan­i­cal ver­sion might also do it if the gover­nor was stick­ing a bit.

Could any gas or other volatile com­bustible ma­te­rial be leak­ing into the en­gine bay?

I can set your mind at rest about a po­ten­tial run­away. For this to hap­pen you would need a lot of diesel in the oil. This causes the sump lever to rise, the oil to thin and smell of diesel. Your words do not sug­gest this is hap­pen­ing.

With high hours, any smok­ing is more likely to be caused by worn/ dirty in­jec­tors but in­jec­tors do not nor­mally cause the en­gine to rev it­self up. Burn­ing lots of oil may cause it to rev up but for that to hap­pen you would also have clouds of ex­haust smoke and heavy oil con­sump­tion.

You make no men­tion of how reg­u­larly you change the fuel fil­ter(s) and clean any wa­ter traps. Like­wise you say noth­ing about reg­u­larly pump­ing, si­phon­ing or in some other way re­mov­ing what­ever is lurk­ing in the bot­tom of the fuel tank. Tank drain­ing needs do­ing an­nu­ally.

I think the first thing you need to do is to see what is in the bot­tom of the tank and re­move and dis­pose of any­thing that is not clear diesel. If you find black, brown, or grey slime you prob­a­bly have diesel bug. If you find a lot of pink­ish emul­sion it’s a re­ac­tion be­tween an emul­si­fy­ing fuel ad­di­tive and wa­ter. It all needs get­ting rid of but if the con­tain­ers are al­lowed to stand for sev­eral days you may well find emul­si­fied fuel sep­a­rates and as long as there is no sign of bug the fuel part can go back into the tank. Then change your fuel fil­ters and drain/clean any wa­ter traps. Take a great in­ter­est in what is trapped inside them. Again you are look­ing for wa­ter and signs of bug.

Check for diesel bug

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