Fuel delivery issues (so close!)

[alexanderfoti]

I have finished off all the major aspects of my build now, but there is one consistent issue that is bugging me, and that appears to be fuel delivery.

When idling, the engine is fine, give it a load (ie 3000rpm) for 2-3 minutes and it starts to miss, then plumes of white smoke comes out the exaust and it slowly dies down. Occasional it powers on through and it runs ok, other time it will stall out.

I pulled the fuel pipe from the injector on the last time it stalled, and there was BIG vacuum and a nice splash of diesel to greet me, so I have fuel.

I tried ruling out the fuel filter by replacing it with a Mitsubishi fuel filter, which seems to have helped but the issue is still there (and intermittent! sometimes it will rev happily all day), I have also tried running a straight pipe (with a pass through filter ) straight from the tank, but this didnt seem to help.

so I am thinking I have a faulty/blocked fuel pump, and it should be replaced, what do you think?

[Stuart]

I take it the filter is a Diesel filter and not petrol? Maybe the fuel passes through better when warm? Should it be pressured through? Only ideas I'm afraid as I am no expert

[alexanderfoti]

Yeah a Its from a Mitsubishi Pajero Fuel filter, I think I need to take it for a proper run and see what happens, so far I have only been testing it by revving it.

[Nanko]

Valve clearence?
Pushrod and valve stem expands when temperature rises.
When the clearence is not enough the valve doesnt close when engine is hot

[alexanderfoti]

Hmm it is possible, although it recovers on it own sometimes (2-3 seconds later) so im doubting its this. I initially thought it was water in the fuel so I bought some new fuel but still having issues.

[OilyPhil]

Blocked breather in fuel cap? Try opening fuel cap next time it happens.

Phil

[alexanderfoti]

I thought that so I did just that, no change

[snoopy]

White smoke is air in the system, are your rubber pipes compressed at the end with connectors?

[alexanderfoti]

White smoke is air in the system, are your rubber pipes compressed at the end with connectors?

Many thanks, I did think it was air, (Considering I was playing with the fuel system). I have no had it running for a while, (although still not ridden it) and there doesnt seem to be any white smoke/misfiring.

The ends are either clamped with pipe clamps or zip ties.

[XLerate]

No idea what engine we're talking about here or if it's new or used or what work has been done to it. On diesels blue smoke is usually caused by drawing engine oil into system, possibly through valve guides or elsewhere. Black smoke is of course too much fuel for whatever reason, maybe intentional. White smoke at startup is most often improper mixture in fuel/air caused by a fault in fuel system: too much air for the fuel.

Could be injectors stuck open or closed throwing off balance on air/fuel mixture. May be caused by weak injection pump or clogged injectors or incorrect injector popoff pressure, or even air leaks at injector sealing at head or fuel lines. Checking for pressure leaks is easy. Cleaning of fuel system with a high quality injector cleaner might show improvement and if so it at least points to the source of problem. If new injectors were installed and then white smoke shows up it indicates a weak injection pump that can't pump hard enough against new & stronger injector springs.

In some cases timing and timing advance can cause white smoke. If white smoke gets worse with retarded timing then an advance may be needed. If timing is maxed out on advance and has white smoke it may indicate internal timing gears are off one tooth. In some cases the key on pump shaft has sheared or is in process of shearing, causing incorret timing. Also dirty pump components can foul up the timing so that it doesn't advance when it should.

If it's a turbocharged engine design but doesn't have turbo installed then it may not have enough restriction in the intake system, so engine is getting more air than it should at idle causing improper combustion. If smoke tends to clear up when you partially block air intake then you may need a more restrictive air filter. Finally, one other possibility is a blown head gasket allowing air into engine on vacuum stroke.

[alexanderfoti]

Thanks all.

im pretty sure there where air bubbles in the system, as now I have run the engine for a while without disturbing the fuel pipes, there are no issues Fingers crossed it stays that way.

[XLerate]

Another thought struck me while reading this morning. Because it only happened after the engine had run a bit, and not at startup, and the fact that it may be clearing up now: Could be caused by a blockage in the injection pump fuel return line, causing pressure to build too high for the pump to deliver fuel. Maybe something inside the line is now clearing out.

This would have the same result, as too much air, too little fuel. May be something to look at. Also to be sure the return line is of sufficient diameter, big enough to flow the fuel and no real tight bends or kinks.