Occasional puff of white smoke at start

[Arno]

Once in a while my LJ70 2.4TD starts with a puff of white smoke at engine start.
In all cases it's at cold start, never at warm or hot start.

The start with the white puff sounds a bit rough with a bit more engine shake than normal.

I was wondering if it's possible one of the diesel jets could leak a bit of diesel in the cylinder.
This after having cooled down a night or full day.

Anyone seen this with a 2L engine before?

There is no drop in cooling fluid level over the past 5.000 Km.

Cheers
Arno

 

[ozcruiser]

Hi mate sounds like glow plugs to me best to replace as a set.

http://www.ebay.com.au/sch/sis.html...2&_itemId=151649152024&_trksid=p2047675.m4096

 

[StarCruiser]

Or possibly a little oil collecting in intake pipework.

To check glow plugs, remove the commoning bar and test from the block to the terminal with a multimeter set to 'ohms'. You should get a very low reading, not open circuit or zero but close to zero. That will prove if you do need to change glow plugs. They should all be roughly the same value.

 

[Arno]

Thanks for the hints!

The glow plug got me thinking and already checked them with the ohm meter. (with common rail detached)
Plugs seem ok during measurement.

My suspicion is the glow plug relay not engaging properly at all times.
It's an occasional symptom only seen so far at cold start.

So far it stayed away over the past week, though temperatures have been going above 15 Celsius overnight.

Indeed there's a bit of oil in the air intake pipework, the TC20 turbo might release a bit too much oil as it's aged and has been standing for a few years.

Cheers
Arno

 

[Jimbo4x4]

It's air getting into the fuel system. At a guess probably from the injector seats although I never found where it was getting in on my old 78. It causes bleed-back when left to cool overnight and you end up running lean on start-up because of it. I lived with it as it never got any worse than a slight cough on some cold mornings

 

[Arno]

More news on the white smoke issue - it's still there

In the meanwhile the 2L-T engine has

- new valve stem seals
- new distribution belt
- all valves & glow plugs tested OK
- jets have been replaced
- diesel pump overhauled.

The new valve stem seals are installed without lifting the head.

This LJ70 runs and sounds like new now - very responsive and a great ride.

The occasional puff of white smoke is still there on cold and now also warm starts (after 20 mins off)
During the puff the engine runs rough for 2 -3 seconds or so, eating away a bit of oil.
It's clearly oil, not cooling fluid as the level has remained steady over 2000 Km.

The occasional part seems to have a relation with low RPM maneuvering before turning the engine off.
Like parking requiring a few times back and forth, and so on.
When doing so the engine starts smoking a bit of blue in the process.

If there's no maneuvering, there's no blue smoke and no white puff of smoke afterwards.

No idea where the oil comes from and why it only occurs with low RPM maneuvering.

Any idea's?

Cheers
Arno

 

[StarCruiser]

I would have said valve stem seals had you not already changed them. Other possibles are rings or a cracked piston as you're getting a bit of blue smoke, but I've no idea whether or not the 2.4 70 suffers from this. You could try disconnecting the air intake from the turbo to the engine and see if you get blue smoke then as the turbo won't be on boost at low RPM for manoeuvring. It still could be a bit of oil in there, could be a burned valve, did you check compression when you had the heater plugs out?

 

[Arno]

The valves have been tested with a air pressure tool made from an old glowplug.
Each cylinder was put under 8 Bar air pressure to have the valves pop-up during valve stem seal replacement.
All valves were air tight during the procedure, no abnormalities there.

The LJ70 has been kept on Idle for several hours in different situations to see if it starts smoking blue.
Nothing there - not a single time it started smoking blue.
Oil consumption now is also very low.

Current suspicions goes to sum breather and turbo return line.

Already had an oil catch can connected to the sump breather line to see how much oil comes from there.
No clue's there so far - its minimal what comes from there.

Turbo return line works on gravity it seems (not pressured)
Any obstruction there can cause the turbo bearing to start leaking oil in the air-supply.
Though why it only should happen on low RPM?

The thing is that when it happens it has something to do with oil pressure as it seems the oil leaking continues a bit after the engine is turned of.

Diagnostic is at a standstill now, there's no other clue to go on.

 

[StarCruiser]

I would suggest a compression test as the engine pressures are far higher than the 8 bar you have used to keep the valves lifted, around 500 psi is what I have got on my 80. And temporarily removing the turbo to manifold connection is something I was told about by a local mechanic that enabled him to find a smoking problem. Some sort of temporary air filter would be a good idea while doing this of course.

 

[Arno]

Thanks for the thoughts - much appreciated.

A test with temporarily removing the metal tube between inlet manifold and turbo is a good idea.
The condition to let the truck smoke blue is easy to reproduce.

In the meanwhile I found a few bits of info why a turbo can leak oil at low RPM or Idle

http://www.rx7club.com/single-turbo-rx-7s-23/turbocharger-oil-seal-leakage-explained-727476/

"The oil leak is driven by pressure, like any other fluid flow. When the oil pressure inside the center housing of the turbo is higher than the air pressure outside of the seal, the oil wants to travel outside to the air passage. The air that is holding the oil back on the compressor side is the compressor outlet pressure and for the turbine side, it is the turbine inlet pressure. That is because it is the air pressure that is behind the wheel (depends on wheel geometry and air pumping by the wheel too). This is why turbos leak more at idle/low load conditions and leak less when under full load/boost."

Sounds legit, though other sources do say that a clogged drain pipe can even make a good turbo seal leak.

http://zhome.com/ZCMnL/PICS/turboChargerBasics/turboChargerBasics.html

"Prolonged engine idling also can cause turbocharger oil seal failure, this time on the turbine side. Continued idling causes the turbo to rotate without producing boost. Consequently, a vacuum condition on the turbine side tries to "pull" oil past the turbine-side oil seal and into the turbine housing."

A worn seal / bearing will only make that worse.

Cheers

Arno

 

[StarCruiser]

Good find there Arno and makes complete sense. On to the next stage and good luck finding the cause.