How to De-Coke an Engine

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Anyone any advice on how to de-coke a diesel engine without removing the head? Are there any strong additives on the market that anyone can recommend?

Thanks

[ramdonice]

what makes you think it needs de-coking

just change the oil and use a good oil flush dose the trick

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The cars running on (dieseling) - i've tested the fuel shut off solenoid by disconnecting the lead, cracking an injector and turning the car over to see if diesel is getting past the solenoid in the pump to the injectors. It isn't. My deduction is that it's running on due to a build up of carbon since it worsens the hotter the engine is. i.e doesnt run on when cold. Drive for 20 miles and turn it off and it runs on. Strange! (See my thread on FIP timing problem - it may be linked, it's a head scratcher for sure!)

[E_T_V]

I'd change the fuel stop solonoid first of all. It is virtually unheard of for a diesel engine to run on. Once the fuel supply is shut off there is nothing for the engine to burn. The only times this happens is if the turbo is leaking oil into the air inlet or the engine is drawing up oil into the air intake from the sump via its breathers.

The amount of carbon in a diesel engine is irrelevent to its operation as combustin is started by compressing the fuel air mix until it explodes.

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I've already changed the fuel shut off solenoid but it still runs on. How do i check the turbo? iT'S STRANGE THAT IT IS MORE PRONOUNCED WHEN THE ENGINE IS HOT??

[alex620]

It is combustin is started by compressing the fuel air mix until it explodes.

diesels dont work on air fuel mixture, its the injectors giving decent atomization to help it ignite on the combustion cycle.

[colbex]

diesels dont work on air fuel mixture, its the injectors giving decent atomization to help it ignite on the combustion cycle.


Huh ? scuse my ignorance but why do they have an air intake then ?

[lee220sdi]

i'm not trying to be funny guys but i responed to another electrical question with this answer as it is wat happed to me. basically i have wires under the intake shorting so i removed engine cover to keep cool and spray them with wd 40 when neccessary. you can move them arond a bit but with an engine cover on it gets hotter down there and it goes funny. mine used to fry the engine management fuse which kills the start stop solenoid etc. i think this is a common wireing fault i hear about on here recently.

Lee

[E_T_V]

diesels dont work on air fuel mixture, its the injectors giving decent atomization to help it ignite on the combustion cycle.

Yes they do, its just the fuel air mixture is created in the cylinder rather than in the intake manifold as on most petrols. The air and fuel get hot as the cylinder compresses them and eventually they explode. On petrols this is called detonation and is very harmful. Diesels work using this principal.

If the stop solonoid has been replaced then look at other way oil can get into the cylinders (leaking turbo, faulty PCV valve - this stops the engine syphoning oil out of the sump into the air inlet, or even something as simple as too much oil in the sump).

It may also be worth removing the intercooler and degreasing the insides of it as they can collect a scary amount of oil inside them, and can even get filled with them if the turbo has failed in the past.

If it is oily build up causing it to run on then it could just be a really contaminated inlet manifold. These often get coated with a thick coating of oily carbon crud due to the EGR valve, and when it gets hot it gets thinner and more oily so it could just be drawn into the engine where it would burn like normal fuel. Perhaps a clean out of this might help.

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Thanks E_T_V for your time and a well presented simple to understand explanation of what the fault may be. Appreciate it and i'll let you know if i find out what it is.

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The inlet manifold chamber is covered in a 3mm covering of oily tar that is a nightmare to get out. I;ve cleaned most of it but impossible to clean all of it out. It seems to be a cause of the crankcase vent pushing oil through the turbo inlet through to the inlet chamber to the engine. Is this normal and just a build up over time? My engine has covered 125000 miles.

[E_T_V]

I'm afraid it is pretty normal, although its usually more solid than tar like. The cause of it is actually the EGR valve. This recirculates hot exhaust gasses back into the air intake for emissions and efficiency (if you beleive them) reasons. However when oily mist from the turbo and engine breathers (which is pretty normal) meets hot exhaust gases, the oil tends to carbonise and you get the horrid deposit you have noticed. If you disable the EGR valve by removing and plugging the vacuum pipe to it, then you can prevent this build up from happening.

There are 3 ways to remove it although the last depends on what the inlet is made from
The first is physical, just scrape it out. Its messy and you can't get to all of it as you've found out
The second is to leave it soaking overnight or even longer in a decrease bath, (hot if possible). This loosens out the crud and makes it easier to scrape out
The third isn't really practical on the L series as it has an aluminium inlet manifold, but I'll list it here for completeness. You can set fire to it and apply air and fuel to literally burn the carbon and tar mess out. This only works for steel items as aluminium may well melt!

[ssray]

You could use water-get a plant sprayer and spray a fine mist of water into the inlet when running,steam cleans your engine.
Ray

[E_T_V]

You could use water-get a plant sprayer and spray a fine mist of water into the inlet when running,steam cleans your engine.
Ray

That is a really bad idea on so many levels.

Water spray into a turbo will cause damage to the turbo blades

Too much water injested at once may also cause a hydraulic lock resulting in either a blown headgasket or a bent con-rod or even a holed piston.

Also the sticky mud like tar stuff isn't water soluble and as the air intake isn't hot it won't steam clean anything except the pistons and exhaust. In a diesel these rarely coke up due to the way the engine works.

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Thanks E_T_V i've learned a lot by your advice on this thread and by stripping the old dog down...and have learned to invest in some surgical gloves next time i do that job -that residue is nasty!!......But the car still runs on for a second or two.

Could it be due to my timing solenoid being open circuit? (Just diagnosed)This would cause the pump timing to be constantly advanced. (So the manual says) It's a fix or sell point on the car and i thought if i could fix the running on problem then i would change the pump since the car believe it or not drives really well. No excessive smoking, smoothish power delivery even though the ECU isn't doing a thing and doesn't burn oil. Good mpg returns too at 40+. I can pick up a pump for around £200 second hand but if it's still going to run on then that's just another problem which puts repairs beyond economical sense. I know it's a brain teaser without seeing the car but would appreciate the advice.

Thanks

[E_T_V]

The only thing I can suggest is to remove and get the injectors tested (its usually quite cheap), or replace them with a set from a scrap car again quite cheap. It is possible that you have a leaking injector but it would be unusual for it to make it run on for a significant time.