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Engine judder
Posted: Fri Dec 06, 2013 6:44 am
by rs_v8
Hi guys
I took my car out the other day for a quick blast, when I got home I turned off the ignition and the car started to judder for around 4 seconds like it was trying to keep running.
I took it back out later and the same happened again anyone know what this is?
Thanks Steve
Posted: Fri Dec 06, 2013 7:18 am
by unstable load
It's called Dieseling and is a sign that something is not well in the engine of fuel system.
Dieseling can occur for several reasons:
Built-up carbon in the ignition chamber can glow red after the engine is off, providing a mechanism for igniting unburnt fuel. Such a thing can happen when the engine runs very rich, depositing unspent fuel and particles on the pistons and valves. Similarly, rough metal regions within the piston chamber can cause this same problem, since they can glow red. It has also been suggested that an improperly rated spark plug can retain heat and cause the same problem.
A carburetor that does not completely close can contribute to running once the engine is off, since the extra fuel and oxygen mixture can combust easily in the warm piston chamber. Similarly, hot vaporized oil gases from the engine crankcase can provide ample fuel for dieseling.
Incorrect timing.
An engine that runs too hot or too lean may produce an environment conducive to allowing unspent fuel to burn.
An idle speed that is too fast can leave the engine with too much angular momentum upon shutdown, raising the chances that the engine can turn over and burn more fuel and lock itself into a cycle of continuous running.
http://en.wikipedia.org/wiki/Dieseling
Posted: Fri Dec 06, 2013 9:15 am
by DaveEFI
Was called 'running on' before the US term dieseling started to be used here. Was common when cast iron heads were the norm - ally tends to stop things getting hot enough. Some makers even fitted devices to prevent it like a valve controlled by the ignition switch which admitted air to weaken the mixture so much it wouldn't burn.
Posted: Sat Dec 07, 2013 8:12 am
by rs_v8
Cheers lads now I know what its called I will look into it and see what I can do. Do you think there is an additive I could use?
Posted: Sat Dec 07, 2013 8:35 am
by kiwicar
Hi
you could take the air filter off and get a pump up style plant sprayer like this
http://www.pest-expert.com/pressure-sprayer-170-p.asp put tap water in it start the engine and stick it on a fast idle, better still get an assistant in the car and get them to run the engine from idle to about 2 k revs, while they do this spray the water as a mist into the inlet manifold. Run about a liter or two through the engine, it should do a nice top end de-coke for you, and if carbon build up was the problem it should fix it, put the air filter back on and drive and enjoy.
Best regards
Mike
Posted: Sat Dec 07, 2013 9:18 am
by rs_v8
Cheers mike sounds like a plan
Posted: Sat Dec 07, 2013 9:47 am
by DaveEFI
What engine are we talking about?
Posted: Sat Dec 07, 2013 10:18 am
by rs_v8
Rover v8 mate
Posted: Sat Dec 07, 2013 12:18 pm
by DaveEFI
rs_v8 wrote:Rover v8 mate
Interesting - I've never known of a standard RV8 running on - including some pretty old clunkers. Are the plugs the correct ones? The timing correct - not retarded? The mixture correct - not weak?
Posted: Sat Dec 07, 2013 12:59 pm
by rs_v8
Its a 4.6 its only got 6.5k on it its got stage 3 heads standard bottom end as far as im aware, it runs 100bhp nitrous so if the timing has been retarded for nitrous use this could cause this to happen but why only happen a couple of times recently? I took it out just around the block and nothing now :/
Steve
Posted: Sat Dec 07, 2013 2:52 pm
by DaveEFI
If you are running retarded timing on petrol, then yes, it will run hotter so more chance of running on.
Posted: Sat Dec 07, 2013 3:34 pm
by rs_v8
Ahh ok then cheers
Posted: Sun Dec 08, 2013 8:49 pm
by ChrisJC
I could get my 4.6 to run on when the compression was about 12:1.
Chris.