dhutch
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| posted on 11/12/09 at 06:57 PM |
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Engine 'running on' after switch off.
Just occataionally when i switch of the engine of the kit (cvh on 40's megajolted) it runs on a little rather than just coming to rest as you
would expect.
A freind of mine also has a stock A series that does it almost without fail.
Obvisouly at the moment it doesnt exactly cause me any problems but ive never really come up with a very good explanation for whats causing it.
Is it simply that the engine has suffient heat retained within it that once the spark has been removed it continues to run on compression ignition
breifly? Certainly in terms of the a series its fairly know for hot spots?
Clearly googling 'engine running on' doesnt return very concise results an i dont know any other name for the phenomina
Daniel
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phoenix70
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| posted on 11/12/09 at 07:00 PM |
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Not sure if it affects megajolt, but it could be feedback from the alternator. I know with megaquirt you have to put a diode in to stop this
happening.
Cheers
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Paul (Notts)
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| posted on 11/12/09 at 07:16 PM |
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It may well be to do with how you have wired the alternator in and where the power is taken from for the EDDIS unit and the Megajolt unit. As above
the alternator may well be powering the eddis to produce a spark. untill all the fuel is taken from the carb.
Paul
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Bluemoon
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| posted on 11/12/09 at 08:02 PM |
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Mine (CVH) would do that when the idle was set high.. This would make the plugs get too hot then deisel on switch off..
Have you the correct plugs??
Cheers
Dan
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hillbillyracer
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| posted on 11/12/09 at 08:13 PM |
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The A series was bad for it, I've seen a fair few with a factory fitted valve plumbed into the inlet manifold which needed an ignition live to
keep it shut. When you turned the ignition off the valve opened letting excess air in without fuel that helped to stop it.
I'm sure you could engineer something similar if need be, but better to cure the cause if you can.
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McLannahan
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| posted on 11/12/09 at 08:39 PM |
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quote:
Originally posted by dhutch
Just occataionally when i switch of the engine of the kit (cvh on 40's megajolted) it runs on a little rather than just coming to rest as you
would expect.
A freind of mine also has a stock A series that does it almost without fail.
Obvisouly at the moment it doesnt exactly cause me any problems but ive never really come up with a very good explanation for whats causing it.
Is it simply that the engine has suffient heat retained within it that once the spark has been removed it continues to run on compression ignition
breifly? Certainly in terms of the a series its fairly know for hot spots?
Clearly googling 'engine running on' doesnt return very concise results an i dont know any other name for the phenomina
Daniel
Isn't it called overrun? When a engine continues to run after it's switched off? That's what I always thought?...
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britishtrident
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| posted on 11/12/09 at 08:42 PM |
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It will be worse if the idle speed is set high and the mixture isn't spot on. Another cause is if the igntion is too retarded but if that was
the case you would also expect the engine to run hot.
Unfortuneately twin DCOEs would make using an anti-dieseling valve difficult.
Using super unleaded should stop it.
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britishtrident
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| posted on 11/12/09 at 09:50 PM |
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ebay item 290378398193
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Mark G
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| posted on 12/12/09 at 10:39 AM |
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its normally caused by a build up of carbon on something inside the cylinder. Normally a spark plug, valve coke or part of the head gasket. They get
red hot and when running and then when you kill the ignition it is hot enough to ignite the fuel. Running on carbs the fuel is sucked into the engine
when it needs it so will run on as long as something is there to ignite it.
As said above, you should remove and inspect the plugs, give them a clean with a wire brush (as long as they're not iridium tipped) and re fit
them. If this fails run on V Power! Not just super, it doesn't have the same cleaning properties as V Power. I'd also stick a fuel
treatment in the tank which should kick start the cleaning process. After a few long runs you should be noticing a good difference.
[Edited on 12/12/09 by Mark G]
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ashg
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| posted on 12/12/09 at 06:46 PM |
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i had it on mine. a diode on the battery light cured it.
easy way to test is disconnect the little small wire from the altenator. if it doesnt run on then you need a diode.
if it still runs on then you need to get the air fuel mix looked at.
Anything With Tits or Wheels Will cost you MONEY!!
Haynes Roadster (Finished)
Exocet (Finished & Sold)
New Project (Started)
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plentywahalla
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| posted on 13/12/09 at 10:24 PM |
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Its called 'Dieseling' and is caused by hot elements inside the combustion chamber igniting the fuel air mixture after the spark is turned
off.
Causes can be carbon build up, rough edges in castings or sometimes because the wrong sparkplugs are fitted and the electrodes are glowing hot.
Fit throttle bodies! they don't suffer as fuel supply is shut off.
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omega 24 v6
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| posted on 13/12/09 at 11:11 PM |
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quote:
Fit throttle bodies! they don't suffer as fuel supply is shut off
Mines kept running it needed a diode and yes it was megasquirt getting power from the alternator.
If it looks wrong it probably is wrong.
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dhutch
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| posted on 15/12/09 at 12:28 AM |
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Excellent info guys, thanks.
- I'll have to look into sticking a diode in it and see if that does the job.
Also, my freind says when ever the meastro does it, the engine is actaully running in reverse. If you raise the clutch on it while its doing it.
- Mine however the only time ive raised the clutch on it, was running the convential way.
Daniel
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flak monkey
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| posted on 15/12/09 at 07:51 AM |
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My pinto used to do it if the rad fan was running when you turned the ignition off. Needed a diode fitting really 
Sera
http://www.motosera.com
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NS Dev
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| posted on 15/12/09 at 12:08 PM |
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yea, kind of as above....
There are 2 totally seperate reasons, both mentioned but nobody seems to have pointed out that fact!
The first, and most likely, is the mega ecu or edis module remaining powered via the charge warning light or another connection between permanent live
and the ignition controlled side of the car's wiring, and as said, a diode sorts that out, or a pull down resistor on the ignition fed circuit
live to the ecu.
Second, the engine might be dieselling, but that is rarely "proper running" more chuggling and stuttering after turning off until it
finally stops, and as said its usually due to too much heat somewhere in the combustion chamber.
The former is most likely though
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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ss1turbo
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| posted on 15/12/09 at 07:37 PM |
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Running on based on the "hot spot" theory (carbon deposits or wrong plugs) is normally rather poor - sounds a little "rattly"
and random (as NS Dev says). If it sounds just like a delay between key-off and actually running ceasing, then there's something funny with
your wiring..sticky relay maybe?
Long live RWD...
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NS Dev
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| posted on 15/12/09 at 07:54 PM |
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quote:
Originally posted by ss1turbo
Running on based on the "hot spot" theory (carbon deposits or wrong plugs) is normally rather poor - sounds a little "rattly"
and random (as NS Dev says). If it sounds just like a delay between key-off and actually running ceasing, then there's something funny with
your wiring..sticky relay maybe?
Its not a fault with the wiring as such, I have had it with MBE ecu's and others, not the ecu's fault other than it taking such a small
current to keep it "active".
When you turn the key off, you should shut off the ignition fed live circuit BUT on many cars a slight current can still flow, via a few routes, with
Flakmonkey's car the current came via the cooling fan, so it dropped most of its volts across the fan (or fan relay coil depending on how it was
wired) but there was enough residual voltage to keep the ecu "alive". On mine it was, as others have said, the charge warning light. When
the engine is running, this effectively links the ignition controlled and permanent live circuits via the alternator, therefore, even with the key
off, a tiny current can flow via the warning light bulb.
A common solution is to switch the ecu via a relay. Even though it doesn't need a relay, the relay coil pulls enough current to drop out when
you switch off the engine.
That said, I had one that still ran on then. I just wired a resistor to pull the ignition controlled live to earth all the time, that way on key off
it pulled enough current to knock the ecu off.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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