aleda Posted July 16, 2014 Report Share Posted July 16, 2014 Hi everyone, been doing some research as she has been occasionally dieseling but yesterday she carried on for a bit longer than usual to the point where I thought heck, how do I turn the engine off but fortunately she stopped! Am wondering if it's carbon build up in the carburettors? Have been using standard fuel, not premium. If I switch to premium will it clear the problem? The engine has been rebuilt and converted to unleaded. Does she need tuning? I had Electronic ignition fitted last year. Would appreciate where to look first and how to turn engine off if she doesn't stop! BTW, the bit of rust proofing in engine bay went very well, makes me want to do more to improve the rest now! UJ's still to do. Oh and she has been round the Indy Circuit, Betty loved it! Think she might be in TR Action sometime. Christine Quote Link to post Share on other sites
AlanT Posted July 16, 2014 Report Share Posted July 16, 2014 We had a topic on this quite recently. Its hard to find these, using the forum search facility, which is not really very good. I always use Google restricted it just the TR-register like this: site:www.tr-register.co.uk "running on" 4a This will give you some reading matter! Quote Link to post Share on other sites
RogerH Posted July 16, 2014 Report Share Posted July 16, 2014 (edited) Hi Christine, to turn her off simply engage any gear, hand and foot brake on, let the clutch out slowly and it will stall. The 'dieseling' could be caused by too advanced timing or weak mixture or piston 'blow by'. Using 97 or 99 fuel would help a lot but isn;t necessarily the answer. Carbon in the carb is not the problem. What colour are the spark plug tips - light brown is good. Too light could be the problem. Too oily could also cause it. You need a tune up. Roger Edited July 16, 2014 by RogerH Quote Link to post Share on other sites
Peter Cobbold Posted July 16, 2014 Report Share Posted July 16, 2014 Christine, Its caused by heat build up in the cylinders. There's several adjustments to try. Advance the ignition a couple of degrees static. Make the mixture richer by lowering the jets a couple of flats at a time. Check you have the righ heat grade of plugs. If the carburettors are being fed hot air from above the exhausts, rather than by a proper cold air feed, that wont help. You can stall the engine by lifting the clutch, in gear, when it diesels. It'll probably go away when the weather cools down a bit. A lot of slow running, careful driving, can lead to carbon build up in the combustion chamber, so regular full throttle driving helps - keep up the circuit work. Peter Quote Link to post Share on other sites
AlanT Posted July 16, 2014 Report Share Posted July 16, 2014 I'd try better petrol first. Quote Link to post Share on other sites
peejay4A Posted July 16, 2014 Report Share Posted July 16, 2014 I agree with Alan. Simple test first, try premium fuel. Quote Link to post Share on other sites
Peter Cobbold Posted July 16, 2014 Report Share Posted July 16, 2014 (edited) The octane of a fuel makes no difference at tick-over at all. RON is only significant at wot, and then only if detonation is imminent. But trying other fuels is still a good idea. It may be that cheap fuels use a lot of butane, which could conceivably cause dieseling if allowed to go stale. Gases like butane burn faster than the rest of the petrol, so loosing butane slows the burn, equivalent to retarded spark, and the combustion chamber gets hotter. There no easy way to find a low butane fuel. But butane is cheap, so buying non-supermarket petrol is a good place to start. And fill-up from pumps with a fast turnover another. Edited July 16, 2014 by Peter Cobbold Quote Link to post Share on other sites
ianc Posted July 16, 2014 Report Share Posted July 16, 2014 Don't let it diesel - it can damage the engine. Quench it as suggested above, using clutch slip as you turn the ignition OFF. Ian Cornish Quote Link to post Share on other sites
RogerH Posted July 16, 2014 Report Share Posted July 16, 2014 I've mentioned before my black magic with 'dieseling' effect. I found that if I turned the ignition key to the off position very very slowly it would not diesel. No logic, no sense. But it did work - very odd. Roger Quote Link to post Share on other sites
Peter Cobbold Posted July 16, 2014 Report Share Posted July 16, 2014 (edited) I've mentioned before my black magic with 'dieseling' effect. I found that if I turned the ignition key to the off position very very slowly it would not diesel. No logic, no sense. But it did work - very odd. Roger Roger, That is Interesting! If the switch were to arc and make intemittently during that slomo switch-off then the engine might be kept spinning by the firing strokes while the combustion chambers cool down on the 'misses'. ? Peter Edited July 16, 2014 by Peter Cobbold Quote Link to post Share on other sites
do8erman Posted July 16, 2014 Report Share Posted July 16, 2014 Anti run on valve worked fine for me Quote Link to post Share on other sites
Tony Millward Posted July 16, 2014 Report Share Posted July 16, 2014 You should be using premium fuel...full stop. Tony Quote Link to post Share on other sites
BlueTR3A-5EKT Posted July 16, 2014 Report Share Posted July 16, 2014 (edited) Advance ignition to 8 or 10 or 12 degrees BTDC - sensible to try out. Anti run on valve, - useful and effective. Slip clutch to stall engine when turning off - most useful. Italian tune up - last resort Edited July 18, 2014 by BlueTR3A-5EKT Quote Link to post Share on other sites
riverstar Posted July 17, 2014 Report Share Posted July 17, 2014 I found that if I let the engine idle for ten seconds rather than turn off immediately problem solved also premium fuel with a octane boost does the trick Quote Link to post Share on other sites
littlejim Posted July 17, 2014 Report Share Posted July 17, 2014 My 4A did that when the timing was not spot on. Quote Link to post Share on other sites
stuart Posted July 17, 2014 Report Share Posted July 17, 2014 Tuned properly you shouldnt need expensive fuel or any extra valves or anything. Check timing and fuelling. Stuart. Quote Link to post Share on other sites
Peter Cobbold Posted July 17, 2014 Report Share Posted July 17, 2014 (edited) Apologies for harping on, but dieseling does indicate there's a hot spot in cylinder(s) that is igniting residual mixture and which should not be there. Hot spots that ignite the mixture prematurely in an engine under load are really nasty - can melt pistons through 'pre-ignition'. And preignition is silent - there's no knocking to warn the driver. A hot spot will ignite the mixture near the start of the compression stroke. So the piston is trying to compress a hot expanding flame- the crown melts in a second or so. So if I had dieseling I'd would worry about where the hot spot could arise: running too advanced or too retarded ( timing marks shifted?), too lean, newly machined heads/valves with sharp edges, wrong plug heat rating for the state of tune, carbon deposits, etc. If the answer is to dieseling is to use highRON fuel then the engine must be detonating on lower octanes and that is lighting up a hotspot. Why? too high compression ( shaved head)? too lean? too advanced? too retarded?air intake hot? water jacket issues? The high RON will have no effect on combustion during running-on, it doesnt make the fuel any less likely to be ignited by a hot spot. Peter Recommended read: http://www.contactmagazine.com/Issue54/EngineBasics.html Edited July 17, 2014 by Peter Cobbold Quote Link to post Share on other sites
Tony Millward Posted July 18, 2014 Report Share Posted July 18, 2014 Hi Peter, I refer you to your previous post #7. You are confusing me a tadd me lad. Cheers Tony Quote Link to post Share on other sites
Peter Cobbold Posted July 18, 2014 Report Share Posted July 18, 2014 (edited) Hi Peter, I refer you to your previous post #7. You are confusing me a tadd me lad. Cheers Tony Tony, The stale fuel retards the burn so the combustion chamber runs hotter, may even detonate the end-gas. So generating the hotspot to ignite the fuel when running on. 'Dieseling' is a misnoer - its not compression ignition, it neeeds a hotspot. Pter Edited July 18, 2014 by Peter Cobbold Quote Link to post Share on other sites
Peter Cobbold Posted July 18, 2014 Report Share Posted July 18, 2014 (edited) So, if running-on is caused by hotspot ignition why arent we seeing 4s with pistons melted by preignition ???? The lack of holed pistons may be because there's no hotspots. If there's no hotspot then we need a spark. Maybe, somehow, the coil is continuing to supply sparks after the key has been switched off. Is is feasibe for the still-spinning dynamo or alternator to supply a few volts to the coil? eg through the ig warning lamp?? Perhaps an electrical expert can help. If continued weak sparking is possible then the spark plugs may be the key to killing the running-on. To make a spark easily the central electode needs to be hot - so we only see running-on in a hot engine. That also suggests a grade ot two colder plugs might eliminate running-on. And allowing the engine to idle could cool the plug to the point where weak sparks wont get across the gap. Opening up the gap deters weak sparks. If the plugs have smaller diameter central electrodes, as many modern plugs do, then reverting to the standard ca3mm diameter electrodes might help - the spark is less easily generated. Peter (who melted three pistons in as many seconds......once.) Edited July 18, 2014 by Peter Cobbold Quote Link to post Share on other sites
Tony Millward Posted July 18, 2014 Report Share Posted July 18, 2014 Cheers Pete, I understand what you mean now. Tony Quote Link to post Share on other sites
Peter Cobbold Posted July 18, 2014 Report Share Posted July 18, 2014 Cheers Pete, I understand what you mean now. Tony Tony, But it might not be due to hotspots...see above. I dont yet understand whats going on - hotspots dont really 'fit'. Peter Quote Link to post Share on other sites
graeme Posted July 18, 2014 Report Share Posted July 18, 2014 So, if running-on is caused by hotspot ignition why arent we seeing 4s with pistons melted by preignition ???? The lack of holed pistons may be because there's no hotspots. If there's no hotspot then we need a spark. Maybe, somehow, the coil is continuing to supply sparks after the key has been switched off. Is is feasibe for the still-spinning dynamo or alternator to supply a few volts to the coil? eg through the ig warning lamp?? Perhaps an electrical expert can help. If continued weak sparking is possible then the spark plugs may be the key to killing the running-on. To make a spark easily the central electode needs to be hot - so we only see running-on in a hot engine. That also suggests a grade ot two colder plugs might eliminate running-on. And allowing the engine to idle could cool the plug to the point where weak sparks wont get across the gap. Opening up the gap deters weak sparks. If the plugs have smaller diameter central electrodes, as many modern plugs do, then reverting to the standard ca3mm diameter electrodes might help - the spark is less easily generated. Peter (who melted three pistons in as many seconds......once.) Peter, In my case, the 4 pot engine runs backwards when 'dieseling'. If the spark was still existant then i would expect it to 'run on'. When I try to stall the engine in third gear and slip the clutch, the car tends to move backward, proving the engine is running backward. ??? Cheers Graeme Quote Link to post Share on other sites
Peter Cobbold Posted July 18, 2014 Report Share Posted July 18, 2014 (edited) Peter, In my case, the 4 pot engine runs backwards when 'dieseling'. If the spark was still existant then i would expect it to 'run on'. When I try to stall the engine in third gear and slip the clutch, the car tends to move backward, proving the engine is running backward. ??? Cheers Graeme Graeme, I think that can happen even with the spark coming at the right timing. At 12 BTDC the piston is still rising so any cylinder that fires will give the piston a push backwards: its normal**. This I think could reverse the crank when the rpm go much slower than normal tickover. RPM will drop below t/over if not all cylinders fire to keep the crank/flywheel turning in the right direction. At the very slow rpm when 'dieseling' there is much more time for the burn to run and the gas to expand and pressure to rise, even at 12BTDC spark. That powers the crankshaft reversal. The flame burns at roughly the same speed, but the crank's turning slower. I dont think its hotspot issue. But something has the light the mixture. It cant be compression as the cylinders area starved of mixture and the effective compression ratio very low - 'dieseling' is the wrong word. But why the spark after the key has been switched off?? I am puzzled. Unless all running-on TR4s have electronic igntition that fires off a few sparks? Cheers, Peter ** For other readers' background info. A backwards push is of course part of every firing stroke at all engine rpm and loads. Its a necessary evil to get peak pressure to happen around 15ATDC. Its not widely appreciated that the 'bang' in 'suck squeeze bang blow' is not an explosion happening after TDC. Here's a plot of in-cylinder pressure from the compression stroke through TDC into the power stroke. Note the pressure rise as the piston is rising: http://pacsoft.ca/tdt/wp-content/uploads/2012/03/pressure4.jpg ( panel on left of screen) The other plot shows the max oomph is with the spark at 33BTDC. Its a compromise between pressure rising BTDC and ATDC. Light the flame too early and the flame tries for too long to push the piston down while its rising. Light the flame too late and the expanding gas chases the piston as descends when it should be pushing on it. Thats why spark timings for superficially very different engines are so similar they all use that flame. Even MGs Edited July 18, 2014 by Peter Cobbold Quote Link to post Share on other sites
AlanT Posted July 18, 2014 Report Share Posted July 18, 2014 Back inthe 80s i had a new Ford Sierra. It ran fine for about a year and then started running on when you turned off the key. It had only done about 15K when the trouble started. At about this time the fuel began to change and lead was maybe being reduced. So I assumed that fuel was the cause. I always assumed that the edges of exhaust valves were being run hotter and this made it run on. I just leaned to stall it. Quote Link to post Share on other sites
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