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Engine running on.


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As a new TR5 owner I am learning about all aspects of TR ownership.

My latest question is about engine run on after the ignition is switched off.

Only seems to occur on a hot engine. Is there a cure?.

I know that an air entry valve can be fitted to a carb engine but not sure about a PI engine.

 

Steve.

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Hi Steve,

forget the valve until you find the cause.

Keep tickover low as suggested by John.

What spark plugs are you using. Perhaps a hotter plug may be useful.

 

During the run-on have you been tempted to remove the 12v wire from the coil. If this kills it then you were getting sparks.

If it continues to run-on then it is a possible hot spot.

 

Have you got a Kenlowe fan. It as been known for a leccy fan to power the coil :huh: - fit a relay or diode.

 

What fuel are you using - try a quality fuel - Shell or Texaco 97/98/99.

 

Roger

Edited by RogerH
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Thank you Roger and John.

I have pulled the LT connection from the coil and it still runs on, The tickover is a little over 1000 RPM but it is fitted with a fast road cam and light weight flywheel so anything less is very lumpy.

 

I will try a better quality fuel and see if that improves things but Rogers thought about a hot spot then it has got me thinking that as the cooling system is filled with waterless coolant I seem to remember reading somewhere that waterless coolant does not transmit heat as well as water and that can lead to increased cylinder head temperatures,

Any thoughts?

 

Steve.

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Yes - ditch the waterless coolant. The next step up from running-on is preignition and you really do not want go go there.

Here are the downsides to waterless that the ads dont mention:

http://www.oilem.com/potential-issues-with-waterless-engine-coolants/

Peter

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Hi Steve,

 

better fuel may b the first step.

By removing the coil lead and the enigne keeps going shows that a hot spot is keeping it going. Consider hotter plugs.

 

The waterless coolant is more akin to a waterless heating system. Although the coolant does not boil at 100'C+ it will allow the enigine to get hot, much hotter than normal.

Ditching it may be financially painful but may also assist in sorting your problem.

Good quality normal antifreeze at 40% dilution will give good cooling and rust inhibiting.

 

Roger

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What fuel pump system are you using ? My 5 has Bosch pump and ran on persistently. I tried everything even suspecting the pump relay which I changed to no effect. I then tried removing the relay from the circuit and bingo, immediate and total cure, no more running on. No one has been able to explain to me why this should be, maybe both relays were faulty but unlikely.

 

Anyway if you have a relay in the fuel pump circuit, worth a try to isolate it.

 

Matthew

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  • 2 weeks later...

I have had Evans Coolant in my car for over 2 years, and have no problems with running hot, or it running on. I tend to stick with Shell V-Power, and as I think the head is still for leaded fuel, (I've never changed it), I use Castrol Valvemaster Plus as well. Mine runs fine.

 

Michael

Edited by mafield
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I've always used v power and had no problems

 

Recently I had to use 97 octane and it immediately started to run on

 

Added octane booster and topped up with v power, still runs on but only after short journeys

 

Will run the tank very low and fill up with v power again and then keep my fingers crossed

 

Nigel

Edited by Nigel A
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"....still runs on but only after short journeys"

 

That is odd. Running-on needs abnormally high temperature in the cylinders. That could happen in a short journey if the thermostat is not opening soon enough. Time to investigate the cooling system I think.

Edit:

Or the inlet manifold, before it has heated up, allows liquid fuel to pool to supply the mixture for running-on.

 

Running-on is not normal so the cause, whether waterless coolant, hot water jacket, poor injector sprays, should be tracked down. Uisng high octane fuel masks the problem, but doesnt cure the cause.

 

The pump stops the instant the ignition is off . But fuel might still be coming out of the injectors if a high pressure fuel hose is swelling up under pressure. It could act as a reservoir sufficent to feed running-on. There are recent reports and photos of swollen, delaminated hoses at the MU . If one of those lets go, fuel will spray all over the disy and elsewhere: fire risk. Running-on is not normal, and in my view a symptom of something wrong. "Curing" it with high octane is masking potentially more serious faults.

 

 

Peter

Edited by Peter Cobbold
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Peter,

 

Could the original poster just have an MU which is running too lean (I appreciate note the usual case from reading the forum and my own 'black plug' experience).

 

Perhaps Flinty should look at the plugs and see if one or two are 'bright white or worse' which might mean the source of ignition is the plug and lean mixture.

 

If the car is way too lean at the bottom end of its MU curve wouldn't it have a lumpy tickover at a normal 700-800 rpm and wouldn't it run rather hot too.

 

Also the "lumpiness" could just be unbalanced butterflies.

 

Did the person who installed the 'fast road' camshaft adjust the Mu to suit I wonder.

 

 

 

I hope this is helpful as opposed to some of my usual guff !

 

 

 

Snowy

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Running on isn't restricted to PI equipped engines. My GT6 suffered from this some years back. It has a 2.5L fed by twin HS6 SUs. The problem persisted despite adjusting the ignition, carbs and changing the plugs.

I eventually committed sacrilege and fitted an anti-run on valve from an MGB. This worked a treat and the running on has never been a problem since even with 95RON fuel.

It's teed into the vacuum pipe running between the inlet manifold and the brake servo and electrically wired into the ignition. It operates by being opened electrically when the ignition is switched off and dumps a great gob of fresh air into the cylinders effectively weakening the fuel mixture beyond the point of ignition. I've seen a TR6 with two fitted so running on isn't that unusual with the 6 cylinder engine.

This might be the answer to your problems.

 

Alan

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Peter,

 

Could the original poster just have an MU which is running too lean (I appreciate note the usual case from reading the forum and my own 'black plug' experience).

 

Perhaps Flinty should look at the plugs and see if one or two are 'bright white or worse' which might mean the source of ignition is the plug and lean mixture.

 

If the car is way too lean at the bottom end of its MU curve wouldn't it have a lumpy tickover at a normal 700-800 rpm and wouldn't it run rather hot too.

 

Also the "lumpiness" could just be unbalanced butterflies.

 

Did the person who installed the 'fast road' camshaft adjust the Mu to suit I wonder.

 

 

 

I hope this is helpful as opposed to some of my usual guff !

 

 

 

Snowy

Snowy,

Not guff at all . Running lean does indeed make for hotter combustion chambers. And looking at the plugs is a good idea to check.

 

I am puzzled where the fuel is coming from - the pump cant be pumping.

And my 6 when on PI never ran on in 200k miles, but it was younger in years back then....so I think running on is unusual. Mind you, fuel has changed too.

Peter

Edited by Peter Cobbold
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I think most old engines run weak on the current fuel, which is very different to what we had way back. My Healey was particularly bad at running on till I put it on a rolling road. Hasn't stopped it completely, but it's much faster and much better. I think it's worth having done. My Bentley was miles out too, just have to get the TR done now.

Edited by Ashley James
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Great news, I followed Rogers suggestion and got rid of the waterless coolant and replaced it with ethylene glycol/water antifreeze and this seems to have cured the problem.

I did read that the use of waterless coolant raises the temperature of a cylinder head by 20 to 30 degrees C.

Thanks everyone for your input.

Steve.

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Running on, by and large, needs fuel to be being drawn in and then ignited by a hot point in the combustion chamber.

 

Given that on a PI car the fuel should stop injecting once the fuel pump switches off, there shouldn't really be any fuel for a hot spot to ignite. (In the past many owners of 5s and early 6s found running on to be an issue when they converted to SUs or Strombergs but kept the 150bhp cam)

There might be a little fuel perhaps from pooling of fuel in the inlet manifolds or from a dribbling injector, however that should go momentarily unless the fuel pump continues to run and provide enough fuel to open an injector.

 

One way of testing if the pump is still being energised is to try disconnecting the feed to the pump with the engine running - if it stops immediately then suspect an electrical gremlin continuing to supply some current to the pump when you switch off with the key. (Such as a dodgy relay, if fitted, as someone has already suggested or ignition switch. Potentially it may well be feeding back to the ignition circuit too. Perhaps not enough to sustain running but enough to cause running on.

Edited by andymoltu
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