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Rough running, loss of power and oil on spark plugs


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Hello

 

I aquired a TR6 last summer that hadn't been run regularly for approximately 10 years. I had been using it regularly at weekends and experienced no problems until recently.

 

The symptoms of the problems are:-

 

- Rough running (low rpm at idle, chugging air sound, louder than usual)

- Sounds like the exhaust is blowing but it dosen't seem to be

- Loss of power

- Spark plugs severly oiled, when cleaned oil up again quickly.

 

The car is a 1971 TR6 with fuel injection.

 

The problems occured suddenly rather a gradual degredation.

 

I would appreciate any suggestions as to what might be the problem.

 

Thanking you in advance

 

Phil

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Phil,

Its highly unlikely to be pistons all failing at once.

Is it really oil on the plugs? or unburned petrol?

My first suspect would be the MU diaphragm - if punctured it gives an excessively rich mixture which wont burn well.

Do the 'tongue test': with engine off! suck on the hose that connects MU to inlet manifold, while sucking close the bore of the tube with tongue tip and stop sucking. If the low pressure in the hose persists for a couple of seconds the MU is OK, if it wont hold the suction replace the diaphragm.

Or the choke control not returning on the MU.

Peter

Edited by Peter Cobbold
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Phil,

Its highly unlikely to be pistons all failing at once.

Is it really oil on the plugs? or unburned petrol?

My first suspect would be the MU diaphragm - if punctured it gives an excessively rich mixture which wont burn well.

Do the 'tongue test': with engine off! suck on the hose that connects MU to inlet manifold, while sucking close the bore of the tube with tongue tip and stop sucking. If the low pressure in the hose persists for a couple of seconds the MU is OK, if it wont hold the suction replace the diaphragm.

Or the choke control not returning on the MU.

Peter

 

Yes if it is not oil! I agry Peter

 

Rien

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Hi Peter

 

I have tried both of the above suggestions.

 

The tongue tests suggests that the MU diaphram is working ok.

 

The operation of the choke control also seems to be fine (full movement, not jamming).

 

The more I listen to the engine running i'm sure it sounds like the exhaust is blowing (very load air sucking/blowing noise) Other than that the engine seems to be idling fairly smoothly when warm with all cylinders firing most of the time.

 

I wonder whether it could be the exhaust, but could this have such a drastic effect on performance?

 

Rein, I don't have a compression tester. I take it the 14/18mm ones sold at halfords etc wouldn't fit the TR threads. Do you know where I could get hold of one?

 

Thanks

 

Phil

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Hi Peter

 

I have tried both of the above suggestions.

 

The tongue tests suggests that the MU diaphram is working ok.

 

The operation of the choke control also seems to be fine (full movement, not jamming).

 

The more I listen to the engine running i'm sure it sounds like the exhaust is blowing (very load air sucking/blowing noise) Other than that the engine seems to be idling fairly smoothly when warm with all cylinders firing most of the time.

 

I wonder whether it could be the exhaust, but could this have such a drastic effect on performance?

 

Rein, I don't have a compression tester. I take it the 14/18mm ones sold at halfords etc wouldn't fit the TR threads. Do you know where I could get hold of one?

 

Thanks

 

Phil

 

Phil,

 

I have this leak tester, they work very satified:

http://www.ebay.nl/itm/Cylinder-Leak-Down-Tester-Compression-leakage-/190282797330?pt=UK_Diagnostic_Tools_Equipment&hash=item2c4dbd1112

 

A compression tester are a different thing I have a Bosch scriber tester but they are very expensive.

 

The leak test tell you enough in the case it are a worn cylinder wall, bay the way to you have a external oil line to the rocker gear and no valve seals?

 

Rien

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Phil

Did the blowing noise coincide with rough running/ contaminted plugs?

Try to locate the blowing noises with a length of hose used as a stethoscope. If an inlet manifold has worked loose that might make noise and richen the mixture on all the cylinders.Check that the inlet manifolds are solid against the head. Each manifold is held by three studs- the lower pair being shared with the exhaust manifold using bridge pieces. The top studs/nuts are easy to check, the lower ones need a cold exhaust and some dexterity. The gasket may have gone around the inlet tracts, allowing air in and the mixture to run richer than it should. A gasket that has gone between the inlet and exhaust tracts would give very strange running under load, allowing exhaust to contaminate the inlet, yet might be OK at tickover. Changing the manifold gasket is not difficult DIY.

 

The short balance rubber hoses between the manifolds can also let air in and rich running.

Peter

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  • 4 years later...

Perhaps have a local 'expert' help you look over the car Phil

 

Being in londont, there are plenty about, do you go to register meetings?

 

Whereabouts in london are you?

 

Steve

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Phil,

 

The chugging noise is often down to an injector or injector(s) not spraying as it should, which then affects that cylinder(s)? I had this problem yesterday! Have you checked all the black injector tubes for pulses? Any that have no pulse is usually the problem. Another sign is the tick over drops?

 

Bruce.

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