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Opel Manta 1.8 S Running Lumpy On Idle


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Hi people am new to this site. I just bought a manta a few weeks ago. It's running lumpy on idle putting out the exhaust. Done a compression test all cylinders fine. I thought maybe a burt valve. When u remove cylinder 4 lead does make any difference?

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If it passes a compression test (all cylinders roughly same) then a valve is not burnt. If disconnecting one plug makes no difference but it does on all other cylinders then you have an ignition problem for that cylinder, fouled plug / no spark / bad leads / tacking dizzy cap etc

This assumes you have all leads on right plugs

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You need fuel - well car runs and one carb so if one cylinder runs they all have fuel

You need compression - well you checked that.

You need the cam / crank / dizzy timing synchronised

And you need the leads to be to the right plugs or you could be lighting two on exhaust stroke.

Basically all an engine is is an air pump. You need air and fuel at about 14:1 in the cylinder, compression and to light it at the same time. That is it.

If the other 3 cylinder definitely work you could move a plug and lead and see if you move the problem.

Your choice.

After that it is unlikely stuff like checking for one broke follower

Beware sparks on electronic ignition they can damage your health

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I had the same problem, turned out to be the servo to inlet manifold pipe that was drawing air.  It is connected to the inlet  to number 4 cylinder.  Disconnect the servo pipe at the manifold and plug the hole and if the engine runs smoothly thats your problem. hope this is of help to you.

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 To check the firing order set the engine to top dead center mumber one cylinder compression stroke.


 So this is the notch in the bottom pully wheel lining up with little pointer.


 take off the dizzy cap and the rotor arm should be pointing to number one plug lead, if it is pointing completely the oppsite dirrection then number one cylinder is one the exhaust stroke so crank the engine round one revolution ( half a revolution of the rotor arm )


 From there the firing order is 1-3-4-2 round the dizzy cap


 But if the other three cylinders are firing the forth one can not be in the wrong place


 Even if you have a spark at number four it could be a weak spark and not igniting under compresion


 A good move would be to obtain a strobe timing light, it is the best way to set the ignition timing plus you can check for sparks on all the leads with the eingine running by seeing if each lead triggers the gun.

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