3.5 EFi

Hello. Just picked up a quite tidy discovery 3.5 EFi. She starts on the button but runs on 7 cylinders for a while, kinda till she’s warm then the 8th cylinder kicks in. What is likely to be the cause please?
Ta
Terry

Would you mind telling us what test you have done?
i.e. electrical, are all 8 plugs sparking
mechanical, are all hydraulic tappets functioning? (Usually make a rattling noise until it finally fills with oil)
fuel, are all injectors getting fuel and spraying properly?

If the 8th cylinder finally kicks in it doesn't sound like the end of the world.
These engines are renowned for wearing camshafts so it could perhaps be a worn cam lobe, but without a bit more info we are a bit in the dark.
I suppose another possibility could be a valve not seating properly or loose in the guide, but I don;t think that would be the case as it wouldn't get better once warmed up.

Best of luck
Stan

Terry O Sullivan said:

Hello. Just picked up a quite tidy discovery 3.5 EFi. She starts on the button but runs on 7 cylinders for a while, kinda till she’s warm then the 8th cylinder kicks in. What is likely to be the cause please?
Ta
Terry

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Identify the cylinder that giving u the issue first, it could be as simple a faulty ignition lead/plug.

They are notorious for only liking high quality ht leads and a genuine dizzy cap. Id change the cap and leads for magnecor/genuine anyway and it may solve the issue.
Potentially that cylinder is flooding due to poor spark then coming back when warm.

ronsealdeath said:

They are notorious for only liking high quality ht leads and a genuine dizzy cap. Id change the cap and leads for magnecor/genuine anyway and it may solve the issue.
Potentially that cylinder is flooding due to poor spark then coming back when warm.

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Sounds about right, if it is ignition, the OP could simply remove the spark plug lead one at a time until he finds the faulty cylinder. Then he could swap that lead for another and see if the fault follows the lead. If so, its the lead.
But regular lead and dizzy cap replacement is a given on these motors. He could obviously check that the plugs are all sound and properly gapped!

split hose from the plenum to the extra air valve allowing too much air in.
Goes away once warmed up coz the valve closes.

I'd put a fiver on it

Of course check ignition etc etc

Henry_b said:

split hose from the plenum to the extra air valve allowing too much air in.
Goes away once warmed up coz the valve closes.

I'd put a fiver on it

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And that sounds like a single cylinder missing? Interesting!

Also worth noting They don't like cheapie dizzy caps DO NOT use a rotor arm that has the metal strip riveted to the plastic arm. If you want to remove the rotor arm you MUST press down on the reluctor Which is the eight pointed star shaped jobbie under the rotor arm becuase as you pull up you might disengage the auto advance/retard mech in the bottom of the dizzy bowl & it may not run at all. Check by turning the rotor arm with your fingers, Once released it should snap smartly back to its original position.

Stanleysteamer said:

And that sounds like a single cylinder missing? Interesting!

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Very interesting if the engine had an Extra Air Valve but it doesn’t.

Yes i put a cheapo rotor arm on mine and it chewed chunks off the dizzy cap! It was a 3.9 but never liked being cold. It flooded one time and refused to start until the cap had been wd40 soaked, cleaned and refitted . I deduced that they appreciate quality ignition components

Thanks for all your input chaps. Ive stored her away now till the new workshop is up and running.
Thanks again.
Terry