Starting my 420 SEL is very difficult and the car runs very "lumpy" missing and spluttering after many attempts to start.
I notice that the air pump is not engaged when startup occurs but after a few minutes the clutch engages and the car begins to idle ok.

The clutch on the airpump then disengages when the engine warms upand the car runs well slowly and on the highway.

Starting the car after it is warmed up is not a problem ....she starts first time.

When the engine is cold again the same problem re-occurs and she is difficult to start.

It seems to me like the airpump is working ok but is not being activated on startup? Can anyone help?

I've never seen an air injection pump with a clutch on it. Are you sure you aren't looking at your air conditioning compressor? That shouldn't have any relation to hard starting.

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There is an electromagnetic clutch on the front end of the pump. It has wires running to it which obviously control the clutch.
My question is why is this not activating at start up but activates a few minutes after the engine runs.

This is the pump as the air conditioning unit is on the other side of the engine.

Your airpump is working normal the delay is normal concentrate on fuel system or adjustments, after youve checked condition of cap,rotor and plugs, it sounds like leaking injectors

auscaptain:

There are two devices which may be involved in your problem:
1) the cold start valve, which injects extra fuel into the idle air distribution ducts when the temperature is below approx. 20C. If that valve is not operating due to disconnection, sticking, or clogging, cold starting is quite impaired.
2) the coolant temperature sensor, which, if it is shorted to ground or is otherwise sending a low resistance signal to the mixture controller, will cause a very lean mixture.

As nulu has indicated, the operation of the air pump clutch is normal, and in any event is not involved in the mixture preparation.

Thanks for the advice I will investigate....

Stumbling start is most likely: Spark plugs, rotor, cap, wires, fuel pressure accumulator, or leaking injectors or vacuum/hoses under the air cleaner on top of the engine.

At high miles/age, pretty much all of that can use replacing.


As for the air injection pumps....I chopped the belt off of it on both of ours....

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Sounds like fuel pressure bleeding off. Put a gauge on it and see if it drops overnight. If you don't have a gauge try this. At the next cold start don't crank the engine at first. Turn the key to position 2 for a few seconds then turn it off. Repeat this several times. Every time you do this the pump will run for a second or two building static pressure. If it then fires and runs smooth you'll know the pressure is dropping.