hard to start when cold

[Blu-spot]

i have a 1972 280 SE 4.5. I have to pump the gas pedal to get it to start when its cold. my best guess is either it needs new spark plugs, or there's something amis with the cold start injector. if it is the later, do i first check the injector, or the temperature sensor, and how do I go about doin that?

[Blu-spot]

the spark plugs are rather old, think i may start with that.

[mercmad6.3]

You are not helping by "pumping the gas pedal".There NO acelerator pump so pumping the pedal only leans out the fuel when you are trying to start the engine.
Proper starting method is to leave the gas pedal alone and just turn the key until the engine fires.
Check the that the fuel filter has been changed in recent memory.If not, change it now.
The cold start injector in on the front of the manifold with a blue electrcal plug and a fuel line,just unscew the two small nuts and gently lift it up high enough to see the end of it. aim it into a small CLEAR CONTAINER.
Get some one to crank the engine while you watch the injector.If it sprays any fuel it's OK as is the cold start sensor.
Check the connections on the aircleaner( cold air sensor) and the sensor in the water jacket in the front of the manifold.Any cracked or broken wires should be fixed.
Fit new Plugs as a matter of course.Run the Ohm meter over the plug ends,the resistance value is writtne on the ends.
But don't swap the plug leads for silicone carbon string leads because the stock items are good for 30+ years and only the ends break down.

[Blu-spot]

that is some awesome info. didn't know that about the spark plugs. i didn't even think about the filter, it looks pretty new, but the car had been sitting for a long time before i bought it. i guess the engine would in fact have eventually fired if i had left the gas pedal alone then. BRB, gonna go check it out. thanx a million!!!!

[carnut1]

To put it in perspective, a fuel injected car has no "gas pedal" it has an air pedal. Giving the engine more air with the pedal enables the system to provide more fuel by leaving the injectors open longer! By stepping on the air pedal prior to cranking you can delay start up because the sensors are given wrong info. Some cars can even have their throttle blades damaged by being opened prior to cranking the engine! On this engine the thermo air valve next to the cold start injector provides a controlled air leak to raise the idle upon cold start. It works much like a coolant thermostat in that it closes based on engine coolant temp and restricts this air eventually lowering the idle once eng. temp raises. Many of these valves are corroded internally because they are submerged in coolant and either dont open at all or very slightly so the cold start and driveability is affected. Years ago I was told a crude way of testing this valve was to start the engine stone cold and once running, to tap on the top of this valve with a small hammer. If the idle raised or was affected at all, this valve was suspect. My 72 280SEL 4.5 would idle stone cold at about 12 to 1300 RPM for at least 3 to 5 min. then lower to approx. 7 to 800.