Air Flow Sensor

[Ron Norwood]

Car is a 74 914 1.8. Pulled off the air flow sensor cap and found water (and rust). Will a defective air flow sensor prevent an engine from firing?? I'm trying to diagnose several potential problem areas. Also....I've heard the term "capacitor pack" but can't seem to find a reference in the Haynes manual. (Maybe I need a better source?)

[Dave at Pelican Parts]

A defective air flow meter can cause the fuel pump not to run, since the AFM cointrols the pump. It can cause too little or too much fuel to be delivered (depending on its exact failure mode). It may even be able to cause no fuel at all to be delivered--not sure on that one.

All of those could cause the engine not to start.

Engines need three things to run: About the right amount of fuel, air (or compression), and a spark at about the right time. Are you getting any fuel? Pull the injectors off one side of the engine, put them in a jar, and have a helper crank the starter. Look for a cone-shaped spray of fuel squirting out of the injectors. Are you getting a spark? Take a spare plug, tape it to a ground like the fan shroud, hook it to a plug wire. Have a helper crank the starter. You should be able to see the spark. Are you getting any air? Hook up a compression tester and see.

I don't know of any "capacitor pack", but there should be a "resistor pack" hanging off of the battery tray. These resistors limit the current (and voltage) going to the injectors. The injectors always have +12V while the FI is "on", and the ECU gives them a ground (or disconnects the ground) to open and close them.

--DD

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Pelican Parts 914 Tech Support

A few pics of my car: http://www.pelicanparts.com/gallery/Dave_Darling

[Ron Norwood]

Thanks, Dave...you've been very helpful!!

[Ron Norwood]

Thanks!!