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Chevy Silverado won’t start

How to diagnose and fix a Chevy Silverado start problem

Some Chevy Silverado owners with the 4.3 engine complain that it won’t start. The Chevy Silverado won’t start issue symptoms are: engine will crank but won’t fire up. Since it cranks, that eliminates the battery, charging system, and starter.

Why won’t the engine fire up?

To fire up an engine needs the right cranking speed, spark and fuel. In this 4.3 engine the ignition control module (ICM)  is in the distributor. It’s also the crankshaft position sensor (CKP).

The powertrain control module (PCM) uses input from the CKP to determine when to fire the spark and trigger the fuel injectors. But the PCM doesn’t actually contain the driver that interrupts power flow to the IGN coil. That’s in the ICM. The distributor contains a camshaft position sensor (CMP), but a bad CMP would not prevent starting.

To diagnose Chevy Silverado won’t start conditions with the 4.3 engine, start by checking for good fuel pressure. Then check for spark. If you don’t see spark, check for pulsed ground to the IGN coil while cranking. If you see pulses, the PCM and ICM are working properly and you can suspect a bad coil (as long as the primary power is good). If the coil isn’t getting pulsed ground, check to see if the ICM is getting proper pulse signals from the PCM. If it is, the ICM is most likely bad. Replace it.

silverado ignition control module

Chevy Silverado 4.3L Ignition Control Module (ICM)

If not, check the CKP input to the PCM.

Here’s how it works:

PCM sees CKP input to determine engine RPM. Based on engine temp, it determines spark timing. It uses CMP signal to confirm timing. PCM sends signals to ICM to pulse ground side of coil primary. PCM also pulses ground to injectors.

©, 2015 Rick Muscoplat

Posted on by Rick Muscoplat

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