Why can't I start my truck without popping the clutch?

Maintenance/Repairs
1

Hello. I have a 98 GMC 2500. Generally a reliable truck, though at times it seems the clutch doesn’t disengage (hydraulic system issue maybe??). Over the last week, I’m generally unable to start my truck without a push start. Battery is fine, occasionally starts without a problem. Thoughts?

2

Is this a no-crank (no rrr rrr rrr sound with key in "start), or cranks ok, but won’t catch and run?

3

I’d check to see if it has a clutch safety switch. If it does, yours might be sticking.

1 Like
4

The headline is misleading and NOT your problem.

The clutch is your problem. Fix that first. Clutch master cylinder, slave cylinder or maybe a failing pressure plate. Assume a hydraulic problem first.

1 Like
5

The no start problem might be due to a faulty ignition control module.

https://www.rockauto.com/en/catalog/gmc,1998,c2500+pickup,5.7l+v8,1304716,ignition,ignition+control+module+(icm),7172

ICM’s function in two modes. These are the start and run modes.

When starting the engine, the ICM allows full battery voltage to the ignition coil to ensure that the spark is hot enough for the rich mixture during a cold start.

Once the engine starts, the ICM goes to the run mode, and drops the voltage to the ignition coil. If this wasn’t done, the secondary ignition components would burn up from high voltage from the charging system.

This the same as having a ballast wire/resistor, like in older ignition systems.

So, what may be happening is, ICM works intermittently in the start mode, but works fine in the run mode. So the engine always starts with a push start when the clutch is popped. Because the ignition switch is in the run position.

Tester

6

@George_San_Jose1

No crank

7

No cranks on m/t vehicles are usually due to one of these

  • faulty or discharged battery
  • faulty battery connections
  • faulty clutch safety switch (used to prevent cranking unless the clutch pedal is depressed)
  • faulty starter motor

The best way to get to the bottom of it is to measure the voltages at the two starter motor terminals during attempted cranking. Both should measure at least 10.5 volts. If they both do and it doesn’t crank, replace the starter motor. If one or both is less than 10.5 volts, trace the circuit from the starter towards the battery to find out why.