How To Diagnose A Broken Timing Belt (1993-1997 1.8L Toyota Corolla)

The 1.8L (7A-FE) engine in the 1993–1997 Toyota Corolla is a timing-belt-driven engine. If it (the timing belt) were to fail, your Corolla's engine would crank but fail to start.

Finding out if the engine isn't starting due to a broken timing isn't difficult at all, and in this tutorial I'll walk you thru the three tests you can perform to find out.

NOTE: Your Corolla's 1.8L 7A-FE engine is a non-interference engine, so if the timing belt breaks, you won't have to worry about wrecked pistons or bent valves.

APPLIES TO: This tutorial applies to the following vehicles:

• 1.8L (7A-FE) Toyota Corolla: 1993, 1994, 1995, 1996, 1997.
• 1.8L Geo Prizm: 1993, 1994, 1995, 1996, 1997.

What Does The Timing Belt Do?

The timing belt synchronizes the rotation of the crankshaft and camshaft(s), ensuring a "harmonious" (LOL) operation. Any disruption in this synchronicity, and rest assured my friend, the engine is gonna resent it and run poorly or not start at all.

As you may already know:

• The crankshaft converts the up-and-down motion of the pistons into rotational energy.
• The camshaft(s) manage the opening and closing of intake and exhaust valves, facilitating the air/fuel mixture inflow and exhaust outflow respectively.

The timing belt is responsible for coordinating the operation of these valves to open and close at the correct times, aligning them with the pistons' movement. This synchronization enables the engine's four-stroke cycle (intake, compression, combustion, and exhaust) to function correctly.

Symptoms Of A Broken Timing Belt

If the timing belt on your Toyota Corolla's engine were to snap:

1. Engine cranks but won't start:
   • When you try to start it, the engine will turn over, but it won't start.
   • The timing belt ensures the crankshaft and camshafts run in unison. If it breaks, the camshafts cease rotation, which causes the intake and exhaust valves to stop functioning.
   • As the distributor is linked to one of the camshafts, this also means no spark will be generated.
   • With stationary valves and no spark, there will be no air/fuel mixture entering, no compression, no combustion, and no exhaust leaving.
2. Engine cranks faster than usual:
   • Since the valves remain stationary without the timing belt, they won't compress the air/fuel mixture during cranking.
   • If there is no compression in any cylinder, the engine will crank faster than usual (and believe you me -you're gonna notice it!).
3. Zero compression in all cylinders:
   • A compression test will indicate zero pressure in all cylinders. Since the valves aren't functioning, there is nothing to compress.
4. No camshaft/valve movement:
   • Upon removing the cylinder head valve cover and cranking the engine, you'll notice that the camshafts won't move.
5. No spark at all four spark plug wires:
   • Since the 7A-FE 1.8L engine uses a distributor connected to one of the camshafts, the broken t-belt prevents the rotor in the distributor from spinning, leading to no spark at the spark plugs.

NOTE: The 1.8L (7A-FE) in your 1993-1997 Toyota Corolla is a non-interference engine, meaning a broken timing belt won't cause internal piston/valve damage.

TEST 1: Checking Distributor Rotor Rotation

As I previously discussed, the Corolla's 1.8L (7A-FE) engine is equipped with a distributor-based ignition system. If the timing belt snaps, it prevents the camshafts from turning.

If the camshaft isn't turning (the one that drives the distributor) as you crank the engine, the distributor rotor isn't turning either.

If the distributor rotor isn't turning, the engine is not gonna start due to a lack of spark.

• To verify:
  1. Disconnect the distributor from its connector(s).
  2. Remove the distributor cap.
  3. Have a trusty helper crank the engine.
  4. Observe the distributor rotor during (as the engine is cranking).
  5. If the rotor fails to spin, the timing belt is broken (or in some very, very rares instances, the camshaft is broken in two).

NOTE: I want to let you know that in some extremely uncommon instances, I have encountered the camshaft responsible for driving the distributor broken in two pieces. So although the t-belt is OK and driving the camshaft, the broken end does not rotate the distributor shaft. The end result of this type of camshaft failure is an engine no-start.

TEST 2: Observing Camshaft Rotation

As already mentioned, the t-belt drives both of the engine's two camshafts. We can easily inspect them by removing the cylinder head valve cover.

Once the valve cover is off, we can observe whether they spin or remain stationary (as a helper cranks the engine).

Removing the valve cover will also grant us visual access to the timing belt and confirm its condition.

• How to check:
  1. Take off the valve cover.
  2. Inspect the condition of the timing belt.
     • If the t-belt is broken, no need to continue to the next step.
  3. Crank the engine.
  4. If the camshafts do not move, it indicates that the timing belt is damaged.

TEST 3: Check For Zero Engine Compression

A timing belt failure results in the loss of synchronization between the valves and pistons, causing a loss of compression in all four cylinders.

Consequently, the engine, with nothing to compress in all four cylinders, is gonna spin faster than usual (as you crank it), but it still won't start.

To confirm this loss of compression, you need to perform a compression test in all four cylinders.

NOTE: This engine compression tutorial walks you through the compression test step by step and explains how to read the results: How To Test Engine Compression (1993-2008 1.8L Toyota Corolla).

• How to check:
  1. Remove all four spark plugs.
  2. Check the compression in each cylinder individually.
  3. If your compression readings for all cylinders show 0 PSI, it's likely that the timing belt has snapped.

TEST 4: Inspect For Timing Belt Service History

Your Toyota's 1.8L 7A-FE engine requires the timing belt be replaced every 60,000 to 90,000 miles (y'know, to keep it from breaking).

If you find yourself in a situation where your engine cranks but doesn't start, there's an increased likelihood that the timing belt may have broken if you haven't replaced it during it's replacement interval.

More 1.8L Toyota Corolla Tutorials

You can find a complete list of 1.8L Toyota Corolla tutorials and wiring diagrams in this index:

• 1.8L Toyota Corolla Index of Articles.

Here's a sample of the tutorials you'll find there:

• How To Test For A Blown Head Gasket (1993-2008 1.8L Toyota Corolla).
• How To Test Engine Compression (1993-2008 1.8L Toyota Corolla).
• How To Test The Fuel Injectors (1993-1997 1.8L Toyota Corolla).
• How To Test The Throttle Position Sensor (1993-1997 1.8L Toyota Corolla).