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Autopapyrus · Ford Focus 1.6 Duratec Ti-VCT (HXDA, 115 hp) (2008)
https://autopapyrus.com/guides/ford/focus/diagnosing-intake-manifold-backfire-after-timing-belt-work/
Compiled automatically from service literature and owner experience. Specs are for the typical configuration — check them against your exact car before you start.

Ford Focus 1.6 Duratec Ti-VCT (HXDA, 115 hp) (2008): Diagnosing Intake Manifold Backfire After Timing Belt Work

A pop at startup and hot gases blowing back into the intake manifold after an overhaul of the 1.6 Duratec Ti-VCT engine indicate incorrect valve timing (the timing belt is off by one or more teeth). On this engine the camshafts use the Ti-VCT (Twin Independent Variable Camshaft Timing) system, the camshaft pulleys have no keys and no marks on the pulleys, so the belt must be installed ONLY with the special crankshaft and camshaft locking tools. Even a one-tooth error causes early or late ignition and ignition of the mixture in the intake manifold (popping, backfire). In the worst case, the valves contact the pistons and damage the cylinder head.

Difficulty: Hard Time: 3-5 hours Steps: 16 Tools: Timing tool set (303-1097, 303-735, 303-748, 303-1054, 303-1059, 303-1552), 10/13/17 mm sockets, breaker bar, torque wrench, jack, jack stands

Part

  • 🔩 If reinstallation is required: the existing timing belt (only if the engine has not been rotated), tensioner pulley, idler pulleys. If valves are damaged by incorrect installation: cylinder head repair kit (valves, guides, seats)
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Step by step

16 steps
  1. Disconnect the negative battery terminal, raise the front right side of the vehicle with a jack, and support it on a jack stand for access to the underside of the engine.
  2. Remove the upper engine cover (if fitted) and disconnect the air duct from the air filter housing for access to the upper part of the timing drive.
  3. Turn the crankshaft clockwise by the center pulley bolt (use a 17 mm wrench) to TDC (top dead center) of cylinder 1. The mark on the crankshaft pulley must line up with the pointer on the engine block.
  4. Remove the plug in the lower part of the engine block (left side, near the flywheel) and install the crankshaft locking tool (303-748). It will enter the hole only at the exact TDC position of cylinder 1. If the tool does not go in, slowly turn the crankshaft a little further until it lines up.
  5. Install the camshaft locking plate (303-1097 or equivalent, 5 mm thick) into the slots on the rear ends of both camshafts (intake and exhaust). The plate must slide in freely, without force. If the plate does NOT go in, the timing is INCORRECT and the belt is off.
  6. If the camshaft locking plate does not go in with the crankshaft locked, the timing is off. Loosen the timing belt tensioner pulley (pulley bolt torque 25 N·m (18 lb-ft); loosen counterclockwise) and remove the belt from the camshaft pulleys.
  7. Free the camshaft pulleys: loosen the center bolts of the pulleys (tightening torque 68 N·m (50 lb-ft) each; use holding tool 205-072 or equivalent to keep the camshafts from turning). Remove the pulleys from the camshafts.
  8. Turn the camshafts by hand (with a wrench on the hex on the shafts, or a breaker bar on the bolt) so that the 5 mm locking plate slides freely into the slots on the rear ends of both shafts at the same time. This is the CORRECT camshaft position for TDC of cylinder 1.
  9. Reinstall the camshaft pulleys on the shafts (without tightening the bolts). Fit the timing belt over the pulleys starting from the crankshaft, going counterclockwise: crankshaft → tensioner pulley → exhaust camshaft pulley → intake camshaft pulley → upper idler pulley. Make sure the belt is not twisted.
  10. Tension the belt with the tensioner pulley (turn the pulley counterclockwise until the marks on the pulley body and the slider line up), then tighten the tensioner pulley bolt to 25 N·m (18 lb-ft).
  11. Tighten the camshaft pulley bolts to 68 N·m (50 lb-ft) each (use the holding tool to keep the shafts from turning).
  12. Remove the camshaft locking plate and the crankshaft locking tool. Turn the crankshaft by hand two full revolutions (720 degrees) clockwise. Rotation must be smooth, with no binding or knocking (a knock while turning means the valves are contacting the pistons and the cylinder head is damaged, so it must be disassembled and inspected).
  13. After two revolutions, install the crankshaft locking tool again at TDC of cylinder 1. It must go in freely. Then install the camshaft locking plate. It must also slide freely into the slots of both shafts. If the tools go in, the timing is CORRECT.
  14. If the tools do NOT go in after two revolutions, repeat the procedure from step 6 (the belt is still off).
  15. Reassemble in reverse order: install the timing cover, connect the air duct, the engine cover and the battery terminal. Start the engine. It should start smoothly, with no popping or backfiring into the intake.
  16. If the popping and gas blowback into the intake continue AFTER the valve timing has been set correctly, check: a) that the spark plug wires or ignition coils are connected to the correct cylinders (swapped firing order), b) cylinder compression (after an overhaul it should be an even 12-14 bar), c) intake manifold sealing (air leaks), d) injector operation (leaking or not opening).

Common mistakes and warnings

  • The 1.6 Duratec Ti-VCT (HXDA) is an interference engine. If the valve timing is incorrect and you try to start the engine, the valves hit the pistons and bend, which requires expensive cylinder head repair (replacing valves and guides, lapping the seats). NEVER try to start the engine without checking the timing with the locking tools after an overhaul or timing belt replacement. If you hear knocking while turning the crankshaft by hand through two revolutions, STOP IMMEDIATELY, remove the cylinder head, and inspect the valves and pistons for contact. A timing belt that was removed to reset the timing can be reused ONLY if the engine was NOT turned after the incorrect installation (no valve-to-piston contact). Otherwise, replace the belt and all the pulleys.