Diagnostic Procedure
SCAN TOOL DATAUse the Hyundai Scan Tool to retrieve DTC codes and freeze frame data. Any Diagnostic Trouble Codes other than misfire codes must be repaired before attempting to correct the misfire code(s). Retrieving scan tool freeze frame data can be just as valuable as the customer's information. Engine operating conditions at the time the DTC was set can indicate what system to inspect. A vehicle that misfires on initial start-up may indicate a problem with oil pressure and/or hydraulic lash adjusters. Ensure that the Coolant Temperature Sensor, Intake Air Temperature Sensor, Air Flow Meter, and Long Term Fuel Trim are reading normal values (when compared to a known good car).
IGNITION WIRES
Inspection Before Removal
Before removing the wires from the spark plugs, mist the exteriors of the wires and boots with water and look for arcing of the spark plug wires with the engine running. Or, in a similar check, ground a heavy (16 gauge) jumper wire, connect it to the shaft of an insulated screwdriver, and idle the engine. Then drag the screwdriver tip lightly over each plug wire, watching for sparks jumping from the wire to the screwdriver shaft. After removing the wires, they can be measured with an ohmmeter. Resistance should be approximately 4000 Ohms (4K ~) per foot. If the car has a distributor ignition, lift the cap and touch one lead of the ohmmeter to the terminal inside, the other to the terminal in the plug boot. Spark plug wires will usually set a specific cylinder DTC code (i.e. P0301, P0302 etc.).
When removing plug wires from the spark plugs, you must use spark plug pliers. Twisting the boot to break the heat seal often is necessary, even when using the pliers. Never try to pull on the plug wire itself. You may cause a separation (open) in the resistance wire, or at the terminal end.
Route The Wires
Always duplicate the factory routing of the plug wires. The guides are there to ensure the separation necessary for the high-voltage to follow its intended path. Also the guides assist in reducing the affects of electromagnetic interference on the standard 5v to 12v electrical/electronic systems.
Dielectric Grease
Before installing the spark plug boot onto the spark plug, smear a thin film of Permatex Dielectric Tune-Up Grease (or equivalent) to the following three locations:
1. Terminal stud at top of the spark plug
2. Around the tip of the spark plug boot (just inside the opening)
3. At the bottom of the spark plug boot (on the terminal connector)
The dielectric grease helps prevent any voltage leakage from the terminal stud to the metal shell of the spark plug. Do not attempt to "waterproof" the spark plug boot by filling the boot with dielectric grease. This can prevent the terminal inside the boot from locking onto the spark plug terminal stud.
Spark Plug Tubes
A common cause of misfires is moisture accumulation in the spark plug tubes. Engines like the 1.8/2.0 Elantra/Tiburon and 2.0L Sonata may hold moisture after engine degreasing/cleaning. Moisture can cause a phenomenon described as a "Corona Discharge" (see spark plug section). Problems caused by water in the spark plug tubes can be cured by removing the moisture and applying a little dielectric grease as described earlier. Moist spark plug tubes will usually set a specific cylinder DTC code (i.e. P0301, P0302 etc.).
Spark Plugs
If you have a misfire, there's a fair chance a spark plug is the cause. Although plugs won't lead-foul with today's unleaded gasoline, they can oil-foul, carbon-foul or even be fouled by some fuel additives. Look for excessive oily-black or sooty carbon-black deposits. Causes of deposits include oil entering the combustion chamber past the valve stem seals or piston rings, an overly rich fuel mixture, continuous low speed driving, a spark plug that has too cold of a heat rating, or deterioration of the ignition system. Spark plugs will usually set a specific cylinder DTC code (i.e. P0301, P0302 etc.).
A "Corona Discharge" is a phenomenon that occurs in a humid environment, or when the insulator surface is dirty (see photo's). This condition occurs if an electrical charge builds-up and there is moisture in the air (or spark plug tube) or the plug has a dirty insulator. The worst case result is a flash-over spark from the metal shell to the terminal stud. A result of the discharge is carbon tracking.
A. Ionization is building on the porcelain at the top of the metal shell (seen as a pale blue light);
B. The ionization is creeping up the porcelain insulator.
C. Flash-over occurs when/if the ionization reaches the terminal stud.
Photo: Corona Stain caused by oil particles in the air that are attracted to the corona discharge. The corona stain causes no deterioration to the function of the spark plug; however, any moisture adhering to the porcelain or the stain will cause flash-over
Carbon tracking (see photos) not only builds on the spark plug, it can also leave carbon deposits on the inside of spark plug boot. If carbon tracking is found, replace spark plugs and ignition wires in sets.
Ignition Coil
When misfires occur in paired cylinders (ie. P0301 and P0304; or P0302 and P0303 for inline four cylinder engines), the coil should be inspected using HDS to verify the signal waveform, or swapped with a known good coil to see if the misfire codes travel to the other cylinders. Two examples of how properly operating and malfunctioning coils appear are shown below.
- The above example shows the ignition signal viewed on HDS. Firing duration on Coil 2 & 3 indicates the coil is functioning properly (test with engine as operating temperature
- HDS plot for Coil 1 & 4 shows an insufficient firing duration.
Fuel Quality
Fuel quality concerns usually appear as multiple cylinder or random misfire codes. A sample of the fuel should be taken from the bottom of the fuel filter. Inspect the fuel for traces of water by using a test kit, or by letting the fuel "settle out". If water and/or contamination is found, replace the filter and inspect the fuel tank for water or corrosion. If no water or contamination is found, install a new filter as contamination in the fuel tank is not likely. Additionally, if large amounts of very fine rust are found in the fuel filter, fuel tank and at the fuel injectors, replacement of components between the injectors and fuel tank may be required. Fuel quality will usually set a random misfire code (P0300) and/or specific cylinder DTC codes (i.e. P0301, P0302 etc.).
Fuel Injectors
Fuel injectors can be checked by swapping locations of the suspect injector to another cylinder and checking if the misfire code travels with it. Fuel pressure and fuel pressure bleed down should also be inspected. Fuel pressure at idle must be 35-39 psi with the vacuum hose connected to the fuel pressure regulator. With the vacuum hose disconnected from the fuel pressure regulator, the pressure should rise to approximately 42-46 psi. Fuel pressure must not bleed down for 5 minutes (after the initial settling that occurs when the engine is turned off). After 20 minutes, the pressure must remain above 25 psi. If rust is found at the fuel injectors and fuel tank, replacement of components between the injectors and fuel tank may be required. Fuel injectors will usually set a specific cylinder DTC code (i.e. P0301, P0302 etc.).
Cylinder Leakage Testing
Performing a cylinder leakage (leak down) check should not be confused with performing a compression check. A cylinder leakage check measures the rate at which air leaks past the valves, rings, head gasket, cylinder wall, etc. Cylinder leakage equal to or below 10% is considered acceptable. Leakage greater than 10% in any one cylinder indicates valves/seats or piston rings need attention. This tool can also help locate the source of the leakage by listening for the escaping air. Listen in these areas to help determine the condition:
1. Oil dipstick tube - for worn cylinder walls or broken/worn rings.
2. Radiator cap - for cylinder wall crack or head gasket leakage (will be seen as air bubbles).
3. Adjacent cylinder - for head gasket leakage.
4. Exhaust pipe - for exhaust valve leakage.
5. Throttle body - for intake valve leakage.
NOTE: Some leakage will always occur past the piston rings. Experience will be required to discern "normal" amounts of leakage.
To save time, the leakage check can be performed when the spark plugs have already been removed from the engine. The leakage check should be performed with a warm engine, but cool enough to remove the spark plugs without damaging the threads in the cylinder head (removing spark plugs out of a hot engine with aluminum cylinder heads will damage the threads). Follow the manufacture's instructions for specific tool usage.
Cylinder Leakage Testing Versus Compression Test
A compression test is a tool to check "general" engine condition which will compare cylinders to each other and/or to a published specification. The limit to this test is that there are too many variables. Variables such as cam profile, engine cranking speed etc., will affect the readings. At best, a compression test can determine a specific cylinder problem and possibly separate valve from ring problems.
A cylinder leakage test will provide the same data a compression test provides, but the leakage test will be more accurate and pinpoint where the leak is coming from.
Lubricating Oil System
The lubricating oil system should be inspected for "thick oil", "thin oil", or evidence of sludge build up. "Thick oil" also causes high oil pressure because it is difficult to make the oil flow (high viscosity) through the engine. Oil with too high a viscosity may not flow into the hydraulic lash adjusters properly causing them to collapse. "Thin oil" that is diluted by fuel or other substances or just the wrong viscosity for the ambient temperature can cause low oil pressure. Oil that is too thin can bleed down too fast in the hydraulic lash adjuster and cause ticking noises. Particle formation in a "sludged-up" engine can enter the valve-train and block oil feed passages to hydraulic lash adjusters (see TSB# 98-20-002). This causes low oil pressure at the hydraulic lash adjusters and can cause them to collapse, thus causing improper valve opening and timing, leading to a misfire. Conversely, high oil pressure can over extend hydraulic lash adjusters causing a loss of compression, leading to a misfire.
Oil pressure should be measured with the engine at operating temperature, with a gauge connected at the oil pressure sensor port. Typical oil pressure reads 10-20 psi at idle (depending on the vehicle), and 35-45 psi at 2000 rpm (depending on the vehicle). If the oil pressure is too high or low and the oil and filter have been changed, inspect the oil pressure regulator at the oil pump for a possible stuck open or stuck closed condition. For Elantra and Tiburon engines, there's a check valve located in the cylinder block near the cylinder head deck. The check ball should be able to move freely in its "cage". The check valve also acts as an orifice so that the cylinder head receives less pressure at the head than at the main bearings.
Cylinder head bolts must be tightened in the proper sequence, and to the specified torque value. Cylinder heads that are improperly torqued can lead to cylinder head gasket leakage between cylinders. Be sure to follow the specification in each shop manual for proper torquing of the cylinder head bolts. The 1996-1999 Elantra-Tiburon engine and the 1999 2.5L V6 Sonata engine use the "torque-angle" method to clamp the cylinder head to the cylinder block. The "torque-angle" method involves torquing the fastener to a predetermined starting torque, then tightening the fastener to the additional angle(s) published in the shop manual. Use Snap-On Torque Angle Gauge P/N TA362 (or equivalent) to aid in determining the proper angle to tighten the fasteners to.
Hydraulic Lash Adjusters
Hydraulic lash adjusters are sensitive to oil pressure and oil viscosity. As discussed in the lubricating oil section, oil pressure that is too high will cause the lash adjuster to over extend, and oil pressure that is too low will cause the lash adjuster to collapse. If the oil is too viscous (thick), it may not enter into the lash adjuster causing a collapsed lash adjuster.
In some cases, the lash adjuster bore in the cylinder head can become distorted and mechanically bind up the lash adjuster. The lash adjuster should always move freely in its bore. An example of this is on the 1.8/0LOL engine used in the Elantra and Tiburon. The number four cylinder has an M12 cylinder head mounting bolt located next to one of the intake valve lash adjuster bores. It the cylinder head bolt is overtorqued, it causes the lash adjuster bore to distort, thus binding the lash adjuster. This can hold a valve open long enough to lose compression in the cylinder and cause a misfire. This condition may not show up in a leak down test or compression test, but should be visually inspected if a P0304 code is stored.
Cylinder Head Bolt Torque
Crank Angle Sensor and Crankshaft Tone Wheel
The crank angle sensor (GAS) and crankshaft tone wheel work together to provide the ECM top dead center (crankshaft position) information. The tone wheel is mounted to the crankshaft and rotates with the crank. The GAS is mounted 0.020 - 0.059" from the tone wheel. As the tone wheel rotates past the GAS, the signal appears as shown in graphs 1 & 2 on HDS. Large voltage "drop-outs" can be an indicator of a loose or damaged tone wheel causing random and specific misfire codes (P0300, P0301, P0302 etc.).
A loose tone wheel can quickly be checked while the GAS is removed from the engine. Use a long, narrow, flat blade screwdriver to push, pull and/or by on the tone wheel through the GAS hole. Any movement of the tone wheel indicates its loose. The tone wheel is mounted to the crankshaft with four screws.
Coolant Temperature and Intake Air Temperature Sensor
The Hyundai scan tool should be used to measure the engine coolant temperature and the intake air temperature. When the engine is cold, both values should be near the ambient temperature. When the engine reaches operating temperature, verify that the coolant temperature reads higher than the intake air temperature. This check rules out any possibility that the wire harness connectors might have been inadvertently switched, or that there is a faulty sensor.
Oxygen (02) Sensor
If any misfire code is accompanied by an oxygen sensor code, repair the oxygen sensor code before attempting to repair the misfire code. Oxygen sensors that malfunction can cause excessive carbon in the cylinders, thus causing a misfire. If the carbon build-up is verified, consider the top engine cleaner treatment before proceeding with repairing the misfire code. Refer to TSB 97-36-004 for proper diagnosis of the oxygen sensor.
Rough Road Sensor (Acceleration Sensor)
The rough road sensor (acceleration sensor) is used to interpret road conditions that may make the engine move in its engine mounts. Unexpected movement of the engine block relative to the crankshaft will cause a misfire if the rough road sensor is not operating. If the vehicle is driven on a very rough road, the sensor will send the ECM a signal to inhibit misfire monitoring. The Elantra, Tiburon and Accent all use sensors mounted on the shock tower. The 1999 Sonata uses information from the wheel speed sensor at the right front wheel to determine a rough road.
Cylinder Head Assembly
Removal of the cylinder head should only be performed after the ignition, fuel, and engine management systems have been eliminated as possible causes of the misfire code(s). Removal of the cylinder head should only be done when cylinder leakage is suspected past the valves. Before removing the cylinder head, visually check the valve springs to see if any are broken, the valve keepers to see if any are missing, the lifter bores for distortion or scoring, and the intake and exhaust ports for any debris holding the valves open. Also, check the intake and exhaust ports for signs of oil leakage past the valve stem seals.
After the above inspections are made, the cylinder head should be ready for removal. The cylinder head should be left as a sub-assembly (valves, springs, retainers, and keepers) and sent to a competent, professional machine shop for the following:
- Replace all valve guides and ream guide inner diameter to establish correct guide to valve fit
- Cut valves at 46°
- Cut the seats with a "three angle" cut (30°, 45°, 60°), aiming to the minimum published seat width specification
- Measure valve spring tension and replace out of spec springs
- Measure the installed height of the valve spring
When the finished head is returned from the machine shop, it may be necessary to bleed the hydraulic lash adjusters so as not to bind the camshaft during installation. As a final check before installation, fill the combustion chamber (or intake and exhaust ports) with solvent and wait 5 minutes. The solvent should not bleed past the valves. If it does leak, the cylinder head should be returned to the machine shop for corrective measures.
MISFIRE DIAGNOSIS WORKSHEET