Engine Performance - Misfire Code Diagnosis: Overview
Group: ENGINE ELECTRICALNumber: 99-36-014
Date: SEPTEMBER, 1999
Model: ALL OBD II VEHICLES
Subject
MISFIRE CODE DIAGNOSIS
This Technical Service Bulletin supersedes 97-90-012. Please discard the old TSB and replace it with this new one.
TABLE OF CONTENTS
* A Guide To Repairing Misfire Codes
* ECM Misfire Detection Methods
* Diagnostic Trouble Code Definition
* Customers Description of the Symptom
* Scan Tool Data
* Ignition Wires
* Dielectric Grease
* Spark Plug Tubes
* Spark Plug
* Ignition Coil
* Fuel Quality
* Fuel Injectors
* Cylinder Leakage Testing
* Cylinder Leakage Testing Versus Compression Testing
* Lubricating Oil System
* Hydraulic Lash Adjusters
* Cylinder Head Bolt Torque
* Crank Angle Sensor and Crankshaft Tone Wheel
* Coolant Temperature Sensor and Intake Air Temperature Sensor
* Oxygen (02) Sensor
* Rough Road (Acceleration) Sensor
* Cylinder Head Assembly
* Misfire Diagnosis Worksheet
A GUIDE TO REPAIRING MISFIRE CODES
Please read through this entire bulletin before using any portion of this repair guide. All terms, components and specific procedures are described in the main body of this TSB.
ON THE 1ST REPAIR ATTEMPT:
Record misfire codes. Choose the most appropriate category from the four (4) selections below:
1. One cylinder has a misfire code (see procedure A)
2. Paired misfire codes as described below (see procedure B)
- Cylinders 1 and 4 or cylinders 2 and 3 (4 cylinder engines)
- Cylinders 1 and 4 or cylinders 2 and 5, or cylinders 3 and 6 (V6 engines)
3. Multiple cylinders have misfire codes, and/or there is a random misfire code (see procedure C)
4. Misfire code (one or more) occurs only on cold start-up (see procedure D)
Procedure A (One cylinder misfire code)
1. Mist spark plug wires and check for arcing.
2. Remove spark plugs and check for evidence of carbon tracking.
3. Perform cylinder leakage (leak-down) test.
A. If leakage is less than 10%, continue to step 4.
B. If leakage is 10% or greater, remove the head to perform valve job. (See specifics in cylinder head section).
4. Replace spark plugs. Lightly apply dielectric grease to the spark plug wire tip/boot base.
5. If misfire is in cylinder #4 (P0304) on Elantra or Tiburon, loosen and retorque the M12 cylinder head bolts to 26 ft-lbs + 60° angle + 60° angle.
6. In the misfiring cylinder, swap injector with another cylinder.
Procedure B (Two misfire codes that are coil paired; Cylinders 1 and 4 or cylinders 2 and 3 (4 cylinder engines); Cylinders 1 and 4 or cylinders 2 and 5, or cylinders 3 and 6 (V6 engines))
1. Mist spark plug wires and check for arcing.
2. Remove plugs and check for evidence of carbon tracking.
3. Perform cylinder leakage (leak-down) test.
4. If leakage is less than 10%, continue to step 4.
5. If leakage is 10% or greater, remove the head to perform valve job. (See specifics in cylinder head section).
6. Replace the coil.
Procedure C (Multiple cylinders misfire codes, and/or a random misfire code)
1. Check LT (LongTerm) fuel trim. If over 10%, check fuel pressure.
2. Check AFS calibration against known good value.
3. Check for proper operation of EGR and purge control valve.
4. Mist spark wires and check for arcing.
5. Remove spark plugs and check for evidence of carbon tracking.
6. Perform cylinder leakage (leak-down) test.
A. If leakage is less than 10%, continue to step 7.
B. If leakage is 10% or greater, remove the head to perform valve job. (See specifics in cylinder head section).
7. Check fuel sample from the inlet (bottom side) of the filter to check for the presence of water or contamination.
8. Check intake air supply for evidence of oil in the air cleaner or on the AFS.
9. Tweak pins on AFS and TPS (TSB 96-36-003)
Procedure D (Misfire codes occurs only on cold start-up)
1. Check oil level and viscosity for evidence of "thick" oil.
2. Check for after market oil filter (no bypass valve).
3. Mist spark plug wires and check for arcing.
4. Remove plugs and inspect for carbon tracking.
5. Perform cylinder leakage (leak-down) test.
A. If leakage is less than 10%, continue to step 6.
B. If leakage is 10% or greater, remove the head to perform valve job. (See specifics in cylinder head section).
6. Check oil pressure against established standards. Service relief valve, orifice plug, or replace case to correct excessive oil pressure situation.
7. Replace hydraulic lash adjusters.
NOTE: 2nd and all subsequent repair attempts Call the Hyundai Technical Assistance line at (800) 325-6604. Be prepared to answer the questions on the Misfire Diagnostic Worksheet. You may be asked to fax a completed copy of the worksheet to expedite the diagnosis / repair process.
ECM MISFIRE DETECTION METHOD
It can be tough to hear or feel a misfire, which is one reason why new emissions-control standards require the on-board diagnostics (OBD-II) of the engine control module (ECM) to monitor each cylinder for misfire.
Engine misfire detection is based on the difference of engine rotational speed between the firing cylinders and the missing cylinder. When a cylinder is misfiring, it takes a "longer time" for the crankshaft to rotate to the next cylinder in the firing order. This "time" is measured by the crankshaft angle sensor (CAS) which measures the actual rotational travel of the crankshaft in real time. This information is evaluated by the ECM. If the misfiring cylinder took "longer" to rotate the crankshaft than the other cylinders, the ECM will set the appropriate diagnostic trouble code (DTC) for that cylinder. As an example; an inline 4 cylinder engine's crankshaft rotates 1800 as each cylinder fires through the firing order. In a properly running engine with a firing order of 1-3-4-2, the time between the firing of 1-3 will be the same as 3-4, 4-2, and 2-1. In an engine that has a misfire in cylinder #2; it takes the crankshaft longer to travel through the 2-1 firing rotation.
The repair of today's misfire is more difficult than pre-OBD-II vehicles because the ECM is programmed to detect the slightest change of crankshaft rotational speed. The criteria for detecting a misfire is set by the Federal Government and all vehicles sold in the U.S. must comply with these requirements. The engine management system must be able to perform three critical elements of misfire detection:
1. Monitor, identify and if severe enough, illuminate the "check engine" light for a misfiring cylinder;
2. Set separate diagnostic trouble codes for multiple cylinders;
3. During a misfire great enough to damage the catalyst, the "check engine" light must blink.
DIAGNOSTIC TROUBLE CODE DEFINITION
P0300 - Misfiring in more than one cylinder, but unable to detect the specific cylinder because the misfire is random.
P0301 - Misfire in cylinder number 1 is very likely.
P0302 - Misfire in cylinder number 2 is very likely.
P0303 - Misfire in cylinder number 3 is very likely.
P0304 - Misfire in cylinder number 4 is very likely.
P0305 - Misfire in cylinder number 5 is very likely.
P0306 - Misfire in cylinder number 6 is very likely.
CUSTOMER'S DESCRIPTION OF THE SYMPTOM
The customer information plays a significant roll in misfire diagnosis. The customer should be asked the following questions.
1. Is there a driveability or performance issue?
- Has the car been in before for the same condition? Can it be duplicated?
- How often?
- Under what conditions?
* Use this information to verify any corrective action performed.
2. When did the "check engine" light illuminate?
- At start up?
* If cold engine, see Hydraulic Lash Adjuster Section.
* If warm engine, all items should be considered.
- While driving at operating temperature?
* All items should be considered.
3. How does the customer typically drive the vehicle?
- Short trips in the city?
NOTE: This can set a misfire code due to poor combustion leading to excessive carbon deposits.
- Long highway trips?
* All items should be considered.
4. Did the "Check Engine" light blink or remain illuminated?
- Blinking light indicates misfire is severe enough to cause catalytic converter damage.
* Check fuel injector section.
- Steady light.
* All items should be considered.
5. Does the car experience excessive oil usage?
- This can set a misfire code due to poor combustion leading to excessive carbon deposits.