OBD II Misfire And Diagnosis
When diagnosing misfires, it’s important to use tools that allow you to go beyond a simple code reader that displays a P03XX. Even an OEM-level scan tool can’t tell you what the firing voltage is or what the ignition pattern looks like. Nor can it tell you if the serial data is accurate or correct. For that kind of information you need a DVOM or a graphing multimeter/oscilloscope that can look at sensor voltages directly and display primary and secondary ignition patterns.
Pulling Codes: Advanced Misfire and Fuel Trim Analysis, Part 2
Contributing writer Carlton Banks continues with his series on Advanced Misfire and Fuel Trim Analysis, using fuel trims and oxygen sensor behavior to determine if the misfire activity is ignition, engine mechanical or fuel related. This article focuses on fuel-related misfires.
Pulling Codes: Advanced Misfire and Fuel Trim Analysis — A P030X Detailed Analysis
Carlton Banks documents the use of fuel trims and oxygen sensor behavior to determine if the misfire activity is ignition, engine mechanical or fuel related.
PCM Diagnostics Case Study: No-Code Misfire Diagnosis On A 1998 Toyota 4Runner
When doing mobile diagnostic work for other shops, contributing writer Gary Goms usually sees more than his share of random no-code engine performance complaints. In the following case study, the customer of a client shop complained about an intermittent rough idle on his well-maintained 1998 Toyota 4Runner, but only when it was driven in hot weather. The client shop couldn’t duplicate the complaint, no matter how long the engine ran. Of course, the lack of DTCs didn’t help the diagnostic process.
Diagnosing A P0301 Misfire Code On A 2001 Mercedes-Benz E320 Sedan
Since the advent of OBD II, every vehicle is equipped with a sophisticated system that measures each cylinder’s contribution to engine power, becoming one of the most difficult challenges we face. Each time a cylinder fires, the misfire monitor uses a highly accurate crankshaft angle measurement to measure the crankshaft position. This system needs to have an accurate crankshaft position sensor that is able to read the crankshaft position, even at high RPM, sending a clear signal to the PCM. Then the PCM monitors the crankshaft acceleration time for each cylinder at the firing time.
Tech Tip: Coil-On-Plug Misfire Diagnostic Tips for Ford/Lincoln/Mercury Engines
The misfiring cylinder must be identified through Self-Test misfire codes or through WDS Power Balance. Rule out base engine problems; rule out fuel problems; and then look at ignition problems (be sure to rule out coil primary circuit issues).
Mercedes: Diagnosing a P0301 Misfire Code Harnessing the Benefits of an Amp Probe
Electronics Diagnostic Specialist Sergio
New Free Wells Technical Video Covers Ford Mode 6 No-Code Misfire Diagnosis
The Technical Services team at Wells Vehicle Electronics has introduced a free diagnostic training video that the company says can help automotive repair professionals save hours in identifying and troubleshooting intermittent, “no code” cylinder misfires on Ford vehicles through the use of Mode 6 diagnostics.
Pulling Codes: Intermittent Misfire/Idle/Stall on Dodge Stratus, Codes P0300, P0303 and P0171
This month’s column comes to us from Bill Fulton. He takes us through a Pulling Codes case of a 2004 Dodge Stratus with intermittent misfire/idle/stall using his symptom-to-system diagnostic strategies.
Misfire Testing with a Scan Tool Tip Clip
In this tip clip, instructor Jim Wilson talks about P0300 codes and misfire testing using your scan tool. He talks about how you would look at certain things such as RPM, MAP, changes in load, and long term fuel trims. He goes on to mention some things technicians should be aware of on Ford and Chrysler vehicles.
This clip is an excerpt from the 90 minute comprehensive “Functional Scanner Testing” with Jim Wilson, available from Automotive Video.