Pulling Codes: Advanced Misfire and Fuel Trim Analysis -- A P030X Detailed Analysis

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.

This article will document the use of fuel trims and oxygen sensor behavior to determine if the misfire activity is ignition, engine mechanical or fuel related. We will address this in a two-part series from the viewpoint of moments in time to offer a deeper understanding of these concepts.

Our first article on this subject will address ignition-related misfires. We will explore other misfire research in the next article. The first step is to visualize these failures from the beginning figures 1 and 1a: pre- and post-oxygen sensors under normal activity.— picture that an ignition-related misfire has occurred on a subject vehicle. We come to define it as a single cylinder misfire, prior to failure the pre-oxygen is switching and working as designed. The post-oxygen sensor is also working as designed and almost appears as a straight line when looked at per graphical data or a Pico lab scope. ­Figures 1 and 1a denote how the pre- and post-oxygen sensors may look on a subject vehicle prior to any type of misfire-related activity.

Let’s use a 2007 Ford Taurus as an example. The IDS scan tool will be used to show the activity.figures 2 and 2a: pre- and post-oxygen sensors under ­ignition misfire activity.

Figures 2 and 2a denote the activity of the pre- and post-oxygen sensors at the initial point of ignition misfire activity. A close examination shows the pre-oxygen sensor went low, indicating that it saw oxygen in the exhaust stream at the very moment the misfire activity occurred. The post-oxygen sensor went high, indicating how the vehicle has a tendency to run (rich).

Note that at the very point of failure, the short-term fuel trim (STFT) will increase and, depending on design and strategy of the system, may show impressive numbers for short term, after the processor has acknowledged this, the resources of long-term fuel trim (LTFT) will work to get the short-term numbers back as close as possible to at or near zero. The end result is that after corrective action has taken place by the processor, there will not be a significant impact on the total fuel trim (ST + LT). This analysis is based on a subject vehicle that has good fuel trim values to start with. A range of +/-5% is optimal on many systems today, but a range of +/-10% may be acceptable.

A great example is a vehicle that has a total correction of 15% prior to fault; you’ll have higher numbers once ignition misfire activity occurs. I’ve found that on many vehicles with ignition misfire activity after the corrective action has taken place, single-digit numbers appear to be reasonable.

 

2004 Chevy Impala

Now let’s take a look at a 2004 Chevrolet Impala with a P0300 stored in memory.figure 3: the firing order shows that cylinders 5 and 2 are sister cylinders.

Upon review of this failure, note that the vehicle has a misfire code and freeze-frame information as well. The data shows that a STFT of -4% and a LTFT of 7% was noted; this is a total correction of 3%, which is not a significant impact on the total fuel trim correction. Figure 4: Is this misfire activity ignition or fuel related?

The misfire activity appears to be on cylinders 2 and 5, and, based on service information, it appears that these two cylinders are companion cylinders. See ­Figures 3 and 4. After careful review of this case study, it was clear that a bad coil assembly was at fault. The Tech 2 scan tool was used for this analysis. This observer would also ask that you take into ­account systems that will turn off the injectors when misfire activity occurs, the fuel trim values will go to zero once the fault is set.

This Pulling Codes case is now considered closed, however, we invite any questions concerning this fault analysis. 

 

You May Also Like

Impact Wrench Technology

Interchangeable anvils are a feature on some new impacts.

Technology is defined as the application of scientific knowledge for practical purposes, especially in industry. We often picture technology as something that has computers and electronics attached, and often it does. But, in the world of impacts, both in the realm of pneumatic and cordless, technology bears much deeper roots.

Brake Lathe Basics

Resurfacing drums and rotors is a machining process with its own specific guidelines.

Refrigerant Oil Has to Be Right

Oil type is just as important as oil capacity.

Three bottles of refrigerant oil
Top 5 Tools: Steve Coffell, Auto World, Hazelwood, MO

Steve Coffell, a technician at Auto World in Hazelwood, MO, says his Top 5 Favorite Tools are: Related Articles – Mayhew Introduces New 14-Piece Micro Hand Tool Set – New Small Stud Extractor Now Available from Mayhew Tools – Matco Debuts 5-Piece Purple Screwdriver Set   OTC Genisys Touch – Quick scan, bidirectional control Snap-on

Wheel Bearing Adjustment Tools & Equipment

A wheel bearing that’s out of adjustment can reduce bearing life and can affect more than just the bearing. It’s important to adjust the wheel bearing endplay to the proper specifications. If the bearing set is adjusted too loose or too tight, it can cause the bearing to fail prematurely. There are a few types of assemblies, so using correct procedures and tools will ensure a comeback-free wheel bearing installation.

Other Posts

Fuel Pumps and Cranking

Diagnosing the problem comes down to understanding what causes a loss of fuel pressure.

Tools in the Eye of the Beholder

We’re here to help you see all the tools, so you can invest wisely.

Multimeter Accuracy: How Important Is It?

Multimeter accuracy is critical for EV diagnostics.

multimeter
More Than A Scan Tool

Scan tools serve as indispensable diagnostic hubs, offering access to a wealth of resources, from OEM technical bulletins to community-documented repairs.

scan tool