COP Diagnostics Part II: Those Pesky Ford Coils

Written by Scott Shotton

The Driveability Guys

http://driveabilityguys.com

INTRODUCTION
FINDING THE CYLINDERS RESPONSIBLE
THE HOOK UP
ANALYZING THE CAPTURES
PRACTICLE EXAMPLE

INTRODUCTION

If you have been in the industry a while you probably know that Ford COP ignition coils are a common failure item. They can often be easy to pick out when they are misfiring, but what about when they are intermittent? Another potentially worse situation is a vehicle that leaves a shop after a coil has been replaced only to return in a couple of weeks with a different coil failing? Should the shop have replaced all 8 (or 10) coils? That is an option, albeit an expensive one. However, there is a way to determine coil health that can help a technician make that judgment call.

FINDING THE CYLINDERS RESPONSIBLE

The first step in misfire analysis is identifying the bad cylinder or cylinders. This step can be done with a scan tool in most cases. The next step is to scrutinize additional test data so that we have confidence when we point at a particular fault. That is what diagnostics are all about correct?

P03xx codes are usually a pretty good gauge of what cylinder is the problem. These codes may, or may not, be set due to ignition issues. Regardless, we still have to find the cylinder and the cause. For the sake of education let's tackle some misfires, explain the theory and learn some techniques.

This first place to look for a misfire on a Ford, especially a miss that doesn t set a code, is in the Mode $06 data. Rick Seagle wrote an article Ford Mode$06 Misfire Data that does a great job outlining how to use this information effectively. You can read that article here: Ford Mode $06 Article. Below is an example of a 1999 E150 with a 5.4 liter engine and a noticeable single misfire occasionally.

In this case the Mode $06 data shows that the PCM has counted a minute number of misfires on cylinder number 3. The misfire is definitely there, but its failure rate is well below the threshold that would set a P0303 code. Now this doesn t mean we just throw a coil at cylinder number 3, but it does alert us as to which cylinder we might want to keep an eye on during further diagnosis.

This technique can also be used to draw our attention to potentially weak coils during other P03xx code diagnostics. This next example is of a 2000 E150 with a 4.6 liter engine and a P0302. We can see that cylinder number 2 is over the limit and fails the misfire monitor, hence the code and MIL command. We can also see that cylinders 1 and 7 also have some recorded misfire but remain below the code setting limit. Would these be good coils to keep an eye on during our diagnosis? Later in this article we will explore how to verify potentially weak ignition coils. In this case coils 1 and 7 were in fact weak and were replaced along with coil number 2 to fix the vehicle properly and avoid a comeback.

A side note on Mode $06 it should be taken with a grain of salt. In theory it should work, but it doesn t always. It is a good tool to point us in the direction of which cylinders have misfired when it does work. When it does not work, however, we may end up back at diagnostic square one. To illustrate my point here is a Ford with a P0301 stored and the MIL commanded on. This Mode $06 data is worthless in regards to our misfire diagnosis on this particular vehicle.

Now that we have identified a cylinder we need a method to test the ignition system to see if it is the cause of the misfire. Secondary ignition patterns can be tough on COP vehicles to say the least. Primary ignition patterns are relatively easy to obtain on most Ford vehicles with individual coils. D-Tip's Coil on plug ignition testing with a scope article does an excellent job of explaining these primary voltage patterns. But what good does a primary voltage pattern do for us if the vehicle isn't misfiring at the time of testing? And can it give us an idea of an ignition coil's health?

The answer is current. Ford's multi-strike system combined with our ability to view coil current lends itself to an extremely accurate diagnostic test method. To understand this method we need to understand a few things: how to hook up our scopes, what is good, what is bad and why.

THE HOOK UP

To view coil current we need to clamp a low current probe around the positive feed to all of the ignition coils. On Ford vehicles this is usually pretty easy because most applications feed power to all the coils through one fuse. I usually remove the fuse and install a fused jumper wire in the fuse's place. Then I clamp my current probe around the jumper. Since each coil fires at a different time we can see a string of firing events that correspond to specific cylinders. This allows us to view each coil individually with only one connection. Below is an example with an eight cylinder engine hooked up in this manner. This vehicle does have a dead misfire all the time, and you may see it in the capture. But do you know what cylinder it is occurring on?

A quick glance tells me that there is an issue here. For example, the downward spikes suggest secondary ignition break down. But again, what cylinder(s) are at fault? Basically this capture is useless without the addition of a sync trace. A sync (short for synchronization) trace allows us to pick out a specific cylinder. In many cases it is done with a secondary ignition pickup. In the case of COP however, secondary is tough to access. So we will use the easiest option: primary ignition. If we set up channel B on our scope to see cylinder number one's primary voltage we can synchronize our capture. If we know the firing order we can then identify each consecutive cylinder on our scope screen. In this example the sync is on number 1 and the firing order is 13726548. Can we now identify which cylinders look like they have issues?

ANALYZING THE CAPTURES

Cylinder number 1 is in fact our misfire. The red trace is synched on 1 and the blue trace has obvious downward spikes. I might also be inclined to say that cylinder number 5 is the next in line for a problem. Now let's take a closer look at cylinder number 1. Here is primary voltage zoomed from the same capture above.

It is obvious that this cylinder is misfiring. The hash that represents extremely turbulent electrical conditions and the lack of spark lines for all 3 firing events is very clear. Now let's look at primary current. Here is the current capture for the identical firing event.