Last month we covered a relatively universal method of narrowing potential causes for misfire using scan data.
The timing of the article’s publication was ideal. I was privileged enough to present this very topic at ATRA’s Powertrain Expo a few weeks ago.
I had a wonderful time presenting and, more importantly, discussing the topic with technicians after the presentation. During these conversations, I received a variety of questions. One referred to Ford ignition coils and how often they fail. The conversation struck a chord for me… for multiple reasons.
Ford ignition coils have a high failure rate; a situation you’re probably familiar with. Usually these failures cause a misfire or intermittent misfire that can sometimes be hard to pinpoint.
But failed Ford ignition coils can cause issues other than misfires. They can cause network communication problems, PCM failures, and even put transmissions into failsafe. That’s right: They can stick a transmission into failsafe.
These issues are common enough that some shops are selling eight ignition coils on 5.4-liter engines due to an intermittent misfire. Granted, eight ignition coils will usually solve the problem, but is the additional expense of replacing all eight ignition coils necessary? I think we need to diagnose.
In this issue, we’ll focus on a technique for diagnosing marginal or failing Ford ignition coils. If used properly, you should be able to identify all failing coils. As a result, you’ll have accurate diagnoses, you’ll avoid comebacks, and you won’t have to sell a full set of ignition coils when only one or two are necessary.
Based on everything we discussed in the last issue regarding fuel trim and downstream oxygen sensors, here’s a 2-step process for checking misfire on Ford vehicles. We’ll look at a 2000 E150 with a 5.4-liter engine. The customer’s complaint was the MIL came on intermittently.
STEP 1: GATHER SCAN DATA
The first step is to connect a scan tool. Check for DTCs and freeze frame data to see if you can identify the misfiring cylinder (figure 1). Our test vehicle set code P0302 and provided freeze frame date to suggest an ignition-related problem.
In addition, check the Mode $06 data. The information Fords provide through the Mode $06 data can shine. Mode $06 is included in almost all generic or global scan tools. Mode $06 provides non-continuous monitor test results. It offers more of a “grade” than the “pass/fail” we normally get with a trouble code. We could discuss this for hours, but today we’ll explore its value in Ford misfire diagnostics.
Most manufacturers didn’t provide misfire data in Mode $06 prior to CAN. Ford was the exception and provided this data all the way back to the 1996 model year. From our sample vehicle, we checked the Mode $06 data using a factory Ford IDS scan tool (figure 2). You can do this with generic tools but they may not read the data as well as the IDS.
The important thing to remember is that, for most pre-CAN Ford vehicles, test ID 53 (TID$53) is the individual cylinder misfire monitor and components ID 1 through 8 (CID$01 – CID$08) are the individual cylinder results. Anything other than a zero indicates the PCM may have detected a misfire.
The data reveals that cylinder number two has definitely failed the misfire monitor and is what’s causing the DTC. Closer examination shows that cylinders one and seven have also registered misfires. That leaves us with three cylinders to focus on instead of eight.
STEP 2: TEST THE COILS
Even though we’ve identified three cylinders that were misfiring, your next step should be to connect a scope and observe all eight ignition events, paying close attention to the questionable cylinders.
There are two methods you can use to diagnose Ford ignition coils: The first is a coil stress test, spelled out in Ford TSB 05-22-8. This is a great test but requires caution because it could damage the PCM if it’s performed incorrectly.
In addition, you need to remove the coils to perform the test, which takes extra time. Finally, it requires extensive scope knowledge to perform the test with a generic scope, because the TSB instructions are specific to the VMM; a Ford factory tool.
The second method is much easier but still requires a scope. What you can do is scope the current for the questionable coils. The diagram (figure 3) shows the fuse that feeds power to all of the ignition coils.
- Remove the fuse and install a jumper wire in its place.
- Connect a positive lead to the driver wire for ignition coil number one and a negative lead is to ground. This second connection provides a sync signal for displaying the coils in a consistent firing order, from left to right.
- Clamp a low-current probe around the jumper wire to measure the ignition coils’ current.
- Start the engine.
All of the ignition coils will be visible in firing order across the scope screen (figure 4). The firing order for this vehicle is 1-3-7-2-6-5-4-8, as labeled on the scope capture.
Now you’re ready to analyze each ignition coil’s waveform to determine its health. Obviously, cylinder two’s waveform doesn’t look like the others and the coil needs to be replaced. The downward spikes indicate secondary ignition breakdown. You’ll need to analyze the other waveforms further before condemning any other coils. To do that, you first need to know what good looks like.
Take a look at a waveform from a good ignition coil (figure 5). The blue trace ramps up and then drops off. Because many Fords multi-strike at idle, each coil pulses multiple times; this can be helpful.
Each charging event takes some time. The discharge event should take time, too. The red lines demonstrate how the coil energy should dissipate. Imagine the triangulated peaks. The second and third pulses of the coil have a vertical rise in current, because the magnetic field hasn’t collapsed fully. A weak coil collapses too fast and the vertical rise is absent.
The next capture (figure 6) is from ignition coil number seven. This was one of the cylinders for which the Mode $06 data indicated a problem. You can see that the magnetic field is weak.
In this case, cylinder 2 was the obvious cause of the misfire. In addition, cylinders 1 (not shown) and 7 failed the coil current test.
CONCLUSION
In this case, a single ignition coil on cylinder number two would have resolved the customer’s misfire. With the addition of Mode $06 data and observation of the full scope capture, we were able to identify two more failing cylinders.
Because the diagnosis was thorough, including the use of a scope to check all the cylinders, we were able to present a more detailed recommendation to the customer: one coil, three coils, or eight coils. No matter which option the customer chooses, you’ve covered your bases and the chance for a comeback should be reduced.
In this particular case, the customer opted to replace all eight ignition coils. The customer’s reasoning was “It’s my work truck. If it’s down, I don’t make any money. Just do them all.”
Throwing a full set of ignition coils would have fixed this problem. But the short time spent identifying the actual failure established your credibility and improved your value to the customer.
