Ford Escape Coil

Recently, a friend of mine who owns a local shop called me about a problem concerning a 2003 Ford Escape with the 3.0L V6 engine.

The car had been dropped off with the complaint of low power, running rough and poor fuel economy. The customer first stated that one of his “knowledgeable” friends had spent a sizeable chunk of money on a tune-up and other parts that did not correct the condition, and then he asked if the shop owner would diagnose and repair the vehicle. The customer also said that his vehicle had run this way for more than a year and now it was simply not driveable.

The first step was to get the vehicle inside the shop and warmed up. Getting it started was a challenge in itself. When it did start, there was constant popping out of the throttle body. Fuel pressure was checked and showed to be good at 50 psi. Fuel quality was checked and was good. Spark was crisp and would easily jump a three-fourth inch gap.

Next the scanner was installed and a code P0304 was retrieved in memory. With the misfire code present and popping in the intake, a compression test was performed on the front bank which includes cylinder 4. The compression on cylinders 5 and 6 was good at about 165 psi each, but cylinder 4 was down at 45 psi. The rear bank was checked next and showed to be OK. After talking to the customer, the shop removed the front head. Now the burnt intake valve was obvious so it was sent to the local machine shop for a valve job. When the head was returned it was re-installed using the special tools to set the cam timing and the engine was fired up. The vehicle ran terrible. Power was non-existent. All previous checks were re-done with the same results with these exceptions: compression on the whole bank was now 180 psi and code P0304 set again but now also included code P0306.

When checked, there was no cranking vacuum. The exhaust was dropped and the converters were found to be plugged. I know it is hard to believe, after driving the car this way for only a year. With the customer’s approval, new converters were ordered and, once installed, some ease of starting and power were restored. But cylinders 4 and 6 misfires were still present.

This is about the time I came into the picture. When the shop owner called looking for advice, I asked if we could start from scratch. I had him check spark quality again and swap the #4 and #6 coil-on-plug (COP) units to different cylinders. Next he switched the injectors from those cylinders to different ones to see if the miss would follow the injectors. Nothing worked. I asked him to disable the injectors electrically to confirm those were indeed the cylinders missing—they were. Next I had him do a running compression check, just in case the machine shop had made a mistake or had possibly gotten the cam timing off during assembly. It checked out fine. The shop owner was now panicking.

Every time this vehicle was run, the Bank 2 catalytic converter would turn bright red. He was worried that soon it would melt down and he would need to replace it again. At this point, I recommended that (if the car owner agreed) they tow the vehicle to Identifix so I could look at it during some of my free time.

First I hooked up the IDS scanner. Retrieving codes showed P0304 and P0306. Running a cylinder balance test again confirmed that these were the weak cylinders. The IDS has a nice feature called a relative compression test which identifies weak cylinders by comparing the load placed by each cylinder during the compression stroke while cranking and displaying it in a graph format. All six cylinders showed almost identical readings. With cranking vacuum better than three inches, mechanical efficiency had to be good. This left only one possibility — either spark or fuel timing was incorrect. Consulting a wiring diagram for the ignition, the Powertrain Control Module COP driver wire colors were identified. All COP units share a common power wire, White/Violet.

Each driver wire has a different colored wire for spark control. The color for driver wire 4 is White/Pink from PCM pin 1 and driver wire 6 is Light Green/Yellow from pin 53.

Wouldn’t you know it, the harnesses were swapped! Looking at the way the harness is placed, it is a natural fit to connect to the COP units backwards. To be installed correctly, the harness for the front coils actually needs to be turned over awkwardly and secured by a clip between cylinders 5 and 6. Once this was done, the vehicle ran fine.