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Remember to Check Coil Connector For 4 Wires If Coil Pack Fails AgainPosted 9/12/2000By Jeff Boskowitz
Stall on Acceleration from Stop Stems from Fault in PSOM
During an extremely rare lull in hotline calls, I was kicked back in my chair, trying to come up with an idea for another article, when I happened to overhear one of my Ford teammates on the phone. He was discussing a repeat coil pack failure on a 1995 Mustang with a 3.8L engine. I continued to eavesdrop until I had a pretty good idea of what they were talking about. It appeared that this vehicle was driven into the shop in need of a head gasket replacement (an unusual failure on a 3.8L, right?). When the job was completed, the car was a no-start, with no spark. Intrigued by the one-sided conversation, I kept listening. That article would have to wait. They seemed to be discussing the fact that the coil pack was getting so hot it would literally melt the coil body with the key on. This would indicate a direct short to ground. I heard my teammate trying to make some sense out of the wire colors the technician on the other end of the phone was giving him (and we all know there are NEVER any problems with electrical schematics!). When I heard him mutter, “dark blue with orange,” the light bulb came on. (Some of you won't be old enough to appreciate that ancient Ford commercial). One of the benefits of working at IDENTIFIX is that we track repairs and identify the causes of repetitive failures. I had received four hotline calls in the past two months for problems on a Mustang after a head gasket job. Those four were also no-starts, but they were blowing the 20A EEC fuse as soon as the key was turned on. This would indicate a direct short on the vehicle power wire (VPWR-solid red). All four of the technicians I spoke with swore they had triple-checked their work and that this wire was not pinched to ground anywhere. During one call, I even had the tech unhook all the components that the VPWR circuit went to, including the transmission. In-line harness connectors were also unhooked. This tech told me that the only way the fuse would quit blowing was by unhooking the coil pack. I was stunned at first, since the power to the coil is through a red/light green(R/LG) wire and from a different fuse than the solid red. But the tech assured me that “it was RED.” Probing deeper, I then asked him the colors of the remaining three wires that are used by the module to toggle ground on each of the three coil pairs inside this coil pack. My next surprise came when he stated there were only two more wires! For three sets of coil windings, how could this be? Then for the real surprise: the two remaining wire colors were dark blue/orange (DB/O) and black/white (BK/W)! DB/O is a common color that Ford Motor Co. uses on the Mustang for the signal wire on the cam sensor. The BK/W is a ground wire for the sensor. The cam sensor is a Hall Effect device that modifies the voltage from the VPWR circuit (R) through ground toggles and passes on this signal to the PCM through the DB/O for cylinder identification. It appears that somewhere in the manufacturing process, the connector that goes to the cam sensor somehow “became” the same as the one that hooks to the coil pack only 4 inches away; minus one wire and different wire colors, of course. This leads to the possibility of inadvertently swapping the connectors during reassembly. If this happens, then the result is a hard ground to the coil pack through the BK/W as long as the key is on. If the fuse doesn't blow first, the coil soon overheats from the continued current flow. Swapping the connectors (and a new coil pack in the case of my teammate's hotline caller) took care of all the concerns. If you have a similar problem after replacing head gaskets on a Mustang, remember to check the coil connector for four wires. If you are unsure of the colors, try to match them by looking at the ignition module or an electrical schematic, or call an expert! Now, if I could just figure out a topic for that article ...
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