Client called with a 2006 Ford Explorer with a misfire and codes U0101 in PCM andU1900 in ABS. No codes for the missfire but there are communicaton codes. Codes were taken on 11/3/2015, this Explorer has mutiple codes in multiple modules exept the transmission.
Click on image to enlarge
Due to all the communication codes and there being none in the Transmision Control Module(TCM), the first thought was that the TCM was faulty and pulling down the high speed CAN bus. I set forth to scope the high speed can bus and low speed can bus along with using the Ford IDS scanner. On intial test drive I noticed that the Explorer bucked and jerked under moderatly hard acceleration. This bucking and jerking was definitly a transmission concern and not a missfire. It felt like the transmission was shifting down a gear or two extremely hard. My client was able to produce the missfire, which was the orignal complaint, but upon harder acceleration he was able to produce the bucking and jerking. Scope data looked perfect while scan data was lost due to no communication. Attempts at recording data were futile as the IDS will stop recording and not save when the communication is lost. I have seveeral recordings of when the communication was restablished but not before communication was lost.
Now it is time to see if the issue can be reproduced in the bay or would I need to hook up at the TCM with the scope and drive. Luckly when the Explorer was brake tourqued in forward or reverse it would loose communication which resulted in transmission going into fail safe mode. The TCM is in the transmission on this truck, it relies on communication from the PCM. First test that was perfomed was to scope out the CAN wires at tcm. Doing this is to insure proper communication to TCM bulkhead connector. What was seen could not be explained easily at that moment.
The green trace is the High Speed CAN + at the TCM connector. Theses occilations that run through the data are actually corupting the data. The communication channels were first scoped at the DLC. These occilations were not majorly visible, Possible interference was the first thought. At this time it was unknown where the occilations were coming from, the first thought was that they looked like coil occilations.
After making a quick reference to IdentiFIx, which indicated that the coils could cause no communication issues due to feedback, a suspected bad coil was looking more pheasable.
Zooming out on the waveform capture, a steady repeated signal was epected to be seen.
In the above wave form there are a pair of lines that drop down below the base voltage for CAN. This is marked in the red circle. Upon first look this was repeating itself way to much to be a bad coil, but upon a closer look the occilation pairs repeat themselves 8 times before the curser marked with blue. Since this was at a fast idle right after startup 130 ms was about how long it took for a full revolution.
Ford likes to double and triple strike their ignition coils, meaning that each coild can spark 2 to 3 times per event at lower rpms. Couild the pair of occliations that are seen repeating 8 times within 130ms be all 8 coils?
In the above images power and ground side of the coils have been probed. There is a definite triple strike while idling hot. In the lower image above the green primary trace has been removed. The yellow trace which is power supply to the coil a voltage spike of more than 25 volts can be seen.
In this image the primary side of the coil lines up with those occilations that are seen in the CAN wires.
New coils and spark plugs were able to repair this Ford.