Case studies

 I was called to a new shop today. First time providing service for a young couple that opened a new shop in town within the last year.

This shop I visited while traveling through a part of town I grew up in about six months ago. The new shop stuck out like a sore thumb to me. Like whoa, that’s new in a town that doesn’t change. When I stopped in the wife of the couple was the only one there. He was off driving a car or something. I left my information and explained to the wife what kinds of help I can provide if they got in a jamb. Honestly never expected to hear again from them. They are trying to get the industry figured out and just don’t know what they don’t know. That’s what I provide a chance to get out of a jamb when the technology is beyond their understanding.

We can talk about how they are in a bad business model another time.

2004 Ford F-150 5.4L. See I told you routine repair. History is it came in for a 4wd failure. He repaired the hub actuators and replaced a non-functioning vacuum solenoid as well as the vacuum harness that deteriorated in too many places. Customer says “while it’s there, mind doing a tune up” plugs are pulled and broken plugs removed with no problems to note. New motorcraft plugs are installed as well as new coil boots. After the maintenance is done it developed a misfire.

You already know the situation. The complaint is a misfire felt, codes P0351 and then while trying to fix it P0174 set. New motorcraft coil is installed. Second coil is replaced as a “warranty” Shop is now full of heavy line work and owner doesn’t even know how to go about diagnosing the misfire. I show up prepared with several tests planned to begin the diagnostic process. First is a scan of codes with Snapon Verus. Those that know me know I despise that tool. But in this situation, it is the right tool to grab first. Confirmed P0351 and P0174. Check mode 6. All misfire tests are reset and have not been completed.

Grab IDS and VCM2 for a power balance test. No VCI detected and can’t get it to be recognized. Great, restart laptop after unplugging everything. Start it all back up, still no coms. I’m on a mobile call and I know other ways to get this answer I’m looking for. The question is, “is cylinder 1 the misfire or is it another cylinder.” To confirm this I connected 1 low amp clamp on the red/light green wire at connector C139. This connector is the black in line connector attached to the ECM connector harness right in front of the ECM. You will also note that Mitchel doesn’t think that C139 is important information. Motor diagrams do think it is important. I agree. Second low amp clamp (both Pico TA019 clamps) on the red/light green at the cylinder 1 coil only. Vacuum waveform for possible need later. But the problem sticks out. It shows cylinder 8 with a serious issue. When the ECM releases the ground on the coil all hell breaks loose. This proves the ground is controlled by the ECM as well as the coil is capable of being charged so the connection is good to the coil.

I tap into cylinder 8 primary to watch the primary pattern. Same information there, only more. The spark line is where the problem occurred. That means it’s after the coil on the secondary side. We know we have new parts there, factory brand, so we move the coil at this time. It doesn’t change. It didn’t move with the coil and boot. That leaves plug. We pull the plug expecting to find a crack in the porcelain or tracking. None found. We know the plug is bad so we installed the new plug that showed up. New plug installed and rescoped to confirm repair.