Experiencing erratic shifting in your older Ford motorhome? Is your OBDII reader failing to connect or showing strange readings? You might be scratching your head, especially if you’ve started suspecting transmission problems or sensor malfunctions. However, before you dive into costly repairs, consider this: a surprisingly simple ground wire issue, addressed by a Ford Technical Service Bulletin (TSB) from the year 2000, could be the root cause of your woes. This often-overlooked TSB, initially intended to resolve shifting issues, has proven to fix a wider array of electrical problems in 1999 Ford F53 chassis, including OBDII port malfunctions.
Many owners of these classic motorhome chassis have encountered perplexing shifting problems. They might describe it as harsh shifting, delayed gear changes, or inconsistent performance. Coupled with this, some find their OBDII readers are unable to establish a connection with the vehicle’s computer, or are providing unreliable data. This combination of symptoms can lead mechanics and owners down a rabbit hole of diagnosing potentially expensive transmission or electronic control unit (ECU) failures.
However, the solution might be far simpler and more economical than you think. Ford TSB # 02-11-3 (READ HERE) directly addresses a grounding issue that affects multiple critical systems in the 1999 Ford F53 chassis. This TSB outlines a procedure to improve the ground connection for the Power Control Module (PCM), which is responsible for managing not only the transmission but also various engine and diagnostic functions, including the OBDII port.
The original article we’re referencing highlights the experience of several F53 owners who were plagued by these exact issues. Like many, they initially suspected complex problems. However, after discovering and implementing the ground modification detailed in TSB # 02-11-3, their shifting problems vanished, and their OBDII systems returned to normal operation.
One F53 owner, Bill H., shared his frustrating experience:
“I have a 1999 Pace Arrow… I had a crank no start issue. Contacted a mobile mechanic and after two fuel pumps (nothing wrong with either) or a list of numerous parts. I decided to require that your TSB that you identified be installed if it wasn’t installed by previous owner. Worked immediately it was an open ground issue! Thank you so much for the help. We were without our MH for about four months and several parts and $$$$.”
Bill’s note underscores the severity of the problem and the effectiveness of the TSB fix. His initial “crank no start” issue, seemingly unrelated to shifting, was also resolved by this ground modification.
Another F53 owner, Kevin D., further emphasizes the broader impact of this TSB:
“I have a 99 F53 6.8 that had no injector pulse, no coil pulse, no CEL light, no obd II port functions, and my MAF had low readings as well.… Pin #51 of this TSB supplies grounds to the ECM relay, fuel pump relay, the CEL light, and the OBD II Port.. I performed the TSB today and it fired right up, after sitting dead over a year. Obviously this TSB can fix a LOT MORE than shifting Issues.”
Kevin’s experience clearly demonstrates that the ground fault addressed by TSB # 02-11-3 can affect a wide range of electrical systems, including engine management, fuel delivery, diagnostic capabilities, and even indicator lights. The lack of OBDII port function, combined with other electrical anomalies, should raise a red flag and prompt investigation into this ground issue.
Locating the original ground bolt hole from the engine compartment to understand the drilling area.
Performing the TSB Ground Fix: A Step-by-Step Guide
The good news is that implementing the TSB fix is a reasonably straightforward process for a DIY mechanic. While the original TSB called for a specific harness that is no longer available, the repair can be effectively performed by modifying the existing wiring. Here’s a step-by-step guide based on the original article’s experience and the TSB document:
Safety First:
- Disconnect Power: Before starting any work, disconnect both the chassis and coach batteries. If your motorhome is plugged into shore power, unplug it as well. This ensures there is no electrical current flowing while you are working with the wiring harnesses.
Accessing the PCM:
- Locate the PCM: On the 1999 F53 chassis, the PCM is typically located inside the driver’s compartment, positioned above the floor and in front of the brake pedal. Access can be tight. If your motorhome has a driver’s side door, use it for easier access. Otherwise, you may need to maneuver into position or consider removing the driver’s seat to gain better workspace.
Wiring Modification:
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Prepare the Wires: Carefully open the PCM wire harness to expose the wires. Identify the seven black wires with white stripes as indicated in TSB # 02-11-3. These are the ground wires that need to be addressed. Trace these wires back into the harness bundle, about 4 inches from the PCM connector, and cut them.
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Create a New Splice: The original harness likely has these seven ground wires joined in a common splice. Discard this old splice. Create a new splice by soldering the seven black/white wires together with a new ground wire. The author of the original article used a 1-foot piece of #12 stranded green wire for this purpose.
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Prepare the New Ground Wire: On the free end of your new ground wire, crimp and solder a 1/4-inch round lug terminal. This terminal will connect to the new ground point.
Creating a New Ground Point:
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Locate Existing Ground Bolt: Find the original ground bolt on the firewall in the driver’s compartment. From the engine compartment side, observe the location of this bolt to understand where it comes through the firewall.
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Drill a New Ground Hole: Crucially, do NOT reuse the existing ground hole for the modified ground wires. The TSB specifies drilling a new hole. Carefully choose a location for the new hole on the firewall, slightly below and inboard of the existing ground hole (as viewed from the driver’s compartment). Ensure that you are drilling into bare metal and avoid hitting any wires or components behind the firewall.
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Prepare Grounding Surfaces: Clean the paint around both the new hole and the original ground hole to ensure a good metal-to-metal contact for grounding. A Dremel tool or sandpaper can be used to remove paint and expose bare metal.
Reassembly and Final Connections:
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Install New Ground Wires: From the engine compartment side, insert a 1/4×20 bolt into the newly drilled hole. From the driver’s side, attach the two original ground wires (that were initially on the old ground bolt) to this bolt and secure them with a nut.
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Connect New TSB Ground Wire: Attach the lug terminal of your new green TSB ground wire to the original ground bolt hole. Secure it tightly with the original bolt.
The completed TSB modification, showing the new ground wire and connections.
Testing and Verification:
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Reconnect Power: Reconnect the chassis and coach batteries.
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Test Drive and OBDII Scan: Start your motorhome and take it for a test drive to check if the shifting issues have been resolved. Use your OBDII reader to verify that it is now functioning correctly and that any error codes related to the transmission or engine management have cleared.
Conclusion: A Simple Fix for Potentially Major Headaches
If you are experiencing shifting problems or OBDII reader issues with your 1999 Ford F53 chassis motorhome, don’t immediately assume the worst. A faulty ground connection, as addressed by Ford TSB
