The 6.7 Powerstroke diesel engine, known for its power and reliability, relies on glow plugs for cold starts, especially in colder climates. While glow plugs are robust components, issues can arise, leading to diagnostic trouble codes (DTCs) and engine performance concerns. It’s crucial for owners and technicians to understand the function of these glow plugs, common problems, and how to accurately diagnose related issues. This article delves into the specifics of 6.7 Powerstroke Glow Plugs, addressing common misconceptions and providing insights based on official technical service bulletins (TSBs).
Understanding 6.7 Powerstroke Glow Plugs
Glow plugs are essential pre-heating devices in diesel engines. In a 6.7 Powerstroke, they heat the combustion chamber air to aid in starting, particularly when the engine is cold. This pre-heating is critical for efficient combustion during startup, reducing white smoke and ensuring smooth engine operation. Each cylinder in the 6.7 Powerstroke engine has its own glow plug, and the engine control module (ECM) monitors their performance and electrical circuits.
Common Glow Plug Issues and Diagnostic Trouble Codes
When a glow plug or its associated circuit malfunctions, the ECM typically sets a DTC. Common DTCs related to 6.7 Powerstroke glow plugs include:
- P0671 – P0678: These codes specifically indicate a fault in the glow plug circuit for cylinders 1 through 8 respectively. For example, P0671 refers to cylinder 1 glow plug circuit malfunction, P0672 to cylinder 2, and so on.
These codes can be triggered by various issues, such as:
- Failed Glow Plug: The glow plug itself might be burnt out, internally shorted, or otherwise damaged, preventing it from heating correctly.
- Wiring or Connector Problems: Damaged wiring, corroded connectors, or loose connections in the glow plug circuit can disrupt the electrical signal and trigger DTCs.
- Glow Plug Control Module (GPCM) Issues: Although less common, problems within the GPCM, which controls the glow plugs, can also cause fault codes.
It’s important to note that while glow plug DTCs are often straightforward indicators of a glow plug circuit issue, they can sometimes be secondary codes, pointing to a more significant underlying engine problem.
The Misconception: Are Glow Plugs the Root Cause of Major Engine Failure?
There’s a common misconception, particularly in older online discussions, that glow plug failure can cause catastrophic engine damage in 6.7 Powerstroke engines. However, official Ford documentation and Technical Service Bulletins clarify that glow plug issues are typically a symptom or indicator of other engine problems, not the primary cause of major failures like broken exhaust valves.
Early Technical Service Bulletins, like TSB 12-11-11 and subsequent revisions such as TSB 14-0127, address engine issues in 2011 Ford F-Super Duty vehicles equipped with the 6.7L diesel engine built on or before March 29, 2011. These TSBs describe a “runs rough or no crank” condition and explicitly mention that DTCs P0671-P0678 (glow plug circuit codes) may be present due to a broken exhaust valve.
Alt text: A detailed view of components within a 6.7 Powerstroke engine, highlighting the cylinder head and valve train area, relevant to exhaust valve and glow plug discussion.
These TSBs emphasize that the primary issue in these early engines was often a broken exhaust valve, and the glow plug DTCs were a secondary effect. The diagnostic procedure in TSB 12-11-11 instructs technicians to inspect the glow plug associated with the DTC after confirming the “runs rough, no crank” condition. If the glow plug is damaged, the recommended action was not just glow plug replacement, but engine long block replacement. This clearly indicates that the glow plug damage was a consequence of a more serious engine problem, such as valve failure, rather than the cause.
The progression of TSB revisions further reinforces this understanding. TSB 12-11-11 initially listed part number 6505 (exhaust valve) as the causal part, later revised to part number 6006 (engine long block) in subsequent TSBs like 14-0127. This evolution indicates that Ford’s diagnosis shifted from focusing on individual exhaust valve replacement to recognizing the broader engine damage associated with the issue, necessitating long block replacement.
Diagnosing 6.7 Powerstroke Glow Plug Issues
When diagnosing 6.7 Powerstroke glow plug DTCs, a systematic approach is essential:
- Verify the DTC: Use a reliable scan tool to confirm the presence of glow plug DTCs (P0671-P0678).
- Inspect Glow Plugs: Access and visually inspect the glow plugs for damage. Check for signs of burning, cracking, or physical deformation.
- Test Glow Plug Resistance: Use a multimeter to measure the resistance of each glow plug. Compare the readings to the manufacturer’s specifications. Significantly high or low resistance indicates a faulty glow plug.
- Check Wiring and Connectors: Thoroughly examine the wiring harness and connectors for each glow plug circuit. Look for signs of damage, corrosion, or loose connections.
- Circuit Testing: Use a test light or multimeter to check for voltage and ground at the glow plug connectors, ensuring proper power supply and circuit continuity.
- Consider Other Engine Symptoms: Pay attention to other engine symptoms, such as rough starting, misfires, or unusual noises. If these are present along with glow plug DTCs, it might indicate a more serious underlying engine issue, as highlighted in the TSBs.
Maintaining 6.7 Powerstroke Glow Plugs
While glow plugs are designed to last, preventative maintenance can help ensure their longevity and reliable engine starting:
- Regular Inspections: During routine maintenance, visually inspect glow plug wiring and connectors for any signs of damage or corrosion.
- Proper Diagnostics: Address glow plug DTCs promptly and accurately. Don’t automatically assume glow plug replacement is the only solution, especially if other engine symptoms are present.
- Quality Replacement Parts: When replacing glow plugs, use high-quality parts that meet or exceed OEM specifications to ensure optimal performance and durability.
Conclusion
In summary, while DTCs related to 6.7 Powerstroke glow plugs (P0671-P0678) indicate a problem in the glow plug circuit, it’s crucial to understand that these issues are not necessarily the root cause of major engine failures. Technical Service Bulletins highlight that in early 6.7 Powerstroke engines, glow plug DTCs could be a secondary indicator of exhaust valve problems. Accurate diagnosis, considering both glow plug circuit testing and overall engine health, is essential for effective repairs. By understanding the nuances of 6.7 Powerstroke glow plug systems and referencing official documentation, technicians and owners can ensure proper diagnosis and maintain the reliable operation of these powerful diesel engines. If you are experiencing glow plug related DTCs or engine performance issues, consult a qualified mechanic for a thorough inspection and diagnosis.
