Experiencing misfires in your B7 Audi S4 can be frustrating and concerning. This article delves into a real-world scenario of diagnosing misfire issues in a B7 Audi S4, drawing from a user’s experience and troubleshooting steps. We’ll explore the symptoms, error codes, and diagnostic procedures undertaken to identify potential causes of misfires in this performance vehicle.
Symptoms and Error Codes Pointing to Misfires
The owner of a B7 Audi S4 began noticing some performance issues characterized by a slight miss at idle which, while not severe, was present. The significant problem arose under load, specifically above 4000 RPM. At higher engine speeds, the car exhibited a drastic loss of power accompanied by a solid or flashing Check Engine Light (CEL) and noticeable misfiring. Importantly, there were no rattling or clacking noises on startup, often associated with timing chain issues in these engines.
Diagnostic trouble codes (DTCs) provided valuable clues:
- 005495 Right Engine Mount Solenoid Valve P1577 – 004 – Open Circuit: Indicates an electrical issue with the right engine mount solenoid valve.
- 000768 Random/Multiple Cylinder Misfire Detected P0300 – 001 – Intermittent: Signifies random misfires across multiple cylinders.
- 000776 Cylinder 8 P0308 – 001 – Misfire Detected – Intermittent: Points to misfires specifically in cylinder 8.
- 000774 Cylinder 6 P0306 – 001 – Misfire Detected – Intermittent: Indicates misfires specifically in cylinder 6.
- 001073 Warm Up Catalyst; Bank 2 P0431 – 001 – Efficiency Below Threshold: Suggests the catalytic converter on bank 2 is not operating at optimal efficiency.
- 005137 Secondary Air Injection System; Bank 2 P1411 – 002 – Insufficient Flow: Indicates a problem with the secondary air injection system on bank 2.
These codes, particularly the misfire codes (P0300, P0306, P0308), strongly suggest an issue related to combustion in cylinders 6 and 8, and potentially others. The catalyst and secondary air injection codes might be consequential to the misfires or indicate separate, but related, issues.
Diagnostic Steps Undertaken
To pinpoint the cause of the b7 Audi S4 misfire, the owner proceeded with a systematic diagnostic approach:
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Intake Manifold Inspection for Carbon Buildup: Carbon buildup on the intake valves is a known issue in direct injection engines like those in the B7 S4. The intake manifold was removed to inspect for excessive carbon deposits. While some dirt was present, it was not considered alarming and did not appear to be significantly worse on any particular cylinder. This made carbon buildup less likely as the primary culprit.
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Air Filter and Air Supply Check: A clogged air filter can restrict airflow and cause engine performance issues. The air filter was inspected and found to be clean, eliminating air supply obstruction as a potential cause.
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Compression Test: A compression test is crucial to assess the mechanical health of the engine’s cylinders. A dry compression test was performed after the car had been sitting. The results revealed a significant discrepancy between the left and right banks. The left bank showed low compression readings of 90-105psi across all cylinders, while the right bank exhibited healthy readings of 150-160psi.
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Valve Cover Removal and Timing Mark Inspection: Suspecting a timing issue, the valve covers were removed to inspect the camshaft timing marks. The marks at the front of the camshafts appeared to be aligned. The owner questioned if checking the crankshaft timing mark was necessary given the seemingly aligned camshaft marks and good compression on the right bank.
Potential Causes and Further Diagnosis
Based on the diagnostic steps and findings, several potential causes for the b7 Audi S4 misfire and low compression on the left bank can be considered:
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Timing Chain/Mechanical Adjuster Issue: The user suspects a malfunctioning mechanical adjuster on the left bank. If the mechanical adjuster is not working correctly, it could lead to improper valve timing at higher RPMs, causing misfires and potentially contributing to low compression. While the visible timing marks appeared aligned, an internal timing chain issue or adjuster malfunction could still be present, especially affecting one bank more than the other. A more thorough timing chain inspection, possibly requiring specialized tools, might be necessary.
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Valve Train Problems: Low compression specifically on one bank suggests a potential issue affecting the valves on that side. This could include:
- Bent Valves: If valve timing is significantly off, or if there was a past timing chain jump, valves could be bent, leading to poor sealing and low compression.
- Valve Seat Issues: Damaged or worn valve seats can also cause compression loss.
- Sticking Valves: Less likely to affect an entire bank consistently, but possible.
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Head Gasket Leak: Although less likely to cause misfires concentrated at high RPM, a head gasket leak between cylinders on the left bank or to the water jacket could contribute to low compression. However, other symptoms like coolant loss or overheating might be expected.
Next Steps for Diagnosis:
To further diagnose the b7 Audi S4 misfire, the following steps are recommended:
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Detailed Timing Chain Inspection: Verify the timing chain alignment at the crankshaft and camshafts using appropriate tools and procedures. Inspect the timing chain tensioners and guides for wear or failure.
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Leak-Down Test: Perform a leak-down test on the cylinders with low compression on the left bank. This test can help differentiate between valve issues (leaking valves), piston ring issues, and head gasket problems as the source of compression loss.
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Valve Train Examination: If the leak-down test points to valve issues, further inspection of the valve train components, potentially requiring cylinder head removal, might be necessary to check for bent valves, valve seat problems, or other valve train damage.
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Professional Diagnosis: Given the complexity of modern engines and the potential for timing-related issues in B7 Audi S4 models, seeking professional diagnosis from a qualified Audi mechanic is highly recommended. They have specialized tools and expertise to accurately diagnose and repair these types of problems.
Addressing misfires in a B7 Audi S4 requires a systematic approach to diagnosis. By carefully considering the symptoms, error codes, and performing thorough tests like compression and leak-down tests, along with timing chain inspection, the root cause of the misfire can be identified and effectively resolved, restoring the vehicle’s performance.
