Shop Line - Engine Builder Magazine

Shop Line

Q: Are the cracked exhaust seats in the Cummins 5.9L diesel engine found in the Ram pickup a cause for concern?


A: The AERA Technical Committee says cracked exhaust seats on 1998-2006 Cummins/Chrysler 5.9L diesel engines have been reported by other AERA members as well. The 24 valve engines with four valves per cylinder have been the source of the complaints.

The cracked exhaust seats on the above mentioned engines have been noticed during routine engine service. In some instances the eng-ines were not disassembled as an apparent valve sealing problem.

Most of these cracks have been described as “hairline” but others are easily visible to the naked eye. Despite their presence, though, none of the heads leaked in any of the reported instances where cracks were observed and pressure testing was done.


To repair the cracked seat inserts, aftermarket replacement seats are now available in standard or .010″ oversize. Refer to the chart (Figure 1) for insert information. While the inserts for both intake and exhaust locations are dimensionally identical, the material makeup, is unique to each location.

AERA is unaware of an oversize seat available from anyone other than the aftermarket source located in Nashville, TN.

Q: What’s the relationship between Ford 4.0L “Check Engine” lights and new valve springs?

A: Some 1997-2002 Ford vehicles equipped with the 4.0L SOHC VIN E & K engines may display a check engine light “ON” with diagnostic trouble codes (DTC) P0300 (Random Misfire) or P0301.

The DTC will set when the engine is operated at high rpms (4,800 rpm and higher). The misfire code results due to system interaction of higher than expected transient exhaust system backpressure (under heavy acceleration) coupled with valve spring resonance points experienced at these engine speeds. This interaction may cause the exhaust valve to hang open at engine speeds of 4,800 rpm and higher.

Revised valve springs should eliminate the stored P0300 and P0301 codes on some vehicles.

After verifying that the DTC sets only at 4,800 rpm or higher, remove the old intake and exhaust valve springs (p/n F77Z-6513-M) and replace them with new service intake and exhaust valve springs (p/n 2L2Z-6513-AA).

Note: All twelve valve springs (six intake and six exhaust) must be replaced in order to maintain and ensure the proper valvetrain dynamics.

Some machine shops have elected to replace all springs with the updated version any time the heads are worked on.

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