Chrysler Engine Performance - Position Sensor Relationship Faults:
Real Faults – Mechanical Timing Issues
Sensor relationship testing with a Lab Scope, or even just the Scan Tool Sync PID, is a great way to find actual mechanical timing faults. There are 2 categories of mechanical timing faults to consider, though they both result in timing component replacement:
Changing/Erratic Relationships (watch for an erratic Sync PID):
o Loose timing chain or belt
o Faulty tensioner and/or guides
Fixed but Incorrect Relationship (watch for an incorrect Sync PID):
o Slipped or stretched timing chain or belt
o Bent or sheared timing gear pin or key
o Improperly installed or synchronized CMP sensor
You need no extra information to find loose timing components because the signal relationships are a dead-giveaway. For improper CMP to CKP relationships however, you need to know what ‘normal’ is. Examples of normal CMP and CKP signal relationships are included in this section for comparison, and many more can be found in the waveform library at www.iatn.net.
Jumped timing components often set a P0016 or P1391 for CMP/CKP relationship, but just as often there are other less helpful codes instead. These include:
- P0172/P0175: These Fuel Trim (too rich) codes set because bad cam timing results in low engine vacuum, which is seen by the PCM as a load, and it adds to much fuel.
- P0340/P0344: CMP sensor or circuit fault/erratic CMP signal.
- IAC & ETC Codes: These codes set when the idle control system can’t set the proper idle speed. This is usually due to low engine power and mixture faults due to low engine vacuum (caused by jumped timing).
- Primary & Secondary Codes: These codes set because…well, we don’t know why they set. Whatever the reason, mechanical timing issues often cause the wrong codes to set. This seems to be a bigger problem on 4.7L applications using a JTEC PCM.
Timing faults might also result in drivability symptoms with no codes at all. Possible symptoms may include a no start, hard start, or any combination of other drivability symptoms.
Applications: Timing faults happen on all engines, but are most common on the following engines (in order of frequency): 2.7L, 2.4L, 4.7L, 3.5L & 3.0L. Again, other engines can have this problem, but these are the engines where cam timing is a known and common issue.
The 2.7L V6 engine has the most mechanical timing issues (especially 2000-2002, but it occurs on later models using this engine as well). If you are diagnosing a 2.7L with a no start, hard start and/or a P0016, observe the CMP signal on the Lab Scope. If it looks good, disconnect the CMP sensor and see if the engine starts. If it starts after an extended crank, the root cause is almost always one or more of the timing components (most of the time the chain stretches and jumps 1 or 2 teeth). The timing may be far enough off that it still won’t start, so this test isn’t 100% accurate. Still, it’s a good test and takes very little effort. Many 2.7L timing faults are really caused by the water pump, so be sure to replace the water pump any time you’re in the area.
Some engines have timing mark alignment issues after the cylinder head has been machined. So if you can’t align the timing marks and you have had the engine apart (or suspect someone else has), check for the availability of a shim kit. This is a common fix for 2.4L DOHC engines.
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