Nissan Repair: low compression/car wont start, 2005 nissan pathfinder, crankshaft sensor

Question
QUESTION: Have 2005 Nissan Pathfinder with 160k miles.  Car started occasionally cutting off while running but would then start back up.  No check engine light ever came on.  Car finally cut out while driving and would not turn back on.  Towed to shop (has been there almost two weeks) and they found no computer codes to id problem.  Car has both spark and fuel pressure.  Low compression has been id as the problem (around 50psi).  Mechanic has torn down engine and ruled out all the usual; timing, engine block, valves, pistons, seals, head etc.  Mechanic has no clue and has now called nissan for help.  He thought it might be the crankshaft sensor going in and out but that did not work. I have done some research on my own and come up with possibly the EVAP canister vent control valve or a bad IPDM???  Would these items even affect the compression (i'm not sure)?  I am uncertain what to do at this point? Any help would be greatly appreciated.  Thanks!

ANSWER: JR,

Compression is a mechanical issue and not electronic.  I would look at headgaskets to see if they were blown if he cannot diagnose the valves or rings as defective.  But, with all cylinders at 50 PSI would lead me to the timing being off.  The EVAP system will throw a code and the vehicle will still run.  This is for smog and does not interact with the proper running of the engine.  I would have the mechanic look at the base timing of the vehicle to see it is jumped timing and he was just not aware of it.  Reassemble with new timing components and verify compression.  If he has already torn the engine down to parts you might look at a used engine as a cheaper alternative to a rebuild of this one.  ebay or other on-line sources for engines are pretty reasonable.

---------- FOLLOW-UP ----------

QUESTION: Hey Von,

He has deduced it as a mechanical issue and related to the compression.  He has also checked heads, timing, valves, rings, etc.  This is why it so frustrating that it won't start?  The mechanic even said it has everything to start but can't understand why the compression is so low?  The engine is together and he is still working to find out why the compression is low and why it won't start.  He tried a new crankshaft sensor that might have been working only some of the time, but that to was not the answer to the problem.  He has even been in contact with the Nissan dealership and they to are at a loss as to why it won't start?  I've seen a couple of other people online with this very same problem.  One lady had her car in the shop for 5 weeks with no fix and ended up selling the car and taking the loss.  I'm at 2 weeks at this point and may have to resort to the same.  Any other ideas you may have would be greatly appreciated.  Thanks for your help!!!

Answer
JR,

With 50 pounds per square inch on each cylinder leads me to think it is a mechanical timing issue like the timing has jumped.  No way I would get rid of the vehicle.  The the mechanic is not getting it I would either have it towed to the dealer or have a used motor installed and be done with it.  This is not an electrical issue with the engine like the computer not firing right.  Mechanical compression that is the same on all cylinders means there is something wrong with the timing.  Think of the inner workings of a clock.  If a gear were offf the clock would not show the right time.  If an engine is off, like the timing chain or belt has jumped teeth, the engine will not develop enough compression to actually run.  125 PSI to 140 PSI would allow it to run.  50 PSI will not work...