Nissan Repair: 99 Pathfinder shuts off while driving, fuel pressure gauge, crank angle sensor

Question
QUESTION: Our 99 Pathfinder's (70,000 mi.) engine shuts off while driving. It eventually restarts, sometimes immediately, sometimes after several minutes of cranking.  We've replaced the distributor and the entire fuel system but the problem remains.  We've also replaced the crank sensor and master airflow sensor.  We are told that no codes come up showing that there are any problems.  Even after all of this the problem continues.  The next suggestion is to replace the computer but we're not too sure it will help.  Can you help?

ANSWER: Dave,

Get a fuel pressure gauge and hook it up to the fuel rail.  Now, route it under the hood and tape it low on the windshield so you can monitor the fuel pressure.  When the vehicle dies see if the fuel pressure drops off.  If so, it is fuel related. It could be the fuel pressure relay, you did say you replaced the fuel system, so I assume that means the pump was replaced.  Most shops miss replacement of the fuel pressure relay.  Also, there is a oil pressure sensor that feeds information to the ECM to let it know the engine is running.  If no pressure is indicated, by a bad sensor, the ECM will unground the fuel pump relay and you will have no pressure.  Check it out and if it not fuel related email me back and we will look into this further.

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

QUESTION: You're correct they did replace the fuel pump (fuel assembly).  We think the fuel pressure relay is good finding 45 psi at the rail.
Scanner says oil pressure sensor is active (again no codes) and oil light goes out as soon as we start to crank.
We checked and cleaned the grounds at ECM.

We've seen two conditions when it won't start.  Either  we see no noid light or we have 25ms pulse at the injectors.  After sitting 5-10 minutes it runs fine with 1.9ms.


Answer
Dave,

The cam position sensor and crank angle sensor should both be checked to see if they are generating the correct signals.  My supposition is yes and it should turn out to be the fuel injector relays.  The ECM pulls power to ground the injectors and if it is not a relay check the ECM to make sure the internal circuits are working properly.  What you need is a breakout box to do the job but you can do it with a volt/ohm meter or a test light to see if it is grounding the injectors properly.