V10 1996 Laredo bucks and dies randomly

[Spamcan]

(232K miles on odo) So, I was cruising uphill at 50 mph Wednesday, unloaded, and the truck started bucking (lights out and engine dying) so I began to pull over to the side. But it picked up again and I proceeded to the home another 2 mi. This Friday, I helped my daughter move to her new home (~40 mile round trip) with no problems. This a.m., I headed out to the wand car wash to clean off the front differential prior to changing it's oil and the truck died again... no re-start with oil light lit after ignigion turned on to attempt a re-start. 20 minutes later, I shorted out th oil pressure harness plug connector (simulating oil pressure ok and bypassing the sensor) It started up again and died after about 5 min of idling. So the oil pressure sensor must be good along with it's wiring to wherever. Oil quantity checks OK w/dipstick. I had just changed the oil and new oil filter installed,too. Comments? Ideas?

 

[Nick_rp]

To be fair, the oil light always comes on with the key on. Start at the basics, fuel, spark, air, timing, compression.

Spark is a quick one to knock out but my moneys on fuel. Filter, pick up tube screen etc

 

[Spamcan]

UPDATE: Placed a gage on the fuel rail tap... abt 50 psi running, and super-low leakdown after switch off. Re-started and after abt 10 minutes engine quit. Fuel pressure held steady at abt 48 psi.. Couldn't restart for abt 30 min. (Found blown 40A fuse labeled 40A Trailer. Probably my fault) No other fuses blown.
Oh, and still no CHECK ENGINE light.

 

[Phillyrube]

In tank fuel pump? Had that problem with a V10 3500 I had.

 

[Spamcan]

UPDATE: OK... had to know what the ASD (Automatic Shut Down) relay was doing... built a short break-out harness to insert between the vehicle's ASD relay socket and relay.. Sure enough, after about 5 min. of running, the PCM cut the ground for the relay and therefore ignition, and fuel were immediatly cut off. To build this break-out harness, I used 10 ea 4" lengths of 16 gage soldered to a 1" x 3" printed circuit to form five conductor paths. At one end of a group of five, I crimped male spade-style connectors to plug into the relay's socket on the Power Distribution Center and on the other set of five, I crimped female spade-style connectors to plug the relay into. (TAKE EXTREME CARE IF YOU DO THIS, PAYING ATTENTION TO THE PROPER WIRING HOOK-UP). With this break-out harness, I was able to monitor the voltage state at the relay's pin 85 (or any other relay pins, for that matter) from the Powertrain Control Module, pin C3. Pin 85 is grounded (controlled) by the PCM during normal (running) operation. When the PCM senses a significant problem, it disconnects (isolates) that pin, C3, from ground. So the relay reverts to the power off state and one will read battery voltage on pin 85 at the relay. It went like this... After starting, I saw a tiny voltage on pin 85 showing that the relay was grounded by the PCM. Sure enough, after about 5 minutes running, the pin 85 voltage rose to battery voltage and the engine, of course, died. Pin 85 voltage would not go low again when attempting a re-start. As usual, I had to wait a long time before I could re-start the truck (e.g. the relay's pin 85 was grounded by C3 of the PCM during start and running.

 

[Spamcan]

So, I received my two crankshaft sensors (one for spare and just in case the first didn't check out ) from China (PN "PC161) from Wenzhou Longfar, a Mr. Jack Lin @ Longfarauto.en.made-in-china.com) and verified their operation with my Sensor Tester Plus that they were operational... real easy except for getting the aligator clips of the tester onto the pins without shorting them together. Had to make up some adapter wires. Construction looked identical to the old one, especially length, depth from mounting tab, and diameters. Greased it up and installed it.... Engine started right up and so far so good after 20 mi. While I was at it, I also had ordered a spare Crankshaft Pos Sensor from Auto Zone. Received it and tested it, too, with the STP.