WARNING LONG POST:

After looking for over 6 months I finally found the truck I was looking for- a 1993 W150 short bed with a 5.9 Magnum engine. I found it in Northern California, went up there and drove it home to Los Angeles. No issues except bad gas milage. I replaced the battery terminals and put a ne Optima red battery in it, as well as oil change, new plugs, cap and rotor, air filter. It ran great for and I drove it daily, for about 4000 miles.
On a 100º day, I was driving it with the AC blasting and it was died at idle in an intersection. I pushed it into a parking lot as it would crank but not start. All the gauges worked and lights, but no spark. I left it there and went home to read the factory manual I bought when I got the truck. It sounded to me like the ASD relay, so I went and bought one and put it in. The truck started, and seemed fine. I drove it for another day when I was on the freeway blasting the AC again and it cut out at about 60 mph...pulled over and it cranked but wouldn't start.
While waiting for AAA on the phone, after 15 minutes on hold I tried to start it again, and it fired up. So I drove it off the freeway and went home. Figuring it was an issue with the air conditioning, I drove it a few more days with the AC off.
Then on the way home at night it died again, I pulled over and left it on the street overnight. The next day I went to get it and it started up, so I drove it home. I tried to see if there were any codes using the key method, and it had codes 11, 12, and 55. Code 11 is no signal at distributor so I replaced the camshaft sensor in the distributor. It fired up an ran great again.
I though it was fixed. Then I got to work and it died as soon as I parked it, would crank over but not start. I figured it's the crankshaft sensor which I did not want to change due to the lack of space in this one year only engine/frame combination.
I got a crankshaft sensor from Napa, (I think Standard made it), and changed it out. The truck fired up immediately, I reset the code, and now only was getting code 12 and 55.
It was running great and I thought I fixed it, went home, turned it off, and an hour later it wouldn't start. Cranks over, no start.
I put a fuel pressure gauge on the fuel rail port- 32psi as soon as you turn the key. I was 32psi 45 minutes later too. Not the fuel pump.
I was reading about the capacitors on the ECU circuit board going bad, so I ordered capacitors and replaced them on the board. I used to work with electronics so I'm pretty confident I did it right.
Put the ECU in, cranks, won't start.
Ordered a compatible ECU from ebay- mine is a CA only model, I got the 50 state model correct ecu rebuilt with warranty.
cranks over, won't start.
I tested the sensors, they are getting 5v, I am not getting power at the coil.
I checked the ASD relay, and it is getting power, and when cranked gets power to pin 87 for only a few seconds.
To say this is challenging is to put it lightly. I have looked at al the fusible links, no blown fuses, even looked at all the wiring behind the gauges...the wiring is as nice as can be for a 30 year old truck. There is zero rust anywhere on it and I don't think it has ever seen any bad weather or salt.

Basically what I am trying to find out here is if the crank sensor from Napa only worked for 6 miles, is that even possible?
Also would it throw a code or just not work? The pigtail on that thing is so short the only way I can test that sensor it is by removal.
I have read on this forum that the official Mopar sensor is what I should use, But I am at a loss.
I would probably drop it off at a shop if I thought they would do anything different than what I am doing.

Anyone who has some suggestions for me, please let me know. This truck is awesome but this problem is not.
Thanks! Dan

 

First and foremost, how many miles on the engine and where was the truck sold originally? A federal emissions part may not be compatible with California equipment. I had a Ford Powerstroke that was sold in California and it had a Federal chip in the computer. It finally decided to quit running one day. The chip was removed and everything worked again.

 

Originally sold in Calfornia, 200k on engine, didn't burn oil or do anything unusual when I drove it, the ecu I took out was a "California emissions" ecu but the 50 state ecu I replaced it with was for the same application- 5.9 magnum, light duty, 4wd, automatic w/overdrive. Don't think that is a problem, and I did as much research as I could on it. It is a SBEC with one oxygen sensor, the later ones had 2.

 

does the fuel pressure get any higher than 32 if you keep cranking? anything less than 40 can cause poor running if it runs at all. it is possible the crank position sensor is bad. i tried an aftermarket one and i am pretty sure it was a tiny bit shorter.

 

Test the ignition coil, There are resistance readings in the factory manual. If they are not within spec replace the coil.

 

When it dies, do you get power to the coil while cranking? ASD relay will supply power for about 3 seconds at initial key-on, after that, it has to see the engine turning to turn it back on. If it doesn't, chances are good that's a bad crank sensor. (or the wiring for it.) These trucks are notorious for not liking aftermarket sensors in critical locations, and the crank sensor is right there at the top of the list.

 

Not sure about the fuel but it says in the manual it should be 33# with key on, and 35-45# running. I hav 30 gallons in the tank so I hope I don't have to change the pump! I'll test the coil today, and also track down a Mopar crank sensor. Thanks for the advice...I'll post anything that happens one way or another.

 

Fuel pumps only fail RIGHT after you fill the tank.

 

Update-
I found a Mopar crank sensor at a dealership about 20 miles away. Drove down and picked it up. $170...a little more than the $60 NAPA one I just put in a few weeks ago. Since this truck/engine is one year only (square body with 5.9 magnum) there really isn't much room to get it in. It took about 15 min to get the old one out, and about an hour and 1/2 to get the new one in.
The truck fired up immediately when I hooked everything back up with the new sensor.
I have read on here that these trucks like the Mopar sensors...I can tell you it's true.
Here are some observations on the sensors. The three sensors top to bottom are: the one from NAPA made by Standard, the one that I took out that intermittently failed, and the factory Mopar part
5602 6701.


The Mopar sensor would pick up a wrench with the magnetism, the other two would not. WAY stronger magnet on the factory pickup, as well as exposed metal on the end of the sensor.


The wires were molded into the plastic on the Mopar sensor, and the other two had epoxy or resin where the wires went into the sensor.


Mopar crankshaft sensor


NAPA (Standard) crankshaft sensor


Other aftermarket sensor

 

Anyway after idling for 15 min, driving it around, washing it at the car wash, it died once again. I couldn't believe it. I still had the ECU from ebay in there, and it started up again after a few minutes and ran fine. I drove it around for a while more and it died again. Confused, I decided to change the ECU back to the one that came in the truck that I replaced the capacitors in. It is a one year only 1993 California Emissions ECU ( 5602 6868 ) but I the one from ebay is a 50 state compatible ECU 1993 ( 5602 6866 ).



Before capacitor replacement

After
Anyway with the old ECU the truck runs great again, and hasn't died so far. Anyway for anyone who has this problem on a 1992 or 1993, buy a factory crank sensor as it really was a challenge to change it- twice. Thanks for the suggestions, hopefully this crank sensor drama is over.