Hey there,

I'm here because I'd read a ton of really valuable advice and insights from these forums but I'm absolutely stumped despite having about 150 tabs open at the same time and six pages of notes I've been keeping. I'm warning this is a tricky one, but hopefully there's a true Ranger Guru who can help me troubleshoot and fix.

The vehicle:

1999 Ford Ranger XLT 4.0L manual 4x4. 134k miles.

The issue:
I bought a ranger about two weeks ago. Last week it had trouble starting. Then a few days later it died mid-drive and I had to try a few times to start it up again, only to get it far enough to get out of an intersection before it died again. Since then it has started intermittently, seemingly at random. Day before yesterday it wouldn't start. Yesterday it started fine. Today, no go.

Symptoms:

• Engine turns over, then cycles high rpm low rpm once or twice and then dies. Subsequent attempts turn over but die more quickly.
• THEFT light blinking after turning over shows code 16.
• Check gauges, battery, THEFT, and check engine lights come on.
• When turning off and then turning to ON, all of these lights come on again, but the check engine light is flickering quickly. This is in sync with a ticking sound within/at the fuel pump relay in the power distribution box. There is another synced ticking at the back of the engine near the firewall, somewhere mid or low in the engine that I can't see.
• I have forscan, and it is throwing the following codes:
  • PATS U1262 - SCP Data Link Fault. Something happening with module-to-module communication. My research shows it's likely related to communication between PATS and PCM.
  • GEM P0500 - VSS sensor circuit fault. Forscan says may be caused by bad VSS, suspect PCM, worn or damaged vss drive gear on transmission output shaft.
  • (Showed up once, not every time I check codes)
    • B1845 - immobilizer related (module: anti theft)
    • B1485 - brake pedal input circuit short to battery (module: anti theft)
  • A couple times the PCM test wouldn't run, but generally it now comes back with the generic P1000 (can't do test because I haven't driven it long enough after reset)

UNRELATED, (I think) but worth including because I'm new to this and maybe it explains something I don't understand:

• Mechanic who inspected it before I bought said there was a leak in the valve cover and a 'severe' front crank seal leak
  • I've been keeping an eye on oil leakage and I haven't seen a lot (1-2 dime sized drips in the driveway the next day after driving for 30-60 min) but the bottom half of the engine is definitely coated in old oil
• Previous owner told me it threw a code for a crank sensor not too long ago which he replaced
• When I first scanned with forscan I got historic codes that were pretty much all related to sensors being potentially bad

What I've looked at:

• Looked over everything at a glance - no obvious disconnected hoses or wires or sensors
• Checked battery multiple times to ensure good charge, which it was at 12v regularly. Now it's sitting at 10v because of all my tinkering and not being able to run it. I'm keeping it charged by jumping it off of my other car.
• Checked relays and all fuses. No blown fuses, relays all work (swapped ones I know work with the ticking fuel pump, ticking happens regardless of relay used)
• Checked air filter and intake for a blockage. Air filter looks pretty new
• MAF sensor looks fine, doesn't throw any codes
• Tried all the suggested PATS things I could find on this forum and elsewhere - leaving key in the ignition for 15 minutes and trying again, locking and unlocking doors
• Ensured battery was charged to at least 12.4v before starting
• Disconnected battery for 15 minutes to reset a couple of times as I was testing other things
• Pulled out the PCM connector under the hood and checked the connection, pins and wires. Everything looked fine
• Pulled out the passenger airbag to access the PATS module and did the same checks on the PATS module - wires, pins, etc. Everything looked fine
• Opened up the clamshell case around the steering column to look for loose wires or connections with the PATS key antenna thing. No visible issues
• All of the wiring visible to me looked fine, no evidence of frayed or exposed wires, animal chewing, etc.
• Ran PATS on demand test on Forscan, which came back clean no codes
• Ran PCM on demand test of Forscan, which said "it seems this test isn't supported" and wouldn't run
• Ran the other module tests, which is where the RAP immobilizer codes above came from; everything else was clean besides the GEM VSS sensor code mentioned above

Finally after checking all of that stuff I tried one more time to start it. Started, high and low rev for 5 seconds and then died. Tried a couple more times and same deal, would turn over for a second and die again.

I'm a beginner here. This is the first thing I'm trying to fix and while I feel like I'm doing a decent job of learning (I didn't know what any of this stuff was two weeks ago) I'm really at a loss on where to go next. This is pretty complicated for a newbie but I'd absolutely love to figure it out without a trip to the dealer. I'm pacing around the house mumbling to myself day and night. My wife thinks I'm going crazy.

Final thoughts:
Because of the codes I keep going towards issues with the PCM, where the PATS system and maybe the VSS can't communicate properly for some reason. I say that because the PATS system diagnostic test comes back clean, and the only code is that module-to-module failure and the VSS sensor issue, which Forscan mentions could be a bad PCM. That makes me think it isn't an issue with the keyfob antenna or the PATS system itself.

I've written off a bad fuel pump or another purely mechanical issues, which was my initial thought with the ticking at the fuel pump relay and the symptoms of turning over and dying, and then dying randomly while driving. I'm not getting codes for faulty starters or pumps or anything else besides bad sensors or bad modules.

I did just read that a bad VSS sensor can disrupt the communications between other modules or sensors somehow. I haven't seen any issues related to the speedometer or odometer however. But I think tomorrow I'll crawl under and look at the VSS sensor to see if there's anything obvious there.

So here I am, begging on hands and knees for some ideas for what to check next, or how to go about trying things that might work. I'm very afraid that a mouse or something chewed a tiny bit of wire in some impossible to reach spot that's causing these issues, or even more afraid there's something systemically wrong with the truck that'll force me to a mechanic to dole out a ton of money to fix. I'm willing to try quite a lot here, I have a second car so I can take my time. But I'm somewhat at a loss as to what to try next.

Thank you in advance if anyone can help. I promise to one day return any favors to the community when a newbie like me comes along when I'm battle tested. Which based on this experience seems like it'll probably be the case within the next month...