Maybe go for a drive with the pressure regulator disabled, see if the problem goes away.
P.S. I drove my 96 around without problems for several weeks with the vacuum disconnected unknowingly after some other maintenance work.

 

Update: Took it for a drive around town again and it started acting up on cue at 134f intake temp, 194f coolant temp. About 30 minutes of running. This time I had the fuel pressure regulator vacuum line disconnected (and capped at the plenum, so no vacuum leak). Same old **** at this point. Sputtering, no power only when giving it throttle. I also made note of black smoke coming from the exhaust, so I’m positive now it’s not fuel starvation.

Something is either stopping the spark or the intake of air. I’m going to go back to investigating the Cam Position Sensor & wires, as well as the MAF wire harness for heat damage. That’s all I got… anyone else have ideas on what can prevent spark or airflow only when engine bay temps are high? Still doesn’t affect idle.

 

Fuel temp sensor & coolant temp sensor can cause it to act funny once warmed up. Fuel temp sensor on the rail will make it think fuel is boiling and cause a no start when engine is warm. Coolant temp sensor could be thinking engine is cold and then making it run rich.

 

Thanks for revisiting this thread, Best4x4.
I don’t have any problems re-starting when hot, and my coolant temp sensor seems pretty accurate, reports ambient temp when starting cold and gives a believable hot temp when running. Could the coolant temp sensor be misbehaving despite the indicated temperature on the UG?

 

you did say 'I also made note of black smoke coming from the exhaust, so I’m positive now it’s not fuel starvation.'

 

You have 2 coolant temp sensors. One for the guage & one for ECU/fuel management.

 

I might have misunderstood, reboot. Should I not assume this? I was worried the fuel pump was cutting out causing stalling when the throttle was applied, but since there’s unburnt fuel coming out, my assumption was that there’s plenty of fuel. Also, could too much fuel cause it to choke up like this? I was thinking of ruling out the pump or pressure regulator since tampering with it had no effect on the poor running condition…

 

Oh, thank you. That’s news to me (learning a lot this week)! How would you go about eliminating those sensors from the problem? I’m hesitant to just start throwing parts at it (although most of these small sensors are pretty affordable), and I’ve read that replacing certain sensors will require re-calibrating the ECU.

 

Resetting adaptions is always a good idea whenever you do a tune up or replace hardware. If you have an Android and a generic Bluetooth OBD2 reader you can download The GEMS Reader App for free and do a reset. Or use a scantool like a T4, Hawkeye, Lynx, or Nanocom to do it.

Coolant temp sensors are cheap and it could also just be the plug/connection. If a vehicle is getting to much fuel it will puff black smoke, smell rich, and not run worth a darn.

If it never throws a code I'd be inspecting wiring, VSS (Speedo will usually bounce if the VSS is acting up), CPS, fuel temp sensor, MAF, coolant temp sensor (for ECU), and possibly the TPS. Last thing = check ECU for corrosion on the PCB's.

 

My 96 had a loose ground connection on my ECT sensor. It showed up on the scanner, the temp would start to bounce around on rough roads. Fixed it by cleaning and soldering the splice, which was common to the Fuel Temp, MAF, and TPS sensor circuits by the way.

I would be surprised if a loose connection is your problem, because yours is so repeatable by temperature and time. Seems a loose wire would be more random. The ECT sensor is super inexpensive. TPS can cost quite a bit more. I have been glad to have the GEMs App, as suggested above (be sure to give it a try).