A couple more things to note since you have an early GEMS ECU is to grab the alarm unit that's paired to the replacement ECU. Also you may need to have the ECU reset because the idle may go high (IACV). Both fore mentioned are common issues, I'd like you to be free of this issue (open loop) for once and all. Tom mentioned grounds, I did a little reading and found the ECU internal sensor ground is a common to all sensors, if one short circuits it effects all others. It doesn't appear that's an issue in your case hence my recomdation.

 

Sent the ECU off to be repaired several weeks ago as the physical condition of the unit appeared to be excellent. No rust, dents, ... Figured this option eliminated the matching unit issue between the ECU and security system. Plus, it would eliminated, theoretically, a recurring unknown fault in the ECUs. The repair center technician could not get my ECU to hold any reprogramming. Long story made short, ended up buying a re-manufactured unit which arrived Saturday. Plugged the unit into the truck and she fired up. Truck had no power. Push the accelerator and it would cut-out. My Ultragauge indicated no coolant or air temperature. So, I knew that wasn't correct. Decided to check the connections to the ECU and after re-seating the middle red connector the truck came back to life and seemed to be running nicely although the Close Loop indicator was still reading zeros after a short 5 minute drive around town. So, this morning, I took the truck for a long run, 50 miles +/-, through the mountains. She seemed to run fine although the Closed Loop indicator showed zeroes the entire trip. Pulled into the driveway at the house and cut the engine off and immediately tried to restart it. No luck. The engine would crank and turn-over but would not fire. So, the warm re-start issue or whatever is actually plaguing this truck still exists. Any thoughts on what to check next would be greatly appreciated.

 

Check engine light/codes present?

 

Ultraguage indicates check engine light is off and zero trouble or pending trouble codes. The ABS is disabled by prior, prior owner and it isn't throwing any codes. So, it must have been bypassed in some manner. Also, the ignition switch was replaced by the prior owner. Not sure what that has to do with the price of tea. Electrical short or bypass? It does leak fuel from the vent hose if you fill the tank completely. Could that cause a vacuum lock or similar in the fuel line or fuel rail? What perplexes me is the truck seems to run fine otherwise. It doesn't hesitate accelerating or decelerating. It doesn't cut out at stop lights. It doesn't hesitate, shudder or vibrate under heavy acceleration. Except when the warm start "the problem" occurs it starts up easily and idles around 700 RPMs.

 

Perplexed is too lenient a word....... everything obvious has been covered or would be tossing a flag through the ECM. It's good to know that your prior ECM was on tilt, at least that's one thing fixed. This is one of the those problems where it's almost impossible to diagnose without being there in person hands on (for me). You have two problems; open loop and hot no-start. I don't know if they're related or separate. Have you looked at the wiring for the crank sensor? The common issue with it is burned or bare wires, frayed wires or oil soaked bare wires. This problem almost always doesn't set the CEL and may not effect the running condition of the motor but it usually ends up effecting the starting of the motor. Besides high resistance within sensor connectors it's the only thing I have left to offer at this time. Really scan the wires going to that sensor good. Look hard.