87 BII will not kick into EEC test mode

[virginiakid]

After I pulled the codes the other day, the B2 didn't want to start up without me pressing on the accelerator. AFter I got it started again, I killed it, and tried pulling the codes again to see if anything had changed. And the truck will not kick into to test mode. I know my code reader is working because I checked it on another car. I've checked the fuse and I've looked over the wires in the EEC connector. All seems okay.

Would this be related to the ECU (computer). I thought about pulling the ECU out of another B2 I have and switching and then seeing if it will go into test mode. I'm gonna try that today. If anyone has had this happen or has advice I'd appreciate it.

By the way, after pulling the codes the first time I got 31 and 51, both have to do w the coolant temp sensor. I replaced that ($15) and there's a noticeable improvement upon immediate starting. I have no idea why or even what that sensor does.

[dgl6y6]

when your engine is cold, the computer ignores input from the o2 sensor (which isnt accurate untill it heats up anyway) and just uses a preset air/fuel mixture (which is a little rich) this helps with starting especially in cold weather. this mode is called "open loop" after the engine warms up it goes to closed loop, this is when it measures the leftover oxygen in the exhaust and adjusts the mixture accordingly. also under heavy throttle, that is more than 1/3 or so, it will kick back into open loop again. my guess is that the faulty coolant temp sensor was giving bad info to the computer making it think the engine was warm. since it was cold, the o2 sensor was reading that you were running too rich and the computer was cutting the fuel down to nothing. stepping on the gas made it start because you were forcing it into open loop which it should have been anyway.

how does it run now with the new temp sensor?
do you still have to step on the gas to start it?