I have a b2600i with a MIL light on, the chasis and transmission have 267k on them. I swapped the motor a few years back with a JDM that supposably had less then 50k on it so the motor itself should only have 100k tops on it. Did a cap, rotor, plugs, wires, and did the timing few months ago.

After the truck is warmed up every few RPM's at idle it will cut out like it has no fuel but then instantly picks back up. When I accelrate it will hesitate and act like it its getting shorted or flooded of fuel untill i hit 2000 RPMs then from there and up it runs perfectly fine like there is no problem. But anything below 2000 it hestitates like crazy. The check engine light is on and stays on constantly. So far i tried grounding out the green single connector that is on the passenger side that is suppose to get the MIL light to blink the code and have had no response from it what so ever. I checked it with my DMM and verifyed there is 12 volts coming from that pin. I also pulled out my ECU and gave it a visual inspection everything appeared to be fine.

 

Hey man, I know what you are going through i had the same problem with my 89 2600i, Its the ecm, they had a problem with capcitors on the board leaking and causing alot of problems. The best place to go is www.avproecm.com and they will fix you up the right way for way cheaper then a new or used ecm from the parts store or salvage yard. Trust me check it out and you will see what i mean. Good luck man, let me know how it turns out