99 chevy express 3500 200k miles. Blew the 20 amp Eng-i fuse few days ago after long day of running. replaced original VCM and had dealer program it. ran for 30 minutes on a 80 degree day, Blew 20 amp fuse again. suspected bad or overamping fuel pump. new fuel pump installed,and new fuel pump relay. ran ok for 15 minutes then blew fuse. Engine will run on cold start but still blows same fuse after heat buildup...while engine is hot I Ohm'd underhood 20amp eng-i fuse mount terminals. the 12v is solid on input but oposite side is shorted to ground when heat builds up. what relays or circuits are in series with this fuse that may be shorting upon heat rise. The coil is still original part could that cause hot to ground short after running engine. how can i test that.
Hi,welcome to Just Answer.I will be happy to assist you with this question today.I will try and assist you as best as possible from here,feel free to ask any follow up questions to my info provided here.This fuse which should be ENG 1 powers several components on this vehicle here.It can be any of these components below shorting out and causing this fault.Each one of these should be unplugged one at a time when the fuse is blowing to locate which component is at fault.Below is the list of components this fuse powers up:Oxygen sensorsMass air flow sensorEGR valveCanister purge valveVCM (engine and transmission computer)Secondary air injection relay (if equipped)Crankshaft position sensorAny of these components heating up and shorting to ground will cause this fault here.If you need any info on where any of these components are let me know.Let me know if you need anything else and positive ratings are appreciated.Thanks Pete.
14 years GM dealer Technician.