Great site! Lots of useful information. Hoping someone can bail me out.
My '01 F150 4.2L auto started with check engine light 6 months ago. Each time I checked the code it showed "Lean Mixture Left Bank." I cleared the codes and weeks later it would re-appear.
A week ago while driving down the road the truck suddenly dropped to 2nd gear and the A/C quit cooling. I was able to drive but only in 2nd gear. The transmission appeared to be in limp mode. I checked for codes and got a long list of seemingly unrelated codes. I checked fuses under the hood and found fuse #23 blown. It's labeled "HEGO and Transmission." I replaced the fuse and everything worked again for a few minutes but then the fuse blew again.
Thinking my O2 sensors were bad I replaced all four and again everything seemed to work. I drove the truck for 60 miles or so without a problem and then suddenly fuse #23 blew again.
I bought the auto store repair book in hopes of getting a decent wiring diagram I could track the circuit with. Unfortunately the diagram is vague.
I found a post by DaddyZ of a very similar situation but there was no final resolution so I'm starting a new one.
Thanks Steve! I haven't found the problem yet but did find one pair of worn wires to some sensor on the air intake assembly very near the A/C compressor. The harness had fallen onto the compressor pully and had a spot worn all the way through. I experimented with shorting the damaged wires to ground but the fuse didn't blow. I repaired them and went on to check leads to the O2 sensors Nothing looked out of the ordinary. Interestingly everything seems to work fine until I put the truck in gear and within a minute or so the fuse blows. I'm going to try and trace the wire by color code and sensor looking for worn harness.
Okay guys, so I decided that somebody should come back to this thread and show their findings after actually correcting the issue. Sorry my pics are what they are. It's tight quarters and your gonna have to look hard and compare it to your truck.
On my truck I was able to replace the fuse and sometimes it would last a few days before blowing, but by the time I decided it had to be fixed I could blow a new fuse just by turning the key to the "run" position.
Here's the deal, passenger side of the truck on the firewall there is a bracket that 2 harness connectors mount to. Follow both of those harnesses down to where they go behind the head of the passenger side of the engine. On my truck one of the harnesses was touching the hot side of the AC line that runs from the back to the compressor. Once I removed the bracket mounting the harnesses from the firewall and the battery I was able to see where the chaffing had occurred.
If your curious as to whether you have a short south of the connectors on the wiring harness, use a 10mm to undo the connector and with it unplugged see if your truck will NOT blow a fuse. If your don't blow a fuse with one of those harnesses disconnected you know your short is on that harness south of the connector.
I really wanted to inspect all of the wires to make sure none were shorting on each other but due to the tight space I elected to wrap the entire bundle and secure it with a zip up and out of the way after I tested to see that I didn't blow any fuses just by lifting it up off the AC line. The harness is very close to the transmission dip stick tube which I noted in the images for reference.
If I had the time and energy I would have removed the passenger front wheel, plastic fender well and I could have had better access to inspect the individual wires.
But anyway, I hope these help some of you others that stumble across this thread/issue.
I am having the same issue.
checked "ALL" fuses and wires, none bad.
with my 99 4.2 5 months ago I take it to school to automotive tech. class to replace my lower end, when I pulled in with my truck the trans worked great no issues besides a small leak at the pan gasket. we pulled motor and trans both. no work was done to the trans at all besides new fluid/filter and new internal wiring harness. we reinstalled motor and trans and now it seems like I am in limp in mode. I get to about 50mph and no OD rpms keeps going up but no speed. even my instructor said it sounds like a fuse but every fuse I have in the truck is good. any other idea's?