'01 F150 4.2L blowing fuse 23, multiple codes

[mrjaffe]

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 in advance for any all help!

[projectSHO89]

See my posts in that thread, http://www.ford-trucks.com/forums/59...ral-codes.html for details on what is involved.

While the OP in that one never replied back or followed up, all the information provided there is relevant.

Too bad you spent all that money on new sensors you didn't need...

Steve

Check your harnesses.

[mrjaffe]

Thanks Steve! I did look at that post but as you said didn't see the final outcome.

Is your guess that it's a damaged harness more likely than a failed component on that circuit?

You mentioned also in that post that you might have a wiring diagram. Would you be willing to share it?

Thanks again for the help!

Mike

[projectSHO89]

2001 4.2 Engine Schematic

Click on the link to download a pdf of the schematic.

F23 is shown on cell 23-1. Its loads are detailed on pages 23-4, 23-5, & 23-8.

If you need additional documentation, let me know. If you want your own, it's amazing what happens if you google "ford service cds" :wink:

While any of the load components might be intermittently shorting to ground, I've yet to see one of these faults that wasn't due to a harness intermittently shorting to chassis.

Steve

[mrjaffe]

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.

Thanks again for the assistance!

Mike