Hello everyone.
I'm in serious need of some electrical help. I've tried searching, hours and hours of searching and still nothing, close to solutions but not the solution. On top of the hours of diagnosing and swearing hah. Quick backstory- I live in northern Ontario and we have started getting snow, not lots but 3"-4", it was mild out today (0 C) -- 2006 f150 5.4 lariat, 3rd owner, PO was NOT mechanically inclined and maintenance was minimal at best. Truck has roughly 265000kms, engine has roughly 140xxx kms and trans has roughly 80xxx kms. Ok, about a month or so ago I had driver side header changed, put about 250 kms, washed the truck, drove about 200ft, engine fail safe mode came on, limped it home. After checking several things, found fuse 32 blown, as soon as key is turned to the Run position (anywhere from 3-10 seconds) fuse 32 would blow. I found out that multiple systems (evap, MAF, Cam sensors, etc) are all tied into this fuse so, I put a resettable breaker in and started chasing the systems back. Finally I got to the 2 large plugs under the driver seat on the frame, pulled them apart and bang! No popped breaker, so, figuring it had to be one of them, I cleaned them both then plugged them in one at a times no guess what, no popped fuse. ??? So, thinking it was ok (ya, I know) I tapped up all the plugs, reinstalled them under the truck and all was good.

Fast forward to tonight. I used the truck all day, garbage run, bush cruise with the dog, checked out a Bronco and got fuel. Truck sits for about 3 hours, my sister borrows it and get 20 minutes away and bam! Engine fail safe mode, she limps it home, I pull it in the shop and check the last culprit, the plugs under the seat, unplugged them, reset the breaker, turned the key to Run, pop goes the fuse..... So I guess problem wasn't fixed..

I know I'm getting ahead of myself without rechecking all sensors/systems before posting but I feel like I'm going to end up asking these questions anyways... Does anyone have any idea on where it could be shorting? As I said,header was changed and noticed upstream o2 sensor was bent during process. I tried unplugging it last time with no change. Did I miss something? Only got a few more days off and I hate electrical :-( .... Any help would be amazing :-) Thanks.

 

Go back and examine the work that caused the problem - the driver's side header replacement.

Based on the information provided, I'll bet $10 that the wiring harness for the upstream driver's side O2 sensor is damaged, probably laying on the exhaust or, if a 4x4, on the LF driveshaft, and is intermittently shorting the sensor's heater circuit to ground, That heater circuit, not coincidentally, runs off fuse F32. Examine it for any nicks, melts, scrapes, pinches, etc that would cause power wire to make contact to bare metal. The wire is red/yellow on the main harness side of the connector, the OEM sensor's wire was red/white on the sensor side of the 4-pin connector. Might be a defective or damaged sensor, unplug it to see if the short goes away.

Similar posts:
https://www.f150online.com/forums/v8...rown-once.html
https://www.f150online.com/forums/v8...-fuse-f32.html

 

Yup 02 harness and trans harnesses are pretty vulnerable when people don't get the hung back where they are supposed to be away from danger

 

I narrowed it down to the plug that connects the furthest left and middle PCM plugs. So my short is on either side of that plug (8 pin I think). Any idea on what system is on that plug? I've checked the wiring near both the driveline and exhaust, I could not find any damaged wiring. I'm heading out to work on it now. Thanks for the help

 

Hello again everyone
So, as it turns out I was looking far pass the problem and completely forgot about one thing... While at the shop for the header replacement, I had gotten plugs 4 and 8 changed. So, as I was unplugging the wiring harness from the back of the engine, I noticed the #4 coil plug was loose.... plug was not loose, male end of coil was cracked and broken! I also noticed the rubber grommet was broken and falling apart... So, plugged evening back in, minus the coil, and no popped fuse, put wheel back on, plugged in all sensors, changed the coil and went for a short drive (far longer then needed to pop fuse lol) and so far so good. I didn't have my wallet so didn't venture too far but will go for a good drive to confirm. I'm hoping that solved the problem. I would like to thank those who took time to give advice. It was very appreciated :-) I will do my best to keep updated with truck and look forward to spending more time on F150online, hopefully being the one giving advice tho lol

 

 

Only one problem with that explanation - the COPS are on fuse F33 along with the downstream O2sensor heaters, not F32. If F33 blows, the engine immediately STOPS.

 

I was getting the 02 code when 32 would blow, so your saying they are on the same circuit as the COPs or ? I've gone out for a short drive, prolly 6 or 7kms, run time prolly 15/20 minutes and all seems good. No codes yet except for oil temp sensor but I think I know what's wrong with that lol

 

Unless it was coincidence that the codes showed up when the engine fail came on?

 

I see nothing in any of your posts about any fault codes, O2 or otherwise.

Look, somewhere along the line, there's either a chafed wire on the circuit from F32 that's shorting to ground or one of the components that is fed by that circuit has been shorting to ground. We've covered the most common stuff, but it all boils down to the fact that the problem, according to your reporting, began right after you had specific work done. Therefore, the odds are overwhelming that the work was done in a manner that caused a new problem. Additionally, since your most recent work seems to have mitigated the issue, it would be my suspicion that you moved a wiring harness or bundle during your efforts and managed to move the exposed wire away from ground, thus clearing the short.

There should be fault codes stored anytime the PCM enters it's "limp" mode.

 

ProjectSHO89- seems you are a very wise man hah, as my problem came back about 7/8kms later after hitting a bump (hit bump, lights dimmed and fuse popped) .. And I'm sorry for not posting the codes as I ASSUMED (I know) they were attributed to the fuse being blown after reading (the first time this happened) similar problem postings.
Truck gave very similar codes last time problem happened, all codes last time pertain to fuse 32. Here are the codes that I just pulled from the truck. (Carquest code reader cpe30433)
P0198- engine oil temp sensor circuit high input -- x2
P0010- intake camshaft position actuator circuit / open(bank 1) -- x2
P0020- intake camshaft position actuator circuit / open(bank2) -- x2
P0059- HO2S heater resistance (bank2/sensor1) --x2
P0060- HO2S heater resistance (bank2/sensor2)-- x2
P0135- 02 heater circuit (bank1/sensor1) -- x2
P0155- 02 heater circuit (bank2/sensor1) -- x2
P0443- evap emission sys purge control valve circuit --x2
P0446- evap emission says vent control circuit--x2
P2272- 02 sensor signal stuck lean - bank2/sensor2 -- x2
P0103- mass or volume air flow circuit low input

The x2 is the reader repeating the codes, I know most of those are on the fuse 32 circuit. The oil temp only changed after I removed the twists out of the wire and reinstalled. I had unplugged all sensors I could relating to those systems, including the ac relay. I'm currently losing my mind changing this wire.... Good thing I'm night shift tomorrow and have the tonight/tomorrow morning to find it :-(

 

All those codes frequently mean the main harness plug at the firewall has an issue.

 

Meaning the plug or a wire in that harness.. And is there a "main harness" ? There is some heat damage to the harness running down the pass. Side wiring protector but the wires look ok, I even zip tied it to the trams dip stick, so I'm going to try there first.. But not getting my hopes up

 

I found that if I unplug the join plug that is wrapped into PCM plugs 1 (furthest left) and 2 (middle) the breaker doesn't pop, any suggestions on where those plugs go or which side is the power side?

 

All of those codes are due to the blowing of F32. Your assumption in post #11 is correct.

Can you post several photos of those connectors so we can get oriented to them? We don't have your truck in front of us and we need to be able to correlate whatever you're seeing to the technical documentation on our screens. That might help...