2007 Ford Explorer blowing fuse #43 (coil) when accelerating

[Bob H...]

Hi everybody!

My 2007 Ford Explorer XLT (6 cyl, 114k miles) often blows fuse #43 when I accelerate hard or medium-hard from a stop -- causing the coil to lose power and the vehicle to stall, often in a busy intersection, which is fun. I can go a few days without blowing a fuse if I accelerate more gently from every stoplight, but I inevitably blow the fuse when I do a more "normal" acceleration. So far I've burned through about 10 fuses in the last 3 months.

#43 is a 15A fuse, found in the fuse box under the hood on the driver's side. Without it the coil has no power.

It takes maybe 3-4 seconds of acceleration before the fuse blows. It might possibly be at the moment when the tranny would be shifting into 2nd gear, but that's just a wild guess.

The problem doesn't seem to occur when the engine is cold. All the blown fuses have occurred after driving at least 10 minutes.

I took the vehicle to a professional shop twice, but they couldn't get the problem to repeat, and they couldn't find any obvious frayed wires, so they gave up.

I replaced the radiator and thermostat housing because they were both leaking badly and I thought the excess water might be the cause of a short. Everything is dry now, but the fuse blowing continues.

A couple days ago I replaced the coil pack, but the problem continues.

The problem started 2 weeks after I did an oil/filter change, but otherwise no work was done in the months before the problem. There haven't been any electrical modifications or customizations to the vehicle.

Anybody have any ideas?

 

[08EddieCA]

When you start driving and have fully warmed up the truck, does the coolant leak cause the coolant to "fly" around the engine bay? Had an issue with the coolant spraying out of the upper part of the thermostat housing at the upper rubber seal - just below the upper coolant hose. Coolant was spraying all over the battery and fuse box. Just a hunch....

 

[Bob H...]

Before I replaced the thermostat housing, yes, the coolant was pooling on top of the engine and possibly flying around. But I resolved all the coolant leak problems 7 weeks ago when I replaced the radiator and thermostat housing. Everything has been nice and dry since then, and yet the problem continues.

 

[08EddieCA]

I might check the wire harness to the coil pack. Carefully peal back the cover a bit and see if you have a short.
#15 in the manual states rear defrost/heated mirrors. I also might check the wires for any cracked or arched.

 

[Bob H...]

Thanks for the reply. I did what you suggested and I did find a frayed yellow wire up against foil-wrapped wires, about 6 inches from the coil, inside the plastic corrugated wrapping leading to the coil. I assume the foil wrapping is to cut down on radio interference. Anyway, I taped everything up very nicely with electrical tape and went for a test drive. No problem for 10 minutes, but once the engine was warmed up the problem came back -- fuse #43 (not #15) blows on hard acceleration from a stop.

I'm thinking maybe it isn't a short at all. Why would a short suddenly happen when accelerating? It happens when accelerating both forward and backward, by the way.

 

[08EddieCA]

Do you have Motorcraft COPS?

 

[Dora2007]

[QUOTE=" Why would a short suddenly happen when accelerating? It happens when accelerating both forward and backward, by the way.[/QUOTE]

My only (small) contribution is I once has a wiring problem that was connected to engine movement under acceleration - I mean how the engine rotates slightly on the motor mounts Wire harnesses move under that rotation and may rub against something. 10 minutes does not sound like the engine would be so hot, but exhaust manifolds would be.

You say 'coil', and one asked about COPs. I'm not familiar with V6 - do you have one coil, or 6 coil-on-plugs? One coil could have insulation breakdown causing intermittent short as coil heats. What I don't know is does the coil load (and therefore internal generated heat) differ with load?

The way a modern shop would diagnose is to remove fuse and make a wiring adaptor with external fuse and portable scope measuring current (with memory). Go out and make condition occur and look at current trace.

Does fuse #43 ONLY feed coil? If not, can other circuits be isolated?

I normally don’t like to throw $$$ at symptoms, but a new coil sub would eliminate a freaky coil-shorting issue, leaving the problem being other than the coil if it still occurs.

 

[08EddieCA]

I would peal back the coil wire cover further. Apologize if I used the Wong term. Pealing Bach the harness cover is free. I made the mistake of paying $1,200 to the dealer to do the same thing. A v6. Even better. You have one harness connecting to the coil. Peak it bak and make repairs. When the engine heats up the wire are incline to touch and short. I'm West Coast so when I get moving, I'll check the diagram. Coil new, Tuned up? Alll fluids changed? Flush radiator? Compression test?
You have a short or an under rated fuse. Condition of wires spark wires good? Pardon the questions.

 

[tripplec]

Key circuits like fuel pumps and ignition etc are never shared with other items especially accessories. I know I have seen some published assignment charts are wrong. Owners manual reference and markings on the cover can be used to confirm.

I suppose pulling the fuse and see if something else stops working (but shouldn't) unless some option has be spliced into the circuit. Trail hitch lighting installers usually look for a HOT lead for the converter power lead for example.

 

[Bob H...]

By "coil" I meant "coil pack". On this vehicle all 6 coils are packaged together in one rectangular block, a coil pack, which I replaced last week.

I replaced the spark plug wires today (and spark plugs), with great difficulty. No help though, the problem still occurs. I'll have to peal back more wiring harness in a few days to look for more frayed wires, I guess.

 

[boominXplorer]

Did the fuse blowing problem happen before the thermostat housing replacement? If not check the crank sensor harness

 

[Bob H...]

Yes, the fuse blowing problem started about 3 months ago, long before I replaced the thermostat housing. And long before the radiator replacement, coil pack replacement, and spark plugs/wires replacement.

This morning (the day after replacing plugs/wires) the symptoms have changed some. Now the fuse blows immediately upon trying to start the car. The starter cranks and the engine starts to fire up but then immediately dies, with that same #43 (coil) fuse blown. I tried starting 3 times, blew the fuse all 3 times. So I unwrapped all the wires I could get to at the top of the engine, and spread out all the unwrapped wires so nothing was touching. Fuse still blew. Then I disconnected the wires to the fan clutch and tried again. This time the engine started up fine. The I re-connected the wires to the fan clutch and tried again - the fuse blew. Disconnected the wires to the fan clutch again - fuse still blew. Now, no matter what I wiggle, spread or disconnect, the fuse blows.

 

[Bob H...]

I experimented with a 20 amp fuse (just now), but it blew just as quickly.

 

[tripplec]

Odd, wondering if the wire is ground in grounding out somewhere worn through the insulation?

When it blow can you ohm the load side and see if you see a short or not?

 

[Bob H...]

tripplec: Not sure what you mean -- measure resistence between the battery positive cable to the fuse socket pins?

 

[tripplec]

Pretty much, the load side (which goes to the coil pack etc), other side may have 12V whether ignition is on or not. But verifying the load side has no voltage at the fuse socket (so as not to blow the meter!!). Switch to Ohms, and see if there is low resistance <100 ohms or a short to ground (battery ground or engine block).
Wiggling wires may make the resistance change or go direct to ground for a full short. Since you're blowing fuses that easily it should show up without have to run the engine.

 

[Bob H...]

I disconnected both battery cables and measured resistance from each battery cable to each pin of the fuse #43 socket, with the ignition in the On (run) position:

Pos cable to fuse pin A: 19.1 KΩ
Pos cable to fuse pin B: 0.33 KΩ
Neg cable to fuse pin A: 18.9 KΩ
Neg cable to fuse pin B: 0.28 KΩ

 

[tripplec]

280 ohms (lowest) won't blow a fuse
All were are concerned about is the output power side (when the fuse blows the feed has 12V, and other side nothing as its feeding the circuit). i Don't whow what else is on that circuit but it maybe the coil pack itself failing under load/heat/stress shorting out internally. A lot of these must be in the wreckers and if all else is eliminated the coil pack may have to be swapped out with a working one.

 

[Bob H...]

Yeah, but I put in a brand new coil pack a week ago (Spectra Premium C-507, $30 Amazon). It didn't help or change the symptoms in any way. I suppose it's possible that it is also defective.

 

[tripplec]

I am doubting that then whats left?

As per an earlier post. Are there any aftermarket add ons??
Trailer wiring harness (non oem) used convertor etc
Add ons inside accessories, circuits....