probed the fuse box... oops...SOS

[Bustang523]

I'm sure I'll look like an idiot but the other night I was working on my mustang and Ii was installing some fog lights on my car. When I was installing them I was probing the fuse box to find a key on power source and then use a fuse tap. When I was done and went to start the car the car would turn over but not start. Thinking I must've accidentally tapped a fuse I shouldn't've I undid my fuse taps and the car started. but I was getting low fuel pressure. I later learned that you're not supposed to probe the fuse box on these cars for some reason. this morning I got a code for the fuel pressure sensor (P0191) I tried replacing the sensor since it was easy to get to and that didn't fix it but the code did go away. as it sits right now I've undone all the wiring I added to the car, you can start the car after it cranks for a while, and once the car does start if you try to rev it by putting your foot straight to half or more throttle the car will sputter and die. although you can get it to 4k rpms if you give it 1/4 throttle and baby it up. I also just noticed the fuel pump was making a weird sound that didn't sound like a normal humming. The fuel pump sounded more like it was struggling to run or like something in the pump was binding up as it spun. my next suspect is that the fuel pump got fried or the control module in the trunk for the fuel pump got fried. any ideas? has anyone else probed the fuse box then ran into fuel system issues? I really dont know where to go from here other than replacing the fuel pump and module. thank you in advance to any advice.

 

[07gts197]

Which circuit did you tap into?


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[DieHarder]

Probing the fuses with a test light or VOM should not affect the SJB or any circuits. They are simply fuses so as long as you don't directly connect a ground to a 12v source you should be fine. That said, you may have jostled something in the fuse box. I would go back and pull each fuse you touched and reseat them. I would also check out online manuals to see which fuses affect operation of the fuel pump and chase that circuit to determine if it's a fuse/wiring or you have a problem with the fuel pump. 9 times out of 10 the problem is usually something you moved/changed/disconnected/connected improperly vice actually having items fail out of the blue.

 

[Aussie-Parnelli]

Hi
I just had a similar problem, fitting heat exchanger fans. Has taken a couple of months to rectify.
Car would start but run in limp mode, I got throttle body codes after replacing throttle body and sensors didn't change.
Removed my wiring, and swapped out fuses and relays still the same.
Then last week swapped the fuse box and now everything is ok, I guess whilst all the pins look ok something inside the box went haywire

 

[Juice]

Coincidence IMO.
Low fuel pressure + struggling fuel pump = I would be looking at the fuel pump or fuel filter. Filter could be clogged/restricted. Fuel filter is an easy job and does not cost much.

I can tell you that these cars do not like wiring alterations on circuits controlled by the SJB. There is overcurrent protection built in and it will power off a circuit in case of an overload.