Blowing fuse 9 engine management 20 amp

Tiny
MRSLEGER
  • MEMBER
  • 2002 FORD FOCUS
  • 2.3L
  • 4 CYL
  • FWD
  • MANUAL
  • 190,000 MILES
I do not know but something is cause the #9 fuse in the under hood fuse box. It says in the manual it is 20amp big fuse for engine management. So I change it and when I restart the car it starts rev up once and blows that fuse after not even two seconds. Still have all power, but turn key and nothing. Please help
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Saturday, February 11th, 2017 AT 2:48 PM

8 Replies

Tiny
CARADIODOC
  • EXPERT
You have power but you have "nothing"? Can you explain that better?

A simple trick to finding a short is to replace the blown fuse with a pair of spade terminals, then use small jumper wires to connect them to a 12 volt light bulb. A brake light bulb works well. When the circuit is live and the short is present, the bulb will be full brightness and hot so be sure it is not laying on the carpet or against a plastic door panel. Now you can unplug electrical connectors and move things around to see what makes the short go away. When it does, the bulb will get dim or go out.

For intermittent problems like yours the bulb may be dim already. Watch what takes place when it gets bright. That is when the short is occurring. It could be due to the rocking of the engine when you shift between reverse and drive. It could be due to the body flexing when you drive over bumps in the road. The bulb limits current to a safe value when the short occurs, in this case about one amp. If the engine will not start with a brake light in the circuit, try a headlight bulb. The low beam filament will limit current to five amps, and the high beam filament will allow about six amps to flow. That is still low enough to prevent doing damage to the circuit.

I will dig up a wiring diagram to figure out what the likely suspects are.
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Saturday, February 11th, 2017 AT 3:05 PM
Tiny
CARADIODOC
  • EXPERT
I think we are going to have to approach this a different way. There are just way too many things on this circuit. We need to bypass the "Power Hold" relay. That will allow you to run the circuit without trying to run the engine. You can do this by removing the relay, popping the cover off, reinstalling it that way, then squeezing the contact or holding it squeezed with a rubber band. You can also remove it, then install a jumper wire if you can figure out which two terminals to jump, or you can install a new fuse, then install my light bulb and jumper wires in place of the relay. Any of those things will work and will avoid blowing more fuses. All that is needed is the test bulb is in place of the fuse or the relay.

The relay terminals that must be connected together in the socket are numbers three and five on Ford's wiring diagram. I'm including a drawing of the common Chrysler relays with their numbers. If your relay looks like either of these, use the drawing to figure out which terminals to connect.
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Saturday, February 11th, 2017 AT 3:34 PM
Tiny
MRSLEGER
  • MEMBER
I do not know how this will help because just already know I have a short and I need to find it and fix it. How will this help me find it?
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Sunday, February 12th, 2017 AT 11:49 AM
Tiny
MRSLEGER
  • MEMBER
I cannot find the power hold relay.
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Sunday, February 12th, 2017 AT 12:11 PM
Tiny
CJ MEDEVAC
  • EXPERT
Listen to Doc!

His "Brake Bulb" short finding technique works well.

(I keep saying that I am going make another one and take a picture of it, as seeing one is easier to understand than the long explanation!)

He is probably trying to figure out a methodical way to find your short now.

Your vehicle has a 2.0 Liter engine, not a 2.3

I grabbed part of a diagram from 'Prodemand' showing the relay and its location.

See diagram below.

The Medic
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Sunday, February 12th, 2017 AT 3:03 PM
Tiny
CARADIODOC
  • EXPERT
Hi CJ. How are you copying and pasting the diagram? That is the same one I was using, but I cannot copy them.

If you follow the red/green wire from terminal five of the relay, you will see it goes to four other relays. Three of those can be removed and the engine should still run. I suspect the fourth one, for the fuel pump, does not have the short because the engine does run at times. Regardless, my test bulb in place of the fuse would no longer be full brightness if the short is removed by removing those first three relays.

After that, if you follow the red / blue wire down to the lower half of the diagram, you will see it feeds all kinds of things. The engine is not going to run with my bulb in place of the fuse. Not enough current will be able to get through, so we need to energize the circuit manually and leave the engine off. That is where bypassing the relay comes in. As you eluded to, this is way easier to do than it is to describe.

The alternative is to disconnect or remove one of the dozens of items, plug in a new fuse, try to start the engine, blow the fuse, and repeat with a different item. Let me know before you do that so I can buy stock in a fuse company! You will need dozens of fuses before you realize there has to be a better way to find what is shorted, and that is with my test bulb.

To answer your question about how this will help, you need a way to know when you did something to remove the short. You can do that by removing things and replacing fuses until the fuse no longer blows. That can take weeks or months of trial and error. You sure would not want to pay a mechanic by the hour to find it that way! You also want a test procedure that does not involve blowing hundreds of fuses, and you need a way to limit current to a safe value. The test bulb does all of these things.

You cannot see how much current is flowing through a fuse, but you can tell how much current is flowing through a bulb by how bright it is. Even with something shorted in the circuit, the most the bulb can be is full/normal brightness. Once you do anything to remove the short, current will go down and the bulb will go out or will become less than full brightness. In most circuits that will be a significantly-lower brightness that is real easy to see. In some case where normal current is relatively high, as in heater fan or radiator fan circuits, the difference between the bulb's brightness with the short in the circuit and without is barely perceptible. That is when it works better to use a head light bulb instead of a brake light bulb in place of the fuse. A brake light bulb will be full brightness when it passes the one amp it is capable of. A head light bulb will be full brightness when it passes its maximum five amps. That is still well below the rating of the 20-amp fuse it is temporarily replacing, and will protect the wiring just fine.
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Monday, February 13th, 2017 AT 9:57 AM
Tiny
CJ MEDEVAC
  • EXPERT
Doc,

Takes time and patience!

Some drawings and diagrams can be "save as" in your pictures/ documents with no "entire webpage" involved. This seems to also not work if they are enlarged (with Prodemands tools)

Screenshots is how I do most of the diagrams.

Take it to Microsoft Paint (or whatever), Crop it, save it (usually as a JPEG) into my pictures.

Here's the kicker!

If it is a diagram with big print, minimal information, one screenshot may do it.

If you hit "enlarge" on a big wire diagram, it actually makes it into one full diagram (if screenshot-It is impossible to read if you try to enlarge it on your computer.)

Once you do hit "enlarge" in Prodemand, it turns into that one diagram (too small to read), Using Prodemand's 'SLIDE DEALLY" you can size it to whatever! You use "The Hand" to scroll it in any direction to see what you want. (Careful fast sliding will highlight the whole diagram and lock you onto that portion)

I usually Make the diagram big enough to fill my screen Left and Right, scoot it to where I get the most of the diagram or where the "CUT OFF Portion" is Between rectangles or on bare wires. Then I Screenshot that Top portion. (Take to paint/get in my pictures)

I then go back to my Prodemand tab

Then I use "The Hand' to scoot the diagram up, insuring I catch the bottom little bit of what I screen shot first. This gives the next screenshot overlap and no info got missed. Same as before/ screenshot/ paint/ pics/ back to the Prodemand tab.

Sometimes it takes four or five screenshots to get the whole diagram. I also label the pics like T-Bird 1/ T-Bird 2/ etc. So that I post them in the right order.

I am getting faster at it!

Do you understand my hillbilly explanations? If not, we can do this in 'Messages' or Email

All righty then,

Let's hear some good news from MRSLEGER!

The Medic
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Monday, February 13th, 2017 AT 4:35 PM
Tiny
RENEE
  • ADMIN
Awesome CJ MEDEVAC!
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Monday, February 20th, 2017 AT 7:02 PM

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