got a short some were

[tmaxxman]

ok i have a 88 ranger 2.9 4x4 and out of the blue i got a short in it some were but i dont know were to start looking for it what is going on is that i can have the key in my pocket and i can hear my fuel pump kicking on and it will just keep going it till i unhook the battery but it only dose it some time not all the time im not good with this kind of shit so any help would be greatly appreciated

 

[tmaxxman]

bump

 

[Earl43P]

Replace the fuel pump relay.
While you are in that area, do a thorough visual inspection of the wires going to the relay.

http://www.therangerstation.com/tech_library/EDiagrams/files/Diagrams_ElectronciEngControls2_9_1of3.JPG

 

[jhammel85]

My thoughts were definitely on the relay as well

 

[tmaxxman]

ok will do that i just didnt think the relay would be getting juice with the key not in it but i dont have a clue thanks for the help

 

[Earl43P]

If you look at that schematic, it's clearly marked that the FP contacts have power at all times, regardless of key position.

I was completely wrong by saying "anytime that LB/O wire gets a ground (that is your potential "short"), the fuel pump will run". That would only be the case if the EEC (computer) relay was also energized.

I would still replace the fuel pump relay for your problem though.

I edited out that wrong part.

 

[tmaxxman]

If you look at that schematic, it's clearly marked that the FP contacts have power at all times, regardless of key position.

I was completely wrong by saying "anytime that LB/O wire gets a ground (that is your potential "short"), the fuel pump will run". That would only be the case if the EEC (computer) relay was also energized.

I would still replace the fuel pump relay for your problem though.

I edited out that wrong part.

thanks alot

 

[Milton]

Relays are electro-mechanical devices and can fail in multiple ways. Here is a typical relay:

The armature is connected to the power being controlled, in your case it is connected straight to the battery.

The top contact is the normally closed (NC) contact, meaning that with coil is not energized the armature is making a connection with that contact. In your case this contact connects to nothing.

The lower contact is the normally open (NO) contact meaning it should only make a connection to the armature when the coil is energized. In your case this contact is connected to the
fuel pump

If the coil opens the result is the relay remains in the non-energized state and your fuel pump never runs.

If the coil shorts the result is the relay remains in the non-energized state and hopefully a fuse blows.

In some applications, the normally closed contact is connected to something so current is flowing from the armature to this contact. This means that one failure mode is when the armature and normally closed contacts "fuse together". So even when the coil is energized the armature remains in the non-energized state. sometimes you can diagnose this by tapping the relay causing the fused contacts to "unfuse" and the relay armature then connects to the normally open contact. Fused contacts can be an intermittent problem.

A weak spring, along with the armature and normally open contacts fusing, can result in the symptom you have, i.e. the fuel pump keeps running with the key in your pocket. Again tapping the relay may result in the armature returning to the correct state.

So anytime I have a problem with a circuit controlled by a relay, I tap the relay. If that clears the problem then I know the problem is likely the "fusing contacts" on the relay, so I then replace the relay.

If tapping the relay does not diagnose your problem, then you have to see if the proper voltages are getting to the coil and armature. If that's good then is the you check to see if the proper voltage is exiting the relay, i.e. what's the voltage drop across armature and the NC/NO contacts? Worn armature, normally open or normally closed contacts can result a significant drop in voltage exiting the relay. If all of this is good, then the problem is not the relay, so look elsewhere.

 

[Earl43P]

Milton brings the tech.....

 

[tmaxxman]

thanks alot

 

[tmaxxman]

ok i know there is some were i can look to find this but im to lazy to go look were can i find my fuel pump relay on the truck at thanks

 

[Spott]

You are aware that the word "short" is a layman's term meaning, "It's got an electrical problem but I don't know what", right?

On a more serious note, you will need a basic multimeter to find and fix this problem. You can get one cheaply at Radio Shack or Harbor Freight that will do the job quite well.

1. The EEC turns the fuel pump relay on and off with a tan/light green wire, that runs between pin 22 of the EEC, and the fuel pump relay (which is mounted above the passenger's fender, in the engine bay). The same tan/light green wire is also connected to the self test connector, a red connector right next to the fuel pump relay (it's just hanging there, not connected to anything). If that tan/light green wire is grounded, your fuel pump will run.

When the problem is happening, unhook the battery, and measure the resistance between that T/LG wire in the red connector, and the frame of the truck. It should show a very high resistance (over 10k ohms) or even an open circuit. If it shows a low resistance (under 10 ohms) then you need to follow that wire until you find where it's grounding.

2. If that's not the problem, it's most likely the relay. Sometimes a relay can get the contacts inside "welded" together, with lots of use. That's what Milton was trying to say.

To test the relay, while the problem is occurring, unhook the battery (do not bump the relay, or you may accidentally "fix" it, and then you can't find the problem until it happens again.) Measure the resistance between the center pin of the cigarette lighter, and the Orange/Light blue wire at the inertia switch (the inertia switch is located in the passenger's footwell, up against the firewall, just under the edge of the carpet.) If it shows a low resistance, the relay is bad, or the fuel pump wire is getting power from somewhere it shouldn't. Then unplug the relay, and measure it again. If the resistance is now very high, or open, then you know it's the relay, and not the wires, so replace the relay. If the resistance is still low, then you know it's the wires that run from the relay to the fuel pump.

3. If it's the wires that run from the relay to the fuel pump, then unplug the inertia switch. Measure the resistance again from the center pin of the cigarette lighter, to the Orange/Light Blue wire, and again from the cigarette lighter to the Pink/Black wire. If you find a low resistance either time, the wire you're measuring has worn through the insulation and made contact with a wire carrying power. Trace that wire until you find the problem, and fix it.

I recommend cutting the wire at that point, slipping some heat-shrink tubing over it, soldering it back together, and shrinking the tubing over the wire. It makes a good weather-resistant repair.

4. If it's none of those problems, then you've missed it. The "gremlin" escaped this time, and you'll have to wait until it happens again, to try and trace it down.

Let us know what you find,

Spott