Dumb Relay Question

Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=38940
Printed Date: May 15, 2024 at 12:47 PM

Topic: Dumb Relay Question

Posted By: Philtenn
Subject: Dumb Relay Question
Date Posted: September 10, 2004 at 5:47 PM

My son has been having problems with his 1994 Ford Ranger. Specifically it has failed to start on 2 occassions, both times when low (but not empty) on fuel. After putting fuel in the tank to 1/4+ tank, we find that there is no fuel pumping from the fuel pump. Assuming that it has a bad (weak) fuel pump and is losing the prime, we purchased a new pump.......but before installing we were told to check the fuel pump relay. Switching 2 identical relays (air conditioner and fuel pump) makes the car run smoothly, but now when i switch them back to their original positions, the pickup still runs....not as smoothly though.

My questions is: Can a relay get weak and fail to hold the switched position for a higher draw component, such as a fuel pump? Or will relays always just crap out all at once?

The puzzle is that no mater what relay is where, the A/C works fine......HELP!

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Philteen

Replies:

Posted By: Teken
Date Posted: September 10, 2004 at 5:56 PM

A relay upon terminal failure will exhibit what you have discribed.

The primary failure point is caused by contact arching. Each time the relay is energised (turned on) the act of opening and closing will leave a small amount of carbon build-up.

ie. corrosion / burnt oxidization debris

After many cycles, the contacts are simply too dirty, and the resistance within goes up, causing the relay to be internally insulated by the debris / corrosion.

Which at that time, will not allow sufficent current to be transferred.

The secondary fault is from the coil itself. Those who insist upon applying a under rated relay will simply burn out the coil, and the contacts.

Regards

EVIL Teken . . .

Posted By: hotwaterwizard
Date Posted: September 10, 2004 at 6:50 PM

I had the same thing happen to my Ford Ranger and the problem was the Fuel filter not the Relay.

Sediment settles in the bottom of the tank. When you let it run out of fuel the pump will pick up this sediment and plug up the fuel filter.

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John DeRosa (Hotwaterwizard)
Stockton California
When in doubt, try it out !

Posted By: Philtenn
Date Posted: September 10, 2004 at 6:57 PM

Thanks Dudes......i think it's a combination of maybe both things....it's a full time job with an 18yo boy and his vehicle....i think i'll throw his tools away and have less trouble too,

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Philteen

Posted By: Teken
Date Posted: September 10, 2004 at 7:09 PM

Philtenn wrote:

i think i'll throw his tools away and have less trouble too,

LMAO . . . posted_image

Remember, you were once young as well. posted_image

Regards

EVIL Teken . . .

Posted By: Philtenn
Date Posted: September 10, 2004 at 7:22 PM

yea......but i didn't lose all my dad's tools....lol

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Philteen

Posted By: Teken
Date Posted: September 10, 2004 at 7:27 PM

LOL, make him cut the grass NFL style. Cross cut boy !!

Posted By: delphidoc
Date Posted: September 12, 2004 at 5:05 PM

Philtenn wrote:

yea......but i didn't lose all my dad's tools....lol

Sure you didn't. Me neither. posted_image

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