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Fuel cutoff relays??
self

Posted on 11/30/2011 8:03:27 AM PST by varmintman

The topic here is this little guy:

Somewhere around the early 90s Honda and Toyota started making cars to last longer than their owners last. I have a 96 Honda Accord with around 210K miles on it, synthetic oil all the way, bulletproof 5-speed manual transmission and all the main parts of the car seem set to live for another 30 years, assuming I replace spark plugs, timing belts, radiators, windshield wipers and that sort of thing once in a while.

But I've seen cars killed by over-engineering things and that fuel relay is just that. When one of the things dies, the car cannot be started easily unless it's dead cold, so that running errands is basically off the agenda. I replaced the original one of those around June and that one died about two weeks ago and I had to replace the thing again yesterday i.e. either the one from June was defective or there's some electrical problem killing the things.

What I'm wondering is, does the car really need that thing?? I mean, cars in the 50s, 60s, and 70s never had those and didn't seem to need them. Has anybody ever just shorted the two real wires together on one of those things and basically just defeated its function altogether??


TOPICS: Society; Travel
KEYWORDS: automotive; electrical; gearheads

1 posted on 11/30/2011 8:03:29 AM PST by varmintman
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To: varmintman

I have a friend with a late 1990’s Toyota Camry that had nearly 400,000 miles. It is one of the best riding cars I’ve ever been in.


2 posted on 11/30/2011 8:07:07 AM PST by isthisnickcool (Sharia? No thanks.)
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To: isthisnickcool

The ‘92 Toyota Camry and the ‘65 Dodge Dart will go down in history as the two sturdiest cars ever. Virtual Urban Tanks.


3 posted on 11/30/2011 8:12:46 AM PST by Bloody Sam Roberts (Attacking Wall Street because you're jobless is like burning down Whole Foods because you're hungry.)
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To: varmintman

Is that the thing that turns off the fuel pump if you get into an accident?


4 posted on 11/30/2011 8:13:08 AM PST by smokingfrog ( sleep with one eye open ( <o> ---)
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To: varmintman

I had a 1987 Toyota Van Wagon that racked up 500,000 miles before putting her out to pasture in a junk yard.


5 posted on 11/30/2011 8:20:51 AM PST by Jack Hydrazine (It's the end of the world as we know it and I feel fine!)
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To: Bloody Sam Roberts
Second engine from Japan and third rebuilt transmission... 400 miles a week, my daily commuter...
6 posted on 11/30/2011 8:20:58 AM PST by AngelesCrestHighway
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To: varmintman
Cars in the 60's and 70's had carburetors and camshaft-actuated low-pressure mechanical fuel pumps, that may have pumped a quart a minute. Modern fuel-injection systems have a very high-pressure electric fuel pump that pressurized the injector rails. This is done so that opening the injector for a specific amount of time always injects the same amount of fuel, regardless of RPM. If the engine is killed for some reason, and the high-pressure end of the fuel system breached, this normally low-volume high-pressure pump becomes a high-volume pump dumping gasoline everywhere at a somewhat lower pressure. It will do this until the gas tank is empty or until the battery runs down. Or until the vehicle becomes a fireball.

Hence the need for the fuel pump cutoff.

Cars are indeed more complicated these days, but much more reliable. Our cars start literally every time we turn the key. Do you remember, as I do, your parents saying you couldn't go to school or they couldn't go to work because the car wouldn't start on a cold winter morning? Do you remember "vapor lock"? I do. These things are gone because of computer-controlled fuel injection.

7 posted on 11/30/2011 8:24:05 AM PST by backwoods-engineer (Any politician who holds that the state accords rights is an oathbreaker and an "enemy... domestic.")
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To: backwoods-engineer

Good answer, thanks.


8 posted on 11/30/2011 8:32:28 AM PST by varmintman
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To: backwoods-engineer

Again I replaced the original relay last June and the replacement didn’t last long, I replaced it again yesterday. Is that more likely due to the June replacement being defective or is there some sort of a common electrical problem which could be killing the things?


9 posted on 11/30/2011 8:35:30 AM PST by varmintman
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To: varmintman

My son just had this same problem on his 2005 Ford Ranger. The fuel shutoff is designed to shut off the fuel pump in the case of a rollover. It shorted out and burned out the fuel pump - which is, brillantly, in the gas tank. $900 later, he is back on the road.


10 posted on 11/30/2011 8:37:33 AM PST by Donkey Odious (I can explain it to you. I can't understand it for you.)
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To: varmintman
The relay to the fuel pump on my late 70’s Toyota 1/4 ton pickup went out when I was in Florida and had to be in California in four days. I just ran a wire from the battery to the fuel pump, inconveniently located on the fuel tank under the truck, but I was a lot more agile then. Drove all the way to CA like that. The deal is though that you don't want the fuel pump running all the time so when the ignition is turned on the relay turns on the pump. You could change out the relay with a toggle switch which would keep a thief from driving very far if he didn't know what was happening, or even a key switch.
11 posted on 11/30/2011 8:52:56 AM PST by dblshot (Insanity: electing the same people over and over and expecting different results.)
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To: varmintman
V-man, as an electronics engineer, I have serious doubts about the relay being the problem. Do you have a multimeter (volt-ohm-ammeter)? You can easily check the relay for function.

Put the meter on "ohms" and hold the two probes of the meter across pairs of terminals until you get a low resistance. (You just found the relay's coil.) Reverse the meter probes on those two terminals, and see if the resistance is lower. Remember which terminal the red meter lead was on when resistance was lowest. (You've just identified the polarity of the built-in snubber diode in the relay). Drop the meter probes now, and clip a couple of alligator clip wires (cheap from Radio Shack) to those two terminals; clip the red one to the terminal that had the lowest resistance with the red meter terminal on it.

Now, put the ohmmeter probes across THE OTHER TWO terminals. Be sure you're not touching the metal part of the probe with your fingers; it'll give you a false reading. The reading you should be getting is either "overflow" (super-duper high resistance, so high the meter can't read it) or something higher than 1,000,000 ohms (1 megohm).

Now, get a helper to clip the other ends of the alligator clips across your car's battery (red one to the +). You should hear a "click" from the relay. Check the ohms (resistance) again on the two terminals not connected to the battery. They should be low resistance now (less than 10 ohms).

If the above tests are successful, your problem is elsewhere.

12 posted on 11/30/2011 8:54:06 AM PST by backwoods-engineer (Any politician who holds that the state accords rights is an oathbreaker and an "enemy... domestic.")
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To: varmintman

It could be a bad relay or it could be due to low voltage or a bad ground at the relay. Use a volt meter to check the voltage going to the relay. Disconnect the relay and use an ohm meter to make sure it’s getting a good ground.

The relay uses an electromagnet to close a circuit. If the relay is weak or the current going through the magnet is weak the switch doesn’t make good contact and the electricity arcs across the contacts. This will cause the switch to prematurely fail.


13 posted on 11/30/2011 8:54:53 AM PST by mbynack (Retired USAF SMSgt)
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To: varmintman

V-man, if you don’t have an ohmmeter, you can do the test with a battery-powered continuity light that you can get at an auto supply store. Substitute “light on” for “low ohms” and “light off” for “high ohms” and you still can use my instructions for testing the relay.


14 posted on 11/30/2011 8:55:40 AM PST by backwoods-engineer (Any politician who holds that the state accords rights is an oathbreaker and an "enemy... domestic.")
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To: varmintman
It looks like you could take it apart. It looks like there's a tang on the short side of it. Try to pry it apart. Failing that, see if the coil that energizes the relay is good. Look in the schematic and see which ones those are and hook a DMM to it and see if the coil is open. If it's not open, then if you can get it apart, you could use a super fine sandpaper (1000) to clean the relay contacts. Then, throw the thing in your glove box and keep it as a spare.


15 posted on 11/30/2011 8:57:38 AM PST by Lx (Do you like it, do you like it. Scott? I call it Mr. and Mrs. Tennerman chili.)
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To: mbynack; varmintman
Use a volt meter to check the voltage going to the relay. Disconnect the relay and use an ohm meter to make sure it’s getting a good ground.

The SMSgt has a great idea here. After you test the relay, this is the next thing to check.

16 posted on 11/30/2011 8:58:05 AM PST by backwoods-engineer (Any politician who holds that the state accords rights is an oathbreaker and an "enemy... domestic.")
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To: Lx

backwoods-engineer is right. I forgot about the diode that keeps arcing down. You have to test for continuity both directions. Otherwise, everything is correct.


17 posted on 11/30/2011 9:00:27 AM PST by Lx (Do you like it, do you like it. Scott? I call it Mr. and Mrs. Tennerman chili.)
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To: varmintman
My understanding is that VIP cars with additions of bulletproof glass, ballistic panels, etc... also have the crash shut-off function removed. I assume they do some engineering to ruggedize the fuel system.

Personally, for a POV, I wouldn't want to disable that function. If the fuel pump shuts off because of an accident in my car, it won't be because kidnappers are smashing into me. And I'm very averse to burning to death. ;)

/johnny

18 posted on 11/30/2011 9:02:55 AM PST by JRandomFreeper (gone Galt)
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To: Lx; varmintman
Lx,

I like your idea of cleaning the relay's contacts if it turns out to be bad, then throwing the cleaned relay in your glove box as a spare. You don't want to trust that relay (metal pieces everywhere, yuk), but as a spare? Absolutely. As a prepper, two is one and one is none. Good advice.

19 posted on 11/30/2011 9:02:55 AM PST by backwoods-engineer (Any politician who holds that the state accords rights is an oathbreaker and an "enemy... domestic.")
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To: Lx
backwoods-engineer is right. I forgot about the diode that keeps arcing down. You have to test for continuity both directions. Otherwise, everything is correct.

Not all fuel pump relays have that diode (my '88 Toyota 4WD didn't), but the newer ones probably will, especially if the relay is actuated by the engine control unit (ECU). Microprocessors hate the little zap that relay coils (and all inductors) emit when the the current abruptly is stopped.

20 posted on 11/30/2011 9:05:18 AM PST by backwoods-engineer (Any politician who holds that the state accords rights is an oathbreaker and an "enemy... domestic.")
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To: JRandomFreeper

My 2003 Ford F-150 has a reset button for the fuel-pump shutoff. It’s fairly inaccessible (below the dash on the extreme right kick panel), so it’s possible to re-locate the cutoff switch where the driver could access it. Or, perhaps they have fuel flow monitoring; if the fuel system isn’t breached, there’s no need to turn off the pump.


21 posted on 11/30/2011 9:07:31 AM PST by backwoods-engineer (Any politician who holds that the state accords rights is an oathbreaker and an "enemy... domestic.")
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To: varmintman

Find a replacement relay from Omron or Idec and forget about it for a while.


22 posted on 11/30/2011 9:10:01 AM PST by Big_Harry (Ecc10:2 "A wise man's heart is at his right hand; but a fool's heart at his left")
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To: backwoods-engineer
The only thing that bothers me is that it might be electronic. The fact that it is enclosed in a removable plastic case instead of being potted makes the case for a relay though.

You should see the spares I carry.

I'm glad you brought up the diode, it completely slipped my mind. If you've got those probes in the correct direction, the ohmmeter should have enough voltage to cross the PN junction and it'll show continuity across the diode even if the coils open.

23 posted on 11/30/2011 9:10:15 AM PST by Lx (Do you like it, do you like it. Scott? I call it Mr. and Mrs. Tennerman chili.)
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To: Lx
Good advice.

If you don't have a meter handy, you can just rig up a set of jumpers from a piece of lamp cord to test the coil. If you can get the cover off, see if the contacts look burnt, and trace the coil wires to the contacts, and give it battery current on those contacts. The points should close. If not, the coil is shot.

If you can't get the cover off, see if there's any kind of diagram on the relay. If it's good you should get a positive "click" out of it when the coil is energized.

24 posted on 11/30/2011 9:26:07 AM PST by tacticalogic
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To: Donkey Odious

Fords. Some things never change. Had the same problem in my old Aerostar van.


25 posted on 11/30/2011 9:47:48 AM PST by pingman (Durn tootin'; I like Glock shootin'!)
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To: All

Good information here from several posters, many thanks!


26 posted on 11/30/2011 8:12:03 PM PST by varmintman
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To: varmintman

If indeed the relay failed again, you might try to determine what current the fuel pump is supposed to pull and what it is actually pulling.

You may be burning the contacts due to too high of a current.

I would be looking at replacing a pump with that kind of mileage just as preventative maintenance.


27 posted on 11/30/2011 8:27:39 PM PST by Clay Moore (The heart of the wise inclines to the right, but the heart of a fool to the left. Ecclesiastes 10:2)
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To: Lx

Good idea but unfortunately the thing cannot be taken apart to the point of seeing any contacts without destroying it.


28 posted on 12/04/2011 7:19:40 AM PST by varmintman
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To: varmintman

It doesn’t look like it’s potted in goo. It looks like it has a circuit board that snaps into the plastic container. If you have to replace it, try and take it apart, what’s the harm?


29 posted on 12/04/2011 7:56:33 AM PST by Lx (Do you like it, do you like it. Scott? I call it Mr. and Mrs. Tennerman chili.)
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