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 EFI Fuse
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deedub626
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871 posts [100%]
Your next door neighbor ca

 EFI Fuse Reply  Edit


What usually cause EFI fuse to get blown out?

My 15amp EFI fuse blown out while driving. After the EFI fuse is blown out, the CEL light will not turn on when the key is in "on" position. I replaced the fuse and the CEL light is back on so i decided to start the car. The car will start and stay on for about a second then die and the EFI fuse is blown again and the CEL light is off while the key is in "on" position.

My question is- where should i start checking for problems? I have a kill switch to the fuel pump and i check the wiring and connection, and they look fine.

What do i need to do to prevent using another fuse? is there something i can do to make sure the problem is fixed before i waste another fuse?

I heard the o2 sensor might cause the problem if its grounded incorretly.

thank you in advance!



Practice makes perfect, but if nothing is perfect then....why practice?




Red




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9661 posts [78%]

 Re: EFI Fuse (deedub626) » Reply  Edit


To blow that fuse you'd probably need a chafed wire or dead short somewhere in the wiring. The factory procedure to test for a short is to replace the fuse with a test light while the power is off. Then disconnect everything the fuse feeds, power on, and reconnect one at a time until the light goes on. When the light goes on you've found the piece that is consuming power, i.e. shorted out.

The EFI fuse is carried across the EFI main relay (could be shorted in there, not likely) and then goes on to power a number of things:
TVIS-VFV and VF lead on the ECU
One lead to the AFM (on the 85, so that's probably to the MAF on the later models)
Two "B" leads on the ECU itself

Maybe more, sometimes the wiring diagram is hard to follow.

I'd use a low-power test light to limit the amount of current that is being drawn by that short, LED if you can. If you can borrow a helper to turn the power on/off as you test each segment, that helps make sure the power is turned off promptly and the wiring stressed less by any overload.





--Original owner, '85 Corolla GTS. Will trade for a Cadillac-Gage V150, or a Ford GT, in similar condition.
deedub626
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871 posts [100%]
Your next door neighbor ca

  » Reply  Edit


resolved. It was my kill switch that was causing this problem...stupid me...



Practice makes perfect, but if nothing is perfect then....why practice?


Red




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9661 posts [78%]

 Re: (deedub626) » Reply  Edit


Well, you solved it, that's what counts.

Memo: Kill switch should *interrupt* starting, not short anything out. Although, if the kill switch blows something important like the EFI fuse...that certainly will slow down the guys trying to steal the car, for a longer time.

So maybe it isn't such a bad thing...as long as you remember to throw that switch before starting the car.



--Original owner, '85 Corolla GTS. Will trade for a Cadillac-Gage V150, or a Ford GT, in similar condition.
deedub626
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871 posts [100%]
Your next door neighbor ca

  » Reply  Edit


After reading what you post in return, you got me wondering and not so sure if i really did solved it.

The kill switch is acting as a by pass for the fuel pump. If the switch is bad (been working over two years), shouldn't the kill switch short the EFI fuse? or could it be something else?





Practice makes perfect, but if nothing is perfect then....why practice?


Red




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9661 posts [78%]

 Re: (deedub626) » Reply  Edit


As a bypass? That would mean connecting the fuel pump wire(s) to something else, to bypass the fuel pump. Not possible. A kill switch on the fuel pump would normally be a SPDT switch. One position breaks the positive lead to the fuel pump, cutting off power. The other position allows power to the pump. ou could use a DPDT switch to make/break both lines but there's not anything to be gained that way except OCD satisfaction.

If the switch was a SPST in the positive lead, it would be most unlikely that it failed in a way that shorted out to ground. Not impossible--but REALLY unlikely. Or as they say on Top Gear "Oh, COME ON!"

Even the unlikely happens.



--Original owner, '85 Corolla GTS. Will trade for a Cadillac-Gage V150, or a Ford GT, in similar condition.
deedub626
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871 posts [100%]
Your next door neighbor ca

  » Reply  Edit


I probably used the wrong word.

The ground cable on the fuel pump is cut, the ground cable is connect to the switch then switch back to the ground cable. How likely does these switch fail?

I took a short drive and everything seen ok, but I didn't want to take a chance and be stranded again.



Practice makes perfect, but if nothing is perfect then....why practice?


Red




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9661 posts [78%]

 Re: (deedub626) » Reply  Edit


AH, so you interrupted the ground to the fuel pump, instead of the hot.

Why on earth??

If the switch failed, either it would fail "open" and nothing would happen, or it would fail and short to ground, and the car might run. Or might blow a fuse from pulling too much current on the accidental ground.

But it you interrupt the ground ot the fuel pump, depending on how it is made and assembled, it is also possible that the fuel pump is finding another ground (a chassis ground) which is also pulling too much current and blowing the fuse, the same way.

In both cases possible, not very likely but possible. More likely the fuel pump is finding a high-resistance path tto ground and blowing the fuse.

I'd eliminate those possibilities by moving the kill switch into the positive lead to the fuel pump, and repairing the ground lead. That way the fuel pump either gets power or not, and the ground is uninterrupted. And while you've got the switch out, you can test it with a meter, or bulb, or buzzer, to see if it works. Odds are it does.





--Original owner, '85 Corolla GTS. Will trade for a Cadillac-Gage V150, or a Ford GT, in similar condition.
deedub626
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871 posts [100%]
Your next door neighbor ca

 Re: (Red) » Reply  Edit


I meant to say positive, i must be half asleep...

I took out the switch and tested it with a multimeter. Black lead connect to the ground on the switch and red lead connect to the positive. The multimeter is not getting any reading.

I wanted to make sure the meter is working properly so I have made contact with black adn red lead. The multimeter started beeping and is showing there's current going thru



Practice makes perfect, but if nothing is perfect then....why practice?


Red




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9661 posts [78%]

 Re: (deedub626) » Reply  Edit


Half asleep? Hell no, that's my job, you go find something else to do.<G>

OK, set the multimeter to an OHMS scale. 200, 2000, 20000, any one of them. The switch is out of the car, disconected for this test.

Put one meter lead on each switch termainl, assuming there are only 2 terminals and it is a SPST switch that just goes on/off, no middle position.

Hold the leads, one on each terminal. The meter should either show zero (and some will beep to confirm that) or something like 1.0 or 0.5, close to zero. Meters aren't always perfect, close to zero is what you want.

Or, the meter will show "overrange" which can be a batch of dashes or blinks or something else, depending on the meter. When the switch is ON, the meter should show zero. When you repeat the test with the switch OFF, the meter should show "overrange".

Now AFAIK with every toggle switch or rocker switch on the market, if the toggle is "away" from the half of the switch that the contacts are on, it normally will be switched on. With a rocker, you push down on the side away from the contacts, and that turns it on. Usually, anyhow.

If the switch is not out of the car, you have to test with the voltmeter settings instead of the ohms settings. But first get some sleep, stop poaching on my job! <VBG>



--Original owner, '85 Corolla GTS. Will trade for a Cadillac-Gage V150, or a Ford GT, in similar condition.
ToeKnee805
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613 posts [90%]
Santa Paula California

 Re: (Red) » Reply  Edit


This happened to me last night. Ended up being my kill switch too. Some of the heat shrink insulation broke off, and shorted it to a metal piece. But i routed my killswitch to the Positive side of the fuel pump, not the ground.



1986 Corolla GT-S
1989 240SX Hatch
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Red




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9661 posts [78%]

 Re: (ToeKnee805) » Reply  Edit


That would do it. If the kill switch is in the + wire, where it should be, and it wasn't properly insulated, it could very easily wiggle around, short out, blow the fuse. Wiggle back, no sign of problem.

This is why that damned poverpriced heat-shrink tubing is cheap at any price. Or butyl tape, to wrap the whole base of the switch in. And some velcro, or a dab of sealant, to stick the switch where it can't move around or get hit.

I'd say put it in the bottom of a 35mm film can but these days, everyone says "Film? Can? Did they really can film?"




--Original owner, '85 Corolla GTS. Will trade for a Cadillac-Gage V150, or a Ford GT, in similar condition.
 



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