Crank no start EFI Fuse?

musthave

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97 Land Cruiser, normal temperatures, no other issues. Great maintenance. New battery. 185K Miles.

EFI fuse blows instantly when put in, thus causing the crank no start issue.

I've been reading through a few posts including : EFI Fuse Blowing -- Ideas?
 
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musthave

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I finally got around to seeing what I could ascertain on this today.

I unplugged the Fuel Pump Relay, inserted new 15A fuse. Turned ignition to ON, fuse blows.

Obviously, no codes.

Based on the threads I've read, it sounds like the fuel pump or wiring. Seems odd that it would have happened suddenly the minute I went from pavement to light gravel. Any other suggestions as to what I should look at before the fuel pump?
 

musthave

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With the Fuel Pump Relay unplugged, and the fuse still blowing, that eliminates the fuel pump being the culprit.
 
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musthave

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I'm not an electrician (though now is probably a good time to take some classes online), looking at this diagram, removing the Fuel Pump Relay eliminates the Fuel Pump as the culprit.

1585233158666.png
 

musthave

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So, I swtiched out the EFI Relay and BINGO! Note to self, that's probably a spare worth keeping.

Also, as @Dave 2000 said, "If you look at the EFI relay socket IIRC there are many terminals but only two that are larger than the rest. Jump the larger of the two, this will run your fuel pump continously, this is a great get you home trick, remember though you have no anti flooding/impact protection with the jumper in place."

Issue resolved. SEE BELOW...
 
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musthave

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1585276218664.png



So I took it for a drive, everything worked great. As I got off the interstate everything turned off, coasted into a perfect parking spot, no problem.

EFI fuse blown. Ok, get a ride home, get another known good EFI Relay and 15A fuse, go back to the cruiser plug in the good EFI Relay, plug in the EFI fuse, as soon as I turn the ignition on, the fuse blows. Sooo....

What next? Upstream is the Fuel Pump Relay, Fuel Pump, and ECU, anything else?

How can I isolate further?
 
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ppc

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You have an intermittent problem that I suspect is caused by an electrical short in a wiring harness. One problem reported in the past are with the harnesses that feed the O2 sensors.
 
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Unplug the fuel pump relay again and see if the fuse still blows. If not put relay back in see if fuse blows. It’s intermittent so it’s gonna be a prick to find. There is not much in the diagrams you posted. Circuit opening relay, fuel pump relay or fuel pump, unless it’s something in the computer or something else as mentioned, O2 sensor.
I would pull the fuel pump, it is only a 30 minute job to swap out pumps. Pull middle row, flip carpet, 2 hoses, 1 plug, 8 screws.

If fuse does not blow, then don't drive. Grab wire harness and start jiggling it, I have found shorts like that before!
 
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short guess is you have a short somewhere on the highlighted circuit
I say that because the fuse blows when power is made at the ignition switch which fires the Circut Opening Relay (behind left kick panel), which then allows power to the Fuel Pump Relay, provided that the EFI main relay has been fired.
The harness passes through the firewall between the EFI main Relay and the COR, look for a chaffed spot.
Do you have the EWD.pdf? In the 1996 version of the pdf you'll want pages 61 through 70 inclusive.
I'll scan you a copy and email them if you need them.

1585324155885.png
 
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musthave

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Unplug the fuel pump relay again and see if the fuse still blows. If not put relay back in see if fuse blows. It’s intermittent so it’s gonna be a prick to find. There is not much in the diagrams you posted. Circuit opening relay, fuel pump relay or fuel pump, unless it’s something in the computer or something else as mentioned, O2 sensor.
I would pull the fuel pump, it is only a 30 minute job to swap out pumps. Pull middle row, flip carpet, 2 hoses, 1 plug, 8 screws.

If fuse does not blow, then don't drive. Grab wire harness and start jiggling it, I have found shorts like that before!
I have a fuel pump and all the miscellaneous parts on order, along with a fuel pump relay, some efi relays, and the resistor. Meantime I will try the above and report my findings.

short guess is you have a short somewhere on the highlighted circuit
I say that because the fuse blows when power is made at the ignition switch which fires the Circut Opening Relay (behind left kick panel), which then allows power to the Fuel Pump Relay, provided that the EFI main relay has been fired.
The harness passes through the firewall between the EFI main Relay and the COR, look for a chaffed spot.
Do you have the EWD.pdf? In the 1996 version of the pdf you'll want pages 61 through 70 inclusive.
I'll scan you a copy and email them if you need them.

View attachment 2250722
The wires are all in a loom, tightly wrapped, I am going to look for any areas where the loom has exposed wires though.

As for the ECU, I don't think that enters into the question yet, but I may be wrong.
 
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I have a fuel pump and all the miscellaneous parts on order, along with a fuel pump relay, some efi relays, and the resistor. Meantime I will try the above and report my findings.



The wires are all in a loom, tightly wrapped, I am going to look for any areas where the loom has exposed wires though.

As for the ECU, I don't think that enters into the question yet, but I may be wrong.
Not sure about your year, but my 93 has the wires for the aft bank O2 sensor running on top of the tranny. It comes out of the bundle under the intake manifold. I am not a large man and extremely flexible. With the front tires all the way right I am able to fit in the l/h wheel well and access that bundle😳
 
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I do not believe you have the same challenge that I did but I had a nasty series of ecu firing troubles, I ultimately found that the harness was deteriorating and had a bad splice which once discovered and repaired solved my problem. I expect that you had a worn wire or splice and the vibration of road to gravel just finished something. I would continue on your path of checking and cleaning but would advise to buy a multimeter and learn how to check for continuity and for voltage, then start tracing thru the schematics you have. It will most likely be a simple failure and easy to fix..... once you find it
 
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I vaguely recall a thread talking about wires chafing by the glove Bock and causing EFI issues.

Could be wrong and didn't search. You can do that.
You are not wrong, but I think it only applies to OBD2.
There is a harness that runs along the glove box lower support frame. It was starting to wear through the bundle when I inspected this area on my 97 LX450.

There is also a small wire harness that runs along the right (Maybe left. Not enough coffee yet) front frame rail that is secured with plastic clips. When the clips break off, the harness can come in contact with the front drive shaft. As you can imagine, this will cause woe and strife as it wears through.

Another area of concern is the fuel pump wiring that runs under the c-pillar on the drivers side.

Instead of going through a bucket of fuses, you can use a multi meter that has a continuity beep tone. One lead in the load side of the EFI relay socket, the other lead to ground. If you start poking around and doing some percussive diagnostics, you'll hear the beep tone when it shorts.

@musthave Please note that the diagram I gave you in the other thread was from a 1991 fuse block. The later models rotated the EFI fuse socket 90 degrees CCW. The pinouts are identical as are the wire colors.

Fender Relay Block.jpg
 
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Here is a tool I made to help with electrical shorts. I am an aircraft mechanic by trade so I have access to various amp rating circuit breakers. It is quite easy to build this tool, as you can see, and it saves the hassle of buying fuses when you have problems like this!

image.jpg


image.jpg


image.jpg
 
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You have an intermittent problem that I suspect is caused by an electrical short in a wiring harness. One problem reported in the past are with the harnesses that feed the O2 sensors.

This

Happened to me when I replaced the old exhaust with a new Bosal system.

Had to do a lot of banging on the old pipes and one of the O2's somehow got shorted and kept blowing the fuse.



Left it unlplugged, drove home and installed a new O2 the next day
 

musthave

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I do not believe you have the same challenge that I did but I had a nasty series of ecu firing troubles, I ultimately found that the harness was deteriorating and had a bad splice which once discovered and repaired solved my problem. I expect that you had a worn wire or splice and the vibration of road to gravel just finished something. I would continue on your path of checking and cleaning but would advise to buy a multimeter and learn how to check for continuity and for voltage, then start tracing thru the schematics you have. It will most likely be a simple failure and easy to fix..... once you find it
I finally got under the cruiser, looks like one of the connectors off of the O2 harness was broken, Neutral Switch I believe. Picture below.

You are not wrong, but I think it only applies to OBD2.
There is a harness that runs along the glove box lower support frame. It was starting to wear through the bundle when I inspected this area on my 97 LX450.

There is also a small wire harness that runs along the right (Maybe left. Not enough coffee yet) front frame rail that is secured with plastic clips. When the clips break off, the harness can come in contact with the front drive shaft. As you can imagine, this will cause woe and strife as it wears through.

Another area of concern is the fuel pump wiring that runs under the c-pillar on the drivers side.

Instead of going through a bucket of fuses, you can use a multi meter that has a continuity beep tone. One lead in the load side of the EFI relay socket, the other lead to ground. If you start poking around and doing some percussive diagnostics, you'll hear the beep tone when it shorts.

@musthave Please note that the diagram I gave you in the other thread was from a 1991 fuse block. The later models rotated the EFI fuse socket 90 degrees CCW. The pinouts are identical as are the wire colors.
Thank you for the updated diagram :) That matches this cruiser.

I'm going to look at the C-Pillar this afternoon and find that wiring and have a look. Regarding the testing, will that work while the key is out? The clips on the O2 harness look good, but I do have a bad connector, looks like a fresh plastic break, perhaps the wiggling of this blows the fuse, possible?

02harness1.jpg


O2harness2.jpg
 

musthave

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You are not wrong, but I think it only applies to OBD2.
There is a harness that runs along the glove box lower support frame. It was starting to wear through the bundle when I inspected this area on my 97 LX450.

There is also a small wire harness that runs along the right (Maybe left. Not enough coffee yet) front frame rail that is secured with plastic clips. When the clips break off, the harness can come in contact with the front drive shaft. As you can imagine, this will cause woe and strife as it wears through.

Another area of concern is the fuel pump wiring that runs under the c-pillar on the drivers side.

Instead of going through a bucket of fuses, you can use a multi meter that has a continuity beep tone. One lead in the load side of the EFI relay socket, the other lead to ground. If you start poking around and doing some percussive diagnostics, you'll hear the beep tone when it shorts.

@musthave Please note that the diagram I gave you in the other thread was from a 1991 fuse block. The later models rotated the EFI fuse socket 90 degrees CCW. The pinouts are identical as are the wire colors.

View attachment 2251649
As soon as I go from load to ground I get a steady beep.


With both O2 sensors disconnected, the Neutral Switch disconnected (broken above). When I disconnect the Fuel Pump Relay by the brake booster on the fender, put in a new fuse, turn the key, it blows the fuse. Safe to say it's not the fuel pump relay, but what else can I summize from that?
 
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