91 FJ80 Engine starts then dies immediatly

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

TownsvilleBloke

TownsvilleBloke

Joined
May 6, 2024
Threads
6
Messages
33
Location
Queensland, Australia
Hi,
so you know how it looks, that's the problem I get:


I've just replaced my MAF sensor (inside blade was broken in half), and the Air Cleaner Hoses #1, #2, #3.
Now it's not working at all. Would you know what could be the problem please ?
 
Nevermind, it "works" (it idles really high but keep running) when the MAF sensor is unplugged.
If I plug back the cable, it fails again.
What's going on ?
 
Is this a 3FE engine?
Please add the details to your signature so we know what you're referring to.

With the AFM unplugged, the engine will fire while cranking the starter and then stall shortly after releasing the key from the START position.
This is because the fuel pump relay, which Toyota calls the "circuit opening relay" has 2 coils. The first (primary) coil is fired from the starter circuit while cranking. The secondary coil is fired when the flap in the AFM opens as the engine starts to suck air.

If your 3FE engine continues to run with the AFM unplugged then someone has changed the wiring or there is a jumper in the diagnostic connector mounted on the firewall which will bypass all the fuel pump logic.

Idle speed is controlled by the ECU. If your idle speed is above 650rpm when at normal operating temp, then it's possible the throttle cable is too tight.
There should be slack in the cable at idle position.
However, if the AFM is unplugged, then the ECU is not getting the correct information to make adjustments.
 
Read what Jon says and add my "me too" to it. ;)

Mark...
 
Well,
first of all, thanks for your help !
I've checked the diagnosis box this morning :

It looks empty to me, I don't see any wire or jumper there.
I've tried to unplug the EFI Relay for 10minutes in the fuse box and I didn't get any improvement from it.

I'll disconnect the 15 amp EFI fuse I didn't touch yet and see if the restarted ECU fix my situation.
I'll keep you updated :) !
 
Removing a relay does not effect the ECU. To reset the ECU, you should remove the 15 amp EFI MAIN fuse.
That said, resetting the ECU won't solve this issue.
The fuel pump should not run with the AFM disconnected. The flap switch inside the AFM provides the ground path for the secondary coil in the circuit opening relay.
It has nothing to do with the ECU.
 
Thank you for your message @jonheld .
I would just like to know please,
is this here the part you are talking about and I should investigate/replace ?
8591030050RELAY ASSY CIRCUIT OPENING (FOR EFI)
 
when was the last time it was running good? your new AFM sounds suspect, i would test it with a multimeter, and make sure it's the right one.
 
TownsvilleBloke said:
Thank you for your message @jonheld .
I would just like to know please,
is this here the part you are talking about and I should investigate/replace ?
8591030050RELAY ASSY CIRCUIT OPENING (FOR EFI)
Click to expand...
You should diagnose the issue as opposed to throwing parts at it. All manuals and schematics are available to download from the resources section.
 
@jonheld Hi, I've had a check under the steering wheel, above the pedals, where the documentation is saying this circuit opening relay is.
This is what I found:


I don't know what I'm looking at but I assume you are right,
so the previous owner surely did some kind of crafting to power the fuel pump whatever the AFM says.
I'm clueless so I can't tell what is in front of my eyes but it does not exactly look like Toyota's work and it's exactly where you told me to investigate.

I would like to know please, what is the right methodology I should apply to start resolving this issue ?

EDIT: Also, I don't see any big red wire crossing the whole bay here:
Circuit opening relay - https://forum.ih8mud.com/threads/circuit-opening-relay.1195282/

____________________________________________________________________________

@TheBussman That's the right AFM, technically speaking I assume, because I did my order based on the Toyota part number.
It's a refurbished Aliexpress one tho, the only one I could actually find online at a reasonable price.
I cross my finger that no additional issue will come from it.
 
Last edited:
TownsvilleBloke said:
@jonheld Hi, I've had a check under the steering wheel, above the pedals, where the documentation is saying this circuit opening relay is.
This is what I found:
I don't know what I'm looking at but I assume you are right,
so the previous owner surely did some kind of crafting to power the fuel pump whatever the AFM says.
I'm clueless so I can't tell what is in front of my eyes but it does not exactly look like Toyota's work and it's exactly where you told me to investigate.
Click to expand...
The circuit opening relay hangs at the bottom of the relay block behind the left kick panel. You're looking in the wrong place.
That red wire is definitely suspect and not OEM, but I would try to trace it out and see where it's going and what it's purpose is before removing it.

1739967791232.webp


At this point I would reach out to your local Land Cruiser club and try to find someone who is familiar with the vehicle.
 
Unfortunately the car can't move right now ( except if I run it with the AMF unplugged 🤔 ) and there isn't any Landcruiser club around, my town isn't big enough for that.
I'll try to figure it out step by step and analyse what's going on, and post there.
 
Last edited:
TownsvilleBloke said:
Unfortunately the car can't move right now ( except if I run it with the AMF unplugged 🤔 ) and there isn't any Landcruiser club around, my town isn't big enough for that.
I'll try to figure it out step by step and analyse what's going on, and post there.
Click to expand...
Can you read/understand schematics?
Do you have a multimeter and know how to use it?
 
TownsvilleBloke said:
@jonheld I understand schematics, I did it in highschool 😄. I have a multimeter also indeed 🙂.
Click to expand...
Excellent.
The fuel pump circuit is shown in the ENGINE CONTROL section of the EWD. It is spread across 4 pages, so I made a single PDF to make it easier to follow. The fuel pump lives on the far right of the schemo and you can clearly see the logic operation of the dual coil circuit opening relay (COR) that runs the fuel pump.
It should be fairly easy to verify correct or incorrect operation of the COR with a multimeter. Pay close attention to the ground path that runs to the switch in the AFM. It's possible that someone grounded that line before the switch to get the FP to run.
You can also see that all FP logic can be bypassed by shorting pins 1-8 in the diagnostic connector on the firewall so I would verify that as well.

The fact that the engine will run with the AFM disconnected tells me that either the COR has failed internally (very unlikely) or that someone had their hands where they don't belong.
The design of the fuel pump logic circuit makes sure that if the engine stalls, the fuel pump shuts down. In the event of a collision, one would NOT want the fuel pump to continue to run.
 

Attachments

Last edited:
The red wires might just be aftermarket speaker wiring.
 
@jonheld Thank you very much for your very detailed explanation, it's instrumental help.
I'll get into it on Monday,
I'll keep you updated 🙂.

@landcrshr Very possibly indeed. It seems to be not involved with the whole "relays area".
 
@jonheld
Hi !
I'm back on it :).
Unfortunately this relay is very difficult to unclip (you have to bend your back between driver seat and steering wheel so you can reach, with half of your body outside the truck, you can't really see where are your hands, it's very difficult to unclip the two sides of the relay simultaneously).
I would like to know, it is safe to remove the whole relay block ( like in this post: 1995 FZJ80 Circuit opening relay - https://forum.ih8mud.com/threads/1995-fzj80-circuit-opening-relay.1006241/) so I can actually work from there or I risk to ruin even more my car ?

I've tried kind of every position this morning, and I start to think I'm doing it the wrong way.
I didn't try to tilt completely the driver's seat yet so I could lay on it on my chest and kind operate from there tho.

Second question, as we know the rig runs without the AFM cable plugged in (weirdly), it is safe to move it around a bit in a parking lot to charge back the battery (the battery is flat right now cause of my multiple attempts to start the truck, I use a jumper kit right now every time I try to start it) ?
By extension of my question there, in a purely theoric manner, if my fuel pump runs without AFM right now, does that mean I was running all that time with a fuel pump running independently from my AFM ? So technically my car could "run" right now ?

EDIT: I've decided to run the engine without AFM plugged just to give a bit of battery charge to my truck and to be sure it's actually running without AFM.
That's the video:
 
Last edited:
Couple of thoughts.
4 bolts and the front seat comes out. Don't know why you're making it painful for yourself.

There should be enough slack in the harness for you to remove the relay block and get to the rear. Just don't yank on it. Those wires are 34 years old.
 
You must log in or register to reply here.

Share this page

Back
Top Bottom