FJ80 3FE Intermittent Hot Power Cut

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mtnbiker4evr13

mtnbiker4evr13

10 Year
Joined
Nov 1, 2011
Threads
10
Messages
295
Location
Asheville NC
Guess its my turn to play "Find the intermittent 3FE fault"..

Symptoms:
On trail rides on warm days idling/going slow in low range, when driving any throttle input over 1/8 to 1/4 pedal will cause the engine to cut out/stumble. Happens under load and in neutral, no codes when checked with CEL flashes.

If you shut it off and restart the problem goes away for a while. Does not happen when driven at road speeds. Seemed to occur getting back on the road after a trail in high range or running down trail at higher speeds in low range.

Zoltar's Prediction:
Searching Mud has me leaning AFM or TPS if the heat is making the ECU see major fault and going into limp mode. TPS and AFM were previously checked and TPS adjusted to spec as part of the resurrection work after I got the vehicle in February as a non runner. Have since put 2,000mi on and it runs great daily. Underhood temps are high when issue occurs.

I've also had the ubiquitous overheated EFI relay but that presents differently where it dies and won't idle, look for CEL light and it is easy to identify. After typing out when it happens I suppose the relay could be suspect if the system pulls more load at higher throttle inputs.

Previous work:
New plugs(ngk), wires(intermotor), cap/rotor(oem), intake boots(oem), coolant temp switch/sender(oem), EFI Relay(oem), fully desmogged..

Pictures for interest:
20250616_102158.webp

20250616_102235.webp


So, wanted to cast the question out to the wider cumulative awesomeness of Mud before I just parts cannon since its hard to get it into the failure mode predictably. It runs amazing the other 99.9% of the time albeit somewhat turdish with 37s/stock gears and gets 11mpg. I like the 3FE so a swap is not in the plan 😄
 
mtnbiker4evr13 said:
AFM or TPS if the heat is making the ECU see major fault and going into limp mode.
Click to expand...
If that were the case, you'd get an error code.

The most common issues would be an intermittent fusible link or poor/corroded crimps/loose terminals in the relay box.
I would suggest a bit of "percussive diagnostics". Give the EFI relay a tap tap tap as well as connector EB1, which runs the show for all of the +12 for the EFI system.
Current draw across the EFI relay remains pretty constant throughout the RPM range.
 
mtnbiker4evr13 said:
Would that code be hard stored to be retrieved after the key is turned off?
Click to expand...
Yes. Codes are stored in memory. Active codes will throw a CEL when the engine is running and the CEL can clear on its own, but the code remains in memory.
This is why it's important to clear codes when troubleshooting. This way you know you're not looking at an old code.
 
Makes sense, didn't know if this ODB1 had volatile codes or if it was just there vs not there. Will do more digging on power side since EFI relay was already suspect.
 
As an update to the thread:

Put 14,000 miles on last year with this issue being there in the background. Had converted EFI relay to a bosch style after issues overheating the relay on the trail at GSMTR, has been solid since.

In Oct it had a weird stumble/low power/overly rich issue at all times and tried more diagnosis but ended up using the parts cannon with Cardone camry AFM, aftermarket FPR, new NGK plugs, OEM cap/rotor, new fuel filter. Ended up being the fuel pulse damper (thanks @Marco Lau)

Ran great all winter as a daily but had heat issues at the Carolina Relic Run this past weekend. Hot weather and long idling times with A/C had underhood temps high (but not hot on temp gauge) and it started doing the stumbling misfire under load again but did not clear after restarting. Still does it at all times now. Fuel tank also built pressure with new vc120 canister and with vent open.

-no codes displayed key on or running
-fuel pressure passes FSM tests with ~19-20psi remaining at 5min leak down test. 37psi running FPR regulating, 41psi vacuum unhooked from FPR and 41psi B+ to FP jumped key on.
-driving FP is 41 when under load throttle pressed (makes sense, vacuum drops as throttle plate opens).
-put original AFM on with no change (had passed FSM ohm testing)
-reset ECM no change
-pulled individual spark plug wires and all cylinders are contributing at idle.
-pulse damper is "pulsing" checked with finger on little Phillips screw under plastic cap while running, FP is steady.

290k+ miles and it uses oil at differing rates 1qt/1000mi average. Coil/ignitor could be suspect but would expect an all or nothing failure with heat vs this kind of issue. Injector wiring could be suspect, did a desmog when first working on it and wires were "crispy" but intact and working. Fuel pump was on my short list with the possible stuck check valve but pressure checks ruled that out.

Tl/rd: heat on trail led to constant stumble under load.

@jonheld calling on the 3Fe messiah.. again.. 😂
 
Last edited:
mtnbiker4evr13 said:
As an update to the thread:

Put 14,000 miles on last year with this issue being there in the background. Had converted EFI relay to a bosch style after issues overheating the relay on the trail at GSMTR, has been solid since.

In Oct it had a weird stumble/low power/overly rich issue at all times and tried more diagnosis but ended up using the parts cannon with Cardone camry AFM, aftermarket FPR, new NGK plugs, OEM cap/rotor, new fuel filter. Ended up being the fuel pulse damper (thanks @Marco Lau)

Ran great all winter as a daily but had heat issues at the Carolina Relic Run this past weekend. Hot weather and long idling times with A/C had underhood temps high (but not hot on temp gauge) and it started doing the stumbling misfire under load again but did not clear after restarting. Still does it at all times now. Fuel tank also built pressure with new vc120 canister and with vent open.

-no codes displayed key on or running
-fuel pressure passes FSM tests with ~19-20psi remaining at 5min leak down test. 37psi running FPR regulating, 41psi vacuum unhooked from FPR and 41psi B+ to FP jumped key on.
-driving FP is 41 when under load throttle pressed (makes sense, vacuum drops as throttle plate opens).
-put original AFM on with no change (had passed FSM ohm testing)
-reset ECM no change
-pulled individual spark plug wires and all cylinders are contributing at idle.
-pulse damper is "pulsing" checked with finger on little Phillips screw under plastic cap while running, FP is steady.

290k+ miles and it uses oil at differing rates 1qt/1000mi average. Coil/ignitor could be suspect but would expect an all or nothing failure with heat vs this kind of issue. Injector wiring could be suspect, did a desmog when first working on it and wires were "crispy" but intact and working. Fuel pump was on my short list with the possible stuck check valve but pressure checks ruled that out.

Tl/rd: heat on trail led to constant stumble under load.

@jonheld calling on the 3Fe messiah.. again.. 😂
Click to expand...
If this is engine coolant temperature related, i would look into the water temperature sensor on the thermostat housing....rule out bad wiring....
a faulty sensor can mismanage fuel mixture....
 
Marco Lau said:
If this is engine coolant temperature related, i would look into the water temperature sensor on the thermostat housing....rule out bad wiring....
a faulty sensor can mismanage fuel mixture....
Click to expand...
That sensor is new denso with new connector from everyone's favorite "SNOW EDITION!!!" supplier. New denso thermostat, gasket, 2 row liland radiator and new denso waterpump and hoses in fall.

Coolant temp seems independent, happening cold and hot now. But reared its head on 90 degree day on trail crawling at snail speed a/c on and winching.
 
Maybe I missed it, but I don't see where you replaced the fusible link as I mentioned in post #2.
You seemed to have bypassed some of the low hanging fruit, unless I'm mistaken.
Remember, it's a tractor motor with 1st generation fuel injection.
 
mtnbiker4evr13 said:
That sensor is new denso with new connector from everyone's favorite "SNOW EDITION!!!" supplier. New denso thermostat, gasket, 2 row liland radiator and new denso waterpump and hoses in fall.

Coolant temp seems independent, happening cold and hot now. But reared its head on 90 degree day on trail crawling at snail speed a/c on and winching.
Click to expand...
Do you have a pic of your engine bay you can share for reference?
 
Update to this:
Went through some other checks and found a gas soaked #2 spark plug and no compression issues. Concluded the #2 injector which was the new Beck Arnley I had installed last year was stuck open. After some "percussive maintenance" it woke back up and it runs fine again. As we already knew, used good OEM beats these new aftermarket ones...

I think in the heat on trails climbing etc. The injector seized and depending on rpm #1 and #3 cylinders were getting some of the excessive fuel which caused the under load stumble as well as #2 being dead. Luckily it didn't seem to fuel wash the cylinder with compression results within a few psi of each other across the board. 3FEs are tough.

Good OEM injector ordered though @cruisermatt and he was what spurred on the compression check so hats off to him!
 
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