3f-e Intermittent throttle?/fuel? loss?

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I went through similar issues with my 91.

Intermittently, it would just fall on it's face when coming to a stop, then trying to take off again. I would limp it to the shoulder, but it would rev just fine in Neutral. Pop it back in gear & it wouldn't rev over 1200 RPM.

Then, suddenly, it'd run perfectly fine again. Sometimes just until another stop sign, other time for hours.

I went through a series of troubleshooting steps & throwing parts at it; including an ECU, AFM, Coil, Igniter, Coolant Temp Sensor, EFI Relay, Fuel Pump & Sock, Fuel Filter, Throttle Position Sensor, Intake Hoses, and... well, I'm sure I'm leaving out a few things.

Through all of this, I did find a couple of issues.

First, was a series of crappy reman brake boosters. One of which appeared to becoming unbonded (the diaphragm to case) when it sat in the sun & warmed up, thus creating a vacuum leak. A new Seikin booster from Curt at Cruiser Yard fixed it. For a while, anyway.

Then, out of the blue, it did it again. ONCE, then it was OK for a few days. Then, one morning on the way to work, at a stop sign, it died & wouldn't start again. After sitting for about 15-20 min, it started back up & I managed to get it home.

Further digging, uncovered a melted wiring harness; under the intake manifold, near the rear of the valve cover.

I managed to obtain a good used harness & this has now resolved the issues. No more hiccups or stumbling. Unfortunately, that didn't seem to improve my horrid fuel economy, as I had hoped it may. But, hey a guy can wish right. I guess 37's with stock gearing & trying to drive it like a hot rod are probably the underlying reason for sub 6mpg numbers.

But remember...

One does NOT drive a LandCruiser because it is financially practical. It's all about that "FEELING"

 
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I went through similar issues with my 91.

Intermittently, it would just fall on it's face when coming to a stop, then trying to take off again. I would limp it to the shoulder, but it would rev just fine in Neutral. Pop it back in gear & it wouldn't rev over 1200 RPM.

Then, suddenly, it'd run perfectly fine again. Sometimes just until another stop sign, other time for hours.

I went through a series of troubleshooting steps & throwing parts at it; including an ECU, AFM, Coil, Igniter, Coolant Temp Sensor, EFI Relay, Fuel Pump & Sock, Fuel Filter, Throttle Position Sensor, Intake Hoses, and... well, I'm sure I'm leaving out a few things.

Through all of this, I did find a couple of issues.

First, was a series of crappy reman brake boosters. One of which appeared to becoming unbonded (the diaphragm to case) when it sat in the sun & warmed up, thus creating a vacuum leak. A new Seikin booster from Curt at Cruiser Yard fixed it. For a while, anyway.

Then, out of the blue, it did it again. ONCE, then it was OK for a few days. Then, one morning on the way to work, at a stop sign, it died & wouldn't start again. After sitting for about 15-20 min, it started back up & I managed to get it home.

Further digging, uncovered a melted wiring harness; under the intake manifold, near the rear of the valve cover.

I managed to obtain a good used harness & this has now resolved the issues. No more hiccups or stumbling. Unfortunately, that didn't seem to improve my horrid fuel economy, as I had hoped it may. But, hey a guy can wish right. I guess 37's with stock gearing & trying to drive it like a hot rod are probably the underlying reason for sub 6mpg numbers.

But remember...

One does NOT drive a LandCruiser because it is financially practical. It's all about that "FEELING"

Thanks for the info. I'll keep those things in mind.
For now the plan is to daily drive it and try to diagnose it on the side of the road if it breaks down. I have an assortment of tools, an FSM and AAA. Hopefully that's enough.
 
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I'd highly encourage you not to wait on me. I daily drove it December thru most of February without this particular problem reappearing. I'm thinking it's heat related, but it's not gonna be hot here for a couple of months and with gas prices going the way they are, I don't think I'm gonna drive it super often.

I did replace the o2 sensors but haven't noticed any glaring difference.
 
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Update: It's hot outside.
I've taken it on several 50 mile+ trips, in the heat of the day and it has not repeated the problem I was having. The only thing that has changed since the last time it died id replacing the o2 sensors. Is it in anyway possible that my problem was caused by a bad o2 sensor?
 
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Finally died(temporarily) today, Here's what I found during no start situation:
Had fuel at cold start injector while cranking.
Had spark at plugs
Started checking resistances at AFM:
E2-VS=255Ω (FSM says 200-600)
E2-VC=250Ω (FSM says 200-400)
E2-THA=.430 kΩ, ambient temp. 104° (FSM says 0.9-1.3 kΩ)
This seems to point to the air temp. sensor in the AFM. Is this the smoking gun I've been looking for?
I don't really understand how the sensor works in the system.
Any insights?
Also, after sitting for around 15 minuets with the hood open I rechecked E2-THA and got 0.855 kΩ. At that point it fired right up and drove home.
 
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A faulty IAT sensor would cause a rich or lean condition, but I have trouble believing it would cause a no-start without further diagnostic testing.
If you have spark and fuel this engine should run, so I think you're still missing one.
I'd bet that the injectors are not firing properly during a no-start.
The 3FE ECU fires 2 banks of 3 injectors. Each injector gets a constant +12 on 1 terminal, and the ECU grounds the other to fire the injectors.
I would verify the +12 to the injectors.
 
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Would you check at the injector, the ecu or both?
The +12 to the injectors is off of the ignition circuit. The ECU just grounds 1 of 2 terminals to fire the 2 banks. 3 injectors fire at the same time. You will most likely need an oscilloscope to monitor the negative pulses from the ECU.

Have you checked for chafed wires where the ECU harness feeds through the firewall?
 
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The +12 to the injectors is off of the ignition circuit. The ECU just grounds 1 of 2 terminals to fire the 2 banks. 3 injectors fire at the same time. You will most likely need an oscilloscope to monitor the negative pulses from the ECU.

Have you checked for chafed wires where the ECU harness feeds through the firewall?
The harness at the firewall looks good to me, the rubber boot is still intact and the harness itself appears unmolested.
This has been over my head pretty well from the beginning. Any testing requiring an oscilloscope is definitely outside my ability.
 
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The harness at the firewall looks good to me, the rubber boot is still intact and the harness itself appears unmolested.
This has been over my head pretty well from the beginning. Any testing requiring an oscilloscope is definitely outside my ability.
I would verify +12 to the injectors. A plain old voltmeter will work just fine.
 
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Just to be sure.
The B-G wire is the +12 from the ign circuit and the W-L and Y go to the ECU where the circuit gets grounded to fire the injectors. So, I need to verify that I have +12 at the B-G wire with the key on.
Is this correct?
 
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Just to be sure.
The B-G wire is the +12 from the ign circuit and the W-L and Y go to the ECU where the circuit gets grounded to fire the injectors. So, I need to verify that I have +12 at the B-G wire with the key on.
Is this correct?
Yes, but keep in mind that you will see +12 on both sides of the injector because you're reading across a coil. The only time you will be able to see a change is when that bank of injectors fire. This is where a scope is helpful.
 
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I went through similar issues with my 91.
...

I went through a series of troubleshooting steps & throwing parts at it; including an ECU, AFM, Coil, Igniter, Coolant Temp Sensor, EFI Relay, Fuel Pump & Sock, Fuel Filter, Throttle Position Sensor, Intake Hoses, and... well, I'm sure I'm leaving out a few things.
...
...
Then, out of the blue, it did it again. ONCE, then it was OK for a few days. Then, one morning on the way to work, at a stop sign, it died & wouldn't start again. After sitting for about 15-20 min, it started back up & I managed to get it home.

Further digging, uncovered a melted wiring harness; under the intake manifold, near the rear of the valve cover.
I would, seriously consider pulling the intake plenum off & looking at the harness, where it runs along the fuel rail.

I went through much of what you are doing, thinking it may be the harness, and HOPING I wouldn't have to pull the intake apart.

I ended up spending WAAAAYYY more money and time, trying to eliminate everything else; when it wasn't nearly as big of a deal to pull the intake apart as I'd imagined.
 

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