3FE surging issue (solved)

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Joined
Nov 15, 2021
Messages
8
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USA
Making this post to save the headache that this issue caused me.

For the past 2 years I have had relatively good luck with my 91 land cruiser with 256xxx on the clock, but there has always been a nagging issue at the mid RPM range only when in gear. The truck would surge with a burst of power like I wasn't firing on all cylinders than all of a sudden I was and it would surge forward with power, but it really wasn't causing a problem in day to day driving

Fast forward to this month where I finally bit the bullet and decided to do my exhaust manifold gaskets and downpipe donut gaskets.

After the job was done and verified everything was plugged in, reconnected, smoke tested for vacuum leaks, etc. I took it for a test drive. New something was wrong immediately. Rev's in first were fine, shift to second fine, start to go through the powerband the truck fell on its face...no power....pressed more on the gas and still barely moving...truck shifted to third and was loping around missing like crazy at 35 mph and falling on its face sputtering. I shifted the lever to 2nd and went pedal to the metal and the truck lurched forward with full power? So lower RPM range good, mid RPM range terrible, high RPM range good?
Brought the truck back to the garage and verified everything that needs to be unplugged when doing the exhaust manifold was still plugged in and checked all injectors with a long screwdriver that I used as a stethoscope, then I started verifying all sensors and meters were in spec with a multi meter. Everything check out, AFM, IAC, TPS, coolant temp sensor for ecu, etc. Even start unplugging vacuum lines to make sure they weren't in the wrong place. Checked fuel pressure regulator with old one I had lying around. Unplugged each sensor one at a time taking test drives in-between, still NOTHING. Still couldn't figure it out.....Figured if I did exhaust manifold gaskets I might as well check the exhaust sensors as well....unplugged each o2 sensor, check engine light came on, took for test drive anyway.....THAT WAS THE ISSUE......the truck drove like brand new.......I had no check engine light prior to the unplugging the sensors?

Currently driving around with a check engine light on due the unplugged o2 sensors but I don't care cause I can actually drive the thing.....if I had to guess, my leaking exhaust manifold threw off the air/fuel ratio at the o2 sensor starving the truck of fuel due to fresh air entering through the blown out exh gasket. The ecu must have stored the data and didn't clear it when I started the truck after doing the gaskets and kept the same parameters OR the sensors are bad and this has been my problem for the past two years....

will keep updated, hope this helps someone!
 
Joined
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I consider it exactly that. You found a probable cause. At this point you have "solved" nothing.
I have solved the issue of my surging problem by indicated that the o2 is the root cause, not hard to understand. What I do going forward is called a solution.

Definition of solve, ”find an answer to, explanation for, or means of effectively dealing with (a problem or mystery).”

Google it.
 
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nor cal
This isn't the guy you want to argue about 3FEs with....
@jonheld is the person's replies you look for when scanning the threads when something is going on with your rig.
 
Joined
Nov 15, 2021
Messages
8
Location
USA
This isn't the guy you want to argue about 3FEs with....
@jonheld is the person's replies you look for when scanning the threads when something is going on with your rig.
not arguing, solved states that I found the cause of an unexplained issue, literally the definition of solving something.

This post was meant to help someone out there who may be going through a similar issue and didn't know where to look next, not to go back and forth over the meaning of the word solve..
 
Joined
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I have solved the issue of my surging problem by indicated that the o2 is the root cause, not hard to understand. What I do going forward is called a solution.

Definition of solve, ”find an answer to, explanation for, or means of effectively dealing with (a problem or mystery).”

Google it.
I enjoy these discussions.
By unplugging the O2 sensors, your ECU that was designed in 1986 is in an open loop mode. It is now ignoring sensor inputs and running a preset set of parameters.
Now I'm not saying that the issue is not the O2 sensors, but it very well may not be.
Until you have replaced the O2 sensors, verified connectivity back to the ECU inputs, cleared the CEL by resetting the ECU, and going on a test drive, you are still speculating.
Remember that this is 1st generation EFI. The ECU has very limited memory and very narrow sensor parameters within the operating range. It's just not that smart.
 
Joined
Oct 30, 2020
Messages
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GA
Help! I'm down in Florida 600 miles from home. On the road I have a serious fuel air ratio problem. My 1992 274k miles landcruiser keeps stalling. I suspect it was fuel related. I confirmed it was in fact a bad a TPS because it was out of spec and was the only CEL. I replaced it and 100% certain it is within the specs because I used a FSM and a feeler gauge to set it. No more CEL while I was at that I checked per FSM the AFM and it was within specs. My car after still keeps dying for fuel so replaced the fuel filter and fuel pump along with the sock. After that it still stumbles so I replaced the green coolant temperature switch that feeds the ECU not to confuse with the dash temperature one. My car still stumbles after operation temperature. So I got a fuel pressure gauge and checked at the port on the rail underneath the manifold for fuel pressure readings it reads 35-38 psi. I came this far so i replaced the fuel damper just in case from NAPA. My car stills stumbles. I got desperate and clamped off the fuel return line from the fuel pressure regulator just in case it was bad and was stuck open and drove it for many miles. Car still stumbles. I checked the open relay it was good along with the efi fuse with the spare used for the heater blower. After all this it still stumbles. I ran into this thread for more info I wanted to see if I can unplug both 02 sensors to see if I can get it to stay open loop. Still stumbles. So I basically replaced everything connected to the fuel line except for the fuel pressure egulator. I clamped off the return for now

So in order of operation.

1. 1 CEL replaced in specs TPS
2. AFM checked per specs
3. Replaced fuel pump and sock
4. Replaced fuel filter
5. Replaced green coolant temperature sensor used for ecu
6. Replaced fuel pressure damper

Did not work still stumbles like dying for fuel.

Last messure tried to get it to stay in open loop by unplugging both 02 sensors

HELP!!! What did I miss??

@jonheld
 
Last edited:
Joined
Nov 9, 2012
Messages
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Olathe, KS, USA
Help! I'm down in Florida 600 miles from home. On the road I have a serious fuel air ratio problem. My 1992 274k miles landcruiser keeps stalling. I suspect it was fuel related. I confirmed it was in fact a bad a TPS because it was out of spec and was the only CEL. I replaced it and 100% certain it is within the specs because I used a FSM and a feeler gauge to set it. No more CEL while I was at that I checked per FSM the AFM and it was within specs. My car after still keeps dying for fuel so replaced the fuel filter and fuel pump along with the sock. After that it still stubles so I replaced the green coolant temperature switch that feeds the ECU not to confuse with the dash temperature one. My car still stumbles after operation temperature. So I got a fuel pressure gauge and checked at the port on the rail underneath the manifold for fuel pressure readings it reads 35-38 psi. I came this far so i replaced the fuel damper just in case from NAPA. My car stills stumbles. I got desperate and clamped off the fuel return line from the fuel pressure regulator just in case it was bad and was stuck open and drove it for many miles. Car still stumbles. I checked the open relay it was good along with the efi fuse with the spare used for the heater blower. After all this it still stumbles. I ran into this thread for more info I wanted to see if I can unplug both 02 sensors to see if I can get it to stay open loop. Still stumbles. So I basically replaced everything connected to the fuel line except for the fuel pressure egulator. I clamped off the return for now

So in order of operation.

1. 1 CEL replaced in specs TPS
2. AFM checked per specs
3. Replaced fuel pump and sock
4. Replaced fuel filter
5. Replaced green coolant temperature sensor used for ecu
6. Replaced fuel pressure damper

Did not work still stumbles like dying for fuel.

Last messure tried to get it to stay in open loop by unplugging both 02 sensors

HELP!!! What did I miss??

@johnheld
@jonheld

OP: You spelled it wrong.....
 
Joined
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Messages
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Location
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Website
www.sdsysdesign.com
Help! I'm down in Florida 600 miles from home. On the road I have a serious fuel air ratio problem. My 1992 274k miles landcruiser keeps stalling. I suspect it was fuel related. I confirmed it was in fact a bad a TPS because it was out of spec and was the only CEL. I replaced it and 100% certain it is within the specs because I used a FSM and a feeler gauge to set it. No more CEL while I was at that I checked per FSM the AFM and it was within specs. My car after still keeps dying for fuel so replaced the fuel filter and fuel pump along with the sock. After that it still stumbles so I replaced the green coolant temperature switch that feeds the ECU not to confuse with the dash temperature one. My car still stumbles after operation temperature. So I got a fuel pressure gauge and checked at the port on the rail underneath the manifold for fuel pressure readings it reads 35-38 psi. I came this far so i replaced the fuel damper just in case from NAPA. My car stills stumbles. I got desperate and clamped off the fuel return line from the fuel pressure regulator just in case it was bad and was stuck open and drove it for many miles. Car still stumbles. I checked the open relay it was good along with the efi fuse with the spare used for the heater blower. After all this it still stumbles. I ran into this thread for more info I wanted to see if I can unplug both 02 sensors to see if I can get it to stay open loop. Still stumbles. So I basically replaced everything connected to the fuel line except for the fuel pressure egulator. I clamped off the return for now

So in order of operation.

1. 1 CEL replaced in specs TPS
2. AFM checked per specs
3. Replaced fuel pump and sock
4. Replaced fuel filter
5. Replaced green coolant temperature sensor used for ecu
6. Replaced fuel pressure damper

Did not work still stumbles like dying for fuel.

Last messure tried to get it to stay in open loop by unplugging both 02 sensors

HELP!!! What did I miss??

@jonheld
Check the intake plenum for cracks. Any unmetered air will play havoc with the ECU.
 
Joined
Jan 19, 2017
Messages
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Apache Junction, AZ
I have solved the issue of my surging problem by indicated that the o2 is the root cause, not hard to understand. What I do going forward is called a solution.

Definition of solve, ”find an answer to, explanation for, or means of effectively dealing with (a problem or mystery).”

Google it.

I like your approach to feedback.

This isn't the guy you want to argue about 3FEs with....
@jonheld is the person's replies you look for when scanning the threads when something is going on with your rig.

Some of us need to learn the hard way.
 
Joined
Oct 30, 2020
Messages
16
Location
GA
Check the intake plenum for cracks. Any unmetered air will play havoc with the ECU.
I think I may have found the source of my vacuum leak.
My neutral safety switch is bad and I cannot start my car so I jumpered the pins in the connector for the neutral safety switch to always stay in neutral/park in order for it to start. The ECU I believe uses this signal to control the the idle air control valve. So I believe the the idle control stays in position to which effects the air flow ratio causing my car to stumble and die. So I'm thinking after the car starts to remove the jumper. But if I remove the jumper I don't know what pins to jumper for it to read drive 😮‍💨

Screenshot_20230208_134517_Samsung Notes.jpg
 
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The ECU I believe uses this signal to control the the idle air control valve.
Where are you getting this information from? According to the Toyota FSM and EWD, there is no input to the ECU from the NSS.
The only connection related to the NSS is the starter circuit which comes from the ignition switch.
 
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Messages
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Location
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Where are you getting this information from? According to the Toyota FSM and EWD, there is no input to the ECU from the NSS.
The only connection related to the NSS is the starter circuit which comes from the ignition switch.
@jonheld . The information I read from a thread. Is where I recieved the files. It reads under the Feed back control section "The target speeds also differ depending on engine conditions, such as whether the neutral safety switch is on or off. And whether the air conditioner switch is on or off"

When I unplugged the jumper off the neatral safety switch. The rpms immediately spiked up.

Post in thread 'A Super-Ultimate 3FE Diagnostics Thread - Let the Battle of Wits Begin'
 

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Joined
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The information I read from a thread. Is where I recieved the files. It reads under the Feed back control section "The target speeds also differ depending on engine conditions, such as whether the neutral safety switch is on or off. And whether the air conditioner switch is on or off"
I read through all 3 of these documents and they seem to be generic information not specific to the 3FE, but more so for the 1FZ-FE. Many statements of "on some models" and mentions of knock sensors which the 3FE does not have.

The only terminal on the 3FE ECU that is labeled NSW originates at the ignition switch in the START position. It is supplied voltage to the NSS which runs the cold start injector, circuit opening relay primary coil, and starter logic.
I don't see how the ECU uses this terminal once the key is no longer in the START position. I suppose it is also possible that there is an error in the schematic diagram for the ECU.
 
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I read through all 3 of these documents and they seem to be generic information not specific to the 3FE, but more so for the 1FZ-FE. Many statements of "on some models" and mentions of knock sensors which the 3FE does not have.

The only terminal on the 3FE ECU that is labeled NSW originates at the ignition switch in the START position. It is supplied voltage to the NSS which runs the cold start injector, circuit opening relay primary coil, and starter logic.
I don't see how the ECU uses this terminal once the key is no longer in the START position. I suppose it is also possible that there is an error in the schematic diagram for the ECU.

I appreciate your feedback. Yes it seems to be in fact for the 1nzfe. Just a tidbit though if anyone else could use this info. Just like how the rpm increases when you switch on the ac. The same thing happens once the the nss is in the off position and in my case the gear being still in the park position through a jumper wire off the connector. This could be the ecu logic expecting a load and increases the rpm to compensate being in gear
 

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