Intermittent cutting out/loss of power (1 Viewer)

[iansplatinum]

I've really tried my best to figure this one out, but I'd appreciate some opinions.

05/1993 FZJ80, 270k miles

Symptom:

When driving on the highway, the vehicle will randomly "cut-out". By this, I mean a noticeable loss in power and throttle response is suddenly observed. If I am driving at 70 mph, the vehicle will lurch forward as if I took my entire foot off the pedal. The engine will become unresponsive to throttle pedal input, unless the input is very slight. I can usually feather the pedal to limp the car to a nearby exit or the shoulder of the road. There does not seem to be correlation, and nothing in particular seems to fix it. I just cycle the computer on/off a few times, open the hood and take various connectors off/on, and it usually fixes itself until it does it again. No CEL, no dash indicators. When on the shoulder of the road, I have put the vehicle in 'Park' and have still observed a struggling engine. Pressing the throttle in 'Park' produced a bumpy rev that struggled to get above 2k rpm. But then, as if by magic, it will heal itself and act completely normal again until it randomly happens again. Could be 15 minutes later, an hour later, or a month later.

My assumptions:
I assume this must be electrical in nature, as a severe mechanical issue would not self-heal. I have driven the car about 3000-5000 miles since this issue first started happening.

I assume the issue is unrelated to the transmission, since I was able to observe the behavior in Park.

Parts Installed (all toyota brand unless otherwise noted):
Good used ECU from '94 FZJ80 (60221 variant)
Good used transmission computer
Plugs, Wires, Cap, Rotor, Ignition Coil.
Fuel Filter
Throttle Position Sensor
Vacuum Lines
New O2 Sensors (denso)
New Fusible Link

Relevant Services/Tests Performed:
PAIR system removed
EGR vacuum lines blocked off (no EGR sensor on early 93 models to jumper)
Tested Vacuum at warm idle- 20mmHg with a little bit of flutter, not concerning amount though
Cleaned throttle body
Cleaned NSS barrel connector
Cleaned O2 sensor connectors
Inspected intake hose for cracks (wrapped in even more tape to be cautious)
Transmission #1 Solenoids
Checked Harness by EGR pipe, no visible damage. Was wrapped in woven fiberglass by previous owner.


Next step for me is to replace fuel pump, EFI relay, Fuel pump relay, and ignitor.
I have to take this vehicle to Colorado in less than a month and need it to not cut out on the side of a mountain.

Mud, anybody got any clues? I feel like I have done all the basic "it's probably the..." maintenance, and now I'm still left with some obscure random intermittent issue that I absolutely cannot figure out or even hope to diagnose.

 

[Road Apple]

Could be a bad fusible link. I’ve had a very similar thing happen to my truck. The truck would die suddenly. I moved the fusible link and the truck would work fine again. Replaced it and haven’t had a problem since. I now carry an extra in the glove box.

 

[iansplatinum]

Could be a bad fusible link. I’ve had a very similar thing happen to my truck. The truck would die suddenly. I moved the fusible link and the truck would work fine again. Replaced it and haven’t had a problem since. I now carry an extra in the glove box.

This is one of the many things that I replaced and forgot to mention. I replaced with a brand new one and also keep a spare with me.
I'll edit my post and add it to the list.

 

[Marco Lau]

check your battery connection. It happened to mine and i was getting intermittent lost of power. Turned out it was a loose battery connection after days of driving on dirt road

 

[Irish Reiver]

The next time it happens, it would be worth putting an mechanics stethoscope on each injector to see if they are all firing. If not check the injector connectors are clicked home. Failing that i would be opening the harness at the EGR to see what the PO has hidden.

 

[iansplatinum]

The next time it happens, it would be worth putting an mechanics stethoscope on each injector to see if they are all firing. If not check the injector connectors are clicked home. Failing that i would be opening the harness at the EGR to see what the PO has hidden.

I had an intermittent misfire a few months ago that was due to a bad plug wire and bad tube seal- This feeling is much different than a single cylinder going out (via fuel or spark or whatever). The vehicle will typically idle fine when the symptom presents itself, but it will bog and stumble under load.
When I am driving on the highway, it will bog down, lose power, then my maximum speed will typically be around 40 mph, so I coast to the shoulder. There, it typically idles fine but I have been able to put it in park before and observe unwillingness to rev.

I opened the harness at the EGR pipe location, taking off the fiberglass wrap from PO. Everything looks great. All jackets are intact and wires are flexible. No visibly exposed conductors or even discoloration.

 

[jonheld]

One of the 100K mile maintenance items has not been mentioned.
The pre-filter on the fuel pump is very often overlooked along with the inline fuel filter.
Symptoms of a clogged fuel pump pre-filter would be normal driving for the first hour until the fuel warms enough in the tank. Then the pre-filter will collapse on itself and cause fuel starvation. Once the engine is shut down, the filter returns to its normal shape, and the cycle repeats.

 

[BILT4ME]

I've really tried my best to figure this one out, but I'd appreciate some opinions.

05/1993 FZJ80, 270k miles

Symptom:

When driving on the highway, the vehicle will randomly "cut-out". By this, I mean a noticeable loss in power and throttle response is suddenly observed. If I am driving at 70 mph, the vehicle will lurch forward as if I took my entire foot off the pedal. The engine will become unresponsive to throttle pedal input, unless the input is very slight. I can usually feather the pedal to limp the car to a nearby exit or the shoulder of the road. There does not seem to be correlation, and nothing in particular seems to fix it. I just cycle the computer on/off a few times, open the hood and take various connectors off/on, and it usually fixes itself until it does it again. No CEL, no dash indicators. When on the shoulder of the road, I have put the vehicle in 'Park' and have still observed a struggling engine. Pressing the throttle in 'Park' produced a bumpy rev that struggled to get above 2k rpm. But then, as if by magic, it will heal itself and act completely normal again until it randomly happens again. Could be 15 minutes later, an hour later, or a month later.

My assumptions:
I assume this must be electrical in nature, as a severe mechanical issue would not self-heal. I have driven the car about 3000-5000 miles since this issue first started happening.

I assume the issue is unrelated to the transmission, since I was able to observe the behavior in Park.

Parts Installed (all toyota brand unless otherwise noted):
Good used ECU from '94 FZJ80 (60221 variant)
Good used transmission computer
Plugs, Wires, Cap, Rotor, Ignition Coil.
Fuel Filter
Throttle Position Sensor
Vacuum Lines
New O2 Sensors (denso)
New Fusible Link

Relevant Services/Tests Performed:
PAIR system removed
EGR vacuum lines blocked off (no EGR sensor on early 93 models to jumper)
Tested Vacuum at warm idle- 20mmHg with a little bit of flutter, not concerning amount though
Cleaned throttle body
Cleaned NSS barrel connector
Cleaned O2 sensor connectors
Inspected intake hose for cracks (wrapped in even more tape to be cautious)
Transmission #1 Solenoids
Checked Harness by EGR pipe, no visible damage. Was wrapped in woven fiberglass by previous owner.


Next step for me is to replace fuel pump, EFI relay, Fuel pump relay, and ignitor.
I have to take this vehicle to Colorado in less than a month and need it to not cut out on the side of a mountain.

Mud, anybody got any clues? I feel like I have done all the basic "it's probably the..." maintenance, and now I'm still left with some obscure random intermittent issue that I absolutely cannot figure out or even hope to diagnose.

Based on your symptom description, I would lean towards two things.

1) Wiring harness by the EGR. Actually strip it out and inspect all sides of each and every wire. Just because the PO wrapped it does not mean they did a good job.
2) VAF (AFM) on the intake tube. It is possible that there is a loose connection inside the VAF or the harness got yanked on by the PO and they were searching for the issue, same as you. Go through the diagnostics on it to make sure the readings are appropriate, or swap out for a known good one (those are getting REALLY hard to find.) I encountered someone recently that had swapped theirs with one for a Camry, but I have no idea how the performance is.

 

[iansplatinum]

One of the 100K mile maintenance items has not been mentioned.
The pre-filter on the fuel pump is very often overlooked along with the inline fuel filter.
Symptoms of a clogged fuel pump pre-filter would be normal driving for the first hour until the fuel warms enough in the tank. Then the pre-filter will collapse on itself and cause fuel starvation. Once the engine is shut down, the filter returns to its normal shape, and the cycle repeats.

This is on order to be replaced soon, along with the fuel pump itself. I hope it solves the issue.

 

[iansplatinum]

Based on your symptom description, I would lean towards two things.

1) Wiring harness by the EGR. Actually strip it out and inspect all sides of each and every wire. Just because the PO wrapped it does not mean they did a good job.
2) VAF (AFM) on the intake tube. It is possible that there is a loose connection inside the VAF or the harness got yanked on by the PO and they were searching for the issue, same as you. Go through the diagnostics on it to make sure the readings are appropriate, or swap out for a known good one (those are getting REALLY hard to find.) I encountered someone recently that had swapped theirs with one for a Camry, but I have no idea how the performance is.

I removed the fiberglass wrap and visually inspected the wires. They all appeared good but I will look again.
I was expecting this to be the issue but was shocked at how nice the wires looked.

I am looking into purchasing a rebuilt VAF. Getting tired of loading up the parts cannon though.

 

[jonheld]

This is on order to be replaced soon, along with the fuel pump itself. I hope it solves the issue.

I would replace the 2 filters before replacing the FP.
You could also do some diagnostics like verify fuel pressure, monitor FP voltage, etc rather than throwing parts at it.

 

[BILT4ME]

I removed the fiberglass wrap and visually inspected the wires. They all appeared good but I will look again.
I was expecting this to be the issue but was shocked at how nice the wires looked.

I am looking into purchasing a rebuilt VAF. Getting tired of loading up the parts cannon though.

Use the FSM and go through a diagnostic on each section instead of firing the parts cannon!

 

[zapatius]

Something that happened to me on another vehicle is wear on the fuel injector wires, exposing bare metal. On any condition except light throttle, the two wires would arc and cause stumbling. I just had to re-wrap the wires and it was fine.

I replaced my FPR when I did the head gasket - do they ever go bad? Might be worth replacing since it's relatively easy.

 

[MickeyB]

Here’s an easy one to try. Mine had very same symptoms and was related to the fuel system. Check the 15amp EFI fuse under the hood. With truck running wiggle this fuse and see if truck cuts off. Also inspect terminals for corrosion. A trick you can do is spread out the fuse terminals to get a more secure connection if it is indeed the 15 amp fuse. After replacing the fuel pump, relay and inspecting all the wires on the engine mine was still cutting out, so I took to Toyota. They found the issue pretty quickly and let me know it was pretty common on these LC to have issues with the 15 amp fuse. So common i fact Toyota made kits that’s dealers could get that had bigger gauge wire to help with current being drawn and heat generation. Based on having no engine lights, I would be inclined to think it’s related to the fuel system.

 

[MickeyB]

I would replace the 2 filters before replacing the FP.
You could also do some diagnostics like verify fuel pressure, monitor FP voltage, etc rather than throwing parts at it.

If it’s still the original fuel pump I would replace as a preventative measure. If your going through the trouble of replacing the filter on the pump might as well replace the whole thing for piece of mind. I like to only do a job one time.

 

[iansplatinum]

Here’s an easy one to try. Mine had very same symptoms and was related to the fuel system. Check the 15amp EFI fuse under the hood. With truck running wiggle this fuse and see if truck cuts off. Also inspect terminals for corrosion. A trick you can do is spread out the fuse terminals to get a more secure connection if it is indeed the 15 amp fuse. After replacing the fuel pump, relay and inspecting all the wires on the engine mine was still cutting out, so I took to Toyota. They found the issue pretty quickly and let me know it was pretty common on these LC to have issues with the 15 amp fuse. So common i fact Toyota made kits that’s dealers could get that had bigger gauge wire to help with current being drawn and heat generation. Based on having no engine lights, I would be inclined to think it’s related to the fuel system.

Thanks for the tip. I had removed and inspected the 15A fuse, no corrosion present. But I'll take a closer look at the terminals, and I did read about the wires for it as well.

 

[MickeyB]

I reread your post and to clarify the engine is actually not cutting out. Just RPMs going low?

 

[sogafarm]

I saw that you replaced your O2 sensors. Double check that they haven't backed out and that the wire going to the harness did not come in contact with the exhaust manifold. I had a similar issue on another vehicle that the O2 sensor had backed out and had the same reaction with the throttle being erratic. Good luck with the diagnosis.

 

[iansplatinum]

I reread your post and to clarify the engine is actually not cutting out. Just RPMs going low?

It's difficult to describe. It feels like the throttle becomes unresponsive, or like the transmission went out of gear. Let's say I'm going 75 mph. My throttle is depressed maybe halfway or so, and everything is fine. Then, randomly, I feel the vehicle lurch forward a bit, as if the engine stopped producing power, or greatly reduced its power output. I then reduce my throttle input to 10%, and I can feel the engine pulling slightly, enough to slow my deceleration, but not enough to overcome aerodynamic drag and drivetrain drag, so I steadily lose speed. If I give it more throttle, the engine sputters. I eventually make my way to an exit or safe looking shoulder, usually going about 40 mph. The engine typically idles fine at this point, but sometimes becomes apparent that it is still being affected by the issue when I rev it in Park, causing it to sputter. This makes me believe it is not related to the transmission. After some time passes, the car acts normally, and I am able to floor it full throttle, revving to 4k rpm and merge back on the highway (full power/full torque) as if nothing happened.

Hopefully that clarifies the symptom better.

I saw that you replaced your O2 sensors. Double check that they haven't backed out and that the wire going to the harness did not come in contact with the exhaust manifold. I had a similar issue on another vehicle that the O2 sensor had backed out and had the same reaction with the throttle being erratic. Good luck with the diagnosis.

I left the originals in their normal location and added 2 new denso sensors in the PAIR pipe location on the exhaust manifold. I zip tied the wires out of the way and have confirmed they are not touching any hot pipes.

Additionally, the issue was present both before and after the O2 sensor replacement.

 

[iansplatinum]

check your battery connection. It happened to mine and i was getting intermittent lost of power. Turned out it was a loose battery connection after days of driving on dirt road

Missed this post. This symptom has been happening for months, I have taken battery terminals on and off since then, and cleaned posts with no change in behavior. Terminals were tight when it was happening, and still are. By loss of power I should clarify: it's more of a loss of torque. Every other electrical item continues to work during the entire episode- blower fan, radio, headlights, dash lights, etc. It's only the engine that cuts out, and not entirely either. It doesn't shut off, just 'reduces power/torque' significantly to where I can only drive 30-40 mph.