1994 Land Cruiser misfire (1 Viewer)

[Armandojavierl]

I need some advice.

I have a 1994 Land Cruiser (US Model 4.5 6Cyl) since i got it, it has a little misfire that became worst with time, there used to be a check engine light which was calling for a rear knock sensor (i think the number was 54?), replaced with a cheap autoparts new knock sensor and the code left but it came back after a few days of driving. I repeat that process 2 o 3 times thinking i was getting a defective knock sensor.

I Ignored the issue and focus on other stuff like wires, ignition coil, spark plugs etc. Kept driving it and off-roading it ignoring the misfire which comes and goes. At this point the misfire its still not happening all the time, but when its there its far worst. A bunch of stuff has been replaced including a new oem toyota knock sensor. Theres no check engine light at all even when its misfiring. Im going crazy at this point but i dont have a lot of experience with older vehicles (this is my oldest) hoping im just making a rookie mistake.

I’ve replaced the following parts since i got it.
-Ngk blue wires
-oem toyota spark plugs.
-rear knock sensor toyota oem
-in-tank fuel pump delphi with filter (twice)
-fuel filter close to the engine (twice)
- rotor and cap toyota oem.
-ignition coil
- ignition contacts inside the rotor and cap with sensor.
-clean throttle body
-clean idle air control valve
-clean AFM
-tape intake boot
-pour some fuel injector cleaner in the tank.
-pcv valve replaced
-2 brand new o2 sensors relocated to manifold.
-water pump aisin
-fan clutch aisin blue
-all pulleys
-toyota v belts
-radiator with cap and fresh coolant
-thermostat aisin
-relays

The misfire its really hard to explain since its not always there. You start accelerating slowly and can feel the truck struggling before hitting 1600-1700, after that the misfire “disappears but if you keep the gas pedal a 2k rpm it will slowly go down like its not stable. Cold or hot you can be driving and it will start struggling, misfire and turn off. You turn it off and on again and most of the time goes a away and comes back later.

 

[ZackR]

How does the wiring harness look, specifically where it passes the EGR pipe?

 

[Armandojavierl]

How does the wiring harness look, specifically where it passes the EGR pipe?

Looks good, no signs of anything. I had to work it a little bit also when relocating the o2 sensors and made no difference and also didn’t see anything.

 

[Irish Reiver]

Can you explain more about what you mean by "tape intake boot"

 

[Armandojavierl]

Can you explain more about what you mean by "tape intake boot"

Months of doing research here. I read somewhere that if your air intake hose its leaking could be causing some type of misfires also. So i used electrical tape and tape the whole hose in case there was some kind of leak that couldn’t be seen by eye

 

[TacoLand]

I know you said you've looked at the harness, but it's probably worth pulling it apart and checking the wires very thoroughly. Start around the EGR and where the harness goes through the firewall. Sounds similar to an issue I had last year with mine.

 

[Mat Jadamec]

I had a similar problem and it turned out to be a rusted vaccuum tube inside the vaccuum hose between egr valve and throttle. I never saw it until the hose was expanded and split due to the rust build up. Haven't had that misfire symptom since.

 

[Irish Reiver]

Months of doing research here. I read somewhere that if your air intake hose its leaking could be causing some type of misfires also. So i used electrical tape and tape the whole hose in case there was some kind of leak that couldn’t be seen by eye

If your intake isn't subtle when you give it a squeeze then it is likely time to replace it. The tape thing a trail fix at best.

 

[OffRoadScott]

Your issue sounds a lot like what I was dealing with. Mine ended up being the harness, @Cruiserhiggs sourced a known good one for me and replaced it and the issue was solved. While in there we had the OEM injectors cleaned too.

This is how my harness looked prior to Scott replacing it. Finding a harness might be an issue as the harness is NLA from Toyota.

 

[Armandojavierl]

I had a similar problem and it turned out to be a rusted vaccuum tube inside the vaccuum hose between egr valve and throttle. I never saw it until the hose was expanded and split due to the rust build up. Haven't had that misfire symptom since.

I checked that but it looks good, 0 rust

 

[Armandojavierl]

Your issue sounds a lot like what I was dealing with. Mine ended up being the harness, @Cruiserhiggs sourced a known good one for me and replaced it and the issue was solved. While in there we had the OEM injectors cleaned too.

View attachment 3578232

This is how my harness looked prior to Scott replacing it. Finding a harness might be an issue as the harness is NLA from Toyota.

I just took it all apart but harness is good, clean on the inside all wires look good no signs of anything.

 

[Armandojavierl]

At this point I realized the misfire gets worst when truck gets to operating temperature. Struggles bad before 1200-1300 rpm and gets better after that.

 

[OffRoadScott]

I just took it all apart but harness is good, clean on the inside all wires look good no signs of anything.

Scanned over the OG post, have you checked O2 sensors for the proper resistance? What about the coolant temp sensors?

 

[Armandojavierl]

Scanned over the OG post, have you checked O2 sensors for the proper resistance? What about the coolant temp sensors?

Do you happen to know what is this? Its between to the knock sensor and water temp sensor
(The black marks not the red lol)

While changing de water temp sensor I realized that the clip was broken but i plug it in and out and it didn’t make a difference on the truck while it was on idling..

 

[OffRoadScott]

Do you happen to know what is this? Its between to the knock sensor and water temp sensor
(The black marks not the red lol)

While changing de water temp sensor I realized that the clip was broken but i plug it in and out and it didn’t make a difference on the truck while it was on idling..

View attachment 3594950

Hope this help you out.

 

[Armandojavierl]

View attachment 3594979

Hope this help you out.

Thanks man! So which one of those is the one that could be affecting my misfire? I read somewhere that the ecu has a specific temperature sensor

 

[OffRoadScott]

Thanks man! So which one of those is the one that could be affecting my misfire? I read somewhere that the ecu has a specific temperature sensor

Honestly if your in there might as well replace both, don't forget to order the crush washer for the ECT as well.

 

[Armandojavierl]

Honestly if your in there might as well replace both, don't forget to order the crush washer for the ECT as well.

This is what i was dealing with.. My water temperature sensor looked fine until i screw it out and it broke in 2 pieces of how badly the inside was corroded.. Shes running a lot better now but ill keep you guys posted in case in comes back because my misfire was really inconsistent.

Thank you so much for the help i was going crazy

 

[OffRoadScott]

That is awesome to hear. Anytime you have an issue with running rich/lean. The first things to check are the air meter, both O2 sensors, coolant sensors, etc.

Find yourself a spare air flow meter and if it isn't working properly oh well send it out for service that way you have spares for a part that is NLA (no longer available) from Toyota. People say that either a Camry or Corolla will work but those motors are 2 different sizes so I would assume they are not calibrated correctly.

 

[ppc]

None of those sensors, if failing, will cause a misfire. Start looking for problems with the ignition system, plugs, wires, ignitor, main wiring harnesses where it passes through the egr and any loose connectors to fuel injectors.