Engine stumbles under heavy load. Land Cruiser specialist gave up trying.

[Darin Hollings]

I have a 93 80s series 1FZ-FE with 250k on it. It is in great shape and I have spared no expense through its life to keep it as close to new as possible. It runs perfectly around town, on the freeway. UNLESS you floor it going up a grade, onramp, or just accelerating hard. Once the engine shifts down in to its highest gear. (It down shifts once, than twice to go faster) Once it down shifts twice as the RPMs reach about 3000 the engine cuts out for a millisecond, then the RPMs drop, then it comes back on back to that RPM then cuts out again. This results in a very strong stuttering of the engine. It feels like there is an RPM limiter but it is nowhere near red line. The Land Cruiser specialist (K&H) claims to have tried everything. I believe him. He spent three weeks with it and charged me nothing so I don't want to throw any shade his way. He checked the wiring the distributor, the MAF sensor (which is new). The two things that I can think of left for me to try are the ECU and the distributor. It is to the point that I will just start replacing parts and cross my fingers. Has anyone ever came across this? What parts would you target? I tried the specialist now I am reaching out to the LC community! Please help. And please be kind and don't tell me to search the forums because I have- for years!

Thanks!

 

[N22]

Sound like its possibly fuel delivery issue. Fuel flow not keeping up with demand.
That's my first guess.

 

[Seth_O]

'93s are known to have a bad ecu in circulation. No idea if that would cause this issue, but its easy to search the specific known bad PN and check it against yours.

 

[Tools R Us]

Is the main engine harness contacting the EGR pipe?

 

[Brimley]

Is the main engine harness contacting the EGR pipe?

My guess too

 

[Twinair]

Check the wiring harness as it passes the EGR valve. There are many instances where the wire insulation melts together due to the intense heat in that area.

 

[whitey45]

Hook up a fuel presure gauge and tape it to your windshield, go for a drive and quickly eliminate a fuel presure issue.

 

[Darin Hollings]

Hook up a fuel presure gauge and tape it to your windshield, go for a drive and quickly eliminate a fuel presure issue.

Thank you for this advise! I doubt its fuel due to the abruptness of the cut in and out.

 

[Darin Hollings]

The Land Cruiser Specialist claimed that he checked the wiring harness and it was fine. How would you even take a look back there? It it something that is obvious visually? Do you have to unwrap it to see? Endoscope?

 

[Tools R Us]

Can tie it back, like it was from the factory and see if it makes any difference?

 

[Seth_O]

The harness is usually wrapped up in a (deteriorating) heat reflective tape. You'll probably need to unwrap it and inspect the wiring. Its a good time to redo all the heat wrap.

 

[LS1FJ40]

Seems like it is related to the engine torquing back which points to the wiring harness by the EGR or a vacuum leak in a hose.

The wiring harness by the EGR needs to be cut open and inspected.

Careful laying across your engine while doing it, done you don't want to break the nipple off of your radiator!

 

[slo60]

The harness runs down through the intake manifold and is very difficult to see. I had a very similar problem with stumbling and it turned out that wires were shorting out. Mine were not that bad so I split a piece of 1" heater hose and wrapped it around the wire harness. I slid it down over the compromised wire and zip tied it. No more problems. That was 3 years ago and it's still good.

 

[Tools R Us]

More than the wrap, the harness should be tied in place so it cant flip around, touch the pipe. This is how it was from the factory, the clips age/break.

 

[whitey45]

After 25 years as a professional mechanic, you have to check everything, and eliminate all possibilities. Fuel pressure drop can easily cause an abrupt cut out. Did the tech check fuel presure? A harness issue can be checked by engine running and grabbing and moving the harness.

 

[NLXTACY]

FWIW the "specialist" at K&H was Richard. He's gone/retired. Armando is now running it/owns it. I like him personally and is a real enthusiast...but, he's not exactly the most knowledgeable out there.

 

[Darin Hollings]

Sound like its possibly fuel delivery issue. Fuel flow not keeping up with demand.
That's my first guess.

WOuldn't that just cause it to fade away? When this thing cuts out it is very abrupt. I will buy a meter and run the test! Thank you for helping me!

 

[Darin Hollings]

Thanks for replying!!!

Richard! He fixed my last engine stumbling mystery! Any other Land Cruiser wizards around LA?

 

[Darin Hollings]

After 25 years as a professional mechanic, you have to check everything, and eliminate all possibilities. Fuel pressure drop can easily cause an abrupt cut out. Did the tech check fuel presure? A harness issue can be checked by engine running and grabbing and moving the harness.

Thank you so much for this info! Very useful! I doubt he checked fuel pressure. I will! Thanks!

 

[Darin Hollings]

I had my head resurface at TLC a few years ago- They might have recovered and strapped the harness because it looks ok. Should I cut in to this to inspect?