1991 FJ80 feels jerky/RPM loss when trying to climb certain hills

[evicta]

Hi all. I have a 1991 3FE FJ80 Land Cruiser that I bought as a winter beater with basically an unknown condition to me. I've been wrenching on it for the past few months and I think I'm at the point where I'm mostly happy with how it drives.

Relating to the engine here is what I've worked on (tried to use as many OEM parts as possible):

• Spark Plugs, wires, rotor, and distributor cap
• thermostat, green coolant temp sensor, cold start injector switch
• Air Filter, replaced most of the vacuum lines
• Fuel Filter
• PCV valve and grommet
• Adjusted the throttle & kickdown cables. I'm idling around 650 RPM and transmission shifts smoother now.

I live in northern Nevada and recently put over 1000 miles on the FJ80 going back and forth from the Bay Area. It drove great, I was able to cruise around 70 mph for most of it and I think I even got better gas mileage than I expected. The main issue I've experienced is going back east doing the climb over Tahoe (Echo Summit & then Spooner Summit) where I get some sort of delayed throttle response/RPM drop and then the truck jerks around for half a second for these harder climbs. I'd like to climb these areas around 3000 RPM but it immediately drops to the 2000's and the truck jerks periodically. It's hard to describe. I'm not sure if the truck is hunting for gears or if the throttle is off.

The first time it happened, I drained and filled the transmission fluid (it was brownish-red) after Echo Summit and it seemed to climb normally at Spooner after that. My second roundtrip, I experienced it again at Echo and this time I tightened down the kickdown cable a bit.

Has anyone experienced this before or have some suggestions? I've read through the forums and saw recommendations for the TPS (will do this weekend) and the fuel pump/sock. I am at about a quarter tank when I hit Tahoe so maybe it is the fuel pump.

 

[jonheld]

If the pre-filter on the fuel pump is original, that could be the issue. It can collapse on itself when the fuel in the tank warms after driving for an hour or so. It will manifest as a loss of power when you're climbing a reasonable grade.
It is a 100K mile item IMO.

 

[evicta]

If the pre-filter on the fuel pump is original, that could be the issue. It can collapse on itself when the fuel in the tank warms after driving for an hour or so. It will manifest as a loss of power when you're climbing a reasonable grade.
It is a 100K mile item IMO.

I replaced the pre-filter with a Delphi FS0087 and put in a new OEM clip and gasket as well. The throttle body was cleaned and I tried recalibrating the TPS when I had it off. I drove a shorter trip from Nevada to Sacramento and back. It went up the mountain without any jerks or any feeling that the engine was gonna die out.

I am seeing that my RPM won’t go higher than 2500 with my foot to the floor. There are certain times where it’ll go up to 3500 RPM for a quick burst and then it’ll settle back down to the 2000s. Any ideas on this? Is this more fuel issues or an issue with the exhaust system?

 

[jonheld]

I replaced the pre-filter with a Delphi FS0087 and put in a new OEM clip and gasket as well. The throttle body was cleaned and I tried recalibrating the TPS when I had it off. I drove a shorter trip from Nevada to Sacramento and back. It went up the mountain without any jerks or any feeling that the engine was gonna die out.

I am seeing that my RPM won’t go higher than 2500 with my foot to the floor. There are certain times where it’ll go up to 3500 RPM for a quick burst and then it’ll settle back down to the 2000s. Any ideas on this? Is this more fuel issues or an issue with the exhaust system?

Hard to say. I would test fuel pressure. Pages FI-47 to FI-49 in the FSM. You should probably replace the inline fuel filter as it's likely original and this vehicle has an unknown history. OEM part # 23300-69035.

 

[jonheld]

I am seeing that my RPM won’t go higher than 2500 with my foot to the floor. There are certain times where it’ll go up to 3500 RPM for a quick burst and then it’ll settle back down to the 2000s. Any ideas on this? Is this more fuel issues or an issue with the exhaust system?

What were the driving conditions when you couldn't go above 2500 rpm?
With the throttle wide open, the transmission should have downshifted. Did that happen? Did you adjust the transmission kick down cable according to the FSM? If you manually downshift do the RPMs go up?