Stuttering under heavy load (1 Viewer)

[Southbound]

Hi All,

So I've had this occasional issue with my 87 fj60 (A.K.A. Big Mama) where it would stutter/hesitate really badly under full throttle and heavy load (e.g. climbing a hill for a long time). It was so rare I didn't even bother with it, and just easing back the throttle a bit would address the issue. But now that I've gotten phat new 33" tires my truck is under "heavy load" a lot more often and this is turning into a headache. Everything is running smoooooooth otherwise. Within the last 1000K miles I've installed new plugs, wires, cap, air filter. Within 10K I've had the carburetor rebuilt, new fuel pump. I tried changing the fuel filter and already have the EGR disconnected because that causes its own hesitation issues. Any ideas what I can check given this info? Again, the truck is running better than ever (at 212K miles!) except under heavy load and full throttle, and then it seems like it's just not getting enough gas (or getting too much air?)

Thanks!
Mark

 

[Southbound]

hah, well 3 years later and I finally figured this out, by accident as part of having to pass emissions. Fix = reinstalling the air intake hose. Without it I'm assuming the fuel/air mixture was too lean, which only became apparent under heavy load (climbing up steep hills with the pedal to the floor). No problems at all with the new air hose attached.

 

[Infinity00]

Nice!
I better get mine hooked back up. Thanks for posting!

 

[blbuck12]

Mine has done the same thing and it was running the fuel bowl empty on long hills or under full throttle. Letting off the throttle and staying in gear or pulling over for a minute would fill the bowl back up and would be good to go again.

 

[OSS]

I'm glad you followed up with this. All of your prior fixes before replacing the cool air intake hose I would have guessed would have fixed the problem... but none of them did!
I would have guessed fuel starvation- but that wasn't it either.

Cool air (vs hot air) is denser & therefore contains more oxygen than hot air. Cooler air also helps cool things down in the combustion chamber (obviously). The HIC valve installed in the air cleaner housing tries to keep the air temperature going into the carburetor between 81° to 91° F on cool days via the HAI valve in the air cleaner neck. According to Toyota, that is the ideal air intake temperature for this engine.

Without the cool air intake hose, the engine will suck in too-hot air from the engine compartment after it has passed through the extremely hot radiator. That air temperature (however hot it may be) will always be hotter than ideal.

Thanks for the follow up / real world proof that that hose actually does something!