Hey guys I'm sharing a link to my youtube video below but basically im having issues with my 4runner constantly having to downshift to maintain a highway speed.
Video is on flat ground, no wind. It doesn't matter if I run cruise control or not, it acts the same way with cruise control off and myself controlling the throttle.

Transmission shifts good, truck just acts like it doesn't have enough power in overdrive to maintain the speed so it slows down and then has to downshift to get back up to speed, shifts back into overdrive once back up to speed, and then speed bogs down and it has to downshift to speed back up. This occurs over and over again on the highway. Definitely worsened with hills/head wind but it does this even on flat surfaces with no wind.

My dads 2000 has absolutely no issues cruising in overdrive. His can drive into a wind and easily still maintain speed without his transmission downshifting at all. Both of us have 4.30 gears and similar sized tires.

I do have 33s and a lift, otherwise stock BUT THIS ISSUE WAS STILL HAPPENING WHEN I WAS ON 31S WITH NO LIFT.

Engine acts like it has plenty of power accelerating, just has issues cruising in overdrive.. I have done a full tuneup plugs, wires, fuel filter, Cleaned air filter, cleaned throttle body and MAF sensor. Still has the issue. I have been having this issue for a long time so any help or ideas is appreciated. Thanks guys!
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YouTube

YouTube

So your not climbing a hill or any kind of grade??

You don't have a brake drum hung up or anything causing drag.


What's your engine compression and mileage on the rig?

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No, this is on a flat ground. I live in Kansas so we dont have much for hills here, mostly just wind. I havent checked brake drums yet but this has been happening for a long time so id imagine if it were a brake dragging issue, it would have been worn to bare metal and squealing by now but idk. I Havent done a compression check but the engine runs great. It is actually a lower mileage jdm engine that i put in 4 or 5 years ago. Basically i just used the JDM longblock and swapped over all the USDM goodies from my old engine.

Oh Kansas yes not many hills in the plains. Even low milage engine. Hmm.

I am just thinking here.


I start with compression check. Which is probably good. Then I go after the fuel filter and verify your fuel pressure at the rail.

Do you ever run fuel injector cleaner through the system?

Being your losing power you may want to run some cleaner through the fuel system.

You may have injectors or the fuel filter starting to plug up as possibilities.


I change my fuel filters every 100 to 150k

I also use locus fuel injector cleaner several times a year in a fuel tank of gas.

On occasion, some seafoam through is good stuff as well.


Well that's what I do. Other users may not agree and that's fine.

However, I havent had to change an injector yet in almost 30 years. So I am thinking that these 2 products can help keep the injectors clean. Or I just been lucky..





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After ruling out most of the mechanical issues that would cause drag, it could be the rig is not maintaining a optimal fuel air ratio during cruising speed, leaning out and loosing power. I can see you have no ECL.
When was the last time you changed out the front a/f sensor? Is cruising fuel pressure ok? Having a scangauge or ultragauge hooked up is great in aiding in troubleshooting
The trans shifting back and forth long term like that can't be good for the fluid. Make sure your not over heating the trans and burning the fluid.

You may be onto something here.
I have noticed a ticking coming from my drivers side engine bay, I dont notice this sound from my Dads 2000.

Sounds to me like its coming from the injectors. It is a quiet and consistent tick. Definitely not a knock, sounds more like direct injection but quieter. I ran a can of that BG cleaner stuff through the gas tank right after i swapped in the jdm engine about 5 years back but havent ran any type of injector cleaner since.

On the same token, under throttle it feels like it has plenty of power and is very smooth. That's what makes me kind of think it isnt an engine/loss of power related issue. My dads 2000, which doesnt have any issues cruising, actually has a little bit of a miss under throttle in the higher RPMs whereas mine doesnt. But mine still cant maintain a highway speed without constant downshifting like his can.

I do have a scan gauge hooked up. Cant remember if my 98 shows Air Fuel ratio through the gauge or not though. Ill have to check and see.

How exactly would i check cruising fuel pressure?

I have owned it for 10 years and have never changed out an 02 sensor from what i can remember.

A plugged up cat could cause a significant loss in power. I'm not sure; is there a pre-cat O2 sensor and an after-cat sensor or just one. If just one; where is it? Before or after the cat.

I forgot to mention but i replaced the Catalytic converter recently as well.

5 years is a long time with ethonal gas. I am beginning to think that the ethonal is starting to eat the lacquer out of our systems and thus causing issues but I could be wrong. :[

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No easy feat on the 3.4l. You'll have to get the reading on the rail which has no provision to do so. It is possible though.

Has it been doing this since you put the JDM engine in?

Did you do a timing belt before you put the JDM engine in?

If you did replace the timing belt I’d recheck the cam timing.




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I'm thinking the motor is running a little weak so the sensor tells the shift solenoid to shift down to maintain speed.

I don't know if it's because the injectors are getting plugged up or maybe the throttlebody has an issue or even an intake air leak or the MAF sensor is dirty or bad or if the engine is simply getting tired.

Does it use oil at all? Does the trans fluid look good and red? Smell burnt? Are there any cracks in the intake ductwork anywhere? I've been known to spray some WD-40 or carb cleaner on areas I think may have a leak.

Does the engine feel weaker when driving around town or does it still have plenty of pep in its step? Could be a weak plug, weak plug wires, or even a coil pack creating resistance.

This is one of those times a Scotty Kilmer $5k scanner would come in handy and of course knowing how to decipher all that data.

From what i can tell, my 4Runner feels like it does perfectly fine in town. Also has no issues accelerating at all. Just seems like it lacks the torque (only in overdrive..) to maintain a highway speed for some reason. Whether thats a power issue or not, im not sure but like i said, sure does feel fine other than on the highway cruising.
Would a Tired Transmission cause this issue? I am approaching 300k miles on the trans.

Its been so long since the JDM engine i have a hard time remembering if it was like this before, or after... I know.. shame on me..
It has done this for the last 2 or 3 years i can say for sure tho. somedays it seems like it does it worse than others. But when it started exactly... im not sure.

I did do the timing belt when i installed the JDM engine.