Loss of high end power, help!

Hey, first time poster, tried searching everywhere and no one seems to have the same issue I do. So here's my best shot at explaining it.

Drove from San Diego to northwestern AZ, going just fine at highway speeds (85-90mph if I'm being honest...) no issues. Stopped for gas at an exit, got back on the freeway. Truck can't seem to get any speed faster than 75 on level ground, uphill is slowed to >60. So I try to give it more gas, downshift into 4th, doesn't help much. Then I noticed I had the gas pedal to the floor, which I've never had to do since owning it. So I let off a bit, but didn't notice any difference in deceleration until the pedal had already traveled quite a ways. Basically I had a whole "dead zone" on my top end in 4th and 5th gear.

Tried some simple remedies hoping for the best. Cleaned the MAF sensor and air filter, scrubbed off some black gunk in the throttle body by the butterfly valve. Nothing's helped yet. It still drives fine around town, but highway speeds are gimped pretty badly. Any ideas?

 

When is the last time you replaced the spark plugs, those engines have really short intervals.

They have issues with the two speed fuel pumps, but usually the effects are much more severe with acceleration.

 

I have yet to replace the spark plugs in the 2 years I've owned it. It's got about 159k on it and I don't have any service records prior to me buying it. But I don't have any acceleration issues. It drives pretty much as expected until it gets to the upper highway speeds. What's really annoying is it's not throwing a light at me so I don't even know where to start.

 

Weak fuel pump?

 

Your description shows "5 speed"...so you have a 4cyl right?

I'm impressed that you got it going that fast in the first place

 

just messing with you man. I love my 4cyl.

I can't think of what would cause a loss of power like that

 

In my experience with my four banger driving from nothern NJ to Moab there were two major factors. Head winds and elevation. Around were I live is 500ish feet on ove sea level. Truck runs great and does highway speeds all day long. Heading out west though as the elevations got higher the truck struggled more and more. Also headwinds no matter how small were like getting punched in the chest. Both conditions cause effects exactly like you are saying. I've also noticed these motors are very sensitive to changes in weather.

It could very well be mechanical I'm just giving you a few things to look into before you start going crazy lol.

 

is it still able to rev high?

 

bad fuel mixed with good fuel = Kinda crappy fuel. I'm guessing that if you run it down low and fill with a nearly full tank of good fuel you'll see improved performance.

 

If it were the fuel pump wouldn't that give me issues all the time and not just at high speeds?

That sounds like it could be possible, the only thing that I don't understand is that it was doing fine while I was driving back, and it came on suddenly just after I filled up.

I haven't tried revving it past about 3500 RPM or so, just the usual revs I typically shift at from gear to gear.

I haven't put anything but 87 in it since I've had it, though I did put a tank full of 91 a few fill ups back. Could mixing the fuel just be a fluke thing? I've burned it down to just about empty a couple times since putting the premium into it though.

 

Have you filled up again since the problem started? I'm thinking you got some bad fuel right before the problem started. You said it started right after stopping for fuel.

 

I haven't refueled since then, haven't gone back to empty yet. I'm at about half a tank now, though there's a lot of distance driving around where I live so I imagine I'll burn through it in the next few days or so. I've refueled at that place before, but I guess it could just be a bad batch or something? Do you think it'd be a better idea to fill up with good fuel to mix with the stuff that's in it now or run it closer to empty so there isn't as much overlap?

 

Maybe try adding some octane booster to the current tank of gas I stared of waiting for it to go empty

 

That's an idea. I'll give that a shot, at least it's cheap. I'll update after I try it, let you all know if it worked. Gotta say, fantastic community here, I think I'll have to start being a more regular user. Thanks for all the input everyone.

 

Sounds like you probably picked up some water, or trash on your last fill up. You might need a new fuel filter.

 

Add dry gas, not octane booster. Seafoam might be a good option too.

 

Well, maybe, maybe not. I drove my father in laws Expedition on a road trip once and noticed an intermittent loss of power when there was a lot of stress on the engine, usually going up a steep hill on the freeway. I had it floored and could barely go 55 mph. On flat ground it would go 75 as normal, didn't really try and go above 80. I think he ended up replacing spark plugs but that didn't help much. Don't remember for sure what else he did, but I think fuel pump was part of it and eventually he fixed it.

But as the other guys said, if it started right after a fuel up, hopefully it is just a bad batch of gas or the fuel system just needs to be cleaned and you won't need to replace any parts.

 

Update: I was driving it today in a 55 zone, looked down and realized it'd picked up to 70 and I didn't realize. So I pushed it a little harder and it seemed to get up to high speeds pretty easily. Granted, as Wheelspinner suggested, I had a particularly strong tailwind pushing me along, but coming back the other way with the wind against me, it still didn't seem to be giving me the same issues as before. The wind slowed me down but I could still feel like the truck was giving power like I expect it to.

All said and done, I cleaned the air filter, verified there wasn't anything blocking the airbox into the throttle body, scrubbed some gunk out from around the butterfly valve without immediate results. But it seems to have resolved itself now. I got a bottle of that fuel system treatment that I'm gonna use on my next fill-up anyway just because I already bought it though. Thanks to everyone for the suggestions, I'll definitely be consulting TW with DIY issues from now on.

 

Glad it's better. Your symptoms would point to typical starting places though, should it recurr or others have similar, and 'bad gas' not be the root cause.

Restriction. Either in the fuel filter or exhaust stream. A minor to middling restriction will not reveal itself in low performance driving, idle, etc. But raise it's head quickly at higher loads.

Fuel filters are logical, because more load requires more fuel, and a restriction does not allow that. Now then, I think I've read around here somewhere that not all Tacomas have fuel filters? I don't know what year that started, or if 4s are different than 6s. Just pointing it out in case there is a serviceable filter to consider.

Key. If a fuel filter is the problem it won't get better on it's own. No tank additive will clean it. However, it will almost never create a no run condition.

Exhaust is logical too. Either converter beginning to clog or break up and clog, or I've seen muffler baffles fail and create restriction as well.

Both of these can get 'better on their own', at least for brief periods. Things that are breaking up can move around, shift, stop restricting. Often you can determine bad parts by whacking with a rubber mallet and hearing rattling going on. However, either of these can create a no run condition, should an internal break up suddenly create a significant clog. Like a potato in the tailpipe. So I've heard.

Just a couple of things to consider.

 

It's the catalytic converter for sure.

Fuel delivery is easy to pin at first. However, fuel delivery would be noticed at all speeds and variables of them.

The exhaust restrictions are not as noticeable in lower RPM's as they are in higher RPM's. Which would lead me to believe the cat is broken down.

Not to mention I had EXACT symptoms and my cat was replaced by Toyota. Never had a high RPM lag problem since.

(Just piggybacking your post @Clearwater Bill)