Odd lack of acceleration '01 4x4

'01 2.7L 4x4 ext cab. 125k A/T.

The truck has very sluggish acceleration at low RPMs. From a dead stop, I will slowly but steadily accelerate, even if I have the thing nearly floored (just above the kickdown switch) acceleration will not improve. The same slow steady climb. Its not stuttering, doesn't feel like any misfiring, its just a major lack of power. It feels like im towing a house uphill.

Now the odd part: As soon as I get right around 2500 RPM I suddenly have power and the truck takes off. Its a very sudden and dramatic boost, not a gradual increase. Ill have crap acceleration at 2400 RPM and then have excellent acceleration at 2500. It is not the tranny downshifting (that was my first thought), its just like something kicks in at 2500 RPM that makes the engine go. This happens 100% of the time when accelerating from a stop.

I've had the truck about 2 months, I have replaced the front O2 sensor, MAF, fuel pump, TPS. Have fresh synthetic fluids in all the gear boxes and tranny. Did a piston soak and put new spark plugs in. Ran some fuel system cleaners through the gas. PO told me the fuel filter had just been done. The air filter is some cheap chinese thing with a crappy gasket, I have a OEM one on order but I have my doubts that will solve the problem. I am really out of ideas.

 

/bump. any ideas?

 

It's a 2.7 auto 4x4 ...get use to its performance cause that's all it has. If you bought a 5 speed like I did you can wind the gears out a little more. You are kinda up shits creek with an auto.

 

I don't agree with this. My rig is about the same, and the power is consistant throughout the rpms. Not great power (its a 4cyl auto afterall) but adequate. Compared to my old 22r (98 hp) its like a V8.

There is a problem somewhere.

Are there any other symptoms? Temp guage work ok? Gas mileage as expected (18 - 22)?

 

Sorry...... yours is fast...just mine is a dog..I didn't buy a 2.7 to be fast. See if the rest of the 2.7 owners agree though. There is alot of threads on it.

 

Temp gauge seems to be fine, but my mpg is nowhere near that, I get closer to 14-15 city and 16-17 highway.

 

I get better than that with the 3.4 v6 mine was down to 13ish city before my fuel injectors were cleaned but I have 199,xxx miles so idk if yours need it.

What tire size are you running?

 

I'd check if your throttle body is free, check your plugs, wire and igniters. Maybe check your fuel injectors after that. The fact that you get a noticeable jump in power at 2500 rpm sounds like it is something that needs fixing.

 

It could be the throttle body like Lumpskie said or MAYBE the cat. If the cat is clogged it would cause power loss but I don't know about the jump.

 

Sounds a lot like my '03 2.7 manual.... But I do have 35's dogging mine down so I figure it's just a lack of gearing on my end. i get 14-15 city and 16-19 highway nowadays. Used to get a good 2mpg better a couple years ago. :noture: Runs great, she's just a dog!

No idea where you problem would be OP. Maybe the knock sensor? But that should trip a check engine light.

 

Did you have a smog check done when you bought it, and it passed?
Could be low fuel pressure (pump or FPR).
Have you done a compression check?

Lost of possibilities to check out, will take some time to check out all of them.

 

I have the stock 16" wheels and tires, no aftermarket mods of any kind. I had the intake off over the weekend when I did the piston soak, the throttle body looked ok, I sprayed it and cleaned it anyway.

I experimented with placing a piece of sheet metal where the EGR mounts to block it off, and that did give me more power at the cost of even worse mpg and a rough idle.
When I had the EGR off I put a vacuum on it and the ball moved pretty well on the spindle. Now I have EGR hooked back up normal and have the vacuum modulator disconnected from it for testing. I don't know if somehow the modulator is broken and perhaps causing the EGR valve to be open when it should be closed, and then closing it at 2500k rpm for some reason. Anyone know if the difference between recirc air or fresh air would cause that big a difference in low end acceleration?

 

The PO had just gotten it inspected the day before he sold it (not sure why), he gave me the state inspection printout and it passed the smog test.

I did have an issue with the fuel pump and replaced it with a new one (OEM) about a month ago. But this problem was happening before that and still now.

Have not done a compression test yet.

 

If your idle is smooth (not rough), then the EGR valve is closing completely, as it is supposed to. The best way to completely disable it (prevent it from opening under any conditions), is to remove the vacuum line going to it, and block it off (both the line and the EGR valve port). Then see if it makes any difference. If no difference, then its not the EGR causing your problem.

 

Update:

I've been messing around with things and discovered a couple bits of info:

-It seems like the "turbo boost" phenomenon is related to the EGR system in some way, as it stopped happening when the EGR was completely blocked off.

-The problem is at its worst when the engine is cold, and especially when going up hills. When the engine is warm the boost effect is dramatically less.

Based on those two bits I am suspecting possible EGR temp sensor issue. However I have no CEL. Could this mean that this whole thing is just a case of the EGR working as intended? I know EGR can hurt your power to a degree, but the turbo boost is still puzzling.


I am trying to better understand how this EGR valve works, I can't figure out what the hose coming out the bottom of the modulator connecting to the EGR valve does. The hose on the top of the EGR presumably provides the vacuum to open the valve; does the one on the bottom simply vacuum it back shut? I would have thought it just closed on its own with its spring.

This diagram isn't specific to this Tacoma but same system applies,

 

Are you saying that the truck runs as it should when the EGR valve is disabled?

 

The problem described in the OP goes away when the EGR is blocked. However that comes at the expense of poor MPG, very rough idle and a CEL.

 

I can understand the CEL, likely the P0401 code. But disabling the EGR shouldn't cause poor MPG, or rough idle

Long shot here, but perhaps the PO worked on the truck, messed with the EGR stuff, and mis-routed the EGR vacuum lines. On mine, there are 3 that attach to the top of the modulator, in addition to the larger one at the bottom. One of the lines has a check valve in the middle of it. Make sure they all go where they are supposed to.

 

I checked the hosing against the attached diagram, seems everything is correct. Is the part circled in the pic the check valve you're referring to?

 

Yank the cheap Chinese air filter out and see if it makes a difference. The PO might have loaded the thing with a bad load of gas and your "recently replaced" fuel filter might be clogged again. I have rode in auto vehicles that couldn't get out of there own way until a certain rpm was reached. Fuel filter was changed and away they went.

Easiest, cheapest things first, then work from there. Granted the fuel filter is not the easiest thing to replace, but it's one of the things left on the list that you yourself did not replace.

If you have ran thru the gamut and checked everything possible to an extent,,then you just might have the autotranny blues.