My power curve ain't right ('98 1UZ VVTi)

George_R

Member
yep long term trims should be zero in all modes i.e. all rpm range, all load range
check afm and primary o2 sensors first of all
 

eicca

Member
Okay @George_R I’d forgotten about this thread, but I got some time to tinker with Techstream and such today.

I don’t think the ACIS is working. The actuator stays in the same position whether the engine is on or off. And, if I unplug what I believe is the ACIS control solenoid (pic attached), I feel no difference whatsoever. There’s still a noticeable WHAM of power right at 3700rpm.

Plus, I messed with all the diagnostic test utilities I could find in Techstream but never saw the ACIS actuator move at all.

There’s a guy selling me a plastic 2UZ intake manifold complete with new injectors and confirmed working ACIS for $140 so hopefully that’ll fix it right up. It will fit, by the way.
 

George_R

Member
Different runner length => different optimal RPM and load for ACIS on/off operation
I would prefer just to buy new valve which is way cheaper btw
 

eicca

Member
My Tundra intake arrived today, and I’ve decided to relocate the VSV and vacuum reservoir during the swap to make it easier to change that little part.

@gloverman do you know of an aftermarket equivalent for that VSV or is the OEM part he only option?
 

gloverman

Well-Known Member
I only ever fit the genuine item. I don't think they are too badly priced although I do get a bit of a deal being a workshop. Why bother relocating the VSV and chanister when the units fit nicely where they are and they VSV should last at least 10 years?
 

eicca

Member
If I remember right, the reservoir doesn't actually fit under the Tundra intake manifold, and I've got a free bolt hole where my intake tube resonator used to be. So it's easy and if there's some kind of problem after installing I don't have to rip the manifold off again.
 

eicca

Member
So while I’m acquiring all the parts to install the Tundra intake, I used wire to tie the ACIS into the closed position. The difference in torque is noticeable. Much more eager to move. HOWEVER, I still get the power surge right at 3700rpm! I’m not sure what to look at now. Is this an indication that the VVTi isn’t working right? Am I getting a bad reading from a sensor in the VSC system that’s interfering with the power delivery?

What parameters should I inspect in Techstream?
 

gloverman

Well-Known Member
Id be making the AVIS work properly first before trying to diagnose anything else. I also ways fix the stuff I know is wrong before trying to fix stuff I don't know. Did another one this week. Well owner did it while I fixed wiring.
 

eicca

Member
So today I discovered that our 1999 2UZ sort of does this too. In first gear, under maybe 30-40% throttle, I can feel a sudden power jump right at 3000rpm. Most noticeable in first gear. Not as significant as my 1UZ, but noticeable.

Since this engine has no VVTi or ACIS, what might be the common denominator?

Both engines are over 200k miles.
 

eicca

Member
Well! Almost two years later, I think I finally found the issue!

The fuel pump.

I was reviewing the symptoms in my head: sudden surge in power at 3300rpm, like a NOS bottle. Not a gradual bump like a torque curve, but a sudden kick in the pants. It only happened at part throttle. Floored, no issue. It occurred to me that the fuel pump runs on a two-stage setup, low and high pressure. If the car was floored, it would switch immediately to high pressure. At part throttle, it would make sense that it would change over to high pressure at 3300rpm or thereabouts, based on airflow and other sensor readings. The jump I was feeling was the switch to high pressure.

So I changed my fuel pump preventatively, since I didn't want to end up stranded on any road trips.

Issue seems solved! No matter what amount of throttle I use, the power is nice and consistent at all RPM. No jumps or flat spots. The engine feels stronger in general, and even a little louder to boot.

At 215k miles on the original fuel pump, I can 100% believe that it was getting weak.
 
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