I developed the dreaded 3,000-3,300 RMP hesitation about a year ago and solved it today - completely gone.

The solution was in the O2 sensor. I had moved my factory O2 sensor down near the cat and put a wideband O2 sensor in the stock location for A/F monitoring.

This weekend I put a meter on the factory O2 sensor. Some of you may not know that it is a so-called single wire sensor & unheated. Our O2 sensors are heated by the exhaust and it has to be hot, 500 to 600 degrees, before it starts generating voltage and working, usually a couple of minutes so the motor can go into closed loop.

What you are supposed to see on the meter is 100-400 milivolts when the motor is lean and 600-800 milivolts or so when the motor is rich as the O2 sensor tells the computer to switch from lean to rich to lean to rich aiming at that 14.7.

What I got was 26-30 milivolts at idle, meaning that the O2 sensor was not generating voltage to produce a signal. That is not necessarily unusual at idle but I got just about the same insufficient voltage at 1,500, 2,000, 2,500, and 3,000 RPM. And when did it get hot enough to work? Drum roll - 3,200 RPM. Right at that point voltage jumped up to the proper 100-400 range.

I moved the O2 sensor back to the stock location where it gets nice and hot in a hurry, and no more hesitation. The sensor simply was not getting hot enough in the more distant location.

So if you have the 3,000 RPM hesitation problem. look at your O2 sensor first. It might be working, but not all the time because it is not hot enough, or because it's fouled or because its worn out, or it might be "lazy" - slow reacting. But if it's not working well, it is one potential source anyway, of the hesitation problem.

Pettit now sells heated O2 sensors that will start producing voltage sooner and is probably a worthwhile upgrade.

 

Hello-

Heated sensors are a great idea, but not unique to Pettit. Any auto parts store should be able to get you a 3-wire sensor. They're all more-or-less the same. Connect the signal wire to the old signal wire, then put the other two to +12V from the ignition and ground.

Take care,
Shad

 

I don't want to rain on your parade, but wide band O2 is suppose to be placed at least 36" away (down stream) from the turbo. Wide band O2 is quite sensitive to heat and will have a very short life span placed too close to the turbo. So in effect your placement of the Wideband O2 and stock O2 is backward to begin with.
You havn't really solved a problem, you simply found the mistake you made to cause the problem.

 

No rain on this parade Trex.

If a badly functioning O2 sensor can cause the "classic" 3,000 RPM hesitation problem, seems reasonable to me for others to look at the O2 sensor as a possible solution. That's why I posted, to try to be of some help to others dealing with the issue but feel free to tell me no problem was solved. My car thanked me anyway.

Does not really matter why it was malfunctioning, only that the "classic problem" materialized when it was malfunctioning, and went away when it wasn't malfunctioning. How I got there is just part of the story. (And I didn't place anything. The tuner who sold me the wideband did the placement.)

 

so many conflicting tales.

 

Interstingly enough, I only get 3,000 RPM hesitation when the car is cold. Once it's warmed up everything is fine. Whenever I take out the turbos Should be real soon I have just developed an exhaust leak in that area.) I will replace the O2 sensor to see what happens.

 

I had the hesitation problem... then i bought a PFC and it doesnt happen anymore lol. Maybe the map on the PFC changes things? I still need to do a TPS sensor adjustment anyway. I KNOW its off. As for my 02.... thanks for the info tcb, i'll take it into consideration if i adjust my TPS and happen to still get hesitation... even though its mostly gone.

Jeremy

 

interesting, I tend to believe the VOR (that's how us folks in DoO affectionately refer to him)

I've also heard it's a transition point for the fuel pump....anyway, I don't have problem when the car is warmed up so the O2 sensor is a good bet

 

Yeah, my 3k rpm hesitation is only intermittent as well....usually dont get it after the car is nice and hot, and been run to redline in a couple gears. O2 sensor is a good bet.

 

Jeremyb, your experience seems to be frequent - a lot of people report that the PFC solves the problem.

Just out of curiosity, does the PFC use the factory engine harness and all the factory sensors?

Is there anything in the PFC install procedures, for example an instruction that addresses adjustment of the TPS before during or after, installation that might lead to the correction of a problem at the same time as the PFC install?

It's hard to believe that the Mazda engineers could not produce a "hesitation free" map but the PFC obviously does something that the factory computer does not.

I still think a heated O2 sensor is a winner. At extended idle for example, crappy traffic, there is not enough exhaust heat to make even a brand new unheated O2 sensor work.

 

Couldn't you simply tell if it's O2 sensor or not with disconnecting it?


Also, is this hesitation so apparent with light throttle and could it develope into bucking?

 

Yeah, the PFC does totally eliminate the 3000 RPM hesitation. One of the key reasons why it's on my "to-buy" list .

I might have to try a quick trip with the O2 sensor unplugged and see if that changes anything. I am also planning on verifying the fuel pump switchover to see if that is related to the hesitation - I kind of doubt it, though.

I wonder if part of the reason for the hesitation is the ECU can't react quick enough at a changeover point. Might be part of the reason why they went to faster computers in '96. Not to mention they fixed a BUNCH of weirdnesses in '96 in Japan, including going to the "black box" for the solenoids.

Dale

 

I had the 3000 RPM hesitation. Tried grounds, voodoo, heated O2 sensor, etc. Nothing worked. Then I installed a PowerFC and the hesitation was 100% gone and never came back. I did not adjust the TPS or change anything else of that nature when I installed the PowerFC.

-Max

 

Yep, PFC cleared it up for me too!