the only indication I'm seeing is the IPW dipping around 5800 and your NB02 sensor is dead or disconnected it seems, so I can't see what the fuel is doing

 

A couple guys in various threads reported that a bad O2 sensor caused similar problems.

I'll look into replacing/reconnecting it... hopefully it doesn't cost me an arm and a leg.

 

I found a pre-cat O2 sensor (direct fit, OEM) by a company called Walker. Looks like a few guys have been using these, so I might pick one up.

I'm going to try to get under the car tonight and see if the O2 sensor is simply loose/unplugged... if its dead or damaged, I'll replace it and see if that does anything.

 

Update:

I just checked both O2 sensors, and they're in their bungs securely. The wiring all looks factory (no splicing) and all the plugs were clean and tight. I'm guessing the front O2 sensor went dead on me. Is this reasonable with only 47,000 miles on the car?

Also, has anyone done the work on swapping one of these? Any tips or recommended tools?

 

I'd say it's dead too...

tips... lots of leverage

 

Alright...

I got the new front O2 sensor in, which wasn't too much of a hassle (20 minutes, tops). I took the Evo out for a few runs, and it was certainly driving smoother and more responsive, but I'm still getting the stuttering. It's happening at higher RPMs now, but is still very consistent. I'm getting good, legit O2 readings... so I guess its a step in the right direction.

I'm going to try to get a new set of plugs this week and see what happens.

In the meantime, I did 6 WOT runs and posted up the .csv files... let me know what you think.

run1
run2
run3
run4
run5
run6

Thanks.


Update: I also installed a fresh set of NGK BR7ES plugs gapped at .026-.027

 

6 logs is quite a bit of data to sift through so at a glance I don't see anything related to your issue

please narrow it down to one logged pull and let us know what RPM you feel the problem.

p.s. did the spark plugs help?

 

Take a look at run6...

The stuttering begins around 6300 rpms and lasts until 6800 rpms. If you check out rows (in excel) 145 through 177, you'll see the fluctuation in RPMs. I really don't know how to interpret the O2 or timing... I'm hoping you can make better sense of it all.

Run6 was also the only run with any serious knocking issues.

The second set of BR7ES did not make a difference. The O2 sensor had a fairly noticeable impact, in that it eliminated the problem from happening at 5000-6000 rpms altogether.

 

it looks like a misfire, if the plugs didn't help then I would be suspicious of the wires

 

Is the stock timing really that aggressive?

 

Mellon, I hope you see this and comment because you are much more familiar with narrowband reading than I am.

From looking at my logs a narrowband reading of 0.858 equals a 13.6:1 on my wideband. A 0.8775 equals 13.0 - 13.2!

 

during spoolup you'll see some scary NB02 numbers well under .90 which is normal but I don't like to see under .89 at WOT

 

I replaced the fuel pump with a relatively new Evo XI unit. No good. I'm still having the issue around 6500 rpms and up.

Considering the car is basically stock now, I'm at a loss. Any ideas?

 

if you have a local friend I would swap plug wires long enough to determine if that's the issue.

 

Why is your accel enrichment 200? Is that normal for an evo 8?