Help! Constant Wideband Surging

[h4x0r]

Hi guys, I need some help trying to fix my tune. It kind of started surging rich/lean a few weeks back.

Its more noticeable at low rpm as you feel the car hesitate but once you get to higher rpm its less noticeable but the log shows it does it constantly throughout the whole drive.

surging.png

Fuel pressure is good at 43.5psi

I did a vacuum leak test and the only place air can leak is from the shaft that contacts the throttle body butterfly to the throttle position sensor (TPS). Not sure if that's normal or if there is a seal that can be replaced inside there.

I have been playing around with VE to see if something is out of whack but can't get it to smooth out no matter what i try.

Car is 304 v8 using 424 11p. Here is a copy of the log:

11p surging log.xdl

[vlad01]

Looking at the graph, that looks like it's in closed loop fuelling mode. Did you check the flag to force open loop before doing your tuning?

[h4x0r]

Your right... I can see the narrowband o2 sensor going crazy up and down in the logs. I'm using a simulated narrowband from the spartan 3. I just unplugged it while i was driving and all the craziness disappeared.

[vlad01]

I recognise that wave form a mile away. Glad it was just that. Make sure you check the flag to force open loop, if you just disconnect the input the ECU may still try to use it and mess with the tuning in some areas.

Once everything is done, you can set it all back and let the closed loop do it's thing as per factory.

[h4x0r]

Thanks very much!

Car purrs like a kitten now!

I'm assuming my VE was out so much that the narrowband o2 sensor was trying to overcorrect everything making things worse?

[vlad01]

Nah, the narrow band and closed loop deliberately swing rich and lean so the cat can work correctly, but if you are tuning the VE with that all going on, the VE table will go out of whack. That's why it's important to turn off closed loop so that you can get the VE accurate, then when everything is done, turn it back on and the emission side can do it's job.

[delcowizzid]

And kf you want to run closed loop add a narrow band sensor just for closed loop the simulated output isn't great compared to a real narrow band sensor

[vlad01]

Some do the job ok, some don't. I found my spartan 2 did a reasonable job with the NB so I never bothered changing it out for am o2, but my spartan 1 I used some month or so ago was offset by a fair amount and the BLMs went quite rich just above and around idle.

Once I put a real o2 in there, it went back to the correct 0-ish BLMs that the WB dictated in the first place, so go figure.