Sounds more like this is somehow related to the simulated narrow band O2 output or other O2 sensor problems. All of you are also experiencing bucking during closed loop operation (closed loop occurs under light load, from about 2k to the secondary staging point) In this region of operation the AFC table corrections are not used at all, the pulsewidths cycling up/down is based on the O2 sensor reading. Try disconnecting the O2 sensor input, this will cause the ECU to throw a code and not enter closed loop.

-Henrik

 

Well, it's not the o2 sensor. At least not in my case. I disconnected it and I've been tuning with the 2.0 for a couple days now and it still happens just less frequently. If it weren't for the fact that others are having the same issue I'd assume it had nothing to do with the ecu. It's inconsistent. I'm swapping in new inj, soon I'll let you know if that helps.

Brent

 

My turbo went so I have not been able to get down and dirty. WIll get back soon.

 

I'd wager that if the stock 02 sensor was working you won't see the afr in the 16-18 afr range because the ECU will not let it go to those values in closed loop. Closed loop will equal no buck at steady cruise.

Also, if you want to try something radical..................take a hour or so and reinstall the factory airbox with filter and snorkel. Then go for a ride with the 02 DISCONNECTED and see if the buck at steady cruise still happens and IF the afr has now gone down from the 18's mentioned above to more normal 14's afr.

 

I should have specified that the afr's at idle went completely off the guage lean. So I'm sure my o2 sensor was working at least some of the time. I also realized now that I've done more tuning that the lump in my idle (about half the time) is simply due to the aggressive porting that I've done. I went a bit further on the exhaust ports with this motor than I ever have before.

Hailers, I'd say you and Henrik are most likely right in the other cases.

A lot of times when guys do custom piping they mount the afm on an angle and it messes up the rate at which the door opens in relation to airflow. Definitely something to watch for. And also the afm should be located within 18" of the turbo.


Brent

 

Can the rtek guys (or anybody who knows) comment on what are the conditions for closed loop? From what i have noticed, it will go out of closed loop if:
RPMs above ~3.5k
or
Boost above ~0psi
or
very low throttle/high vacuum:

In closed loop, if i let off the throttle, but not so much as to set TPS fuel cut off, the afrs will usually get really rich, in the 11-13 range. This is when it appears my problems occur, but right around the 2k-3k range in 1st and 2nd gear (low loads, high vacuum). the hesitation always happens if i try to maintain speed in 1st gear around 2.5k rpm

also, should the o2 sensor wiring be shielded? I remember a writeup about the stock wire being shielded, but it doesnt appear so. If you cut it and look at it, it only has 1 conductor. I also have a wire going from the o2 input at the ecu to a nb o2 gauge, which could also be picking up interference. But if it runs fine in closed loop mode, doesnt that rule out any o2 sensor problems?

my afm is angled slightly upwards, but i have only started having this problem recently. the car has had the same afm and tid setup since 2 years ago before i bought it. Same thing with the cone air filter

 

my afm is angled slightly upwards, but i have only started having this problem recently. the car has had the same afm and tid setup since 2 years ago before i bought it. Same thing with the cone air filter[/QUOTE]

Don't quote me on this one but I seem to remember reading that you can mount the afm up (or down) to a 15deg angle without issues. When it's the afm it will usually cause starting issues.

Brent