Looking for input on a very strange problem.

Car is an 06 MT with BP 6266 kit at 9 psi. Tuned with UpRev by reputable professional tuner.

Under high load WOT the car hesitates when the accelerator is first pushed down. It stutters for about 1 second and then takes off. It is most noticeable when shifting, as soon as the pedal goes down after getting into the next gear it stutters. It doesn't happen if I roll into the throttle, only when stabbing it. It doesn't have to be a hard shift, even cruising in 2nd or 3rd gear at 3000 rpm and getting on the gas hard will cause it to happen.

We have confirmed that timing is being pulled which would indicate knock. BUT, listening with headphones shows no knock and monitoring the ECU indicates it isn't seeing knock. To test it we disabled knock monitoring AND changed the timing on the knock table to match the normal conditions timing. That didn't help at all, it still pulled timing and stuttered.

Tuner provided a new tune earlier this week after getting an UpRev update. The stuttering was gone in every gear except 2nd and it felt great to finally have all the power when running through the gears. Fast forward to last night and the first time I drove the car since the test drive after the new file. The stuttering is back in every gear and I'm at my wits end.

Has anyone experienced this issue or have any ideas?

 

I battled it for a while and it ended up being the 100% tune related. Since flattening the entire fuel table to +/- 5% and redoing all the fueling on the MAF table it's 99% gone. It's not so much the 'quality' of tune (e/g/ reaching your target A/F), rather it's the method of getting there. Basically timing becomes unstable when you have sweeping changes on the fuel table and the load point crosses over those changes (left to right). In my original logs you could actually see the timing going negative for a couple seconds on tip-in when boost kicked in, and it usually correlated to the areas of the fuel table where there were large increases.

 

I have an 06 mt as well with the BP kit and same turbo. I always noticed the "hesitation" between shifts, I always thought it was turbo lag. It is very noticeable like you said. It's weird because I can't chirp 2nd or third because it hesitates for that split second, but then it goes great! I always wondered if it was a tunable issue.

 

Thanks for the detailed info. The tuner is on it and I will post back with results.

 

Best way to tune by far!

 

Sad to say the revised tune using the MAF table was unsuccessful.

Stuttering was unchanged in 2nd and 3rd gear but did seem to be almost gone in 4th gear. Although logging on the street/highway at WOT in 4th gear with an open dump wastegate is a tricky proposition so I didn't spend a lot of time at it.

Next up we will try a new GT MAF and see if that helps. If that fails the ECU will be replaced.

It still seems strange that the first revised tune (still using the fuel table) fixed it in most gears but then reverted the second time I drove it.

 

I have never been able to get a perfectly smooth tune using osiris. With haltech as cheap as they are now (some even under 1000$) you could sell your osiris tuner and gt maf and have about the same amount as needed for a used haltech. A cheap solenoid valve and you get a built in boost controller that can be adjusted by speed or any obdII setting. It is simple to tune as well.

 

New GT MAF installed and the issue remains. We will replace the ECU next and report back. The tuner hasn't seen this issue before and has been awesome with helping me troubleshoot (even sent me the new MAF to try out no charge!)

If the ECU doesn't fix it I guess I will start looking for used Haltechs. I'll be really pissed if I go through that hassle and this issue is still here.

Anyone have any other ideas? I was really expecting the retune to solve it based on the issue and symptoms sounding identical to djamps.

 

Strange... can you post cipher logs? Mainly A/F, timing, throttle position, rpm. When mine was doing it my tune was overly rich during boost tip-in (ECU over-correcting during boost ramp-up basically). Not saying yours is but it would be interesting to see. You want a smooth curve from 13's (0 PSI) 12's (1-3 PSI) to 11.5-11.7 (full boost) as boost ramps up. Anything richer than 11.5 on the OEM widebands especially if they bottom out (they bottom at 11.25) will cause these kinds of issues. Generally uprev is a bit rich on the first stab -- do a couple pulls before deciding if it's any better.

 

^I agree with the above. Those stock widebands bottom out too quick so what might look like low 11's could be 10's or even 9's.

 

The tuner has me tuned to low 11 AFR's (using my Zeitronix to monitor, not factory WB's)

Here's a log from Cipher and one from Zeitronix so you can see a more accurate AFR. You need to download the Zeitronix software to view the log but AFR is between 11.2-11.5.

https://www.dropbox.com/s/g314opnt7rgzvkg/log0008.zdl

https://www.dropbox.com/s/oox4u5bfb3...1-43-41_PM.csv

 

You should up it to high 11's. Like I mentioned, the ECU freaks out and pulls timing (the hesitation you're feelign) when the OEM WB's bottom out at 11.25. Another thing to watch out for is closed loop compensation and make sure it's spot on (not constantly add/pulling fuel) all the time even if the A/F looks good it'll cause instability transitioning out of closed loop and into boost. You can drive around in closed loop and run your logs through my uprev log parser to see your average compensation at various MAF voltages (you will need to add bank 1/2 corrections to the logs):

http://djlab.com/uprev/maf.php

EDIT

Ran your log thru the tool...minimum TPS 2V, minimum hits 1, minimum RPM 3000. some notes:

* MAF voltage is quite hot @ 4.3 V -- is this an upgraded MAF? My HPX logs low 3's at full boost red line. I recall vaguely about the ECU not liking to see more than 4.5V or so...cutting it a bit close.

* A/F has flatlined 11.25 above 4.0V and for most of the pull. No bueno.

* lean spike at 3.67V when you stab the throttle. Almost full lean... the ECU is most certainly hearing knock as you can see in the timing. Super no bueno.

* Timing settles at 8 degrees by 5k rpm and 11 degrees at redline after the lean spike...the timing is so low it could actually be causing 'ghost knock' and compounding the peoblem. Either that or the ECU has gone into failsafe (high-det) timing map.

Fix the lean spike, get the timing up to at least 14-15 deg by redline which is still very conservative (mine actually peaks ~18 on my pump map, 20 on the high octane map), and bring the A/F to 11.7 and it should make a huuuuge diff. To be honest the tune looks like it's all over the place...not sure if I'd believe he'll bring it into spec on his third attempt...

 

Thank you again for the excellent info. I will work on this some more with what you've given me to go on.

It is an UpRev GT MAF.

The timing is lower than it should be as I remember the first tune had near 16 degrees on the top end. I may have ran it on the 2nd map which has more conservative timing but even that should only be a few degrees less so it may have switched to the high det map.

Really appreciate your help. Will post back when I have an update.

 

I had the same problem.
Took it too 3 tuners, blah blah blah, ended up building engine, and going haltech.

This is 100% Tune related. Shitty thing is I have yet to find a tuner in Canada that can anything BUT WOT Dyno pulls.

Id get Hal @ Dynosty to do an Etune.

 

Vince at R/T tuning is very conscious about part throttle tuning. If you can make the trip it's worth it -- he used to do F/I e-tuning but not sure about it any more. Prolly a case by case basis.