OFT+OFH: Cold vehicle stumble
 

All,

I currently have the OFT+OFH setup on my 2014 and have been having some strange drivability issues in the past couple weeks.

Setup: OFH+OFT (V2.0X non beta, 91 octane map)+berk axle back+93 octane (winter blend- Mobil). Note that when I was on the older 1.59 maps, it had the same issue (which is the reason I updated to the 2.XX maps a couple days ago)

Condition: Cold start (>3 hours parked outside in ~30 degree weather)

Issue: Vehicle has some hesitation that you can feel at cold start around ~2750rpm at low throttle, feels like a slight hesitation/stumble along with a clear change in the exhaust note right ~2700 rpm (sounds somewhat close to a very mild backfire). It does this 2-3 times after being turned on in each gear only at that RPM zone (usually as I'm merging onto the main road from work) and then doesn't do it again for the rest of the drive.

I've been trying to log this a few times and have come up empty handed. Here's the latest log from tonight, from a cold start. I was specifically trying to get into the throttle a bit in each gear up to 3000rpm so that it would show this; you could feel and hear the stumble for the first few minutes and then it went away. Here's the log:

http://datazap.me/u/sirsol66/1217-co...t?log=0&data=1

And, for reference, here's a WOT log from earlier this afternoon. Everything seems to be fine with the car (no knock, no stumble, no issues, once its warmed up)

http://datazap.me/u/sirsol66/12172014-log

Any thoughts? The car isn't showing any misfires, timing seems normal to me (can someone confirm cam timing? I'm worried a bit as my car is an early build date vehicle from 2013), and doesn't show any knock. Thoughts? (side note: already pm'ed Shiv yesterday and have yet to receive a reply)

@shiv@vishnu
@steve99

Side note for things I have already ruled out:

Bad gas- changed gas stations and same issue
Bad tune- Switched from V1.5X tune to V2.XX tunes a couple days ago and same issue

I wouldn't rule out a bit of water in your fuel. I doesn't take much empty space in your fuel tank to collect a bit of moisture when temps drop.

instead of logging the misfires and vvt stuff log, ltft, stft ,engine load ,coolant temp, and intake air temp

is you intake stock ? ?

it more likely it an intake or exhaust leak.or crook thermostat.

is the coolant up to operating temp of arround 170F if not car will likely be on rich startup mixtures

on a cold start in near freezing temps you should be waiting till idle settles at about 750 rpm before driving off

Sounds like it could be an intake issue. A bad MAF scale down low causes hesitation for DD.

I experience this exact same issue on cold starts. Once up to temperature it goes away. Looking at my LTFT's during cold starts I often see them in the 8+ range. The problem resolves itself and LTFT is in the 3-5% range once up to temperature with the exception of very low throttle angles in upper gears where LTFT skyrockets again. The temperature adjustment to MAF scaling might be part of the problem during cold starts but I suspect there is something else at play. Its slightly annoying to say the least. If I had to guess adjustments to the temp adjustment scale along with a proper MAF scale would fix most (if not all) of the problems but I've been to busy with work and school to devote any time to it. The closed loop fueling table at the lower end might also be partly to blame as my open loop fueling looks spot on. Then again my knowledge on tuning is extremely rudimentary and I could be completely off base here. The only way for me to know for sure is to probably get it tuned professionally or do some serious reading up on tuning, which I don't have the time for.

I've ruled out exhaust leaks since I finally got tired of that being blamed for it and took it to a shop for them to check for leaks where none were found. I have recently switched from a Perrin panel filter and perrin intake tube to a grimmspeed intake which resulted in just shifting the range of the trims to be more lean. Before I was around +7% max at low throttle input and around -5% at highway speeds and now I'm sitting at +10% at low throttle inputs and -1% to -2% at highway speeds.

Im having the same thing with mine. More of annoyance than anything else, it goes away after about a minute or 2 of driving.
OFH+OFT 2.xx non beta, Invidia N1. Happened with un-catted FP and stock FP. Only Intake mod is a K&N drop in.

Steve I'll log these and get back to you. My intake is completely stock and has never been taken apart.

Shiv, any feedback? @shiv@vishnu

Hey Guys

I have the exact same problem after my software was upgraded. The car doesn't pull timing anymore but this has now creeped in. All I do to make it less noticable is to keep the revs up in the morning untill the car has warmed up.

Anyone found a solution to this?

Log when it a problem.

do you have stock intake ?

if its in the first couple of minutes after cold start then tone down or remove the large maf offset at startup.

if you drive off before the cold start sequence has completed engine will still be running very retarded timing from startup. you should be letting it warm up for a couple of minutes on a cold start.

Hi

I had the Perrin panel filter but removed it and replaced it with the stock one. Still have the Perrin cat-back though. I will inform the guy who did the upgrade regardingthe maf offset. Im still a noob when it comes to these things. :bonk:

filters dont generally throw of maf scaling unless it was an oiled one and it was over oiled and oil got on maf sensor.

maf scaling is effected it you change the tube the maf sits in or the position of maf sensor.

I haven't updated this in a long time but my problem never went away. I updated OFT files to the latest revisions, tried the 91 octane tunes just in case my CALid one was a fluke, switched to summer blend, leak checked the (stock and never been touched) intake, leak checked the exhaust manifold, and many others.

Car still has the same stumble first couple times you pass that RPM range; after 2-3 times in that range, it goes away. Only way to avoid it is if the car idles for a couple minutes before moving.

Logs don't show any thing strange happening, but you can definitly feel it. I've also verified it against 10+ stock FR-S's (we have a lot at my work) and none of the stock cars to this. Any thoughts?

ok i would try the following

lean out the OL FUEL TABLE as per shivs post here

also try adjusting the pI\di ratio at low loads to be 100% direct injection at loads below 0.2 for manual and 0.3 for auto see tune tweaks link below.

you might also try reducing the MAF offset tables at startup as per the Tune Tweaks thread as well see the Cold start noise reduction part, if the ol fuel table adjustments dont work.

Its probably best to warm car up first rhough.

After startup it runs port injection only for first few minutes
http://www.ft86club.com/forums/showp...3&postcount=27