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Old 02-10-2008, 06:15 PM   #1
MRX WRX
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Default utec, speed density, and misfire codes

i have converted three cars to speed density and all of them get a random misfire code only when warming up??? i cannot figure out what is causing this.
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Old 02-11-2008, 08:00 AM   #2
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Let me take a wild guess…
  • Repeated misfires, all 4 cylinders, typically on cold-startup only?
  • Cold start idle surge? RPM surges during warm up from 1k to 1,500 then back down to 1k, every 10~15 seconds? Completely goes away once at optimal operating temp.

I’ve seen the exact same symptoms. Had my UTEC-DELTA installed for 3 months, just recently switched to SD and retuned fuel, and BAM misfire codes on cold start, never there before. And I’m not even running injector scaling either (infamous for misfire codes).

Everybody experiencing this issue with SD {misfire / idle hunt} please chime in. Maybe we can get TXS to comment?
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Old 02-11-2008, 08:04 AM   #3
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The idle hunt doesn’t bother me too much; but the misfire does as it throws a CEL and in the newer models, disables cruise-control until cleared. So even if you disable the CEL indicator within the UTEC, you can still throw the code and not have any functional cruise-control
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Old 02-11-2008, 08:55 AM   #4
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BINGO......THAT IS EXACTLY WHAT MINE DOES!!!! and what sucks is that to clear the code the ECU has to reset and relearn everything and it runs sluggish for a day or so.
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Old 02-11-2008, 09:15 AM   #5
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Quote:
Originally Posted by MRX WRX View Post
BINGO......THAT IS EXACTLY WHAT MINE DOES!!!! and what sucks is that to clear the code the ECU has to reset and relearn everything and it runs sluggish for a day or so.
with utec?? utec uses a set matrix to adjust fuel.. the only area where it should be "learning" is under your open/closed loop threshold...why would clearing codes cause it to run sluggish?? mine never changes when i clear codes..
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Old 02-11-2008, 02:48 PM   #6
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UTEC only comes on after 25% TPS (depending on your setup) so it runs sluggish until that point. the ECU will ramp timing up slowly as time goes by, just like the ECU relearns idle after a reset.
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Old 02-11-2008, 04:18 PM   #7
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Originally Posted by MRX WRX View Post
UTEC only comes on after 25% TPS (depending on your setup) so it runs sluggish until that point. the ECU will ramp timing up slowly as time goes by, just like the ECU relearns idle after a reset.
But to use SD mode you have to be in Open Loop fueling where the UTEC has full control @ all times, right?
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Old 02-11-2008, 10:29 PM   #8
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no you still have to use the MAF for light cruising mainly because you only have one row to tune anything below vacuum its not impossible but very difficult to do. i just tried adding 10% fuel to the water temp correction on the lowest one (cant remember the celsius degree!!) and it seemed to take away some of the surging. see what happens tomorrow
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Old 02-12-2008, 02:20 PM   #9
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Try using the temperature compensation for fueling during warm up. If you have larger injectors you will also need to correctly tune the injector latency.

use a wideband to check the fueling during warm up. Misfires could be due to too rich or too lean.

FYI - None of my SD tunes exhibit this issue
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Old 02-12-2008, 06:15 PM   #10
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The idle hunt that resulted in misfires drove me batty.

It was frustrating because I have all the tools to know how to fix it... just nothing I tried worked. I went back to OLF.
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Old 02-12-2008, 06:26 PM   #11
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Quote:
Originally Posted by xcntrk75 View Post
Everybody experiencing this issue with SD {misfire / idle hunt} please chime in. Maybe we can get TXS to comment?
Does anybody from turboxs still post here? Nathan is gone, Jermain is gone too?
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Old 02-12-2008, 08:09 PM   #12
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Originally Posted by mick_the_ginge View Post
Try using the temperature compensation for fueling during warm up. If you have larger injectors you will also need to correctly tune the injector latency.

use a wideband to check the fueling during warm up. Misfires could be due to too rich or too lean.

FYI - None of my SD tunes exhibit this issue
latency is 1028 on modded stocks
fuel compensation is 10% tapering to 0 by full warm up
and it still hunts A/F is around 13.0 while warming up (with FJO wideband) kicked out a misfire code even after the adjustment


what temp comp settings do you use?
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Old 02-12-2008, 08:48 PM   #13
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Well I went out and captured the idle hunt/surge issue in a big log. Basically I hooked the laptop up and began logging from the first turn of the key through until the car was fully warmed up (about 7min total – yeah it’s cold here). Here’s my data formatted and graphed into some charts for easier presentation.
SD-IDLE-LOG.xls

A few observations:
  1. The idle surging issue doesn’t begin until well into the warm-up cycle. At cold start the RPM’s average around 1,600rpm. Then they slowly fall as the vehicle warms. It’s not until they drop down to the 1,250 range that the issue begins.
  2. The surging begins “all at once” in the logs/charts. But prior to that event there’s a long period of slightly “rich” fuel state. The AFR dips from rather consistent 14.5~7 down to 14 and eventually down to 13.5 before the “surge” begins. Soon as the surge starts the AFR swings wildly (in harmony with the rpm) from 13 to 15AFR.
  3. The surge condition slowly tapers off at the end of the cycle and becomes more subtle until it’s eventually gone and the idle drops to 900rpm and obviously well into full warm-up and normal operation.

So these are my results. I have no idea how this translates into the cold-fueling adjustments capable with the UTEC. Anybody have any advice of which parameters need adjusting in my case?
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Old 02-13-2008, 01:47 PM   #14
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I don't really get why the UTEC would even mess with cold start. I mean heck, that's half the point of the way the UTEC works, so that you don't have to deal with things like that. Obviously it does, since the problem doesn't start until you hook up the UTEC, but it just doesn't make sense why.
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Old 02-13-2008, 02:16 PM   #15
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i agree!! i added more fuel in the cold start and it surged worse so i am gonna go negative on the fuel and see what happens. in 2 days i have 6 misfire codes!!
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Old 02-13-2008, 02:34 PM   #16
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It's definiately a rich condition. I've had some work done on my car by a dealer, and they keep telling me that the car is running rich every time.

I always think it's odd that people try and shoot for 14.7:1 AFR's at idle. I highly doubt the car needs even that much fuel to idle. I've seen quite a few cars that OEM run 20:1 AFR's at idle, because you just don't need that much fuel to make the car idle. I've no idea what the Subies run from the factory at idle though, nor have I messed with idle on mine, so maybe our cars do. But it definiately runs rich during cold start.
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Old 02-13-2008, 06:03 PM   #17
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Quote:
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I don't really get why the UTEC would even mess with cold start. I mean heck, that's half the point of the way the UTEC works, so that you don't have to deal with things like that. Obviously it does, since the problem doesn't start until you hook up the UTEC, but it just doesn't make sense why.
It's because the UTEC messes with MAF voltage even when it's NOT in control if you have larger than stock injectors.
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Old 02-13-2008, 07:03 PM   #18
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Ah yes, I didn't think about that fact!

Hmmm, I'll try the temp compensation and a few other settings once I get my BPV in (some bastard stole my old one, ****ing worcester) and the car can actually run.
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Old 02-13-2008, 08:11 PM   #19
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It's because the UTEC messes with MAF voltage even when it's NOT in control if you have larger than stock injectors.
That's what I thought too. But in my case, I have stock injectors and I'm still encountering this issue... There's no scaling in my setup, just SD fuel table manipulation
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Old 02-13-2008, 09:54 PM   #20
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ok guys, temp compensation does NOTHING!! why??? because the utec does nothing except for injector scaling until you reach the crossover points, i datalogged the warm up cycle twice with negative numbers and positive numbers and nothing changes at all ?????? hey Mick , care to enlighten us with your knowledge, this is annoying, i put a piece of black tape over the light, because it bugsthe****outame!!
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Old 02-13-2008, 11:45 PM   #21
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interesting. Shame I took my UTEC out two weeks ago, run an Autronic now.

All I can say is that I never ran into this issue with the cars that I worked on.

For the person that has stock injectors I would have to say that something mechanical is wrong.... Strange
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Old 02-14-2008, 07:56 AM   #22
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For the person that has stock injectors I would have to say that something mechanical is wrong.... Strange
Normally I would agree with this conclusion, but not the case this time. My UTEC-DELTA is on an 08’ that has about 8k miles total on it, and is only a mild stage-3 (i.e. stock turbo & injectors).

It’s definitely the UTEC and definitely SD related. Why? Cuz I can swap over to MAF fueling, throw a prior MAF based fuel table map in there, and will have zero issues with cold start idle hunt and/or cold start misfire. I know because I was running in this config for months. It wasn’t until just the other day when I switched to SD and retuned my fuel table, that it started doing this.
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Old 02-14-2008, 09:59 AM   #23
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Ok, 08, did you re-calibrate the MAP sensor settings? The 08 stock MAP sensor is different that previous years and needs to be calibrated in the UTEC settings.
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Old 02-14-2008, 12:34 PM   #24
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I don't remember, but does the UTEC do injector scaling in speed density only, or in MAF mode as well? Because if it only does it in SD, then it's possible that even though you're using stock injectors, it's still going to modify the signal slightly because I'm sure the routine in the UTEC for injector scaling isn't written so that when the injectors are stock sized, it does nothing to the signal.

I'm sure there is a parameter somewhere that might be able to help with this. I'll do some searching once my car is running and see if I can fix it.
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Old 02-14-2008, 02:37 PM   #25
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hydra is starting to look better and better!!
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