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Old 02-01-2010, 08:28 PM   #1
EVT_Dan
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Member#: 143534
Join Date: Mar 2007
Default Lean spike under slight load / part throttle

Completely swapped RS including wire harness from an 02 wrx.
Ran great for 1.5 years.

The last 4 months I've been chasing ghosts. At part throttle, under slight load, or right at the onset of boost the car would buck and hesitate real bad until I jumped on the accelerator and powered through it.

Brought the car to a tuner and he said the 02 sensor was bad. So I replaced it, and he tuned it (has tons of utec experience)

Ran o.k for about a week, but now the problem is coming back.

I've heard rumors of a problem when the utec is switching from stock map to the new map.
Again when at part throttle, especially while accelerating, or going up a hill, the car will spike to almost 20 on the A/F ratio and buck and stumble until I power through the problem, at which point it pulls like a raped ape and drops back down to correct A/F ratios

It's completely killing the drivability of the car.

Things I've done to try and fix the problem.

Changed 02 sensor
Changed Fuel pump
Changed air filter
Cleaned MAF sensor
Made sure grounding wire is connected b/w intake mani and tranny
Had car re-tuned which only temporarily made the problem only slightly better,
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Old 02-06-2010, 02:42 PM   #2
LRTct
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You ever figure this out?? I've been having the same symptoms, along with alternating misfire codes. Been chasing for awhile.. Fuel pump was next on my list..
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Old 02-06-2010, 06:35 PM   #3
Texsar32
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Join Date: Dec 2006
Chapter/Region: MAIC
Location: Hampton, VA (from Texas)
Vehicle:
2007 WRX Limited
UGM

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I have an 07WRX and before I purchased the UTEC I spoke with my tuner. He said that before I buy, a couple things that I will notice are 1) when starting the idle will be rough for up to 20 seconds as the UTEC switches maps (not an issue as I use my auto start) and 2) at about 20-25% throttle you will experience what seems to be a "boost cut". Let me clarify that he did NOT say it was a boost cut, but it will seem like it. From his words, it is perfectly normal with the UTEC. Could it be possibly that with a quite older engine you feel it a bit more than I? Hope this helps out.

-Marcus
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Old 02-06-2010, 08:05 PM   #4
john 1badSTI
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Chapter/Region: MWSOC
Location: grove city ohio
Vehicle:
04 sti 10.51@138.5
on e85@ 30psi--spinning

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no what he is talking about is the transition point from stock ecu to utec at 25% throttle and it is possible to tune that transition area to make it smooth.The timing map and fuel map in the utec have to reflect a nice gradual change in numbers compared to the stock ecu.
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Old 02-07-2010, 07:32 PM   #5
LRTct
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Quote:
Originally Posted by john 1badSTI View Post
no what he is talking about is the transition point from stock ecu to utec at 25% throttle and it is possible to tune that transition area to make it smooth.The timing map and fuel map in the utec have to reflect a nice gradual change in numbers compared to the stock ecu.
copt that.. His symptoms just sounded exactly like mine on my completely stock 02 wrx. I know now they really wouldn't relate though.

Mine has just frustrated the livin heck outa me. I've done so much electrical/ sensor swapping, vacumn/boost leak hunting, that I'm at my wits end. The problem came up so severly and yet goes away at full throttle, full boost, so I've been thinking away from a "mechanical" engine related source like valves etc. I don't know and netiher has the 1 dealer and 1 other shop I tried.
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Old 02-08-2010, 09:20 PM   #6
EVT_Dan
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Small update

As quickly as it came up, the problem seems to be sorting itself out. Which on one hand I'm happy about, but at the same time worries me because it will more than likely come back at some point.

The only thing I changed recently was the Y pipe under the intercooler. I went from the stock one, to a perrin version. I inspected the stock one everywhere expecting to find a crack, thus resulting in my problem. However, I found none.
Perhaps the smoother airflow helped things a bit.

My other thought is that somehow the ECU learned what to do over time to run smoother? Similar to reseting the ECU?

Watching the wideband, when the problem occurred at 25% throttle, the readout would go from 14.7 and gradually climb to 20 while the boost increased, until I pushed harder on the throttle.

Now, while running better, the UTEC seems to be switching from stock map to tuned map properly. Instead of hanging onto 14.7 and going up to 20 (resulting in the bucking and sputtering) it is now dropping down to 12.5 and eventually 11.7 under wot.

Gremlins in the UTEC
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Old 02-08-2010, 09:46 PM   #7
EVT_Dan
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This thread... post #8

http://forums.nasioc.com/forums/show...=part+throttle

This has everything to do with my problems, guaranteed


So, who knows an awesome UTEC tuner in New England ?
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