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Discussion Starter #1
I know this has been covered on "The Other Board" several times in the past, but I thought I would see if there has been any new discoveries made. I have noticed that when you run 92 or higher octane fuel, the hesitation seems to go away....but recently it has stayed around even on higher octane. The car is a total slug from 3-4k rpm....and right at 4k it takes off...like turbo lag. I used an OBDII tool to pull some data (Thanks Puckavelli!!) and we did not notice any timing changes while the hesitation was occouring, thus shooting down the long standing theory that this problem is caused by an over-sensitive knock sensor retarding the timing....even though the higher octane changes would point to that theory again. So.....MY'99...no intake mods (blew a few MAF's) fairly new plugs, and it only happens between 3-4K. Let me know the thoughts and your experiences with this issue. By the way, my '97 Legacy Outback has never had this problem.
Doug
"Glad we have a new place for real Impreza's to roam"
 

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2001 STM Sedan
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wow i thought 99's didn't experience the "hiccup" in that range...well i would beg to differ that it's more injector pulse then timing...the Knock sensor on our cars really does jack sheeot! You'll find that out if you go turbo and start to ping...Well anyhow, i need to find and ocillioscope and then i'll be able to get a lil more in depth...too bad the Honda menus(built in ocillioscope) won't communicate with a subaru ECM.
 

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glad to see someone talking about this subject. i too have this exact problem: 3400- 4000 rpm. if you unplug the knock sensor the car feels like that throughout the entire rpm range. plug it back in and sometimes it will go away. i have had this problem foe about 6 months now and it is a constant source of frustration. just when i think i have it solved it reappears. i have tried different intake filters and different exhausts. all cure the problem for about 100-150 miles after a fresh ecu reset. lets all talk about this and try and get to the bottom of this problem. it is making me nuts!
 

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I think the normal pulse waves in the intake manifold cause this, by disrupting the normally smooth airflow in this rpm range. Not much that you could do about it, except maybe playing with the Igntion or cam timing (both can be accomplished with offset keys for the crank and cam sprockets.)
 

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Discussion Starter #5
Has anyone with an SAFC been able to make this go away? I mentioned before that I didn't see any changes in the timing during the sluggish part, but I wonder if it may be a product of a lean/rich condition through this part of the range. It seems worse when the weather is colder...below freezing is the worst...and it will sometimes go away with high octane gas. Maybe a can of 104 would do the trick....anyone ever use this stuff?
Doug
:barf:
 

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I pointed this problem out to my dealer. They test drove it and said "Yes, there's a hesitation - it's normal and there's nothing we can do about it":(
 

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Bulliten

There is a bullitten on this atwww.nhtsa.com web site it is 11-58-99 it's suppost to be a replacement computer part number is 22611ae513 at Subaru parts .com the computer is arount $450
 

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2001 Subaru Impreza RS
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I'm glad to hear others feeling my pain. Mr. Majestic with his 02 RS says he doesn't experience this lag and he has a GanzFlow intake as well, what is the difference?

Nick C.
 

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Yes,I do have the same problem but I have not done anything about it. I have a chip hooked up to the computer and I am afraid to take it in and have it done for fear on what they might say, but I do think that it is done by Subaru if your car is under warranty.
 

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i understand, my dealer hit me for a service charge because i had a non stock air filter! i think i will force my dealer to replace my ecu using this info. thanks.
 

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Discussion Starter #12
It Went Away.....Again

Well, I used up the last tank of gas (BP brand....actually Ammoco gas) and got a full tank of 93 from Sheetz (local to us?). The short version is, the hesitation has gone away completely now. Pulls hard all the way through the range. This is the strangest thing considering I could run any grade or brand in my wifes car and it would run the same (97 DOHC Legacy - 149,000 miles). Anyway, I'll keep updating here as to the status on the next few tanks.
Doug:rolleyes:
 

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noticed with about every mod i've done to the intake and exhaust tract, the hesitation around 4k has gone away and then returned after 100-200 miles. really hoped the brullen header/high flow cat was going to cure it. of course, i thought the same thing with the cobb street cams. it seems as though as soon as the ecu relearns the increased flows, it compensated for it by leaning/richening the fuel curve, back to where it was before the mod was done. this is with requisite resets too. working on this theory, i've checked the ecu mode with an obd2 scanner and found that 4k is where it is changing from closed loop to open loop mode. the differences in the air/fuel map based on those two modes seems to be contributing to the problem. any comments?

mark
 

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I thought that open and closed loop mode was determined by coolant temp. When you first start your engine in the morning, you have a cold engine, so its in open loop, and when your coolant hits a certain temp, it goes into closed loop, leaning out the mix. I guess the ECU just has two seperate maps for low RPM and high RPM, kinda like VTEC without the fancy cams? Talking out my ass?:lol:

A TECII would fix this problem right?
 

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i've never checked with the scanner to see which loop is active when the engine is cold, but when warm the switch happens at 4k - the same place that i see hesitation. and yes, a tec2 would cure it, once it's properly programmed.:rolleyes: it would take over all fueling and ignition, and i'm seriously considering one as the stock fuel maps just aren't well suited for extreme (even n/a)mods.

mark
 

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I just had the same problems with my '01 RS. Hesitation between 2-4G rpm and all of the other symptome taht you all just described. Than finaly after having my car in and out of the shop for a month it turned out to be an oxygen sensor. Car runs perfect now. I dont know if it will be the same on a '99 RS but its worth a look. And I thought that high octane fuel was actually bad for our cars?

fab9joe - you got screwed on that service charge. A different filter? Thats pathetic.
Ben
 

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yesterday my hesitation cam back in a HUGE way. So I pull up the MAF voltage on my SAFC, no drop or spike concurrent with the lag
so I pull up O2 sensor voltage and x-ref it against my AF gauge, no spike or drop with lag
BUT! I did notice my EGT's climbed rapidly during lag then return to normal after it has subsided. They never got over 1350.
After every mod I have mad the lag has disapeared. Then returned, hidden, returned, etc...
I paid careful attention to my knock guard during the lag, and saw no activity, and I have my J&S turned to the pretty sensitive side.
Today the car pulls fine, even with a dime size hole in my BORLA header..POS

So I know its not MAF, or AF related, the stock knock sensor is still a possibility as is fuel injector problems, might they be going static? Max SAFC corection is 15%...

oh yeah, car has been run on 93 octane its whole life

car mods:
99RS 5spd
Borla header
Stromung cat back
ISR Intake
act clutch
safc
J&S knock guard with dual monitor
VDO/Westach EGT in cyl.#3 2" from head
Bosch Platinum +4 plugs
the rest is all chassis and suspension


just giving my findings, hope they help
 

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bumpola

Also noticed if I let the car warm up longer than I usually do (5-7 minutes) the flat spot is gone by the time I reach normal coolant temp...
watching the EGT's rise during the flat spot makes me wonder, also noticed the AF ratio go over to richer than normal..could the hole in my header be causing this condition?
 
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