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Hesitation Issue Question

7003 Views 56 Replies 23 Participants Last post by  squared away
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 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' 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.
"Glad we have a new place for real Impreza's to roam"
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What causes the ECU to learn such poor habbits to cause a flat spot?
I reset the ECU last night and the car runs like a champ again..

Has anyone data logged via an OBD2 scanner the differences from fresh reset to poor running? I think it could be good to log ignition advance, spark duration, etc over the course of a few weeks to see what the ECU is doing over time. If I had the tools I'd do it daily and make a graph pf all functions to see what happens over time..

Any volunteers?
I'll start hooking mine up daily. I have the hesitation occasionaly. I'll do one week as is then do reset then run it another week.
sweet! i think for the data to give an accurate portrayl it must be done for about a month....
If I had a scanner I'd do it...but alas I dont.
OK, I've had the 3400-4000rpm (99 RS) hesitation off and on for a few years now, and after about 3 visits regarding it the dealer decided to replace an O2 that was "out of spec". It hesitated leaving the parking lot after the repair. Apparently the timing WAS being retarded but the guys at the dealership couldn't figure out what to do. I've given up on those guys and am thinking about replacing the knock sensor, or possibly insulating it like people have done with that "flannel kit". I was thinking a quick shot of aerosol undercoating spray? Where is our knock anyways?
I don't know if this is true or not...but........
I had a spare cat section laying around(don't ask me why)
so I hollowed them out....put the hollowed ones back in ...and VIOLA!!!!!!!!! my 4,000 rpm stutter was gone:D
could this just be a coinky dink???????????????
I did notice that the cats have a WHOLE SHIT LOAD of restriction inside them......may this be the problem???
I since then decided to throw the original cats back on(due to the horrible noise) and the hesitation is back.... Hmmmmmmmm:confused:
any thoughts ?????
I have a feeling that the hesitation would come back within a few days. When I installed my exhaust, the hesitation was gone for a couple days then returned.
it goes away after mods becuase we reset the ECU.....
Mine has had the "lag" during the morning till I have driven about 15miles, then it goes away.....weird.
The cat issue is unique...maybe my cat is getting loaded up..I'll have to check it out next week.
I thought about the whole "ecu reset" when I removed the cats....I didn't reset it to see if that would affect the Im kinda convinced that the cats are the cause of this....Hmmmmmmmmmm:confused: thoughts
Does anyone with high flow cats have a hesitation problem?
A problem with the cats would probably not be so RPM specific.
it would also be more low end where there is less gas velocity...
My number 1 wire terminal on the coil pack was corroded, I am replacing the wires tonight..and will report back on monday if it works.

To date I have checked and or replaced:

MAF, checked out fine
02 sensors, checked out fine
Spark Plugs, replaced with SOA NGK's
Fuel filter, replaced with SOA part
plug wires, replaced with SOA parts
my J&S says no knock activity, but has suddenly stopped displaying anything but AF ratio...

More results to follow.

Puckaveli, what did you find via data recorder..
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You ever tell someone " Hey watch this" then they look and it doesn't happen. Since I have been logging I haven't had my hesitation. I'll keep logging away though.
Well, here are my findings...

Plug wires, clean the coil pac connector ends with a wire wheel on a dremel tool, and if your cars plug wire's have any corrosion in them, replace them...this helped make the hesitation go away, a little bit...

Thanks to Phil, aka Damnit Beavis and his wife, Steph (vertically challenged) I got to do some data logging runs with Phil and his laptop, what I found was relieving and frightnening...I had a hunch it was timing related, the car felt like all the advance was being pulled right out of it between 3500 and 4500 was. Using the OBD2 scan tool on a laptop we monitored ignition advance and say it rise steadlily to about 30-32 degrees advance, then plumit to 8 degree's at WOT!!!!! Then return back to 40+ degrees of advance....
We started by disconecting the J&S knock guards knock sensor to see if it was actually seeing knock or just noise...neither. The retard was STILL there......we went back and removed the J&S system from my car, and did the popular Earthing mod (more on that later) and low and behold, it was gone...just the regular tuned RS pull all over the rpm range..boy did I miss that feeling.

So, I beleive my J&S was a bad unit, I intend to call them and ask what might be wrong and hope they can run a diagnostic on it and maybe warranty it..I like the safety back up of it...I will let you all know how that goes..

The Earthing or Ground mod...DO IT! Dont expect any power increases, or better throttle response, just get ready for a MUCH smoother running engine and a better idle. It took all of 15 minutes to do it right, and I ran them from the negative battery post to both strut towers, the intake manifold and the alternator, you could run one to the tranny too, but I didnt see it as needed. The car just plain runs smoother, even Phil noticed it after being in my car for a whole 30minutes of his life, then riding in it does run better.

We'll see if the flat spot comes back, if it does Im gonna try a different ECU, the only code found in my ECU was for an 02 heater wire, which checked out fine later in the day..

As some of you may remember I had an odd driveline noise...we also checked that out this weekend and found a whole lot of NOTHING! We ran it in the air in gear and couldnt hear it, we checked the driveshat, CV's, U joints etc..nothing looked out of place at all...guess I drive it till it breaks....

This is what I found out, YMMV...
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I will go over some unhesitated logs today and see where the retard goes (no jokes please).

If you have the time please put up details on the Earthling mod. It is new stuff to me.
For awhile I have been seeing "earthing" kits in Bonzai, Impreza and other Japanese car mags. They take the negative post of the battery and ground the chassis to it, the motor, alternator and some times tranny to help ground all the sensors on said parts of car. The WRX (GC8 and GDA) crowd both say it makes the car run smoother and helps eliminate the flat spot.
So I tried it and ran 8 gauge wire from the (-) battery terminal to both strut towers, the alternator bolt and a point on the intake manifold. After running the wire, wire loom and soldering all my ends onto the wires,we started it up and went for a drive. The car idled noticeable smoother, and felt smooth all over, like it never has before.
I was quite skeptical at first of this mod, all I can see it doing is providing a better ground for all the sensors and maybe cutting down on some electronic noise...what ever it does the car seems happier. My question is, is why didnt SOA and SOJ provide a better ground to start with?

Just for the sake of technicality, it was 12GA wire, not 8 :)

I was skeptical to the point that I didn't WANT to believe it. But I've witnessed it making a noticible change TWICE now.

I still say it sounds really stupid though.

Why do the instructions call for 8GA anyway? 12GA wire will carry 75-100 AMPS. I don't think the factory grounds are THAT bad. 8GA would be hard to hide too.
for some reason 8 gauge sounded right, but as Phil said..its was 12 gauge and it is HIS wire after all....oops.:eek:
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