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Old 08-14-2006, 12:05 PM   #1
BURTONRIDR
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Default Engine Hesitation

Ok this has been driving absolutly nuts, Ever since I can remember my motor has had an annoying hesitation. If im sitting at a dead stop and I put the pedal to the floor it chokes and stumbles for a few seconds.. almost dies... then takes off... WTF!!! I put on PCV breathers and cleaned the intake and TB really well, I also upgraded my grounds to my battery. Since then it seems worse than before, runs much smoother and has more power, its just getting off the line.. This is driving me nuts, I dont like trying to pull into traffic and needing that power, RIGHT NOW.... COMMON... GO YOU STUPID CONTRAPTION...... I almost got hit the other day because it wouldnt go. Anyways I need sugestions, Im thinking I need to double check all of my vaccum lines but if that isnt it then I dont know what else I can do.

Almost forgot, I have a 97 subaru legacy outback, ej25
Weapon R Intake
NGK plugs
PCV Breather mod
Ground mod
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Last edited by BURTONRIDR; 08-14-2006 at 12:11 PM.
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Old 08-14-2006, 12:09 PM   #2
Tim Sanderson
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What sort of maintenance type work have you done if any? How many miles on it? Auto or manual?
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Old 08-14-2006, 12:15 PM   #3
BURTONRIDR
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It has 150k or so... I just changed the oil about 700 miles ago, changed the transmission fluid not long ago and flushed it. cooling system was just flushed. heads were just rebuild around 20k ago. it has good compression. brand new fuel filter. Im not sure what else off the top of my head. it is in great condition it just stumbles off the line
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Old 08-14-2006, 12:41 PM   #4
Matt Monson
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Front O2 sensor. They will often start to go bad and not throw a code. What will happen is it gets super rich down low in the RPM band...
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Old 08-14-2006, 12:58 PM   #5
FSRBIKER
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Mine did the same thing but also threw the knock sensor code...it eventually was the head gaskets.
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Old 08-14-2006, 01:44 PM   #6
BURTONRIDR
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hmmm I think I replaced one of the o2 sensors not to long ago... but I dont remember which. How do you test them?
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Old 08-14-2006, 05:41 PM   #7
BURTONRIDR
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How many RPMS is the engine supposed to be running at when it is at idle speed? Mine seems really low now that I think of it. it runs at around 600 rpm
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Old 08-14-2006, 06:54 PM   #8
horrorbiz
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my SOHC 2.5 idles at 500, and has no problem whatsoever off the line.
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Old 08-15-2006, 03:47 AM   #9
Toahk
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Im having similar problems. hesitation down low. I replaced the front o2 sensor not too long ago, maybe 3k miles. I read it might be the rear one so I used the old one that was up front. Still hesitates at low rpm but livens up a little bit at higher rpm. I swapped the MAFS and the ignition coil with a buddys of the same year/car, and it didnt help anything. Replaced spart plugs, nothing much diff.
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Old 08-15-2006, 10:44 AM   #10
BURTONRIDR
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Yesh None of the replacements did it huh? ::sigh:: I hope someone knows how to fix this problem, someone out there has to know what to do..... Im going to try replacing the front O2 sensor, Ill let you guys know if it works or not....

Another thing I read somewhere is that aftermarket CAI cause the problem, I will also try putting on my stock intake this weekend and see if it makes a difference...

Does anyone have any other suggestions?
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Old 08-15-2006, 10:47 AM   #11
Matt Monson
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The rear O2 sensor is next to worthless to start with. It doesn't have much impact on driveability. The front one is the one that controls your fuel trim...
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Old 08-15-2006, 02:36 PM   #12
DRKRYD
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Default just my 2 cents

I notice you have a weapon r intake, i as well have an intake and i have similar problems off the line sometimes....i was told/ read somewhere that its the engine starving to air, since replacing the large airbox behind the Tb the motor is forced to pull it from the tube intake...i didnt believe until i put my old air box back on and bam all low end torque came back...i have a c.a.i and its sucking from the fender so hopefully that helps you out a bit...
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Old 08-15-2006, 03:04 PM   #13
FSRBIKER
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I received my JDM 2.5DOHC engine and noticed that it doesn't have the large airbox behind the TB but instead a factory J-Tube intake so I am not sure that should make a difference. I thought the bigger airbox would be for quieting down the engine for the US market.

I am going to just get a cone style filter for it and make my own heat shield/cold air setup to shelter the filter from the hot engine bay air.

Quote:
Originally Posted by DRKRYD
I notice you have a weapon r intake, i as well have an intake and i have similar problems off the line sometimes....i was told/ read somewhere that its the engine starving to air, since replacing the large airbox behind the Tb the motor is forced to pull it from the tube intake...i didnt believe until i put my old air box back on and bam all low end torque came back...i have a c.a.i and its sucking from the fender so hopefully that helps you out a bit...
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Old 08-15-2006, 04:23 PM   #14
Outback Jack
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Quote:
Originally Posted by BURTONRIDR
Ok this has been driving absolutly nuts, Ever since I can remember my motor has had an annoying hesitation. If im sitting at a dead stop and I put the pedal to the floor it chokes and stumbles for a few seconds.. almost dies... then takes off... WTF!!!
I've got exactly the same problem, with the same engine. However, I've found that disconnecting the battery for a few hours will fix the problem for a while.

One theory I have about mine is that the knock sensor is detecting knock at low RPM and the ECU is retarding the timing. Now as to why it would be detecting knock here is beyond me, as I am convinced that it is detecting wrong.
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Old 08-15-2006, 04:45 PM   #15
soccer_freak_m@hotma
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Actually... the problem is the weapon R intake. I had the exact same problem until I removed it and put the big black box back on the throttlebody.

To achieve the same effect as an aftermarket intake I did the following:

1. removed filter in TB-side black box
2. sealed up the box with caulking
3. attached MAF to first elbow coming out of the black box
4. attached the cone filter to the MAF

The cone filter will rest on the intake manifold but it works great.
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Old 08-15-2006, 06:27 PM   #16
BURTONRIDR
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Quote:
Originally Posted by soccer_freak_m@hotma
Actually... the problem is the weapon R intake. I had the exact same problem until I removed it and put the big black box back on the throttlebody.

To achieve the same effect as an aftermarket intake I did the following:

1. removed filter in TB-side black box
2. sealed up the box with caulking
3. attached MAF to first elbow coming out of the black box
4. attached the cone filter to the MAF

The cone filter will rest on the intake manifold but it works great.
You probably dont have a dyno chart huh? I know that the aftermarket CAI make more power by (1) replacing the restrictive air filter, (2) creating a less restriction between the filter and the TB... So how much HP will I lose by putting the more restrictive intake box on what your proposing? Is it more restrictive? I sounds like a great Idea I will give it a shot this weekend, if I can fix the problem for free then great!!
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Old 08-15-2006, 06:32 PM   #17
soccer_freak_m@hotma
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Quote:
Originally Posted by BURTONRIDR
You probably dont have a dyno chart huh? I know that the aftermarket CAI make more power by (1) replacing the restrictive air filter, (2) creating a less restriction between the filter and the TB... So how much HP will I lose by putting the more restrictive intake box on what your proposing? Is it more restrictive? I sounds like a great Idea I will give it a shot this weekend, if I can fix the problem for free then great!!
Actually... according to my butt dyno it's much better than the weapon R by itself.

the key here is the black box itself is like an air storage tank. The ECU thinks that air is there and uses that for off-the-line to get rid of the hesitation. If it's not there it tries to gulp and gets maybe a tenth of what should be there which is kinda why it bucks a bit. the setup is in no way restrictive how I've done it than a weapon R.

I've noticed a better low end and top end than that silly weapon R tube. It light look a little funny but you'll definitely feel it.

oh, and reset your ECU if you change it to the way I have.

Also, the grounding mod is a good idea... it helps.
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Old 08-15-2006, 06:56 PM   #18
BURTONRIDR
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Quote:
Originally Posted by soccer_freak_m@hotma
Actually... according to my butt dyno it's much better than the weapon R by itself.

the key here is the black box itself is like an air storage tank. The ECU thinks that air is there and uses that for off-the-line to get rid of the hesitation. If it's not there it tries to gulp and gets maybe a tenth of what should be there which is kinda why it bucks a bit. the setup is in no way restrictive how I've done it than a weapon R.

I've noticed a better low end and top end than that silly weapon R tube. It light look a little funny but you'll definitely feel it.

oh, and reset your ECU if you change it to the way I have.

Also, the grounding mod is a good idea... it helps.
SWEET!! Im gonna give it a shot tonight (hopefully). Ive done the Ground mod, It did seem to smooth out the engine a quite a bit. I was very impressed. I will update tomorrow or in a few days depending on if I get a chance to do it tonight or not.
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Old 08-16-2006, 10:50 AM   #19
BURTONRIDR
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Ok I tried putting the intake box back on last night, I sealed up the vaccum line holes. The only problem now is I dont have anywhere to hook the vaccum line that goes to what i think is intake pressure sensor. I tried hooking it to one of the vaccum line holes on the black intake box, but I think the hole is to small for it to get an accurate reading. Soccer freak where did you hook yours up to? I ended up putting my CAI back on this morning so I could get to work
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Old 08-16-2006, 10:54 AM   #20
soccer_freak_m@hotma
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Quote:
Originally Posted by BURTONRIDR
Ok I tried putting the intake box back on last night, I sealed up the vaccum line holes. The only problem now is I dont have anywhere to hook the vaccum line that goes to what i think is intake pressure sensor. I tried hooking it to one of the vaccum line holes on the black intake box, but I think the hole is to small for it to get an accurate reading. Soccer freak where did you hook yours up to? I ended up putting my CAI back on this morning so I could get to work
Sorry, I didn't make myself clear. The holes for the breathers and PCV are to be left alone. what you need to do is take out the filter in that box and seal up the edges as the rubber ring on the filter won't be there.
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Old 08-16-2006, 01:55 PM   #21
BURTONRIDR
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I dont think I explained that well enough... Ok ya know on the 3" weapon R intake tube there are 3 holes, (2) small ones and (1) large one. The tube that plugs into the larger hole is my problem.

I set up the intake as follows(In order from the TB to the filter):

Off the back of the TB I attached the "black box" (the piece that is there stock, not the filter box or snorkle), There were two small holes on the black box that I plugged up because I have breather filters on the lines that are supposed to go into those holes.

Then on the opposite side of the "black box" I attached the MAF.

Then directly to the MAF I attached the weapon R cone filter.

Isnt that the way you set up yours, or did I read it wronge?

The problem is that the rubber tube that was plugged into the larger hole on the 3" weapon R intake tube no longer has a place to be plugged into. I tried to cap it off, car wouldnt start. I tried to plug it into either one of the two smaller holes on the "black box", car wouldnt start. I tried to leave it open to the outside air, car started and ran for a few seconds then stumbled and died.

I think Im going to drill a new hole into the "black box" for the tube to be plugged into, unless you have another suggestion?
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Old 08-18-2006, 12:25 PM   #22
BURTONRIDR
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Update: Problem Solved

Upgrade: borla headers,
Problem: Disconnected O2 sensor

Ok so as im installing my new borla headers last night, I dropped the intake down and there it was. The wires to my front O2 sensor were just dangling there!! So I hooked them back up, finished installing my headers. Then on top of that I also did the motification soccer freak suggested. I did a little fabricating though.

Problem: No place to attach Vacum line with intake setup decribed above,

To fix the problem with the big vaccum line that was causing me issues (which I described above).

First I drilled a hole into the side of the black box that attaches to the TB. Then I cut off the nipple that the vacum line was attached to on the stock intake tube. Then I plastic welded the Nipple to the black box where I drilled the hole. Then I attached the vacum line to the nipple. I wish I had pictures because its a little difficult to accuratly explain.

Results: Its awesome, I would have to estimate a 10HP gain with the upgraded exhaust and all the problems fixed. The engine runs extremly smooth, more gas efficient, much quieter, and has increased power band. The engine no longer stumbles off the line and just gets up and goes.

Thanks for all the help.
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