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Old 12-12-2013, 11:28 PM   #1
kred
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Default Car is ridiculously slow. Help!

My car has been seriously down on power lately. I know it's a 2.5i, but I can clearly tell something's wrong, it's painfully slower than normal. When I take it to redline, that makes no power. It goes fastest shifting at 2500 rpms . I did some logging with romraider and peak airflow was 68g/s (should be 110-130). Also, my calculated engine load starts around 1 g/rev and steadily falls to .7. I would post the logs, but I don't know how.

Mods: AVO intake panel, LWCP, OBX header w/ magnaflow catback, phenolic intake manifold spacers, open source tune on 91 octane.

What I've checked: No restrictions in intake/ exhaust, MAF sensor is good, spark plugs were done a year back, no knock/ misfires in data log, don't think it's a vac. leak because idle is perfectly normal.

Any ideas? I've been dying to figure this out.
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Old 12-12-2013, 11:56 PM   #2
cal_look_zero
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How are you validating that the MAF is good? You're using a filter with less filtering capabilities than a paper element, so your MAF probably needs a good cleaning. Easy enough to do.

Also, you probably have crud built up at the throttle body. Being DBW, if you ever reset the battery, it will lose it's calibration for the buildup, and give a wonky throttle position.

Finally, check out your o2 sensor, and replace if needed.

All of those things can lead to weird readings and poor performance.
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Old 12-13-2013, 12:08 AM   #3
kred
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I cleaned my MAF sensor and even tried a different one. No difference whatsoever. If there was crud building in my throttle body, wouldn't I be able to see/ feel it with the air box off and sticking my finger in the TB? I didn't notice anything last time I was in there. And I forgot to mention, my log shows that the throttle is actually 100% open at WOT. Also, how would I know if it's an o2 sensor? Wouldn't it throw a CEL?
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Old 12-13-2013, 12:10 AM   #4
cal_look_zero
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Quote:
Originally Posted by kred View Post
I cleaned my MAF sensor and even tried a different one. No difference whatsoever. If there was crud building in my throttle body, wouldn't I be able to see/ feel it with the air box off and sticking my finger in the TB? I didn't notice anything last time I was in there. Also, how would I know if it's an o2 sensor? Wouldn't it throw a CEL?
The buildup isn't the problem, it's that it doesn't allow the throttle plate to close all the way, and can cause throttle position reading issues.

As far as the o2, they can get "lazy" before they fully die and cause weird readings.
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Old 12-13-2013, 12:55 AM   #5
kred
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Quote:
Originally Posted by cal_look_zero View Post
The buildup isn't the problem, it's that it doesn't allow the throttle plate to close all the way, and can cause throttle position reading issues.

As far as the o2, they can get "lazy" before they fully die and cause weird readings.
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Old 12-13-2013, 02:09 PM   #6
GrundleJuice
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How did you determine the exhaust is not restricted. Factory cat? How many miles on the cat?
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Old 12-13-2013, 04:34 PM   #7
Back Road Runner
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You can have a plug not fire, and you might not see it for 2 weeks. Don't rely on CEL codes to tell you things right away. In some cases the car has to be almost non-functional for something to show up.

How much corrosion do you have on the battery right now? I ask because I've experienced the same level of corrosion on the knock sensor and an eventual failure of operation and CEL trip some time later. I suggest this because this is the only time I've experienced a moderate loss of power without an apparent reason.
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Old 12-13-2013, 07:17 PM   #8
Ansobsport02
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^hes probably right
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Old 12-13-2013, 11:29 PM   #9
kred
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Quote:
Originally Posted by Back Road Runner View Post
You can have a plug not fire, and you might not see it for 2 weeks. Don't rely on CEL codes to tell you things right away. In some cases the car has to be almost non-functional for something to show up.

How much corrosion do you have on the battery right now? I ask because I've experienced the same level of corrosion on the knock sensor and an eventual failure of operation and CEL trip some time later. I suggest this because this is the only time I've experienced a moderate loss of power without an apparent reason.
My car's been down on power for 4-5 months, lol. Just haven't gotten the time to fool with it, I'm a busy college student. Battery has no corrosion, battery voltage in my data log was steady around 14 volts.
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Old 12-14-2013, 12:39 AM   #10
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Ah, long standing issue.

You have data logging, so what does it say? AFR fine, sensors don't read goofy, anything you can pinpoint from logging?
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Old 12-14-2013, 04:02 AM   #11
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Quote:
Originally Posted by Back Road Runner View Post
Ah, long standing issue.

You have data logging, so what does it say? AFR fine, sensors don't read goofy, anything you can pinpoint from logging?
His mass air flow is just over half of what it typically should be. If it can reach 5000 rpm with the throttle plate fully open it should be above 100 g/s mass flow. Seems like something is reducing the pumping efficiency.
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Old 12-14-2013, 07:58 AM   #12
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Sounds like a bad cat. Car runs fine, doesn't make power/like to rev.

Should pull the plugs anyway. Do a compression test. Should clean/replace air filter. Sometimes the filter will get gummy and LOOK fine when it's not. How old is the fuel filter ? If you don't know, replace it.

Do the simple stuff first.
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Old 12-14-2013, 10:35 PM   #13
kred
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Air filter was cleaned shortly before I started having problems. I have no idea how old the fuel filter is. I did a little logging today. I noticed on my rear O2 sensor it ranges from 0.06-0.92 V. That wasn't an actual WOT pull, it's getting slick out for that now. At idle, it was like .1 V, then I watched it jump slowly to .92V out of nowhere, then dropped back down. Cruising in it/ revving the engine at WOT in neutral showed no change from .1 V. Any idea if it sounds ok?

Last edited by kred; 12-15-2013 at 12:08 AM.
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Old 12-15-2013, 08:42 PM   #14
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Bump! Any ideas? I've researched that the O2 sensor voltage should fluctuate around .45 V. So a constant .1 V could mean running a bit lean or a bad O2 sensor?
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Old 12-16-2013, 06:12 PM   #15
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Well, I was going to try changing the fuel filter today, but then I learned that it's a "non-serviceable part." Apparently it's part of the fuel pump on my car, in the gas tank. I can't even log fuel pressure on Romraider. Then again, I don't want to buy a new fuel pump unless I'm sure I need it. I'm so lost right now, I'm dying to figure this out.
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Old 12-22-2013, 12:04 AM   #16
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I discovered a tiny vacuum leak today in the throttle body gasket. I don't think this would cause that much of a power drop, would it?
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Old 12-22-2013, 03:06 PM   #17
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You'd be surprised how little things can cause big issues. Fix it.
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Old 12-22-2013, 03:15 PM   #18
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I agree with checking the cats. You can clean them with Boric acid I think. Might be worth a shot.
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Old 12-22-2013, 08:00 PM   #19
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Quote:
Originally Posted by kred View Post
Well, I was going to try changing the fuel filter today, but then I learned that it's a "non-serviceable part." Apparently it's part of the fuel pump on my car, in the gas tank. I can't even log fuel pressure on Romraider. Then again, I don't want to buy a new fuel pump unless I'm sure I need it. I'm so lost right now, I'm dying to figure this out.
It is a serviceable part actually and can/will clog up over time. You can change it fairly easily by pulling the pump assembly out of the tank. The pump does not need to be replaced to change the filter.
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Old 12-26-2013, 12:24 AM   #20
kred
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This is getting discouraging. Today I noticed that going light on throttle (say 30%) is the same as WOT in terms of sound, acceleration, and fuel consumption. Yes, the throttle plate is opening all the way, and no my exhaust is not restricted. Ideas?
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Old 12-26-2013, 08:48 AM   #21
GrundleJuice
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Have you reset the ecu? If so, try flashing the stock rom. It might give you some clues if it doesn't fix the problem. Are any DTCs disabled in the current tune?
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Old 12-26-2013, 12:38 PM   #22
kred
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Quote:
Originally Posted by RaceFaceXC View Post
Have you reset the ecu? If so, try flashing the stock rom. It might give you some clues if it doesn't fix the problem. Are any DTCs disabled in the current tune?
Yes, I've reset the ecu many times and tried the stock rom. Only DTC that is disabled is the one for my two missing O2 sensors.
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Old 12-26-2013, 12:59 PM   #23
GrundleJuice
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Quote:
Originally Posted by kred View Post
Only DTC that is disabled is the one for my two missing O2 sensors.
Huh??
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Old 12-26-2013, 01:43 PM   #24
kred
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Originally, I had 5 O2 sensors: 2 right under the heads, 2 in the cats, and 1 after the cats. I'm only using 3 of those now.
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Old 01-08-2014, 01:05 AM   #25
kred
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Took it to a mechanic today. He checked everything and it turns out my car is in mechanically perfect condition. He said his 04 forester 2.5i automatic would smoke my car. He said it might have something to do with my throttle control unit. It's gotta be something electrical/ ecu related. This is driving me insane.
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