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Old 10-11-2010, 05:43 PM   #1
Ools
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Default flat spot in powerband

so i have a 99 rs with an 05 rs longblock.

it still has the 99 rs manifold, egr has an oil pan bolt on it.

my problem is a spot on the rev range from 3600 to 4250 where there is a loss of torque that is huge, it pulls till 3600, where it bogs and then it takes off again at 4250.


what could be causing this?
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Old 10-11-2010, 06:11 PM   #2
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sure that the longblock isn't an 06 with the AVLS? failing O2 sensor causing CL/OL switching delay? Any CEL history?
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Old 10-11-2010, 08:44 PM   #3
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it came with the aluminum manifold, and is from an auto. i don't know for sure if it has the alvs heads, but since i was told it was an 05 i would assume not.

but then again i was told it was from a manual and i got it with a flexplate.

the most recent CEL i had was a knock sensor, and it happened when standing water from the last rain got in there.

i just replaced both O2 sensors with nippon densos approximately 10k ago, and ever since my exhaust tip hasn't had soot on it, so i'm guessing that they are still working.

it is possible that something is causing the CL-OL delay.
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Old 10-11-2010, 11:28 PM   #4
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The combustion chambers and pistons are slightly differently shaped. The intake manifold is VERY different (if you're using that off the 05 as well). In all likelyhood, your stock tune is simply really ****ing bad for the block it was never designed for.
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Old 10-11-2010, 11:33 PM   #5
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Quote:
Originally Posted by williaty View Post
The combustion chambers and pistons are slightly differently shaped. The intake manifold is VERY different (if you're using that off the 05 as well). In all likelyhood, your stock tune is simply really ****ing bad for the block it was never designed for.
i kept the stock manifold.

i wonder if i can get it tuned and still pass smog.
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Old 10-12-2010, 03:43 PM   #6
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still occurring, anyone have any thoughts?
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Old 10-12-2010, 03:53 PM   #7
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A tune will fix the issue.
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Old 10-12-2010, 04:36 PM   #8
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Quote:
Originally Posted by Ools View Post
so i have a 99 rs with an 05 rs longblock.

it still has the 99 rs manifold, egr has an oil pan bolt on it.

my problem is a spot on the rev range from 3600 to 4250 where there is a loss of torque that is huge, it pulls till 3600, where it bogs and then it takes off again at 4250.


what could be causing this?
it's the cam profile. i have the same thing, although my hole is from about 3300-4100.
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Old 10-12-2010, 07:59 PM   #9
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I had the problem with my MAF. Clean yours.
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Old 10-13-2010, 12:39 AM   #10
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thanks for all the suggestions guys.

i'll first clean my maf again, and if that doesn't fix it, i'll try other alternatives.

interestingly though, when it isn't completely warmed up the problem does not persist, but i think it may be because i'm not as hard on it when it's still a little cold.
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Old 10-15-2010, 02:13 AM   #11
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A bad Knock sensor will cause this, or you could have knock.
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Old 10-16-2010, 06:01 PM   #12
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Quote:
Originally Posted by bhilly82 View Post
A bad Knock sensor will cause this, or you could have knock.
during the last rain, a little water got under the knock sensor causing a CEL.

but i reset it and it hasn't come back.

this power band flat spot isn't as bad as it was when the light came on, but it is close.

could the knock sensor be bad without throwing a CEL?
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Old 10-16-2010, 09:46 PM   #13
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I had a knock sensor that was bad and it intermittenly threw a CEL. Either that or the test for the knock sensor takes awhile. It cleared it once itself. Another couple of times I reset the ECU and it took a week or two to come back on. (The car was driven everyday to, so I doubt the knock sensor tests would take that long to finish).
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Old 10-19-2010, 05:09 PM   #14
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Quote:
Originally Posted by Ools View Post
during the last rain, a little water got under the knock sensor causing a CEL.

but i reset it and it hasn't come back.

this power band flat spot isn't as bad as it was when the light came on, but it is close.

could the knock sensor be bad without throwing a CEL?

yes it could. what can happen is it picks up knock or what it thinks is knock and pulls timming, or you could have a real knock problem.
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Old 10-20-2010, 05:34 PM   #15
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next tank i will run premium grade and see if that makes a differance.
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Old 10-20-2010, 08:58 PM   #16
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it won't.
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Old 10-21-2010, 02:38 AM   #17
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Quote:
Originally Posted by vicious_fishes View Post
it won't.
It will if he has actual knock but if you don't then it could be the sensor.
Also do you have any piston slap or valve train noise? If so the sensor could be picking up that as a knock.
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Old 10-22-2010, 03:22 PM   #18
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When my knock sensor went it pretty much gut-punched the car. Could re-set it, but it would always set the code again after a day or two---you'd feel the car lose power the the exact moment the light came on. Given how much better the car felt with the new sensor, it must have been going for a while before it was bad enough to set the code.
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Old 10-26-2010, 03:17 PM   #19
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Quote:
Originally Posted by bhilly82 View Post
It will if he has actual knock but if you don't then it could be the sensor.
Also do you have any piston slap or valve train noise? If so the sensor could be picking up that as a knock.
it is a subaru, so valve train noise is a given, but no piston slap.

the problem seems to have resolved itself, but if it returns, i will revive this thread.
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Old 11-24-2010, 12:57 AM   #20
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problem came back, so i put premium fuel in and it went away........


anyone got any ideas?
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Old 11-24-2010, 12:58 AM   #21
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If octane affects it, it's knock.
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Old 11-24-2010, 01:00 AM   #22
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thanks for the quick response.

i thought as much, but maybe the knock sensor is bad?
it seems unlikely....

maybe there is carbon buildup raising the compression...
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Old 11-24-2010, 01:02 AM   #23
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A bad knock sensor won't respond to changes in fuel. Octane making it better means it's real knock.
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Old 11-24-2010, 01:49 AM   #24
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what could be the cause other than the intake, engine, ecu combination?

carbon buildup on heads? bad PCV? any ideas?
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Old 11-24-2010, 01:50 AM   #25
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Oil recirc
carbon buildup
changing AFR
changing compression
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