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1998 Impreza L wagon, EJ25D swap
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Discussion Starter · #1 ·
Hi everyone, so I’m running into an issue where exactly between 3,000 and 4,000 rpm I lose what feels to be about 30-40 horsepower on WOT. It’s very odd because right when i hit 4,000 it kicks back to being full power. Initially I thought it could be the knock sensor being triggered and then it adding timing advance to cut power and protect the engine. I run 93 so it shouldn’t be knocking and I checked the timing advance and it stays at 15 degrees at WOT throughout the rev range. My next thought was maybe a burnt valve but this doesn’t make sense to me as if it were a burnt valve it would be messed us throughout the entire rev range. I wanted to know if anyone has ran into this problem before and or knows what could be the cause. To me, I think it may be an issue with the coil pack, plugs, and wires so i’m gonna start there and I’m gonna see where that gets me. Hopefully it’s nothing like a burnt valve or serious knock detection. Please let me know if you have ever ran into this issue. I’ve got an ej257 shortblock with phase 1 25D heads and standard bolt ons. Thanks so much guys!
 

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Hi everyone, so I’m running into an issue where exactly between 3,000 and 4,000 rpm I lose what feels to be about 30-40 horsepower on WOT. It’s very odd because right when i hit 4,000 it kicks back to being full power. Initially I thought it could be the knock sensor being triggered and then it adding timing advance to cut power and protect the engine. I run 93 so it shouldn’t be knocking and I checked the timing advance and it stays at 15 degrees at WOT throughout the rev range. My next thought was maybe a burnt valve but this doesn’t make sense to me as if it were a burnt valve it would be messed us throughout the entire rev range. I wanted to know if anyone has ran into this problem before and or knows what could be the cause. To me, I think it may be an issue with the coil pack, plugs, and wires so i’m gonna start there and I’m gonna see where that gets me. Hopefully it’s nothing like a burnt valve or serious knock detection. Please let me know if you have ever ran into this issue. I’ve got an ej257 shortblock with phase 1 25D heads and standard bolt ons. Thanks so much guys!
I ran into losing power when i bad coil out in my rex/02, I think you have the good idea of starting with the coils and plugs first , any boost leaks ?


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1998 Impreza L wagon, EJ25D swap
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Discussion Starter · #3 ·
I ran into losing power when i bad coil out in my rex/02, I think you have the good idea of starting with the coils and plugs first , any boost leaks ?


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Hey thanks so much, currently running it NA so boost leaks aren’t of a concern to me, my other thought I had was I’ve been fighting an exhaust leak between the head and my header since and that could possibly be causing the loss of power. Something with the fuel trims getting out of wack because of it?
 

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Possibility that the cat is starting to go and causing some back pressure resulting in acceleration problem?
 

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2000 RS Coupe
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Don't these cars typically have issues with sub par factory ground wires? I think that's why there are a bunch of options as far as replacing facttgrounds with aftermarket kits. Just a thought...
 

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The explanations above don't account for the problem you are experiencing.
Burnt valves cause severe misfires and don't come and go.
Back pressure would continue to increase at higher rpm.
I find it hard to buy into a ground issue only causing problems in a specific RPM range

im going to think out loud for a second.



I had a subaru come through our shop with a similar problem. took me a few hours to figure out that someone had left a crank pully bolt loose, and it had broken the keyway and shifted the crank a few degrees, throwing off the timing of the engine, however on that car it happend between 2000 rpm and 3000 rpm and that did it at all load points (ie not WOT).

I assume you have the 97-99 EJ25D heads? the 96 had hydraulic lifters that could hypothetically cause this because they operate by oil pressure and at lower revs you have less oil pressure. I would be skeptical of this being the solution.

What if it was a bad fuel pressure regulator?
I experienced almost the same issue on my legacy. I had a 2.2, and swapped it to a 25D and put a turbo on it. it ran like a beast at 90% throttle, but at WOT the stock 22 injectors couldn't keep up with the 2.5 with a turbo on it at peak torque (roughly 3-4k rpm) so the computer would pull timing like a son of a gun. This happened especially in cold weather due to the cold air being more dense (meaning more air)
My buddy had a impreza with EJ18 that he traded out for a 2.5 and had the same problem.
EDIT: in both cases, a rising rate fuel pressure regulator was a temporary solution, but the principle would be the same on yours
so my question would be
a) when did this start happening?
b) what injectors/ecu etc are you running
c) does it happen at other load points?
d) does it happen more, less or the same when the engine is cold?
 

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1998 Impreza L wagon, EJ25D swap
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Discussion Starter · #7 ·
So just an update I think I found the problem / more problems. So it started now surging on idle and i wasn’t too concerned but then it threw a P0130, Now it will not idle, the car just stalls itself out. I’ve been looking at the live data for the two O2 sensors and most of the time they both read 0.000v and the occasionally will show the correct readings. I’ve ordered 2 new 02 sensors and i am hoping this will solve the problem(s) but I’m worried that it may be a wiring issue as the sensors seem to be working intermittently.
 

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Yeah that could hypothetically be the problem. The question I would have is does it do it when the engine is cold? because when its cold the engine should be in open loop and should be disregarding the O2 feedback. does your scanner have a live data mode where you can see if o2 feedback is in open loop or closed loop?
 

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Discussion Starter · #9 ·
Yeah that could hypothetically be the problem. The question I would have is does it do it when the engine is cold? because when its cold the engine should be in open loop and should be disregarding the O2 feedback. does your scanner have a live data mode where you can see if o2 feedback is in open loop or closed loop?
It doesn’t happen when cold and I can also confirm that it’s open loop when cold as it should be. When the car is warmed up and I try to start it this is when I have all of the issues (when it’s in closed loop.)
 

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Discussion Starter · #10 ·
The explanations above don't account for the problem you are experiencing.
Burnt valves cause severe misfires and don't come and go.
Back pressure would continue to increase at higher rpm.
I find it hard to buy into a ground issue only causing problems in a specific RPM range

im going to think out loud for a second.



I had a subaru come through our shop with a similar problem. took me a few hours to figure out that someone had left a crank pully bolt loose, and it had broken the keyway and shifted the crank a few degrees, throwing off the timing of the engine, however on that car it happend between 2000 rpm and 3000 rpm and that did it at all load points (ie not WOT).

I assume you have the 97-99 EJ25D heads? the 96 had hydraulic lifters that could hypothetically cause this because they operate by oil pressure and at lower revs you have less oil pressure. I would be skeptical of this being the solution.

What if it was a bad fuel pressure regulator?
I experienced almost the same issue on my legacy. I had a 2.2, and swapped it to a 25D and put a turbo on it. it ran like a beast at 90% throttle, but at WOT the stock 22 injectors couldn't keep up with the 2.5 with a turbo on it at peak torque (roughly 3-4k rpm) so the computer would pull timing like a son of a gun. This happened especially in cold weather due to the cold air being more dense (meaning more air)
My buddy had a impreza with EJ18 that he traded out for a 2.5 and had the same problem.
EDIT: in both cases, a rising rate fuel pressure regulator was a temporary solution, but the principle would be the same on yours
so my question would be
a) when did this start happening?
b) what injectors/ecu etc are you running
c) does it happen at other load points?
d) does it happen more, less or the same when the engine is cold?
a) 3 days ago
b) I have 98 2.5rs injectors, the red ones and a 98 2.5rs ECU (22611 AD810)
c) Its only wide open exactly between 3,000 and 4,000
d) I don't know if it happens when cold because I don't floor it wide open
 

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replace the upstream O2 sensor and report back.

I had a subaru come through our shop with a similar problem. took me a few hours to figure out that someone had left a crank pully bolt loose, and it had broken the keyway and shifted the crank a few degrees, throwing off the timing of the engine,
i need more info on this. I don't see how leaving the crank pulley lose would damage the keyway. the camshaft gears should have been enough to keep the belt and gear straight. I've ran many engines with the crank pulley off off.
 

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Discussion Starter · #13 ·
The new O2 sensors come in the mail tomorrow so I’ll have another update tomorrow evening once I install them. Thanks for all the help so far.
 

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replace the upstream O2 sensor and report back.



i need more info on this. I don't see how leaving the crank pulley lose would damage the keyway. the camshaft gears should have been enough to keep the belt and gear straight. I've ran many engines with the crank pulley off off.
Yeah, but for how long? driving it for long periods with it loose will damage it. I don't have pictures anymore but a quick google search pulled up a similar picture. This one is less severe than the one i encountered but in illustrates what I am talking about.
Wheel Tire Automotive tire Motor vehicle Locking hubs
 

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Discussion Starter · #15 ·
I’ll double check to make sure the crank pulley is tight, it’s only been acting like this for ~500 miles.
 

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I’ll double check to make sure the crank pulley is tight, it’s only been acting like this for ~500 miles.
I doubt this is the problem because you said it only happens at WOT. Since a loose crank bolt would effect the timing of the engine, it would do it at any load point, meaning even at light throttle.
 

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Discussion Starter · #17 ·
I doubt this is the problem because you said it only happens at WOT. Since a loose crank bolt would effect the timing of the engine, it would do it at any load point, meaning even at light throttle.
that’s what i thought, especially after my O2 sensors going bad i assume they’re the culprit of the issues at WOT. The ecu sees less than desirable AFR’s and pulls timing to protect itself.
 

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Discussion Starter · #18 ·
Okay so update for everyone, I replaced the upstream O2 sensor to hopefully fix the P0130 code. Since doing this i’ve driven maybe 10 miles to get the car to operating temp and the code has not gone away, car it still running in open loop. I cleared the code, turned off the car and drove it to see if it would run in closed loop. Still running in open loop. After looking at the live data, the brand new upstream O2 sensor (bank 1 sensor 1) reads at idle 0.075 volts. When any throttle is applied the voltage drops to zero. Maybe the connector on the harness is dirty? I may also try swapping back to a ‘98 2.2 ecu as I ran that for a while before i got this RS ecu. The car used to run fine on that ecu so maybe it’s a problem there? For now those are my plans, if anyone has any experience with this any help is appreciated, thanks so much!
 

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interesting! didn't see that coming!
on a somewhat ironic note, I think I have ignition problems now. I took my car to the local race track for the open track day, and about 10 laps in, my car started acting up. Its down on power and at WOT I am getting a misfire and/or detonation. AFR is 10.8 ish, seems to run good at lighter throttle. Drove great coming home. I am thinking it is the plugs causing detonation, and the ECU pulling timing. I am going to put colder spark plugs in it and new spark plug wires (ver. 4 STi)
 
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