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Legacy 2.5 GT lacking power...suggestions??


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22 replies to this topic

#1 hi8u3ri

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Posted 21 February 2011 - 08:33 PM

Hey folks,
I was hoping to get some ideas on a tricky problem I'm having on my '98 Subaru Legacy GT Limited (AT, 2.5L). Maybe someone has had something similar happen?

I bought this car back in August after it had not been driven for about a year, and before that, driven by a girl who did no maintenance on the car whatsoever. It has 160k miles.

Here’s my problem:
  • Lacks power going up hills and when accelerating
  • Occasionally car has bursts up to normal power when in “crippled” mode

Let me explain in detail… Going up larger hills (I live in the mountains) sometimes takes the petal to the floor to get up. Sometimes when going up these hills in “crippled” mode I will get a second or so “burst of power” during which the RPMs will raise slightly. This will repeat maybe once or several times in a row rapidly. The problem is much more noticeable when it’s cold outside (considerably worse when it’s 30 F or below), but also when the car itself is cold. It seems to have okay power in lower gears (1st / 2nd) when climbing hills, but if ever I am in anything higher, it’s like I’m towing a boat behind me. During this time the gas petal seems largely unresponsive throughout ¾ of its range (ie…pressing it ¼ or ¾ of the way down does not seem to change anything where normally it would cause a downshift). That’s basically it.

Here’s what I’ve done:
  • Cleaned throttle body
  • New fuel filter
  • Clean air filter
  • Throttle body position sensor (was bad…new one adjusted by Subaru)
  • Also throttle stopper screw adjusted by Subaru
  • Cleaned Mass Air Flow sensor
  • New spark plugs (using NGK BKR5EGP 7090)…these are same specs as the recommended plugs but are the “platinum” version instead of the “double platinum” version
  • New timing belt (old one was installed backwards…doh!)
  • Can of seafoam in gas…several times.
  • New oil change
  • New shifter cable and neutral safety switch (had bad old one)

Can anyone verify if the spark plugs are definitely causing this? Recommended part number is: NGK PFR5B-11 if you want to check the specs and compare.

Another possibly related issue is that the engine has a tick noise on one of the cylinders/valves. A lot of Subarus have this I think but usually it goes away after it warms up (but not with mine).

I am up for any suggestions and thoughts! Let me know if I can clarify anything… Thanks guys!

-Jon

#2 Olnick

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Posted 21 February 2011 - 08:54 PM

Welcome Jon. Can't say whether or not the plugs are the cause of your problem--all I ever use is the most basic NGK copper plug and they are perfectly fine.

Did you change the plug wires? If not I'd recommend you do that, use OEM wires.

Good luck.

#3 hi8u3ri

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Posted 21 February 2011 - 10:10 PM

Thanks! No I did not replace the wires, although I thought about it. Does that count? :) But I did look them over pretty good, and they didn't seem to have any cracks, wear, burnt spots, etc. I think it's possible it might be them but also wonder what else could cause this problem? Thanks for the reply!

#4 Rooster2

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Posted 21 February 2011 - 10:33 PM

Any CEL............Check Engine Light seen?

Does CEL come on when first turning the ignition key to "run" position, before turning further to crank position?

#5 hi8u3ri

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Posted 21 February 2011 - 11:34 PM

No check engine lights after I fixed the previous problems.

I had before a throttle position sensor (new sensor fixed that problem) and a neutral safety switch (problem was a shorted out security system...took forever to find that one!) That was about three months ago now and no lights since then. And it does come on before starting the car when it's on "run"...so light is working :)

#6 Fairtax4me

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Posted 22 February 2011 - 12:11 AM

This type of behavior matches what some have described from a bad knock sensor. These rely heavily on knock sensor input to adjust ignition timing, I suspect the internals of the EJ engine must be sensitive to detonation and therefore Subaru felt it necessary to control knock at all costs. The knock sensors on these are very sensitive, yet also very fragile and susceptible to damage and corrosion. It's hidden well, but is easy to replace once identified.

Vacuum leaks can also cause strange issues like this. Follow the vacuum routing diagram on the bottom of the hood and replace any hoses that are hardened, dry-rotted, or cracked.

#7 bru73

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Posted 22 February 2011 - 12:44 AM

mine dose the same thing mine is due to tne trans not downshifting and wanting to stay in converter lockup

#8 bheinen74

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Posted 22 February 2011 - 01:43 AM

For Subaru's knock sensor standard wear item to replace after 100k
same goes for CTS

#9 davebugs

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Posted 22 February 2011 - 08:33 AM

In light reading of the thread I'd guess knock sensor also.

Consider it a wear item over 100k. Personally I get OEM but I do believe others have has luck with generics.


IIR like 100 bucks.

I've seen many bad without CEL.

#10 hi8u3ri

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Posted 22 February 2011 - 08:46 AM

Thanks, those are three good places to check then... plug wires, vacuum leak, and knock sensor. I wonder how the cold is affecting things...

#11 davebugs

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Posted 22 February 2011 - 08:50 AM

When you get it figured out please post your solution.

If I get a car with any performance issues and NOT OEM plug wires I replace them first. And throw in new NGK BKR6E-11 (or whatever the 2 dollar green writing plugs are).

If sluggish when driving and no reason to suspect bad fuel, filter, pump, etc it's almost always been the knock sensor for me.

#12 Rooster2

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Posted 22 February 2011 - 11:13 AM

Yea, I had the knock sensor go bad on my '98 OBW. Running in limp around mode, or whatever it is called, produced a lack of power, as well as CEL coming on. Writer makes no mention of a CEL. I wonder if his CEL is disconnected?

#13 hi8u3ri

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Posted 22 February 2011 - 05:22 PM

Nope, as I mentioned before my CEL is not on, and it is working. Lots of folks are thinking knock sensor but I'd hate to spend the $90 on it and have it not be a problem. Still haven't decided what to do yet...but leaning toward replacing the knock sensor first and/or the plug wires (not sure in which order).

I think Subaru dealership will "diagnose only" for $35. I wonder if I went if they could tell me specifically what was wrong and save me from buying parts I don't need (yet)? Or perhaps they will take my $35 and guess without doing any testing. Anyone have experience doing this?

#14 Olnick

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Posted 22 February 2011 - 05:31 PM

Still haven't decided what to do yet...but leaning toward replacing the knock sensor first and/or the plug wires (not sure in which order).


Flip a coin? :rolleyes:

Considering the mileage and the presumed lack of previous maintenance, they're probably both overdue.

Check ebay for the knock sensor. I found a decent one for about $45 not long ago.

#15 Rooster2

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Posted 23 February 2011 - 11:56 AM

Nope, as I mentioned before my CEL is not on, and it is working. Lots of folks are thinking knock sensor but I'd hate to spend the $90 on it and have it not be a problem. Still haven't decided what to do yet...but leaning toward replacing the knock sensor first and/or the plug wires (not sure in which order).

I think Subaru dealership will "diagnose only" for $35. I wonder if I went if they could tell me specifically what was wrong and save me from buying parts I don't need (yet)? Or perhaps they will take my $35 and guess without doing any testing. Anyone have experience doing this?


I am thinking that a Subaru dealership diagnose for $35, is simply a code read out, and that is it. Spending only $35 at a dealership never buys you much. Since the CEL is not on, it won't tell much. Maybe they can find some old codes that have not been erased for advise. If they don't learn anything, then they will simply want to throw parts at the problem in hopes of getting lucky. Then it is about $90 for a knock sensor, and prolly $90 (hourly rate) to install the knock sensor. I hope they don't advise this approach!

Does the CEL light up along with all other warning lights, when key is first turned, prior to turning key further to activate the starter? I am wondering if the previous owner deactivated the CEL from ever coming on??

#16 hi8u3ri

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Posted 23 February 2011 - 11:32 PM

No the CEL DEFINITELY works...trust me. It come on when I turn the key half way. I had a heck of a time tracking a neutral safety switch error code to an old shorted out 3rd party security system I was barely even aware of. Turns out it was also causing my car to periodically not start. Then the CEL was on for the first four months I had the car. :-\

#17 Fairtax4me

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Posted 23 February 2011 - 11:59 PM

You can use an after market sensor from somewhere like Rockauto.com. They have one for around $55 + shipping.
Or if there's a junkyard nearby you can snag one or three used ones to try.

#18 hi8u3ri

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Posted 24 February 2011 - 12:05 AM

I wonder when I see two knock sensors on ebay such as here:
Thoughts?

#19 Olnick

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Posted 24 February 2011 - 12:14 PM

Ahhhh . . . the ebay conundrum!

Of the two choices, I would probably go for the "expensive" one since it lists a Bosch part number.

I know ebay can be a crap shoot but I've generally been lucky. So far! :eek:

#20 Olnick

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Posted 24 February 2011 - 12:30 PM

Ooops! Just remembered, I bought my last knock sensor on amazon.com, not ebay.

They list one at $67.50 for your car. Decisions, decisions! :-\

#21 740gle

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Posted 28 February 2011 - 03:55 PM

How is CAT converter? I had these symptoms for a while on my 02' GT, before it started throwing codes.


HTH

-Michael

#22 hi8u3ri

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Posted 29 March 2011 - 09:03 PM

UPDATE :: My ignition timing was reading -12 all the time, according to Subaru dealership's computer. I replaced the knock sensor with one from eBay and it now shows the correct timing.

Unfortunately, the problem persists and is no better. I had the computer cleared three times by Subaru and I ran the tar out of the car in hopes of clearing up anything stuck or clogged, but to no avail.

I remember having error code P0420 when I first got the car (August), and I had it also about a month ago when pulling a big, long hill. Since then I've ran through some cleaner in the gas had the code cleared, and have not heard of it since.

I'm not sure how the CAT is, but the dealership said they could count the number of bad converters on one hand.

So my thoughts are, replace Oxygen sensors now? Any other thoughts?

#23 1-3-2-4

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Posted 30 March 2011 - 03:00 PM

This type of behavior matches what some have described from a bad knock sensor. These rely heavily on knock sensor input to adjust ignition timing, I suspect the internals of the EJ engine must be sensitive to detonation and therefore Subaru felt it necessary to control knock at all costs. The knock sensors on these are very sensitive, yet also very fragile and susceptible to damage and corrosion. It's hidden well, but is easy to replace once identified.

Vacuum leaks can also cause strange issues like this. Follow the vacuum routing diagram on the bottom of the hood and replace any hoses that are hardened, dry-rotted, or cracked.



Does the knock sensor really only come into play at higher rpms? I thought I saw someplace on one subaru related site saying just tapping on the block with a screwdriver was enough to set it off?

Never worked for me.




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