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Sudden and intermittent loss of power


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20 replies to this topic

#1 TahoeOutback

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Posted 31 March 2011 - 01:04 PM

Hi all, I have been having an issue with my subi legacy outback 2000 2.5 with 150k. It just started recently and seems to do it when the car is hot or cold. All of a sudden i will lose power. Pull over and let the car idle. The idle loops and once or twice it has died. Sometimes flooring the accelerator will regain some power and rev but sometimes it give no power, and once even made a popping noise like it was super lean. But shut the car down and let it rest for a while and the problem goes away. 20 miles is the most it is problem free before it comes back. It has been doing this for abotu 150 miles now. I have made sure there is enough gas, and most likey not bad gas as I filled it form different stations.

I have also recently had a PO130 (front O2 circuit Malfunction) but I think that this is unrealted as no codes are currently stored in the ECU. Also when the car is having its issue I unplug the O2 sensor results in no real change in the idle.

The first thing I did was make sure that the air intake is free of obstruction. Then looked at the passenger side spark plugs (good). Seems like all four cyclinders are firing. No noticeable plugs or vac lines unhooked. Fuel injectors are ticking away happily, though I have not ohmed them out.

Thinking it is fuel deleivery related I plumbing in a fuel pressure gauge jsut down stream of the filter. Reads 38 psi. When I pull the vac to the fuel pressure regulator it jumps up to mid/high 40's. Finally this morning the car had an episode while driving to work. Pull over look at the fuel pressure gauge, and it is 42 psi, pull the vac to the FPR and it jumps to close to 50 psi. Seems like my fuel pump is working fine and my FPR is doing it's job. The fuel pressure is a little high, but it could be the cheap gauge being off.

I was really hoping that it was the fuel pump. As now I am at a lose for what might be the issue. please help subi gurus.

#2 unibrook

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Posted 31 March 2011 - 01:17 PM

Unplugging the front 02 sensor would not affect the engine idle....I don't think. A bad front 02 sensor will show up most when the engine is under load. If it hasn't been replaced in the last 40k miles, I would replace it.

#3 TahoeOutback

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Posted 31 March 2011 - 01:31 PM

The O2 sensor has not been replaced in a while. When it "happens" the car could be idleing. Would bad O2s cuase such an issue??

#4 naru

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Posted 31 March 2011 - 02:35 PM

Still sounds like it might be a fuel delivery issue.
Change the filter before anything else.Note how hard it is to blow thru the old one.
Just because pressure is adequete at idle,doesn`t mean it is OK under load.
You want to see the pressure at the same time the engine stumbles.
Plumb the gauge VERY SECURELY,duct tape it to the OUTSIDE of the windshield and go for a drive.

Normally,I would expect to see misfire/leaness trouble codes to be associated,but, you can never be sure about that.

Edited by naru, 31 March 2011 - 02:39 PM.
filter


#5 Rooster2

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Posted 31 March 2011 - 03:04 PM

Agree with others, that it sounds like a fuel problem. Any chance you bought gas after a heavy rain? Sometimes, rain water will leak into the underground storage tanks at a gas station. If so, a small amount of water added with your last fuel fill up is causing the problem. Suggest adding a can of "dry gas." It just might fix the problem.

#6 TahoeOutback

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Posted 31 March 2011 - 03:47 PM

I was driving around with the gauge on the windsheild yesterday but it never stumbled. The thing is that when it stumbles it continues to do it when the car is stopped and ideling. At this point the fuel pressure is good.

Is it worth it to change out the O2 sensor? Experiance tells me that when an O2 sensor stops working it mixes the fuel/air poorly (ususaly very rich), but does not cuase severe stumbling issues like I am experiance.

I will try to get some "gas dry" after work.

#7 naru

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Posted 31 March 2011 - 04:25 PM


Thinking it is fuel deleivery related I plumbing in a fuel pressure gauge jsut down stream of the filter. Reads 38 psi. When I pull the vac to the fuel pressure regulator it jumps up to mid/high 40's. Finally this morning the car had an episode while driving to work. Pull over look at the fuel pressure gauge, and it is 42 psi, pull the vac to the FPR and it jumps to close to 50 psi. Seems like my fuel pump is working fine and my FPR is doing it's job. The fuel pressure is a little high, but it could be the cheap gauge being off.

I was really hoping that it was the fuel pump. As now I am at a lose for what might be the issue. please help subi gurus.


I didn`t realize you drove w/the gauge already,my bad.

Pressure should be 36 psi above manifold,so 50 psi w/the vac. line pulled is way too much.
Should be 26-30 psi w/engine running,line hooked up.

Must be the problem.

Edited by naru, 31 March 2011 - 04:39 PM.


#8 TahoeOutback

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Posted 31 March 2011 - 05:06 PM

I am going to drive with it again since I did not get the engien to stumble the first time I did it.

What would cause the line pressure to be higher than spec. I was not able to get a confirmed value. From the fuel test kit manual. The spec is 32-34psi.

guess you are suggesting bad FPR.

#9 naru

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Posted 31 March 2011 - 05:14 PM

Or a restricted return line.Probably the reg.

Double check me on the specs.I pulled those from the factory ej-25 manual for 1997.Seems to be the same for most subes of the era.

#10 TahoeOutback

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Posted 31 March 2011 - 05:33 PM

From all of my readings my fuel pressure is high 38 psi at idle. SHould be 34. But would 4 extra psi's of fuel cuase my issue. And such an intermitent issue?

Wish these things were cheaper. It is a $90 part.

Bill

#11 naru

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Posted 31 March 2011 - 05:39 PM

If my specs are correct,pressure should be 26-30 at idle.

Does your spec book show any difference between 1997 and 2000?

#12 Manarius

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Posted 01 April 2011 - 09:14 AM

Is your car equipped with a MAP or a MAF (Mass Airflow Sensor)? If it's equipped with a MAF, then what you describe sounds exactly like MAF failure.

Swapping for one from a known good car is really the best way to test for this.

#13 naru

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Posted 01 April 2011 - 11:00 AM

According to rockauto 1997 and 2000 use different pressure regs.
1997 operates at 36psi.
2000 operates at 44psi.
That makes your pressure highish at times the car is stumbly.

Edited by naru, 01 April 2011 - 11:08 AM.


#14 TahoeOutback

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Posted 01 April 2011 - 11:48 AM

People sure ask you alot of questions when you have a fuel pressure gauge running out of your upper cowl and then taped to the windsheild. I used packaging tape instead of duct tape, much more classy.

I also notcied that there is a calibration cert sticker on the back so I assume that the readings are spot on. The fuel pressure reads a steady 38psi. Goes up a little when you stomp on it and down a little when you let off. But it is as steady as a rock other wise. I am ruling out fuel pump. FPR is still bebatable as some sources say that is too high. Though a little low according to Naru and his recent Rockauto finding. Thanks for searching for me. The 2000 is kind of a odd duck. I have found many specs to be different from the years before and the years after.

I believe that the car has a MAP, but am not sure where it is located. Is that the Bosch sensor that sits on the throttle body. My older Outback had a MAF which was inline on the intake.

I have a new theroy as my PO130 came back. And guess what, with the CEL on the car runs great (so far, about 35 miles, which is far enough to have a stumbling episode). PO130 is most often correlated with "wet" conditions and plugs getting wet and shorting out. Sure it has been wet around here lately. But it has been in this enviroment for the last 6 winters. Why all of a sudden is it throwing this code (3 times now). That is unless the O2 sensor is truely toast, which from my understanding is the true meaning behind the code (way out of range for a steady duration). With the the CEL on the ECU goes into some safety fuel map and does not make adjustments based on the O2 reading, but since I cleared it the ECU is taking the bad O2 reading and trying to mix the fuel accordingly. This is what is given me my stumble. Could this be it??

My plan moving forward. Drive home with the CEL on to see if the car stumbles. If it makes it home ok then my theroy still holds true. Clear the fault code, and drive it around. If it stumlbes, my theroy still holds true. Change out the O2 sensor, which i was plannning on doing (I jsut want to make sure it is the source of my anguish). Hope that it solves my issue for good.

Thanks for hearing me out guys. Feed back welcome. I do not mind if you tell me that I am full of it, or point out flaws in my reasoning.

#15 wesmay

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Posted 01 April 2011 - 06:37 PM

random shot, I had a similar problem with a jeep, try cleaning the contacts on your map sensor. For whatever reason it messes with the fuel delivery. Good luck

#16 TahoeOutback

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Posted 03 April 2011 - 12:44 PM

So i am off doing the O2 sensor replacment. Just wanted to know if there is a write up on how to perform this replacement. It seems straight forward enough. But I can not seem to get to it easily. I can't fit my O2 sensor socket over the sensor and still have room for the ratchet. I can't seem to get a open end wrench in there either. I guess if i had a crows foot sensor wrench that will work but I do not.

I am about to drop the skid, and then partially drop the exhaust. Is there a trick that I don't know about??

#17 TahoeOutback

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Posted 04 April 2011 - 11:50 AM

All fixed, and the car runs better than ever. New O2 sensor did the trick.

Had to drop the exhaust in order to change it out. Pulled the header nuts off (6). Then the single hanger just in front of the cat. Replaced the Sensor with a bosch direct replacemnt unit.
The hardest part was figureing out how that plug clip goes back on.

#18 unibrook

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Posted 04 April 2011 - 02:55 PM

Glad to hear that worked. Thanks for posting back here with your fix. That should help the next person.

#19 TahoeOutback

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Posted 04 April 2011 - 03:59 PM

In two forums and a handful of respondes, I only got one correct one.

Unibrooke-wins the prize on what the problem was. (sorry you don't acutally get aynthing, but I'll buy you a beer if I ever meet you)

I should not have ruled out the O2 sensor, esspeically since i got a code saying it was messed up. Funny thing is that in all of the search results for a PO130 they all suggested that the plug was wet and the sensor was shorting out temporarily. No one pointed out that a PO130 could mean dead O2 sensor.

One of you should have said to me "look *********************, your ECU told you you had a bad O2 sensor, stop wasting our time until you put in a new one."

But I am glad that I was able to rule out fuel pump and FPR with a gauge. I guess 38 psi is ok to run.

Thank you all for your time! I hope that this thread helps someone else in the future!

#20 unibrook

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Posted 05 April 2011 - 02:33 PM

I chased a misfire for about a year before I finally replaced my front 02 sensor....it was the cure.

#21 TahoeOutback

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Posted 07 April 2011 - 03:19 PM

Did a full write up on my blog.

http://mrpulldown.bl...nsor-po130.html




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