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2000 OB Auto
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Discussion Starter #1
Hi,

I am trying to debug my P0420 problem. The problem should be during rich to lean based on test results.

I notice the AF ratio goes very high when I release gas pedal. In the first picture, you can see the AF ratio goes up to 22. Is this too high or normal? Most people seem to say it goes to 16-18 (my search results, may not be accurate).

If it is indeed too high, what may be the cause?

The LTFT is generally a high negative number when idling and during released pedal. It is normal when driving (less than 3 + or -)

The second problem, not as quite important (because I want to solve P0420), is hesitation when start from full stop. This is shown in the second picture. There is a dip in the AF when the hesitation happens.

Thanks for your inputs in advance!
 

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Master Caster
2005 XT, Mildly Modified...2006 XT Limited, Highly Modifed
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16,120 Posts
Hitting 22 off throttle is normal.

That .... bababababab ... is lean conditons under no load. There is no ( or little fuel) when off throttle.
 

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On the Super Mod Squad
02 Pair: 3.0 VDC Wag & 2.5 Limited Sedan
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26,222 Posts
the p0420 is a nag code, and does not produce anything but a light on the dash.

it maybe caused by something else though.

did you get your previous PCV problem squared away with a new pcv?

how old in years and miles are your o2 sensors? what do you have in there. (as mine get old and wear out in my H4, been replacing them with denso branded ones off rockauto and amazon, rear one makes for the p0420 code by itself, but the front one -makes for the p0420 and many other codes, hesitation, minor misfires, and drive-ability issues.)

do you have a windows laptop? with a $10 VAG cable you could use free -rom raider and take some logs.. (I also use torque pro, but nothing out there works on subarus like rom-raider logging,

freeSSM does not work on cars as old as yours. ...just 1-2 years too old.
 

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2000 OB Auto
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Discussion Starter #4
Thank you @traildogck and @eagleeye!

So 22 is fine. One possibility crossed off.

Yes I did change PCV OEM. I also changed new air filter with Napa wik because it was running rich during idle but it didn't help. Also cleaned up throttle body. But I didn't clean the idle control valve yet. Idle trim is always high in -7 to -10. But driving is fine, mostly 0 and max +-3.

The car is ~160K 2000 auto OB. The O2 sensors are still original though. Should I change them? Still a lot of money and I can't be sure they are bad. Is it a maintenance replacement item at certain mileage?

I didn't play too much with torque's log. I logged them but never looked at them. Maybe it is easier using rom-raider as I see a lot of people here using it. My main concern is at this time I don't have the ability to understand the data. I will look into the $10 VAG cable you are talking about.

One the second problem: It may have to do with my off brand fuel pump.

Thanks!
 

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what fuel pump did you buy?

____

personally I would just keep watching the codes for now, just let the p0420 expire naturally and see if anymore pop up.

for me on my 2002 H4: I replaced the rear sensor 2x for p0420, and the front one 1x for p0130. (each time with densos).
the car has 117,000miles on it now,...so you at 160,000 miles with the same engine / exhaust seems like a lot to me

here was my thread about using rom-raider to diagnosis a front o2 (AF) sensor, things got worse as time went on.

http://www.subaruoutback.org/forums...89-p0130-2002-ej251-climbing-grades-fast.html
 

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Discussion Starter #6
The fuel pump is "Airtex E8596M Fuel Pump Module Assembly" (from amazon).

Thanks for the link to ease my search. I will read it. I am sure I can learn a lot about diagnosing from it.

Too bad you had to replace twice the rear O2 sensor!
 

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The fuel pump is "Airtex E8596M Fuel Pump Module Assembly" (from amazon).

Thanks for the link to ease my search. I will read it. I am sure I can learn a lot about diagnosing from it.

Too bad you had to replace twice the rear O2 sensor!
its not that bad, its a wear part,...lasts years and 50-60,000 miles in my car.

$50-70 bucks for such densos, and maybe a half a hour of shop labor on a lift,
(in my cars they rust into place, so a little heat from a pro torch helps get them out).

__

what are your driving habits like? what are your mpgs?

I can typically get 29mpg summer on 3 season tires, but mine is a sedan and a little lighter and its straight highway.
(I think I may have one of the highest mpg legacy anythings in these 2000-2004 engines).

my old 2000 auto 2.5 wagon I could get 23mpg on regular gas, and 26-27 on super 93.
 

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Discussion Starter #8
I drive normally I guess. Not aggressive I am sure.

My mileage is pretty bad. Pure local is 18 mi/ga. Highway + local combined is around 20mi/ga, 21 tops. Compared with yours, mine is way down. Gas is 87.

It is a strange thing, sometimes the car has a lot of juice, other times it feels heavy.

Wait: I just hit 100 posts mark one post earlier. Congrats me :)
 

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2005 OBXT Limited, VF37, STI intake, 5MT
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The 20+ AFR ratio during deceleration is normal (as the "overabundance" of air in the exhaust due to no combustion).

Your LTFT should not vary rapidly unless you have just reset the ECU. LTFT means "Long term fuel trim", i.e. learned over many drive cycles. This should be as close to zero as possible, but -7 is not terrible.

It is possible to have a (partially) clogged catalytic converter as well given the age and (assuming) unknown service history.

Have the spark plugs been removed and inspected recently? They can also give you a helpful indication on how the engine is running.
 

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I try not to list a new cat as a possibility

until after someone has replaced old front and rear o2 sensors.

as if you were putting in new cat, you would also put new o2 sensors in it if they were not new already.

____

maybe when the o2 sensors are out, a inspection camera can go into the holes and look at the condition of the media.
 

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Discussion Starter #11
Thank you @RoughDiamond and @eagleeye.

The ECU was reset but that was several hundreds miles before. I can't think of anything that would damage the cat other than maybe the head gasket problem which was fixed. It never had misfire but it did overheat once.

I will check the spark plugs and O2 sensor/cat comb condition. Since this thing is not urgent I tend to sit on it. But eventually time will come for smog.

Does my low mpg say anything? I mean eagleeye's numbers put mine in shame.
 

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Thank you @RoughDiamond and @eagleeye.

The ECU was reset but that was several hundreds miles before. I can't think of anything that would damage the cat other than maybe the head gasket problem which was fixed. It never had misfire but it did overheat once.

I will check the spark plugs and O2 sensor/cat comb condition. Since this thing is not urgent I tend to sit on it. But eventually time will come for smog.

Does my low mpg say anything? I mean eagleeye's numbers put mine in shame.
I don't live in the bay area, to sit in crawling traffic, or sit running my a/c or heat getting zero mpg at the time.

how old are the plugs? =the OEM NGKs that came with the car only last 30,000 miles. I have NGK double plats on mine. (they are still tiny and cheap, despite being great long life things and not fagile like the iridiums can be). = subaru cars like NGK.

plug wires: NGK also. how long you had them in?

how old is the timing belt kit in years/miles. (Aisin is the one to buy, still japanese made).

Subaru maintenance schedules and new car break-in period- 2000 through 2009, links for 2010, 2011...
 

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Discussion Starter #13
The plugs are NGK 6953 BKR5E-11 from rockauto, copper core nickel tipped. TIme belt kit, unfortunately, I got the Gates before realizing it is not the best. Head gasket fel-pro. All these are new less than 10K ago.

The plug wires are still original though.
 

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With a hesitation, I would look at the fuel trim to see if you have a lean condition. I would also put a vacuum gauge on the beast.

I will usually smoke test the intake if I suspect there may be an intake leak. I would expect that the average guy doesn't have a smoke machine at their disposal.

Also the Gates kits are fine inspite of all of the noise you hear around here, you can use them with confidence. I use them all of the time. I have yet to see a problem with them.
 

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Discussion Starter #15
With a hesitation, I would look at the fuel trim to see if you have a lean condition. I would also put a vacuum gauge on the beast.

I will usually smoke test the intake if I suspect there may be an intake leak. I would expect that the average guy doesn't have a smoke machine at their disposal.

Also the Gates kits are fine inspite of all of the noise you hear around here, you can use them with confidence. I use them all of the time. I have yet to see a problem with them.
Thank you dougmac for your input.

The car does not run lean. In fact it is too rich during idle, -7 to -10% LTFT.

About Gates, I think people are saying some bearing is not made in Japan as they claim. I am sure most likely it is fine but people think this affects longevity. And if indeed one bearing goes it will damage the engine. More of a piece of mind I guess.
 

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You are right, the trim indicates a bit rich. The trim is certainly within an acceptable levels.

Some ideas that might help...
Commonly a hesitation is caused by the fuel system not being able to provide enough fuel when the throttle is opened. It needs extra enrichment when the throttle is opened.
I wonder if it's possible that you have a fuel delivery problem? Have you checked the fuel pressure? It may be able to keep up with demand when crusing, but falters when there is higher demand. When monitoring the fuel pressure, it should increase when the manifold vacuum decreases due to the throttle plate opening.

There are quite a few problems that can cause a hesitation.
A vacuum gauge is a great tool. I would still put a vacuum gauge on it to be sure there isn't a mechanical problem. You can also verify the MAP sensor. (converting In-hg to absolute pressure)

Are you certain that the cam timing is correct from the timing belt change? Incorrect cam timing can affect the cataltic converter operation. It can even damage the catalytic converter.

Good luck...
 

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Discussion Starter #17
@dougmac
Thank you for the suggestions. I will try to invest the tools. Harbor Freight is far so I will find time to do it.

Regarding cam timing, I can just check it by opening the timing cover, right? Any other ways to check if it is right?
 

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The only way to be certain of the timing is to remove the cover. If your curbside cover has the inspection hole, you can remove that plug and the small cover over the roadside cam sprocket to check that the cams are in time, but you can't check the crankshaft orientation unless you remove the larger cover. It's a lot of work for just checking one of the possibile problems.

A P0420 combined with a hesitation can be a challenge for a seasoned mechanic with all of the tools. I think the best bang for your buck, would be to start with the vacuum gauge. They are fairly inexpensive and can provide good information.
The fuel pressure check would also be a good thing to do if you can get your hands on a fuel pressure gauge without much trouble.
 
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