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Old 02-24-2008, 07:50 PM   #1
gathermewool
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Default '97 LGT EGR valve replacement

I have a '97 LGT and I just pulled a CEL code: PO400 (exhaus gas flow malfunction) I saw the CEL thread, but didn't find what I'm looking for, so I apologize ahead of time if I missed it.

I'm still relatively new to cars, so how hard would it be to replace an EGR (Exhaust Gas Recirc) valve, and where might be the best place to find a good, cheap part? Thanks in advance! : )
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Old 02-24-2008, 08:15 PM   #2
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The valve is bolted to the manifold, replacement shouldn't be that difficult although it's possible the bolts will be rusted in place. You should have a new gasket on hand as well, the old one will probably not be re-useable.
It's possible that the problem is not the valve itself, but carbon clogging the EGR passages. If this is the case the passages will need to be blown out with air.
The valve may in fact be defective or sticking, if you choose to replace it the best (and possibly only) source will be from Subaru. You can check with our dealer/vendors such as www.subarugenuineparts.com for a price.
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Old 02-25-2008, 10:47 AM   #3
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Thanks for the info! Now that I think about it, the CEL, and all of the associated symptoms (ie, rough idle, hesitation when giving gas) happened after driving over some snow in a parking lot that had the night to harden. I hear it hit bottom after driving over it to get to the next spot. Is it possible that the EGR is not the problem at all, and maybe there's a sensor lead that was detached? I'm not familiar with any of this yet; just asking.
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Old 02-25-2008, 04:49 PM   #4
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P0400 may be hard to diagnose because of the number of components
involved in the system itself, as well as in the feedback loop. It would be better
to look this one up in the factory manual. Maybe in this case you can start with the
oxygen sensor, I understand its signal is one of those used to monitor EGR performance.
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Old 02-26-2008, 02:04 PM   #5
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i often find the cause of egr codes to be the inline filter for the map sensor--the system senses the presurre wave from the opening of the egr to tell if it's working properly. the filter sits in between the intake manifold & the map sensor on the right side of the engine. also, i've seen many plugged egr pipes (between the head & egr valve)--hope this helps.
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Old 02-27-2008, 08:05 AM   #6
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I really appreciate all of the help. I went to the auto hobby shop near me and when they pulled the code, some snazzy software that came with the device stated three things that would cause this code:

1. EGR valve failure

2. solenoid

3. transducer

I'll pull off the EGR valve and check to see if it's plugged and see if I can manually manipulate any moving parts.

Is the solenoid electronic or vacuum acuated? There are wires and an in/out vacuum line. The hobby shop guy, who probably knows a lot more than me about cars, says it's definitely vacuum actuated, and that the electrical leads are part of some feed back loop. Does this make sense???

The transducer looks relatively new, so I'm going to leave it be for the time being.

I'm not sure where the inline filter before the map sensor is...probably because I don't know where the map sensor is haha. I'll look around...I really need to purchase a tech manual : /
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Old 02-27-2008, 09:03 AM   #7
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the egr valve is control by a solenoid & uses vacuum to open it. the map sensor is located on the right strut tower. if you follow the vacuum line from the map sensor towards the engine you'll find a round filter right i the middle. usually you won't find anything physically wrong with the filter, but replacement always seem to take care of the issue (subaru never has given me a solid answer as to why, but i suspect a slight difference in resistance thru the filter). have you checked the egr pipe coming from the head to the valve (they can get clogged with carbon). hope this helps.

Bret
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Old 02-27-2008, 09:07 AM   #8
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That helps out a lot. I'll make sure to replace the filter asap to see if that fixes it.

One question, however: I understand that the egr valve is vacuum operated, but how is the solenoid actuated to allow vacuum operation? Is it an electronically operated solenoid or is the solenoid some how vacuum operated? Thanks again for the help!

thanks again!
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Old 02-27-2008, 09:45 AM   #9
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The solenoid is an electrically-operated valve, controlled by the ECU. By varying its duty cycle, the ECU controls how much vacuum gets to the EGR valve and therefore how much it opens.
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Old 02-27-2008, 11:11 AM   #10
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Thanks, Mulder! Finally got the answer I was hoping for...now, the next question is: how does this solenoid usually fail? Is it as simple as doing a continuity check? (if it's closed-circuit when deenergized)

I'm still going to replace the filter as SubeTek suggested, but if that doesn't work it would be nice to rule certain components out before trial and error by replacing parts...

Thanks again for all of the help. Really appreciate it
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Old 02-27-2008, 11:45 AM   #11
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The solenoid can fail electrically, but if it does it would usually set a code for a circuit problem (high/low input etc.). Since you have a code for low EGR flow, which is a mechanical issue, the only way the solenoid would be at fault is if it's sticking or the passages are blocked. You could remove it and examine it for any visually apparent problems, to check it electrically you can briefly apply 12V to it and it should click. Don't keep the power on it for too long, just a few seconds.
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Old 02-27-2008, 12:13 PM   #12
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Thanks again. I've got my trouble shooting list. I'm going to post another problem, so if any one checking this would like to help with a tie rod question... : D
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Old 02-28-2008, 04:15 PM   #13
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Update: I finally found time to get under the hood and see if I could actuate the the EGR valve by operating the throttle. I was able to see the valve stem raise and lower when I gave it throttle, so I know the EGR valve is operating.

To figure out if the valve was operating, but not letting any exhaust gas flow due to a plug, I manually lifted the stem, which immediately cause the engine to bog down and idle roughly. I'm assuming that this proves that, not only is the EGR valve operating correctly, but so are the solenoid and transducer. Is this a correct assumption???

If I am correct, then:

1. is it possible that there is a plug, and that it's restricting flow enough to set off a CEL, but not enough to restrict flow entirely? (as seen when I manually operated the valve)

2. SubeTek, what you said about the filter seems like a good possibility. When you say the right side of the car, do you mean looking aft or looking forward? If looking forward, I saw a small black, round thing with flat sides perpendicular to its vacuum line. Is this it? If so, how do I change it. Do I have to replace that entire length of vacuum hose with it?

Thanks again for all of your help!
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Old 02-28-2008, 05:50 PM   #14
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sounds like the filter is your problem--right side=passenger side. the part # is 22663AA010 it run's about $10
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Old 02-29-2008, 02:33 PM   #15
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Update: 2 hours after I bought the pressure sensor filter my CEL went out. I started my car this afternoon and the CEL did not illuminate for the entire 10 minutes it took me to move it.

I haven't checked, but I ordered a new tie rod boot so I'm assuming that probably fixed itself, too! lol

I know what it was! I did add a can of Seafoam. That stuff must be magical...

Thanks again for all of the help. I'll keep the filter and only replace it if the CEL comes on so I know whether it was even necessary.

As a final note: I can't sell my civic for a reasonable price so might be keeping it. This means that I'll most likely be selling the Legacy when winter is over. I'll have new struts by then, and POSSIBLY a new pressure sensor filter lol.
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Old 02-29-2008, 02:41 PM   #16
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If the ECU doesn't detect the problem after a few driving cycles the light will turn off. The code will remain in memory however. When the problem is detected again, the light will come back on.
The ECU only checks for EGR function during extended steady-throttle driving (i.e. highway) at operating temperature, so if you've been doing mostly local driving and/or short trips you might not see that code again until you take a highway trip.
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Old 02-29-2008, 03:26 PM   #17
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you just took the jelly out of my donut...You're right. I've only been driving 2-3 miles back and forth to work for the past week, and the CEL DID come on a day after driving back up from NYC... I'm driving an hour down to pick up the gf tonight so we'll see...

I really can't begin to thank every one who has been helping me. It's great being able to post here with questions and have people reply with facts or practical trouble shooting tips.
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Old 03-01-2008, 02:01 PM   #18
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Some people had the problem with the pressure sensor itself (the costliest part of the system by far) and others with the transducer. Then there's metal tubing under the throttle body and they say it clogs sometimes. It's probably better to start troubleshooting by the book. This system is really cumbersome, and those with phase 2 engines (or any 2.2 l w. manual transmission) should be happy they don't have it. For example, ambient pressure reading is taken at the charcoal canister line, and there's a separate solenoid to switch between atmospheric and manifold pressures.

Last edited by avk; 03-01-2008 at 11:16 PM.
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Old 03-01-2008, 02:55 PM   #19
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he's eliminated everything but the filter & sensor with visual checks--my money is still is on the filter. really the system isn't all that complicated if you've dealt with it much.
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Old 03-01-2008, 03:18 PM   #20
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you did the seafoam trick eh ? that stuff does work great...

when I had a similar problem, all it took was a thourough cleaning of the EGR assembly.
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Old 03-02-2008, 02:47 AM   #21
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I drove an hour down to pick up the gf Friday night. After driving around for a bit today the CEL is back. I'm assuming it's the same thing. One thing I noticed is that when I first start the car, the EGR valve stem does not move when I manually operate the throttle...I again lifted it manually and noticed decreased engine performance. I'm going to check again tomorrow before and after driving...

I haven't taken anything apart yet, although I do have a bottle of deep creap ready. I don't really believe in fuel additives, but, after having had great results using the Lucas power steering stuff on my old '88 Ramcharger, and a few of the local shop guys rambling on about how great Seafoam is, I finally gave in and bought some of the Seafoam fuel additive. I feel as if the engine is "running better," but it could just be the placebo effect. ; )

Also, I had a fifteen minute debate about fuel and what requires higher octane with the shop guy. He stated that even an older car should not ever need it. That it was lighter than regular gas and was bad for the engine. I could be wrong, but I argued that premium gas was heavier than regular due to a higher number of carbon bonds in isooctane, but it is completely innocuous in any engine, even if the engine does not knock using regular gas. Any one know who's right?

Furthermore, what would cause knock in an older car? My guess is a bit of carbon built up on the exhaust valve remaining at a high enough temperature after the combustion event to detonate the injected fuel a stroke later before spark ignition occurs. Any clue???

Sorry for the digression, and thanks again for all of the help! Hopefully the filter I ordered will do the trick, and not an expensive component/s..

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Old 03-02-2008, 08:29 AM   #22
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It's normal for the EGR to not work when the car is first started. The ECU won't enable it until the engine is at operating temp.
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Old 03-02-2008, 02:01 PM   #23
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Oh, I though the filter was installed already. Let's hope it will fix it.
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Old 03-02-2008, 02:10 PM   #24
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Quote:
Originally Posted by avk View Post
Oh, I though the filter was installed already. Let's hope it will fix it.
i didn't know my EGR valve had a filter... where exactly is this located??
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Old 03-02-2008, 02:46 PM   #25
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Quote:
Originally Posted by IllNastyImpreza View Post
i didn't know my EGR valve had a filter... where exactly is this located??
It was first mentioned in post #5. The filter is spliced into the vacuum line from
the intake manifold to the pressure sensor, or more precisely, to what's known as
the "pressure sources switching solenoid".
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