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EGR system problem


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7 replies to this topic

#1 paladin_w

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Posted 04 November 2003 - 09:54 PM

I have a problem with my EGR system, I have a newly purchased 1997 Subaru Outback limited, High miles 175K, 5-speed, 2.5L, 4 Cyl. Started off I would get the Check engine light with a code P0400 stating EGR flow problem. System consists of BPT(Back Pressure Transducer), Control Solenoid, and EGR valve. I have done all the tests in the manual. Checked all hoses, the valve functions properly with hand pump applying 10 in. of pressure, and passes diaphragm check. Solenoid has the battery voltage and 41 ohms resistance, within the 10 to 100 range. I have replaced the BPT since the old one I thought was not operating correctly, and everything else checked out. With a vacuum gauge at the valve hose it shows the initial spike in vacuum of 12 then drops to 2-4. However when the cover to the BPT is opened and the little white fuzzy thing is removed there is a round maze looking section with one little hole going down into the main body. When I plug this hole the whole system operates correctly, valve moves and stays, and adjusts with different RPMs. This hole is supposed to be there and the white fuzzy will allow air in at a low rate, plus there are two small holes at the top of the cover so air will be able to get in; the old one smells of gasoline and exhaust. Now I get two codes P0400 and P0325 a knock sensor #1. I do most all of my work and am baffled along with my buddies and mechanic friends, any help would be great.:banghead:

#2 Commuter

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Posted 04 November 2003 - 10:55 PM

Interesting...

I too have been getting this code recently on my 97 OB auto.

I had it in the spring but it was a pressure / vacuum sensor that mounts to the passenger strut tower that was actually the problem. I don't know if the manuals have this sensor. It apparently "tests" the operation of the EGR, as well as provides some 'input' to the TCU. (My shifts were a little sloppy and delayed at times.. this was cured as well after the sensor was changed.)

Let me know how you make out. I haven't resolved mine. It just came back on me several weeks ago. It came on once before I was in for servicing lately. The shop didn't see anything obviously wrong. Then it came on a few weeks ago. And now twice just today.

No noticable difference in operation, although I do have a little hesitation / stumbling that I believe is carbon, but I have heard that a malfunctioning EGR can cause similar affects.

Commuter

#3 paladin_w

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Posted 05 November 2003 - 11:16 AM

Thanks for your thoughts. I am going to pull the EGR valve off today and check for any obstructions and try to clean it, I was talking to another old avation mechanic and he suggested when I cover the hole, I might be forcing a bypass of some of the BPT's operations, and therefore causing it to act as a direct passage line to the control solenoid, suggesting againg that there might be a clog in the lines since the BPT is new.

#4 PAezb

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Posted 05 November 2003 - 12:42 PM

I too am *still* having issues with my 96 OBW/auto. I have cleaned the metal tube lines, and EGR valve, replaced all vacuum hoses, replaced the EGR soleniod - still get the P0400 code. I'm thinking of replacing the BPT as well.

Hey Commuter, how much is that pressure/vacuum sensor you replace?

Funny thing is the car seems to run and shift fine. Watching the EGR valve when revving the engine between 2K/3Krpm it appears to be operating correctly. Maybe the ECU's circuit handling the EGR functions is faulty....

Paul

#5 Commuter

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Posted 05 November 2003 - 01:11 PM

Paul,

That stupid little sensor (< 1" black cube with a couple of mounting tabs, a vacuum line nozzle (or 2?) and a 3 wire connector) listed at $430 Canadian IIRC. Definitely worth shopping around for... or even trying used. It was one of the few times that I felt that a Subaru part was out of line, price wise.

For me, the telltale sign was that my shifts were "off". They seemed a bit slow... delayed... sluggish... almost as if something was slipping. Not real bad at all... and not every time, but there. This cleared up totally after the sensor was changed.

The mechanic told me that this sensor monitors the manifold vacumm and provides some "input" to the TCU's shifting algorithm. As a secondary function, it "looks" for a change in vacuum when the EGR is opened. Therefore (since it was failing), it erroneously triggered a ECL with the PO400 code (EGR malfunction).

I don't know what is going on now. I'm basically letting it develop and get worse, then I'll take it in. It's not something that I feel inclined to tackle myself, especially with colder, rainy weather setting in. The Code reader I bought in the spring is seeing it's use now.

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#6 color-blind

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Posted 05 November 2003 - 01:50 PM

Egr problems are the most fun so here we go. Remvoe the egr valve and make sure that all the passages are clear. In addition make sure the metal tube is cleared out. The most common problem is the bpt valve and second clogged passages.

If these repairs are not the fix you need to look at the map sensor. It monitors vacuum thus it can tell if the egr is working. If the egr is not working the map sensor tells the computer to set the egr code. There is a small filter inline on the map sensor hose it is common to fail be sure to replace it if you believe the map sensor is your problem.

As to the knock sensor code; simply replace the knock sensor. Good luck.

#7 paladin_w

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Posted 05 November 2003 - 09:03 PM

I am really beginning to hate this. Today I have taken the EGR valve off, more than a layer of carbon film on it, cleaned it, found a little blockage in the metal tube going into the #4 chamber, cleaned it out, again checked all componets, and all pass tests, but when I put everything on the car the valve stem does not move. I have a more consistant vacuum from the EGR valve hose, goes up to 12" and kind of bounces, sometimes drops sometime not, but always bounces; and the valve will move nicely with as little as 3" of vacuum as long as it is applied with the hand pump. I replaced all the vacuum hoses cleaned the inside of the EGR valve, and the #4 chamber to make sure there is good flow once the valve starts operating correctly, and placed a new gasket on the EGR valve. I am getting stumped, I have to go on a 30 hour car trip here in 2 1/2 weeks to get my kids for visitation. I really want this to be fixed, if anything else goes wrong, I will not know the check engine light is always on!

#8 paladin_w

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Posted 08 November 2003 - 11:16 AM

I am still researching and working on this problem...does anyone know of somewhere that really explains the operation and inner workings of a Back Pressure Transducer (BPT)??? I have gotten a couple of decient ideas from other posts as its function, but I am not crystal clear on it.
Also is there anyother componets that could directly affect the vacuum signal in the EGR system besides the 3 componets that are listed in the manual as the EGR system?
Karl




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