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Old 02-20-2008, 04:57 PM   #1
fastenova
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Not your usual 1997
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Default P0400 Code - EGR Flow Malfunction *FIXED*

I wanted to document my troubleshooting process here because what I've found by searching has been very incomplete.

I have been getting an intermittent P0400 Code for several months now, and besides the CEL, the main symptom is a hesitation or surging at around 2500-3000 RPM under heavy throttle. This is accompanied by a drastic change in power at approximately 4250 RPM where the motor, out of nowhere, just seems to pull hard and strong.

The car has a custom free flowing exhaust, with borla headers and a stromung cat. Also has a custom intake utilizing custom piping, stock airbox with no filter, and a conical filter located in the fender. Further engine "modifications" include phenolic intake spacers, LW crank pulley and flywheel, TB coolant bypass. All of said modifications have not caused issue since installation, and I cannot say that I think they are related to the problem.

It seems like when I clear the codes from the ECU, the hesitation goes away for the most part. So, I think the computer is doing *something* that is changing the way the motor is running (ignition timing, fuel ratio, EGR amounts).

I have replaced the EGR valve with a known good used one. After resetting the codes, it ran great. After about 200 miles, the light came back on and the hesitation returned.

I checked all intake ducting for leaks, including the PCV and IAC hoses. I have replaced 90% of the vaccuum lines (except for those that had been previously replaced and were still in great shape) related to the EGR system. This includes the lines:

from EGR to EGR solenoid
from EGR solenoid to BPT (backpressure transducer)
2 from BPT to metal lines under throttle cable
2 from metal lines to TB (throttle body)
1 from TB to pressure sources switching solenoid on passenger strut tower
1 from pressure sources switching solenoid to pressure sensor

I will be replacing the larger vacuum line that attaches to the bottom of the BPT (this is the EGR pressure sensor that moves the diaphragm inside the BPT) and goes to the metal line bolted to the EGR chamber just under the EGR valve.

I also took the TB off the intake manifold and thoroughly cleaned it. The three metal tubes on the top of the TB are vacuum lines, and come out near the throttle plate at the top of the throttle chamber. There was a slight amount of residue around those holes, so I wanted to make sure sufficient vacuum was getting out through the holes.

Further, per Subaru FSM, I blew through the metal lines in the system with air to check for blockage or leakage. Apparently corrosion can form in these metal lines and either cause blockage, or create small pinholes which would cause a vaccuum leak. I will be doing the same procedure with a compressor instread of my lungs to see if anything comes out.

The code can be thrown by either the EGR valve not opening all the way,
or potentially by a stuck open/closed solenoid. This is, usually, NOT an electrical code (meaning a connector/wire failing, or a solenoid not working), but rather a mechanical component failure of some sort.

If, after replacing those vaccuum lines, and running compressed air through the metal lines, the code returns, I will replace the BPT. These run about $50 from the Subaru dealership. It is possible that the diaphragm inside the BPT has been damaged from exhaust heat.

I have an issue of The End Wrench which specifically talks about P0400 codes and has been very helpful. It's a PDF, and I don't have anywhere to host it, but if you'd like it I would be happy to email it to you. I can't recall where I found it, but when I remember I'll cite my source.

I will post again as I am able to discover more.
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Last edited by fastenova; 02-25-2008 at 01:00 PM.
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Old 02-25-2008, 12:59 PM   #2
fastenova
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Just to update - I replaced the larger vacuum hose that runs from the bottom of the BPT to the metal line that connects to the EGR Port on the intake, and cleared the codes (now throwing both a P0400 and a P0401).

I did that on Thursday. One tank of gas (300 miles) and a lot of varied driving, and the car is still running like a top. No codes, no hesitation.

I didn't get the chance to clear the codes after I replaced the smaller vacuum lines, so I'm not sure whether the fault was there or in the larger one. The lines were NOT in bad shape, visually, but where they connected to the metal/plastic tubes, they were pretty stiff.

Total cost to repair: $4 for 4' of vacuum line. Total time to fix: 15 minutes. Total wasted time: 7+ hours checking everything else before finding the actual problem...
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Old 02-25-2008, 06:18 PM   #3
mongo46
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Hey Check out what I did for the P0400 I went through just about everything found out it was the metal vacum lines from the pressure Trans to the throttle body that run under the throttle cables also the metal pipe and port on the engine was clogged solid with carbon

http://forums.nasioc.com/forums/show...ighlight=p0400
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Old 03-19-2008, 01:46 PM   #4
lgt2000
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Hey, i had that code and replaced a vacuum hose and it fixed the issue, although I did it the hard way by replacing the egr first
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Old 08-12-2009, 06:52 PM   #5
BoardRider
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Quote:
Originally Posted by fastenova View Post
Just to update - I replaced the larger vacuum hose that runs from the bottom of the BPT to the metal line that connects to the EGR Port on the intake, and cleared the codes (now throwing both a P0400 and a P0401).
I hate to sound like a n00b but will someone please post a pic of the referenced vacuum hose locations? Or tell me where they are? I'm getting this same fault code and want to swap out the hoses before troubleshooting further. Thanks!
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Old 08-12-2009, 08:58 PM   #6
Charlie-III
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Silver Sleeper Wagon

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Find the EGR valve (drivers side of the engine, on the back of the intake manifold, near the top) and the BPT is just in front of the EGR valve. The EGR valve also has a metal tube that disappears down the back of the engine to the exhaust port on the #4 cylinder.

Start replacing all the rubber hoses associated with those 2 main parts.

fastenova, what did you do with the EGR tube from the head to the intake? I am also running Grimmspeed intake spacers and forgot to check the fit of the tube when the engine was out. Now it's a PITA to lengthen it to fix it.
Currently I have an old tube cut in half with the "free ends" smashed shut to prevent leaks.
I am also chasing a P0400 & P0401 CEL.
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Old 08-27-2009, 10:48 AM   #7
fastenova
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Charlie-

Sorry for the delayed response. I'm pretty busy these days and don't get the chance to check the forum as often as I ought to. Thanks to BoardRider, who sent me a PM to let me know you were asking a question, I got my butt back on here!

I used a simple compression union from Napa - like $4 - to lengthen the EGR pipe a little bit. What I had to do was just cut the pipe cleanly with a hacksaw, then grind down the OD of the pipe just a little bit in order to get the compression fitting to fit. I think I did about 3/8" on both sides of the cut.

Then I just loosely assembled the union, checked fit on the head/intake, then tightened it all down. I had to snug the union up outside of the car as I did this with the engine in place and couldn't get my hands and tools in there to snug things up to my satisfaction.

If you're chasing 400/401 codes, it's likely because the ECU is opening the EGR valve and not seeing any difference in combustion. I know it lowers combustion temperature, and I believe it lowers CO emissions and thus is detectable both in the oxygen sensor and in the instant engine speed. Fix this pipe issue and most likely your codes will go away.

I think there are more details on the grimmspeed thread, I'll see if I can find it. I posted pictures and a detailed writeup... somewhere!

Aaron
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Old 08-27-2009, 09:43 PM   #8
Charlie-III
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Silver Sleeper Wagon

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fastenova, thanks for the reply (thanks to BoardRider for passing this on).

What I'm doing now (we'll see if it works) is that I drilled a .060" hole in my crimped tube going to the EGR valve.
I "assumed" the ECU was looking for an engine speed change due to the different "air" coming into the intake.
My hope is that the free air being admitted into the intake will show a difference to the ECU and make things happy.

This issue has been pushed back a few days since I had to do HG's in my wifes 99 Impreza L wagon (yes, it's a 2.2L with a blown HG, go frikkin figure)

Her car is running again, so I am back on mine.
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Old 08-28-2009, 11:24 AM   #9
britimp
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Hi,

I have had a code 440 Evap malfunction and 420 Cat below threshold for ever plus it was running dog rough between 2000 and 2500 rpm. It was in the shop for a while and they got rid of the codes long enough for it it pass the smog test and they noticed the hesitation but we could not afford to let them go at it at the time and just got used to it.

Well the CEL came back and with inspection looming again I've been thinking about taking it in for more work. We also had a niggling alternator problem - it passed all the checks I ran on it from the FSM but it just did not seem right. Last Sunday the charge warning light came on as we pulled off the interstate and we got home ok but it was finally time to change the bloody thing.

Got a used one for $50 and threw it on - its like its a different car! Pulls like crazy, no bogging down a 2000, shifts better (its an auto) and the best bit is that the CEL went out!!! I am yet to scan it but could a crappy alternator be the cause of these codes? I was about to throw major cash at it in the area of emissions but everything seems good now.

Has anybody experienced this before? Is it common knowledge? I just did not get it that alternator voltage output would screw with the sensors and ECU.

Any idea?

Thanks.
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Old 07-09-2010, 10:18 AM   #10
immorion
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First let me say thank you to all who have contributed to this (and other) threads about the EGR P0400 flow malfunction issue.
Mongo46 thank you for your continued updates as you moved through root causing this code. Your advise and guidance is priceless.

I'm not sure how my day is going to go since I spent most the night reading different posts at different forums and Google-Seaching-The-Snot-Outta anything I wasn't clear on or familiar with (happens to be most things when it comes to my Subaru). I can't wait to dig into my emissions system, dig out some carbon, fill my neighborhood with smoke and NEVER EVER EVER wonder about this mysterious EGR thingy again

Did I mention, THANX?!

WHEW... Ok, short history.

I grew up in Stowe, Vermont. My mother decided the car most suited to keep us alive through -20F winter nights while driving on roads covered with corosive salts to melt the black ice was the 4WD Subaru Wagon... We had several.

Flash forward

I now live in Oregon and drive a 97 Subaru Outback Legacy Limited that I bought from my Oldest brother in 2003. I've been ignoring my check engine light for almost 4 years now... I have to pass DEQ testing to renew my registration and in order get tested no indicator lights can be on at the time of the test. So, I have to have the code cleared, drive enough to complete at least one drive cycle to generate some data for the DEQ computers to scan. The trick has been getting to the test center before the CEL light pops back on but after I've driven enough to avoid a "nodata" "notready" result.

I just got my new tags the other day and as I pulled out of the testing station that damn insistent check-engine-light-from-hell popped on. I'm on a mission to fix this issue once and for all (while avoiding damage to myself and my car) and feel I am well armed and ready to git-er-done (update to follow)

I haven't seen this doc linked or referenected anywhere during my research so please enjoy this fine tale of "The Elusive EGR, P0400" brought to you by none other than VCERTT (VERMONT CENTER For EMISSIONS REPAIR & TECHNICIAN TRAINING

Cheers,
Imm-o
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Old 03-10-2011, 09:21 PM   #11
GreenMarine
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Good information here
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Old 12-26-2011, 10:16 PM   #12
cmiovino
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Thanks for the information guys. I have a P0400 code and tried cleaning the EGR valve that was all goobered up from this video:


3 months later, it's back on again. Cleared it. It hasn't come back in 2 days, but I know it's going to. Talked to to the guy at this new Advance Auto that I go to know on the way home from work, who is actually very knowledgeable. He suggested checking out the vacuum lines too. I'm gonna check and replace these as I have a ton of tubing from my old car in the garage (also an EJ22).
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Old 04-18-2013, 10:53 PM   #13
Ronilius
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Black

Default Revival!

Where would I find vacuum tubing, seem to be having an issue finding the right size for the tubes
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Old 04-20-2013, 12:23 PM   #14
Charlie-III
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Silver Sleeper Wagon

Cool

Quote:
Originally Posted by Ronilius View Post
Where would I find vacuum tubing, seem to be having an issue finding the right size for the tubes
Most auto parts places sell line by the foot. I believe you need 2 sizes, just pull off one end of each hose & use a ruler. I think ~3/16" ID & 1/4" ID is what is needed. Don't quote me on that though. I used to do a lot of work on 70's & 80's cars that had crappy rubber for vacuum lines. I kept a supply of different sizes on a roll and then grabbed what I needed to fix lots of idle/running issues.

As to my issues, I found a few things.

1-Vacuum lines were old....replaced.
2-Port in head was carbon clogged, used a drill bit (by hand, NOT in a drill) to remove the carbon after the tube was removed (the ~3/8" diameter metal tube from the EGR valve to head).
3-Make sure the EGR piston moves freely by hand. A manual vacuum pump can also be used.
4-Clean the EGR port in the intake (after removing the EGR valve) using a drill bit like the other port.
5-I did a "similar mod" as listed above due to my Grimmspeed Phenolic spacers.
-I took the tube (already cut in 1/2, make sure it's free of carbon inside) to Home Depot plumbing department.
-I picked up a 3/8" x 3"? brass pipe nipple & 2 3/8" compression/female pipe thread fittings.
-I had to drill the compression nuts & the brass ferrules underneath out a tiny bit so they would slide over the existing EGR tube.
-Screwed the threaded part onto each end of the nipple.
-Slid the cut ends of the EGR tube into the compression fittings.
-install into the head & EGR valve, snug up the original fittings, then snug up the compression fittings, then give a final tighten.

Never had an issue with this CEL again.

Hope my descriptions help out.
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