97 LGT Exhaust Gas Recirc Flow Malfunction (P0400)

[gathermewool]

I researched as much as I possibly could, (and still do from time to time) posted up on the subaru forums, and even spoke with the local service guy a few times about this issue to no avail... Sorry for the long post, guys. I know the system is working so I'm not worried about my NOX emissions. I'm worried about the emissions test I've got coming up at the end of this year. I've tried to spend as little money on this as possible. I was doing well until I let the Subie tech convince me to buy the expensive Xducer... This may only be coincidence, but the code was in last spring, early, and then went away when it got warmer. Code came back this past fall and has been around since. Here's a brief synopsis of the situation, and what I've tried. Early 2008: P0400 code (EGR flow malfunction) pops up sporadically. CEL is clear MOST of the time. As code becomes more prevalent I start researching: Haynes RM, nasioc.com, lgt.com, etc. 1. While at NOT, the EGR control system was tested by manually increasing throttle. EGR valve opened properly. EGR control system ok? 2. EGR valve opened while at idle. Engine only slightly bogs down. Dirty EGR valve? Clogged tube? 3. EGR valve cleaned, new gasket installed. Engine now bogs down considerably when EGR valve manually opened at idle. 4. Replaced all vacuum lines as well as the MAP sensor filter (suggestion from some one on the subie forums.) CEL clears on its own and stays cleared for a while. 5. Fall, 2008: code comes back and does not clear. CEL on constant to-date. 6. Replaced leaking EGR tube after HT RTV "repair" failed 7. Subaru service guy talked me into buying a transducer, even after I told him that the EGR valve seemed to open just fine. He stated that some times, with an old EGR Xducer, it may open TOO much. Code has not cleared in the two months since I swapped them out. EGR system seems to operate EXACTLY the same. 8. Finally had some time today to do a few more checks. a. Hooked up vacuum pump to EGR valve. Applied 10" vacuum. EGR valve opened immediately, and held vacuum constant for >30 sec. I did this 5 times for repeatability. All passed. b. Checked resistance of ALL solenoid-operated vacuum valves, including EGR solenoid. All showed resistance ~40 ohms. HRM says 10-100 ohms is good. With car off, key to ON position, all solenoid connectors showed battery voltage. c. Hooked vacuum pump up to upstream side of TB. Didn't seem to show vacuum on the gauge even after I open the throttle. Downstream side showed 0 vacuum before and >10" vacuum after operating the throttle. Not sure what this means.

 

[SuperEd73]

Do you have the proper Subaru procedure list/problem tree to try and figure this one out? Maybe something like an AllData-diy.com subscription would provide that info or perhaps your local library might have service manuals available. I know you said the valve itself appears to be functioning and you checked the base resistance of the solenoids and you're getting battery voltage at the solenoids. I'm not familiar enough with the engine to know but is there a sensor that measures the position of the EGR valve? Also do you know for sure that whatever solenoid creates the vacuum signal to open the EGR valve is actually functioning? You may have done this already but did you connect the vacuum guage to the vacuum line on that solenoid to see if you get vacuum when you open the throttle? Ed B.

 

[gathermewool]

I've been trouble shooting using the Haynes RM as well as the internetz. There is no measure of EGR valve position. I assumed that because the EGR valve opens when I hit the throttle that the solenoid was working. I'll have to do what you say and see how much vacuum, and if it's an instant open. Thanks for the advice!

 

[gathermewool]

I checked everything again today just to make sure there was nothing further for me to check before I take it in for some one else to diagnose. I Hooked up my vacuum pump to the vacuum line that attaches to the EGR valve, and noticed the valve open immediately and hold when I applied vacuum. For what ever reason I decided to hook up to the upstream side of the vacuum solenoid to see if I could have the EGR valve open and hold vacuum again. Upon application of vacuum the EGR valve would open and immediately shut as vacuum bled off. Multiple pumps and multiple times the EGR valve would open slightly before shutting as vacuum bled off. 1. The vacuum was applied with the solenoid unplugged. Shouldn't the solenoid be shut when denergized? Seems as if it's mechanically stuck open. 2. It seems as though the solenoid has failed, and is allowing vacuum to bleed out some where. 3. The coil resistance is 46 ohms, which is in spec Any thoughts before I order a new one? Also, I sprayed the bolt that attaches the solenoid to the manifold with a very little bit of penetrant, but the bolt will not loosen. I'd rather not snap the bolt head. Any ideas where I can mount this if the old solenoid won't come out?

 

[artificialist]

Many Japanese cars have 2 air temp sensors near the EGR. 1 measure the exhaust gas temp, the other is underneath the EGR, and compares the EGT to the intake air temp immediately after the EGR valve. Perhaps one of those sensors have failed, or the EGT sensor is covered in soot.

 

[gathermewool]

Update: I blipped the throttle after starting the engine cold and the EGR valve slightly opened. The same thing happened with the solenoid unplugged. It's free-flowing even when I put my finger over the vent port. Also, the bolt came loose with a little bit of persuasion, so the solenoid now resides in my shirt pocket. Based on all of this I'm 97% certain the solenoid has failed mechanically. I'm going to check out a new one at the dealer to compare. I don't think that EGT has any input into this system, but I could be wrong.

 

[eljefino]

Most EGR systems have an air bleed so when the solenoid closes the valve closes soon thereafter. Otherwise you'd have a vacuum "bubble" in the line between solenoid and valve. If your valve were inappropriately open at idle, you'd notice it being real shaky and lousy.

 

[gathermewool]

It is my understanding that the solenoid pulses open with a certain pulse width to open the EGR valve a specific amount for a specific period of time, and then, as eljefino stated, will shut and bleed vacuum through the filtered vent port. The old valve bled through the vent port normally, but I wasn't sure whether the valve should be open while deenergized or shut. My hope - to finally fix this freaking problem - was for it to deenergize shut, which would prove mine had failed. The local dealership parts guy let me check the new solenoid before I bought it just to make sure. I blew on one of the ports and air vented out the vent port...uh oh. I put my finger over the vent port, said a prayer, and BAM, no flow! It seems that the old valve was stuck open. A bit of "gentle" mechanical agitation and contact cleaner didn't seem to do anything so I decided to buy a new one. I was so excited I paid $10 more than I would have online just to have it right then and there. I ran over to my car and installed it in the parking lot before I left. After a bit of driving, the CEL is clear, but the readiness status is still "not ready". I have a good feeling about this, though. I'll post one last time what happens.