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1998 forester s
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7 Posts
Discussion Starter #1
So, i have read and read and read all over about the po400 i am understanding that it is a conditional code rather than a actual device failure....still doesn't help my CEL. My current issue is that my 98 forester 2.5dohc automatic not only has a po400 code but also shift knocks between 1 and 2 only and also only once it is warm. seems to idle hard to when first start this all seemed to happen together at one time so trying to deduce where and what is wrong....what i've done so far...
replaced all of the vacuum lines (i mean all of them0
cleaned the BPT valve bypassed EGR solenoid valve and seems to work just fine
hooked that little green connector under steering wheel together and listened for 1.5 sec cycles of solenoids for not only EGR but pressure switching solenoid.
all seems to work there.
EGR valve works just fine engine shudders when i manually open at idle. also put vacuum gauge on EGR and holds a vacumm just fine.
I am in the understanding that the TCM controls a lot of the EGR solenoid cycle function i.e. load and stuff...however i did notice when i was checking EGR solenoid that it seemed to click allowing vacuum through to EGR when i opened the throttle but then would immediately close...is that normal? I am also thinking that something could be up with the drop resistor for duty solenoid A but I haven't wanted to start into all of that yet I just bought a innova auto-ranging meter for the purpose of hunting down the problem. I would really like some advice and help I have the service manual and have already rebuilt this engine once and i'm about to do a Fel-pro gasket conversion kit which means another engine pull in the far future. in other words I know this car very well, yet this problem eludes me.
 

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Registered
1998 forester s
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24 Posts
i would think the code is from bypassing the vacuum purgesolenoid valve or whatever they call that litlle vacuum switch do-dad unless you were getting it before hand, i uplugged my egr line and put a screw in it and it threw a code, you could also have blocked up passages in your egr system, i've seen them completely blocked in older cars, the code i believe is trigerred by lack of flow rather than a component failure, seems like you know what your doing but thought i'de throw my two cents your way, not sure what you are refering to with the trans issue, good luck
 

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1998 forester s
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7 Posts
Discussion Starter #3
Ok so thank you for your two cents...yeah i had this code way before i took out the EGR.
As you may have noticed i rebuilt this engine last year and had the heads hot dipped, surfaced, pressure tested and cleaned the EGR tubes myself. So i diffnently know thats its not a EGR system flow exactly but thats what the code is so i'm back to square one.
I guess my confusion is that it all started when the transmission started its weirdness. i have a schematic break down of the electric and hydraulic signals through the tranny system and it does show that their is a correlation btw the tranny and the cycle of the EGR solenoid thus allowing vacuum to actuate the EGR itself. there is a slight possibility that the flow not only means EGR flow but also hydraulic flow there are some great articles from endwrench.com about the 4eat and its components. my next task is to test the dump resistor which is on the passenger strut tower underneath the pressure sensor switching solenoid somehow it is linked into the duty solenoid A on the tranny helping it during cold start as the tranny heats up, it as other functions but duty solenoid A helps in transmission knock during shifting so thats where i'm leaning now whether or not that helps the po400 code no clue but I would still like anyones help
 

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2010 Forester
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217 Posts
.......... helps the po400 code no clue but I would still like anyones help
Check your PM's. Also, the EGR requires either one or two drive cycles to turn off the CEL. Not sure as I'm new to Subaru as of 3 weeks ago.

Regards,
paul...
 
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