What is this?

[tricked919]

Does anyone know what this vacuum valve/switch is?

 

I just posted a thread yesterday with a handful of questions on a 97 OB I just picked up. The seller had a reoccurring CEL coming on traced to the EGR and he said he bypassed this valve and its been working fine. It has one of the front lines and one of the back lines disconnected and apparently the two others are re-routed from the factory schematic.

 

Along with “What is it?” …I’m curious if he was BS’ing me or is this a part that can be bypassed to not interfere with the normal motor operation. I’m concerned that the CEL was tampered with. Seems to run great otherwise.

 

THis is not my motor BTW - borrowed from google images.

[jerryjer8]

its called a back pressure transducer, i only know becuase i recently needed to change mine, it was bad and it controls the air flow for the egr

[jerryjer8]

and if it was bypassed then im going to say the egr is not working properly, drive the car 50 miles or so and the check engine will probably come back on, easy way to check and see if egr is working, warm car up, and look under hood, when you rev the motor egr valve should be able to see moving, if it is bypassed and light doesnt come on your still not getting the gas mileage you should be getting and could lead to later problems from the car running to rich or to lean, and with that it could also lead to the problem im at now with my car which is either a bad o2 sensor or bad catylic converter, which is most likely due to the previous owner of the car not getting this problem fixed to begin with

 

$79 at any subaru dealer, and no tools required to fix in less then 2 minutes

[wtdash]

Never mind.

Td

Edited April 22, 2010 by wtdash
misread 1st post.

[djmark7]

'98 leg 2.2 no vacuum to back pressure transducer, EGR valve does NOT move at all, when i disconnect egr (the side with one line) and suck through hose it seems like theres a hole but no hole in line? there is NO vacuum to either of the 2 lines that go to the one side? is that the norm? also there a electric switch? thats between the BPT and the EGR valve? thnx in advance

[Fairtax4me]

It has to do with controlling flow rate of the EGR based on a handful of factors. Should be a diagram on the bottom side of the hood that shows where the all of the vacuum lines on the engine should go.

 

You probably won't be able to move the egr valve by sucking on the hose. They do require a fair amount of vacuum to open. The other side of the valve goes to the exhaust system. If there weren't a fairly heavy spring on the valve to keep it shut the back pressure from the exhaust system would force the valve open.

This can happen from time to time when the catalytic converter gets plugged up. The pressure in the system gets so high it does force the EGR vale open, it makes the car idle and run like crap, and it can literally scream at you. More of a mid pitched howl, but it's still a weird sound to hear coming from under the hood.

 

If you really think there is a vacuum leak at the valve, which there may be, and that may have caused the CEL in the first place, then you'll need to connect a vacuum pump to it to test it. Handheld ones are perfect for this, and are fairly inexpensive.

 

your still not getting the gas mileage you should be getting and could lead to later problems

 

An open EGR valve actually has the opposite effect on fuel economy. It lowers it because it "dirtys" the fuel mixture, which makes it create less power. The idea is to reduce NO2 (Nitrous Oxide, aka Nawz! ) emissions by lowering combustion chamber temperature. High combustion temps are what lead to the creation of NO2 in the exhaust gases. By making the mixture "dirty" with already burned exhaust the mixture burns cooler, which keeps NO2 from forming.

A cleaner mixture creates more power but also tends to lean ad create higher heat during extended drives at constant or low throttle (on the highway). Thing is, when you;re on the highway, it's the time when you need the least power, just enough to keep moving, so the difference in fuel economy with the egr valve operating properly is really minimal. When you start running into trouble is when it sticks open, or the diaphragm ruptures and creates a vacuum leak. This leans the a/f ratio, the o2 sensor reads the change in exhaust oxygen content, and tells the ecu to bump up on the fuel.

 

[djmark7]

i can move the valve by sucking, kinda ez too i dunno, NO CEL comes on

Edited April 23, 2010 by djmark7
add CEL comment

[2.5GL]

There is vacuum from two lines on TB at different times going to the BPT valve.

Vacuum goes through BPT valve and is switched by a solenoid.

When solenoid opens (only at certain RPMs, under a specific range of load, after coolant temp reaches its special figure...)

The EGR valve itself will open to "quench" the intake charge of air.

 

To test the EGR system...

Warm car to operating temp

 

Moderately rev engine while watching EGR valve.

 

Valve should move. There is a sweet spot to get the valve to stay open longer. It is a matter of how fast you accelerate. Too slow, it may not open. Too fast, it will barely have time to open before you passed its operating range. you'll have to play with it a bit.

 

If valve does not move there may be a vacuum leak in the valve diaphragm, mechanical or electrical fault in EGR solenoid (vacuum switch), faulty BPT, cracked, split, loose, or plugged hose. Check the metal lines as well, they can corrode from the inside.

 

If everything checks out and you still get a DTC of PO400 EGR flow malfunction, then look into this...

 

While engine is idling, pull open the valve with your finger or hook to a vacuum tester. The engine should stumble or almost die.

 

Option 1: Engine does not stumble... Plugged up EGR valve, easily cleaned when removed. OR a clogged EGR runner in intake manifold. Have fun fixing this one.

 

Option 2: Engine does stumble, but DTC code keeps recurring and all components check out... Replace the MAP sensor filter, opposite side of intake located in the middle of a hose going from the intake to the MAP sensor on the RF strut tower. It is about the size of a quarter in diameter, maybe about a half an inch thick, wrapped in gray or black foam with a white, cream, or gray plastic body. Subaru Part # 22663AA010.

 

For pics of the filter mentioned and more info see: http://www.ultimatesubaru.org/forum/showthread.php?t=84705&highlight=MAP+filter

 

Did I miss anything? Somebody have something to add? This is what I went a few rounds with in my impreza last year and this is what I remember.

 

Thanks WAWalker on the part number.... You saved me from pulling out whatever hair I had left.

Edited April 23, 2010 by 2.5GL

[djmark7]

when i suck on valve engine does almost stall so its working right? i dunno

[tricked919]

I'm trying so hard to wrap my head around this.

 

My EGR seems to be working fine with the BPT completely bypassed. I say "seems" to be working fine because we've driven the car almost 300 miles this week and its doing OK on gas, no CELS's, and it runs like a champ. I have a little bit of a rough idle at a stop light - but that's about it.

 

I ordered a BPT that will be here next week just because I want it to be right.

 

Thanks guys - this is a ton of info.