I'm playing with SAI, O2 codes. I replaced my coolant flange this weekend (a bitch) and had the Combi valve off to make that easier. I had no gaskets left on the combi, and one of the vertical screws down below was missing. I replaced the screw and used RTV to seal both top in and bottom out (I didn't remove the bracket to the motor). Anyway, I'm going to start with a SAI relay replacement in the ECU box. what's a good source? Also, how does the air get from the combi valve to the cat, is there a tunnel from the back of the motor to the turbo?

also, if I buy the $99 version of vcds lite can I trouble shoot the air pump, relay, etc?

2000 a4 1.8 atw.

 

If you have a multi-meter and a general understanding of how relays work, you can easily pull the relay and see if it is good before you replace it. I did that not too long ago with mine. Just find which pin is power and which pin is ground. Take some short leads from the battery and hook up the relay. If it clicks when you put power to it, it's good. If you need help I can go out to mine and see which pins you need. You should also check the fuse for the SAI system. It's a 40 amp maxi fuse found in the relay panel.

 

If you have a SAI fault then the most common cause is a vacuum leak. You can verify this by checking the vacuum supply to the combi valve with the solenoid engaged. Should be around 18inHg.. The air gets into the CAT through the combi valve whihc ports directly into the exhaust side of the head. The ports can sometimes clog up and the only easy way to open them up is to take the head off and give is to a michine shop that can chem bath it. You can also check the combi valve itself by seeing if it holds vacuum at the nipple with a vacuum gauge. I would lean towards a vacuum leak which will sound like a hissing noise if you stick you ear close to the engine around the intake manifold side. The relay almost never goes bad.

 

I pulled the 373 relay and tested it with power (across 30- and 87+) and it closed and there was continuity across the other two plugs (85 and 86 when 30 and 87 closed), so it is good. I checked the 373 seat in the ecu box and it had 12+ volts at cold start. so, I'm moving out of the ECU box. I didn't hear the SAI pump blowing, so I'll try to unhook the power to it and check voltage there, and also hook the battery to it and see if blows. I'll probably first pull the vac line off the combi valve and check for vac at that hose, and see if I can hear the combi opening and closing. any other ideas?

Pump works. Line to combi is open. vacuum on line to combi nipple. Thus, it needs combi valve. Ive filled it with carb cleaner, and I've turned it over and tried to hammer a extension on it to move the plunger open. It is frozen. I need a new one.

 

Seems like you have a handle on it then.. Best of luck

 

Hey SinCity, does the combi valve internal mechanism move DOWN when vac is added, and open the passageway? Thus it 'fails closed' by seating in the UPWARD direction?

So, if the diaphragm is broken (I'm guessing there is one), it will remain closed.

 

I believe vacuum pulls the diaphram open, not positive on that thought. If vacuum isn't present it will fail in the sealed position though.. How much vacuum do you have a the nipple when the solenoid is engaged?

 

Vacuum does pull the combi valve open. With the engine warmed up, put vacuum on the combi valve. If the engine stumbles, your combi valve is good.

 

But does the vac actuator move the plug downward?

I'm surprised to hear guys who have water in their pump, since I expect these combis to fail closed with respect to the exhaust tract. When I had the combi out and started the car, it sounded like a exhaust leak, which in fact is was with the combi removed. Oh, and the CAI pump sounded like a dust buster, because it had no back pressure so it runs away. That may be a good signal that you have a leak in the tubing/piping if you hear the loud sound.

I haven't pulled apart my failed one yet, since it is still in the car, so I can keep driving. emission inspection is due in June. by the way, I unplugged my pump and the only fault/non-readiness is the CAI pump after driving. So, this problem throws o2 and other problems which are not real.

 

Vacuum should move the diaphragm up. I'm guessing since the vac port is higher on the combi valve than the inlet and outlet ports. Also there is a small hole on top of the combi valve that you can hear suck in air when you let the vacuum off. One of the theories for water being in the SAI pump is that exhaust gas is back feeding into the SAI pump and then moisture builds up as the exhaust gas cools. Check your SAI pump and make sure the rivets are still good. If it's a newer unit it will have bolts instead of rivets because the rivets are known to break and then you won't get enough air flowing through the system.