chris walrod

I second that, again!

c993k

Great job Mike, I'm saving everything for reference later. It's better than any book out there!
Chris

YA911Fan

Continued thanks for a beautifully executed tutorial for us armchair wrenches!

Some basic questions...

1. I'm assuming the check valve is designed to prevent the exhaust gasses from going directly into the SAI ports. Is that true?

2. Since the air pump is always running, why is a check valve even needed? Is there only positive pressure at higher RPMs?

Mike J

1 - The check valve is a one-way valve and in only lets air from the pump go into the SAI passages. The air from the exhaust system is not supposed to go pass this valve into the air pump. I am assuming if the valve does not let air go from the ports to the air pump then it does stop the exhaust gases from going directly into the SAI ports. But there would also be a vacuum effect since you have a stream of air going across the port hole in the exhaust chamber so it still might suck some air in but its unlikely, if the valve is doing its job, that air will be flowing into the port hole (does this make any sense?).

2 - The air pump only runs for 90 seconds when the car is first cold started. If you listen you will hear a whine that shuts off once the car get a bit warmed up. So if the pump shuts off the air pressure is off and then, if the valve is blown, the exhaust can travel from the port through all the piping into the air pump....

Cheers,

Mike

g_murray

So what's stopping "us" from introducing "anti-carbon fluid" (e.g. Techron, B12)down the 'ducting' that's attached to the air pump. Is it 'too hard' to get to this ducting (underneath) the air pump? Seems to me this would be the easier route than trying (as we've all read) to 'coax' that stubborn check valve off (never mind the effort to get to it in the first place).

Gerry

tam993

Hey Mike,
When you drilled that last port out on the cam tower, could you see the drill bit in the opening for the SS feed pipe?

By the way, this has been some of the best info I've seen on this bbs. Great job, and pictures.
Thanks again,
Tim

epj993

Yes - it's quite difficult to get to. Both sides of the airbox cover have to come off and you have a fairly small space to work in. In a past thread, there was discussion of rigging up an access port to inject some cleaner directly into the ports on a regular basis. However, several pros expressed concern about the cleaner burning in the cats and causing damage.

To date, the general consensus is that once you've flushed the ports, replace the valve on a regular basis (every 10-15K). Of course, the PITA here is getting them flushed in the first place.

ecobb993

Mike,

I, too, am most appreciative of this effort to educate us all.

One question: If one was (attempting) to clean the ports from the bottom up using a probe or wire, how long would the wire need to be to reach from the exhaust port outlet to the distribution channel at the top of the cam carrier?

Thanks again for the insite

Mike J

Hi Tim,

No, the problem is that the opening is 90 degrees to the cast feed pipe in the cam tower. There is very little to see in the opening other than the bottom of the feed pipe. When the drill bit goes in you can feel when it gets past the carbon and then its free for about 1/2" and then hits the bottom of the "T" junction with the cast in pipe.

I will do some more pictures later today and post...

Mike,

I measured it at about 2.4" from the valve chamber to the interface between th heads and cam tower, and 3.2" from that interface to the bottom of the air distribution channel. So the total length is roughly 5 1/2 inches. So if you manage to get a pipe cleaner or brush into that port that distance that is all you are going to get unless you can get it to turn towards the back of the motor almost 90 degrees. It could be that turn that is causing some problems since that would be an area where stuff would accumulate if the check valve was not working well...

BTW has anyone tried to use a flexible pipe brush (like the one I use in the above pictures) to clean the ports from below. I have not tried it but maybe I will mock it up and try. It is much easier on the bench than on your back from below (yes, I have done that! ;-) )

Cheers,

Mike

Toga

John D if you read, it's time to change the note "addict" to "professor" in Mike's avatar window
we are learning here!!

Thanks Mike!

Mike J

I am just trying to give back to the list all the support I received when I had my rust problems with my Targa Top. The outpouring of support was incredible with over 100 rennlisters signing up...this is a community so anything I can do to contribute is worth it. Hopefully I can keep the pace up as I start to build the engine up again. I have enough material for a few more threads while I wait for the machine shop to do their magic..and then its back to the wrenches again. Right now I am do the cleaning thing...

Cheers,

Mike

Toga

That's the kind of spirit that makes Rennlist such a great place!

KOAN

Mike,
This has helped me understand the problem better than anything I have seen. Forgive my ignorance. I have about 30k (10k track miles) and live in a non-inspection state. Will I hurt the engine, or cause power loss if I let that carbon accumulate, and ignore it?
By the way, the susp. parts you made for me are still serving me well.

g_murray

Lucky you for living in a 'non-inspection' state, but...

i) if they get clogged ...do you REALLY wanna drive around with the CEL on all the time (I see you've a '96 ..so yours is 'obd-ii -- and the clogging WOULD trigger the CEL). How embarrassing would that be?!
ii) if you ever moved out of state or (for whatever reason) your state DID mandate an emissions inspection ..you'd be in deep-doo-doo.
iii) if you ever wanted to sell the car ...see number ii) above.

Since our compatriots, in the UK, don't have this CEL-dilemma, I seriously doubt as to whether having them clogged would affect drivability etc. etc.

My $0.02

G.

KOAN

G.
I'd be less concerned if I knew the light were unimportant, as it seems to be. But, given the difficulty of the fix, and given the fact that my car is mostly driven on the track, I'd rather spend the money on performance enhancements. If I move out of state, I can worry about that if and when the time comes. As far as being embarassed...ironically, I drive my 993 despite what people think, not because of it. If someone rides with me and they are worried about the light...I'm doing something wrong!
Thanks for the info, though.