Lorenfb

"Correct, the check valve is upstream and when it works correctly, it should prevent gases from flowing throught the SAI conduits. If the exit point for the gases is blocked. then no gases can flow through the conduits, correct? Just like a diode in an electrical circuit."

Take a look at these pictures ( www.systemsc.com/pictures.htm ), especially the one
of the head, and please discuss how the valve will prevent carbon buildup from this point
back to the valve. I took these pictures at one of my customers during a valve job on a 993.

Ron

"8. We'd avoid (or further research) shops which claim to have a "quick fix" for cleaning the secondary air passage, as the passage is very inaccessible."

Systems Consulting
Automotive Electronics


Loren,

What do you think of the method for cleaning the passages outlined in this thread? I ask since I reviewed the link you referenced above and see at the time that you had not really expressed an opinion, at least as it related to a "quick fix", which I'm not sure what that would be.

Of course I don't know how long ago you expressed the opinion in #8.

Luis A.

Loren,

I'm trying to imagine, since I've never seen them, what these SAI conduits' path is like. It looks to me like they are each a tunnel bored in the head and cam housing and snaking around, one for each cylinder, all emanating from the the point where the check valve goes into the cam housing.

Your question is the crux of the matter: How exactly does carbon develop in these passages if only clelan air from the air pump passes through them?!?!

All I can think of is that 'dirty' air, or combustion gases, backflowing from the cylinders and in time, especially in cars burning more oil than usual, they fill with crud as your pictures show. Backflow couldn't occur if the check valve seals off air flow coming from the cylinders back to the air pump, i.e., the wrong direction.

Lorenfb

"All I can think of is that 'dirty' air, or combustion gases, backflowing from the cylinders and in time, especially in cars burning more oil than usual, they fill with crud as your pictures show. Backflow couldn't occur if the check valve seals off air flow coming from the cylinders back to the air pump, i.e., the wrong direction."

The gases with carbon still flow in the passages all the way back to the check valve,
even though the check valve is closed.

"What do you think of the method for cleaning the passages outlined in this thread? I ask since I reviewed the link you referenced above and see at the time that you had not really expressed an opinion, at least as it related to a "quick fix", which I'm not sure what that would be."

It's a good solution which some of my customers have started to do. The key, though,
is the extent of the oil burning. For those engines which don't burn oil excessively
(much less a 1000 miles per quart), it's probably a good alternative to an engine
disassembly and a valve job.

__________________

Ron

To actually brush out some of the carbon in those little air passages above and behind the exhaust valve you can use the tool below. It's just a brush, bent to the correct angle, which is use to clean the barrel of an M-16, which I guess makes it about 5.56 mm or a little larger.

jz993

Wow, what a great thread. Thanks to all.

DJF1

Great stuff!!!!!!!!!!!!!

Rob Kwate

I just got an email from Joel Reiser from the technical section of the PCA website, and he says not to use Techron, since it is made for the fuel system. Instead, he says to use two cans of carb cleaner. Though my car didn't suffer any ill effects from using Techron, I think we should listen to Joel. Afterall, he did pioneer this procedure. I may have been the first DIY'er (or at least the first to write it up), but Joel came up with the idea in the first place. It might be worth dropping him a thank you note either here or on the PCA site. Also, Joel recommends flushing the passages every 15,000 miles so that they don't get completely plugged up and become impossible to clean out without removing the heads.

I'll be the first to thank Joel: Thanks, Joel, not only for coming up with this idea and promoting it when others criticized you, but also for walking me through the procedure and giving me the peace of mind that the darn check engine light isn't going to come on at any minute.

Take care everyone, Rob.

jmreiser

Hey Rob- You know, there has been a LOT of talk about this stuff, but as far as I know, you are the first one that actually DID it. I was out there saying it should pe doable, it should work, and taking some flack for it too (dealers still have some clout, let's put it that way). Now if it gets too far along, as I think you know, the ports clog solid and have to be drilled out hard (on a drill press, with the engine apart). If someone follows your procedure on an engine that's that far gone, they may blow out the chewing gum if at least one port is clear and at least one is blocked. If they are all blocked, they will get all of the Techron or Carb cleaner all over themselves up top. You warned 'em. At that point I think they can go ahead and panic, and plan for a top end overhaul. I don't think Techron is bad for it, it should be fine. I would just use the carb cleaner given a choice, and use the Techron in the fuel if & when needed.

Best WAG (wild axe guess) is that every 15k miles should be quite safe. We don't hear of too many cars failing smog with SAI issues with much less than 30k miles, and most seem to be more like 50 to 60k, gut feel. I can't imagine having it clog solid in 15k, unless it was all bumper to bumper daily commuting in a hot weather tier-1 (big) city. I don't think they sold enough Tiptronics for that though.

Anyway, great job, not only on the writeup as noted, but on having the actual gumption to get in there and DO it. Salud!

JasonAndreas

If the ports are clogged solid with encrusted carbon as a last resort before rebuild (and drilling) there is a cleaning solution called Sokoff that should work (its basically methylene chloride in gel form). You brush the stuff on and over a period of several hours it will dissolve the carbon. Most commercial restauraunt supply stores should sell it; we use to use it for cleaning woks.

jmreiser

Hey Jason- Interesting. But I don't think you can get it in far enough. It is not the outlet of the port that is the problem, it is the series of passageways feeding it. To get to the port, there is a straight run of an inch or two at very small diameter. That is the part that gets drilled out on a drill press if it is too late. But it gets worse. Above that there is about a 90-degree angle joint where this last passage is fed by the previous one upstream, in the cambox. That is where the actual soot starts to accumulate, is right at the joint, which is oval shaped, almost like a funnel. We've taken engines apart for other reasons (to make race motors) and seen it starting to collect and solidify right there. So if you can get that stuff in there, it might just work. Maybe we need that Techron after all as a solution to carry this stuff down in there. It may take days and days and repeated applications to work down all the way through. But that would be spectacular if one of the hopeless ones could be fixed in car this way. Any takers?

Joel

cosmic_993

what about using seafoam for this cleaning agent? you can put that in the gas tank and the oil.

also, there is a write up in Excellence by Tony Callas on this issue, with pictures of the engine torn down and plugged.

FlatSix911

Take a look at the article in Issue #191 May 2011 of Excellence Magazine for some great information:

Tech Forum - 993 secondary air injection systems. By Tony Callas and Tom Prine

skl2

I can't get the photos to work..anyone know if they are hosted somewhere else or did anyone save a PDF they can email me...thanks.

jmreiser

Wrong pipe. The cleaning can't be done through the fuel or oil system. Those are separate systems. The SAI system is a separate system which blows air into the exhaust ports. The cleaning process includes removing the exhaust headers and some stuff on top the motor so you can pour solvent into the SAI system. Even so, if the car has gone too long before cleaning, like much more than 30k miles, you would need to rebuild the top end as Tony Callas explains.