mstolo

You might want to read the current post running about top end rebuild "Why engine or top end rebuild? (Multi-page thread 1 2)". At least that will educate you on determining if you have a valve guide issue that might be causing the SAI ports to clog. I am basically t the same point you are at, but don't need an emission sticker as I'm in a rural area. I plan to do a leakdown test to see if valve guides and rings are ok. If ok, I plan to drop engine to do a bunch of maintenance, clutch, wires, distributor belt, etc. and clean out the SAI ports using the brake cable method while the engine is out, and hopefully not have to open up the heads.

Airhead 993

Thanks for all the advice. I am impressed with the helpful responses I received so quickly.

I would like to solve the problem, and not just kick the can down the road. I need to do some research so I can understand the details of the recommendations made. Then, I will talk to my mechanic about checking/replacing the SAI check valve, followed by cleaning the SAI ports. I assume that beyond these steps, further work would involve replacing the SAI.

While I routinely work on my old BMWs, I have not touched the 993. At least, I will be more informed when I talk to my mechanic.

kjr914

Along with searching the RL993 board archives, these are a good place to start:
http://www.pcarworkshop.com/
http://p-car.com/diy/diy.html

NP993

You should get a clear sense of how much oil your car is burning...depending on that figure, it may not be wise to spend money on the check valve and cleaning the ports, when the real problem is worn valve guides.

Jeff U

You might want to talk to the mechanic who works on my car. His name is Taylor Chapman and his shop is out near Dulles Airport. (Annapolis is not that far from Dulles) I have known Taylor for 16 years and he is the only one I let work on my car.

I had been dealing with the SAI & CEL for a year or so and was also coming up on the emissions inspection. Taylor has developed a system using a combination of solvent, plugs to block up the ports on each side to insure the solvent gets into both, and mechanical cleaning using some type of wire.

On my car, the ports on cylinders 1-3 were completely blocked and I was getting error signal P0140 from the OBDII.

He was able to clean out the blockage, get air flow through both sides, cleared the CEL problem, and most importantly I passed Virginia's emissions on Tuesday of this week.

He did some other work on the car at the same time but I think the bill for the clean out was somewhere around $750.

His shop:

http://www.taylorchapman.com/Pages/default.aspx

Jeff U

You cannot "replace the SAI".

The problem is the SAI system is designed to have air flow from the air intake through small ports in the engine block to the exhaust manifold. The ports through the block can get clogged triggering a failure signal from the OBDII.

The primary cause is worn valve guides which allow too much oil into the combustion and the resulting carbon build up. The check valve is supposed to protect the ports but tends to fail. It's not the best design...

The fix is to clear the ports; either in place with the solvent/wire method or dismantling the engine.

If you have to dismantle the engine you might as well do the top end rebuild.

It's that most expensive phrase of car maintenance: "as long as we are in there …"

Airhead 993

I want to wrap this thread up with an update. Based upon a recommendation in this post, I took the car in to Taylor Chapman near Dulles Airport. He successfully cleaned to ports out using the cable/wire method, and since then I have had no error codes - and the car passed the MD emissions check. The cost was about $1,000 for the work.

mstolo

Good for you! Congrats.

I have the same issue, and i'm half way of dropping my motor to clear the SAI ports and a bunch of other deferred maintenance, including the LWFW & clutch. So far, my compression test was favorable. I'll be doing a leakdown test once I get the motor out to see if I need to do to the heads or rings. Hopefully, I will only be cleaning out the SAI ports.

JB 911

That's great news airhead. I'm curious de he replace the check valve as part of that?

If not, there is a good diy thread a few lines down about how to do it yourself. The part is around $75.

JeffU > "The check valve is supposed to protect the ports but tends to fail. It's not the best design...
"

Can you please clarify that. Do you mean the check valve fails (likes get old and rusty)and the ports are no longer protected OR do you mean that is fails in general and doesn't protect the ports from the get go?

Jeff U

Fail as in the check valve gets old and rusty and it's also a pain to get to. My mechanic replaces them on a regular basis. I think he does them every 15,000 miles or so or any time he is doing work that gives him good access. The check valve is not very expensive.

The whole system is not the best design. Small ports running through the engine block which are subject to clogging.

Any system in a fairly expensive car that is prone to fail at fairly low mileage and can require a major engine tear down is, in my book, "not the best design".

JB 911

I understand the basic theory of the SAI system (and agree it is not the best design) but specofically what role does the check valve play in the system?

Jeff U

The check valve's function is to prevent back flow of the exhaust gas into the ports to protect the air pump and the fresh air system.

The problem is the ports are very small and susceptible to clogging. A failed check valve adds to the problem as it allows more exhaust gas, and it's associated carbon, into the small ports.

Here is a very good, with pictures, description of the system and the problem:

http://www.bodymotion.com/check_engine_light.asp

JB 911

Thanks Jeff. Great information.

More questions

Re this Q in their FAQ section

"Q: My check engine light is not on, what preventative maintenance can I do?

A: The system has no maintenance intervals, cleaning the lower ports is not advisable or recommended unless or until the problem occurs"

Seems like this is not entirely correct and that replacement of the check valve could be taken as preventative maint.

I was sad to hear a lot of his 100 cars were from Texas and Fl as I am in Texas. Since I don't have a problem yet I really want to avoid one if I can.

He suspects frequent start stops are to blame and perhaps the heavy ac usage that one would expect in Texas.

I am going to use ac but not a frequent starter stopper.

My understanding it is only on during cold starts is that correct? Or am I confused. Like if you drive 20 mins. Park. Then decide immediately you want to change parking spots. It doesn;t come on again right?

Lorenfb

Here's more info with pictures:
http://www.systemsc.com/pictures.htm

JB 911

Good stuff. Thank you.

Loren do you have a personal rec for frequency on replacement of the check valve and/or feel it is helpful or at least can't hurt?

One question about the link.

"4. We'd minimize that constant revving above 5K, i.e. high revving will NOT reduce the SAI problem but likely increase it.
Note: High speed driving, e.g. freeway driving, versus "stop & go" driving does NOT reduce the likelihood of SAI problems."

Re the "note" portion. I am correct to assume the stop and go portion is ok ONLY as long as it DOESNT result in higher op temps i.e engine tray off, limited ac if for prolonged times etc?

I have previously posted my theory that SOME original and early owners of the 993 may have prolonged oil changes due to cost. complexity of DIY, and Porsches own rec and 'trust' in synthetic oils. I am so glad my PO did engine oil changes on a significantly more frequent basis. Whew. And I intend to keep that up.