the_buch

I have searched, but not found, any attempts to comprehensively correlate possible contributors to this infamous problem(s). There is clearly a strong consensus around the implications of heat, and I know there is some speculation that the '96 cars are somewhat more susceptible, but the sample numbers are so small and the older cars are just more likely to have more miles on them that it is hard to be conclusive.

I wonder if someone who is really good with stats and knows how to set up a poll could ask listers a set of questions to try and relate the mileage (or intervals) at which this problem occurs to variables such as fuel type or octane, typical running temperatures, use of motorsound or drilled out airbox, aftermarket or stock exhaust, etc.?? Contributors to this database should include those that have had the problem(s) and those that have not had it.

I appreciate that this topic is pretty regularly flogged, but as a new owner I would love to have more insight to work with.

Regards,

Ray Calvo

Don't drive it daily to & from work, let it warm up thoroughly when you do take it out (about 1 hour) and give it an "Italian tune up" every weekend with an occassional Techron fuel treatment and you should be fine.

Terry Adams

Doug, it looks like too many variables acting concurrently on such a small population, let alone those willing to respond to the poll. The only correlation I could see is: valve guides wear as miles accumulate, faster with high temps. Guide wear leads to increased oil consumption, which leads to clogged SAI ports. I concur with Ray, though it only takes me about 15 minutes to warm up my oil.

SCMomentum

Using one of Ray's favorite lines....."check the archives"! Not necessarily true. Some folks have had this issue without excessive oil burn. To me this issue carries with it alot of speculation without any really hard facts. Some things are known and some are not, but one thing is certain.....this problem is a defect that can become quite costly and burdensome.

I remain hopeful that as this issue continues to surface and grow that it gets solved. There are alot of really, really smart people here in the 993 community that will eventually devise a more "user friendly" solution for this.

the_buch

SCMo and Terry ... this is exactly what I mean - "this issue carries with it alot of speculation without any really hard facts", and even some conflicting direction ... and the experiential data is all over the place.

Ray ... this is my everyday working car, so off to work in the morning it is ... fortunately, it's a 30 mile 45 minute commute with a mix of city and highway and the occassional 'tuneup' opportunity :-)

Regards,

Terry Adams

Dang, I forgot the "lazybones" part of Ray's advice. The data are indeed all over the place. Mine is just one data point, and an opinion.

Adrienne

Doug -

Here's another data point -- My '96 has been a daily driver in Houston and Austin, Texas, so definitely HOT conditions. My SAI ports were nearly completely clogged when we replaced the valve guides at 110k miles. I was burning about a quart of oil every 600 miles.

According to several shops I have spoken to, the SAI ports will require regular maintenance and cleaning, regardless of replacing the worn guides. They will need to be cleaned mechanically because the design of the port allows carbon to build up easily. So the direct correlation of clogged SAI ports and worn guides seems false. Apparently worn guides speed up clogging, but they will clog over time regardless of valve guide condition.

My current plan of action is to use Techron regularly and budget additional track time as part of my SAI port maintenance program (it's a great excuse, ain't it?!?!). However, I still don't understand how SAI ports are cleaned via "Italian Tune-up" since the ports are only open when the car is cold.

Arrwin

I am curious on what % of people that track their cars get the CEL. If it fact, an "Italian tune-up" alleviates/prevents clogged ports, there should be very few or no cars that are tracked (frequency?) that will have clogged ports.

Could very well be my imagination, but my car felt better, more "clear" (less gunk in the system?) after a track day.

Seems like most ppl that have experienced the CEL problems are daily drivers, with no tracking of their cars in hotter climates. Of course, I have no hard facts or statistics to prove this, but just seems like the trend from the messages on this board.

Lorenfb

"However, I still don't understand how SAI ports are cleaned via "Italian Tune-up" since the ports are only open when the car is cold." - Adrienne -

That's correct! It's total B.S. that high revving prevents/lessens the SAI problem.
If anthing, it ACCELERATES it, because of the increased valve guide wear & additional
oil burning.

trojanman

as someone who's been unwittingly thrown into the deep end of this pool, just my $.02...

valve guide wear contributes to the SAI issue, but is likely not the primary culprit. i think that award goes to both bad design of the ports as well as the infamous check valve. my car has 40k miles and is getting a new top end in two weeks... significant SAI port clogging with CEL, and 20 mm of play in my exhaust valves.

i think another thing that makes a poll regarding this subject difficult is the inconsistency of ownership associated with these cars... how many of us are original owners? I'd guess less than half. To have really good data to feed into the system, you have to know the history... plainly, many of us just don't.

SCMomentum

Below is a thread that I copied to a Word Document a little while ago. It makes for some good reading regarding this issue....especially the heat build-up side of the argument. FYI....

Dave
```````````````````````````````````````````````````````````````

Issue:

Whether the 993 has abnormal oil consumption compared to older Porsches and if so what is the cause,
since secondary air injection (SAI) can be a major problem, i.e. which results from carbon buildup from oil burning,
for some '96 and later Porsche 993s with OBDII systems & causes a CEL (check engine light) with fault code 0410.

Facts:

1. The 993 is the most powerful recent Porsche air cooled engine, and as such runs the hottest, i.e. assuming
that the air cooled engine efficiency is unchanged from the 3.2 and 964, which can lead to accelerated engine wear.
2. The valve guide/guide material is different for all three air cooled engines (3.2, 964, 993), and Porsche has not
updated the 993 valve guide. The valve stem on the 993 is 8mm versus 9mm on the older engines.
3. Porsche recommends an oil change interval on the 3.2, 964 and 993 of 15,000 miles.
4. Both the 964 and the 993 use a lower body pan affecting air flow to/from the engine.
5. Stop-and-go driving in heavy traffic causes an air cooled engine to run very hot.
6. The quality of the machining, it appears, (initially and at valve job time) is more critical on the 993 versus
the 964 and 3.2.
7. The very small air injection passages on the 993 are prone to fairly easy carbon buildup restricting air injection flow.
8. All Porsches engines can tend to burn some oil early on versus other types based on many factors, e.g. the driving
conditions, the valve guide material/seals, and its basic design (high revving).
9. There are non-OEM valve guides being used by some machine shops when valve jobs are done on the 993 and
other Porsches.
10. The late 993s use a light weight synthetic oil versus the 3.2 and 964 based on Porsche's recommendation.
11. The secondary air injection at the exhaust valve guide may result in higher temperatures (lean condition) for
the exhaust valve guide versus no air injection.
12. Continued high engine RPMs accelerates engine wear, i.e. Energy loss (heat/wear) = rpm x friction
13. Infrequent oil changes can cause ring sealing problems, i.e. ring-lands fill with carbon and slug, resulting in
poor oil sealing at the oil ring causing excessive oil burning.
14. Many 993s with 50K or less mileage are requiring valve jobs.
15. Other OBDII cars experience the SAI problem, e.g. Mercedes Benz.


Conclusion:

There doesn't appear be any total consensus as to what is happening either from dealer or independent techs.
One key fact does standout; valve jobs are being done at a much lower mileage for the 993 than for the 3.2 and
964 engine. Excessive valve guide wear does appear to be a major contributor to the oil burning on the 993, but its
cause is at issue.

Some techs feel that the oil burning for the 993 is about the same as for the early engines, but the secondary air
injection problem magnifies it requiring a valve job much sooner. Other techs feel that the 993 was pushed to the max
causing excessive heat resulting in increased valve guide wear. Still others feel that infrequent oil changes (15K plus)
have caused excessive oil burning.

One of our customers is doing two 993 valve jobs. One engine has 107K on it and has had two previous valve jobs
(He did neither). The other engine had a valve job done by a dealer 2K miles ago and now has valve seats coming loose.
This was, more than likely, a machine shop quality problem.

There's not a clear cut answer to this problem without more data. Some facts mentioned above may contribute little
to not at all by themselves. Maybe a number of them, when integrated, cause major problems. Even if a new valve guide
material were used, there's no way without major testing to determine its long term positive or negative effect on the
993 engine, i.e. given that it's the single cause of the problem.

Each 993 owner must assess his own driving and maintenance habits. Without more data, the only answer we have is based
on how we would drive and maintain a 993 if we owned one:

1. We'd change the oil & filter at 7500 miles (Porsche's 930 oil service), e.g. for better ring & valve guide life.
2. We'd probably remove the lower body pan if we did a lot of stop and go driving in hot weather.
3. We'd TRY and avoid using the A/C in stop and go hot weather, as this heats the engine more.
4. We'd minimize that constant revving above 5K.
5. We'd monitor our oil consumption. Greater than 1.5K to 2K miles per quart would not indicate excessive oil burning.
If the secondary air problem does occur, then it's NOT a valve guide problem but only an inherent air injection
design problem or a failed part within the secondary air injection system
6. We'd use the heaviest weight synthetic oil (equiv. to 20/50 in a standard oil).
7. If a valve job is required, We'd assure that good referrals are used to select a dealer or independent shop.
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
SAI Passages With Carbon Buildup


________________________________________
copyright © 2003 Systems Consulting

the_buch

This stuff from Automotive Electronics is compelling. There is reasonable consistency on prevention, except for the engine revving bits. For now, I am going to get an auxiliary oil cooler, change my oil every 5,000miles, use a bit of techron from time to time before changeouts, and if I every need a top end do lots of homework to find the best alternative valve guide material to OEM.

Thanks,

chris walrod

Technically, the portion of the SAI ports that typically occlude (local to the SAI port at the exhaust port), are open all the time. They are open back up to the one-way valve, or SAI check valve via a creative mixture of casting and hard line passages.

Italian tuneups may indeed help keep such passages clear. This from increased positive pressure at the exhaust port at higher RPM's, that in addition to increased cyl head temps, which could aid in burning-off unburnt oil. Me thinks.

As for valve guide life, I feel rocker to valve stem geometry does play a role in lateral loading of the valve stem, which will wear the softest material of all components involved, ie. guides. FWIW

Lorenfb

"They are open back up to the one-way valve, or SAI check valve via a creative mixture of casting and hard line passages."

"Italian tuneups may indeed help keep such passages clear. This from increased positive pressure at the exhaust port at higher RPM's, that in addition to increased cyl head temps, which could aid in burning-off unburnt oil. Me thinks."

- chris walrod -

Without an air pressure exit point, the effect of the exhaust gas back pressure has little
to no effect on cleaning the SAI ports. It only forces more carbon back up the passages
and continues to pack/compress it.

chris walrod

[QUOTE=LorenfbWithout an air pressure exit point, the effect of the exhaust gas back pressure has little
to no effect on cleaning the SAI ports. It only forces more carbon back up the passages
and continues to pack/compress it.[/QUOTE]

Definitely a valid point, now that I gave it more thought.