austin944

I had a recent conversation with a mechanic at a nearby shop which was recommended to me, and it brought up a few questions.

The mechanic claims that the secondary air injection ports get plugged due to infrequent oil changes. They claim that the factory recommended oil change interval of 15K miles is too long, and that a shorter interval is called for. Supposedly the oil gets very "dirty" and acquires sludge quickly, and this is the reason for the blockage. This is the first time I've heard of this cause. Does it sound reasonable?

I've seen 2 cars where the rubber trim around the front bumper cover was sticking out a little or looked uneven. They say this is evidence of repairs/paint to the front end. Again, sound reasonable?

kary993

Can't comment on the oil change sludge blockage topic.

I can comment on the front bumper looking uneven. I have never had anything hit my front end and have some uneven looking molding and alignment of the bumper since it was brand new. I have looked over the years at other 993's and some do have the same problem and others do not. It turns out that my rear right fender is a bit lower and closer to the chassis than the left rear fender. I have been told by some factory folks that is normal for 993's. They vary somewhat from car to car. Anyone else hear this?

24FPS

not always true re: the rubber piping... sometimes a 'dumb' detailer can just poke it in w/ a q-tip & cause it to look uneven, etc. "they" is wrong.

re: evidence of being hit... do a search, that topic is covered (checking under carpets, door jams, etc). also, put the p-car up on a rack & have a good look... that will usually tell about the car. ---- also, ppi's are done for a reason. bol.

Edward

austin944,

Every 993 I've had a chance to admire closely had little variations such as the rubber you mentioned. Mine, for example, keeps wanting to creep up a bit in a couple of spots and in other spots, it just sits deeper but never moves. Chalk it up it age of the car, variations in body moulding, gaps, waxed car, alignment of the planets,.... Real evidence of accident or body work should be checked by someone with experience with paint/body.

As for the mechanic's explanation of the air inj. ports, I do not believe he is correct. As a matter of fact, I think he's completely wrong because those passages are AIR passages that lead to the combustion chamber, and are solely for smog-compliance (helps the engine burn cleaner when the engine is stone cold and running under cold-rich conditions). Thus, NO oil should be playing around in that area, regardless of how often or seldom one changes oil. If oil is causing blockage there, then you've got problems with worn valve guides --evident by high oil consumption. The blockage is typically due to carbon buildup, a normal by-product of combustion. This typically has caused much consternation among 96+ owners since their OBDII systems monitor these passages and sends up a check-engine light. 1995 OBDI systems, though, do not monitor these passages, so no "Fault" is registered, even though the same thing is happening to 95s. There is LOTS of info on this subject; I just gave you a taste of it here. Do a search and you'll find lots of foks here who will know more about this issue. I am assuming you're looking to buy a 993 and looking for a shop for a PPI? You may want to ask around on this board. Hope this helps.

Edward

austin944

Thanks for the replies. I've been reading the board extensively and know about the CEL issue but hadn't seen this mechanic's opinion supported here before so that's why I asked. They came recommended on the Pelican Parts board by two different people.

Something rather curious happened when I called this mechanic. I asked about scheduling a PPI with them, and it turns out they had already seen the car. Then they proceeded to give me the results of the PPI. (I didn't ask for it).

Considering that some other potential buyer spent their money on the PPI, isn't it unusual for me to get the PPI results for free?

993Maineiac

Austin944,

First things first, I'm a UT Ex-long long time ago- so give my regards to your great town.

When I bought my 944 I went to the mechanic who had been servicing it for years in lieu of, as it turned out, a PPI. Actually I was too in love with the car, and too naive at the time, to have considered the need for one. He spent a great deal of time discussing the car and showed me all of the maintainance bills. No charge, although I did of course use his services after the purchase. So its not unheard of for a mechanic who is familiar with the car to share his knowledge with a prospective buyer. If you don't trust him, or just to be safe, have a PPI done elsewhere. There is never harm in being safe before spending $.

Al

Jim @ EuroWerks

If someone did not change oil like they should, it may amplify the possibility of the problem. However, to me this was the only downfall of the 993. Years ago I worked in a reman facility and remember having to air chisel carbon out intake manifolds. Also when in porsche training when we went over small injection ports running thru heads and cam housing I told them about what I had seen from old domestics. Ofcourse they told me I was crazy for worring about that it would never happen. As far as preventing it I don't know if fuel injection cleaner does anything past combustion. What we need at this point is a chemist. I think changing oil regularly will help but I also think running better fuels with detergents already added would also help.

Lorenfb

Here's my post to Rennlist a few months ago:

ISSUE:

Whether the 993 has abnormal oil consumption compared to older
Porsches and if so what is the cause, since secondary air injection
is a major problem, i.e. which results from carbon buildup from oil
burning, for some '96 and later Porsche 993s.

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
reving).
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.


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 my 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 was 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 I have is based on how I would
drive and maintain a 993 if I owned one, which is basically how I
drive and maintain my 3.2:

1. I would change the oil & filter at 7500 miles (Porsche's 930 oil
service), e.g. for better ring & valve guide life.
2. I'd probably remove the lower body pan if I did a lot of stop
and go driving in hot weather.
3. I'd TRY and avoid using the A/C in stop and go hot weather,
as this heats the engine more.
4. I'd minimize that constant reving above 5K. I wind my 3.2
above 5K often but not from every light nor on every twisty.
5. I'd monitor my oil consumption. Greater than 1.5K to 2K 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.
6. I'd use the heaviest weight synthetic oil (equiv. to 20/50 in
a standard oil).
7. If a valve job is required, I'd assure that good referrals are
used to select a dealer or independent shop.
8. I'd avoid shops which claim to have a "quick fix" for cleaning
the secondary air passage, as the passage is very inaccessable.


The lastest issue of "Excellence" magazine (5/2004, pg 18) has
some good insights.

Good Luck
Loren
'88 3.2

Speedraser

I've read everything I can find about valve-guide issues, and I think it is inaccurate to say that 993s require valve jobs at lower mileages than 3.2s or 964s, UNLESS you mean the reason is the secondary air passage issue. It is well known that some 3.2s wear their valve guides prematurely, as do some 964s (hence the whole issue about removing the underpan). Some techs I've spoken with say that the 993 in general has shown less of the valve-guide problem than the 964. I know of several high-mileage 993s that have had no top-end work and use little oil. My 993 is only at 54K miles, and it uses a quart in 3000 - 4000 miles. Of course, since it's a '95 I don't know how clean or dirty the secondary air passages are.

Lorenfb

Maybe it can be better summarized as follows:

The probability of requiring a valve guide replacement at about 50K miles
or less is greater for a 993 than the 3.2 or 964 engine because of many
factors, one of which is a carbon buildup in the secondary air passages.
This probability varies based on how each car is driven and maintained.

Have Fun
Loren
'88 3.2