JasonAndreas

Well that sucks, it looks like we're stuck pulling the heat exchangers to look at the SAI passages as the only definitive way to check or finding someone with a really long scope $$$ (coherent fiber is about a $1000/ft and we'd need 3-4').

Lorenfb

"Jason... the readiness codes were all clear at the time of PPI, 85 miles before the CEL came on. In fact, Laura said it was great that that was the case. In there lies the problem... extremely difficult to diagnose SAI issues, even if the car has had a history of them."

1. If the PPI indicated that the readiness states were cleared/reset, that's an indication
that either the emission system has a problem or a CEL DTC (fault) had recently been reset.

2. By using the Porsche PST2 or its update, "Short Tests" can be run to check the SAI system and
other ODBII functions without driving during a PPI if the readiness states are not complete.

3. The SAI functionality can be determined by monitoring the voltage of the
front O2 sensors at a cold sartup. The voltage will drop to less than 100 to 200mv.
This is easily determined using an OBDII scanner.

4. The key determinant for a SAI CEL problem is oil consumption, whether it's the
the result of valve guide wear, or ring/cylinder wear, and the design of the SAI system.
The SAI cleaning only prolongs the inevitable. The likelihood of a SAI CEL increases
greatly as the oil consumption exceeds a quart every 1,000 miles.

5. As mentioned before, compression tests & leakdown tests will not provide insights
into a SAI problem. Also, trying to measure valve guide wear without pulling the engine
has questionable merit.

Bottomline: When purchasing ANY OBDII car ('96 or later), one must always check
the readiness states and monitor the real time data from the ECM using a scanner.
This should always be requested as part of the PPI.

Steve Weiner-Rennsport Systems

Loren is right on target on this issue. Great post!

I would just add that recently, I've seen some less-than-ideal leakdown figures from bad guides. These were SO worn that the valve was no longer centered over the seat and was really leaking around the edges. When they are REALLY worn, it can show up in a leakdown test. Ultimately, a competant & experienced mechanic can assess guide wear by wiggling the valve & spring assembly but this takes experience to do accurately.

After disassembly, we saw .120 of clearance between the factory guide and the valve stem (which was just in spec). This was the second time that we've seen excessively worn guides. Both engines had less than 40K on them.

Lastly, Porsche does not use a phosphorus-bronze material for the guides. I have no idea what it really is, but its VERY VERY soft and tears out quite easily. We've used the harder P-B guides for many years and have not had to redo any of ours, as of yet.

Mike J

Hi Steve, Loren :

My car has 75,000 miles and I have been getting misfire codes with a bit of a backfire noise from the exhaust. I took it in to get some diagnosis done....the mechanic did the usual tests and concluded that its likely that the valve guides were quite worn and the valves were not seating properly on the seats. Oil consumption is farily high but I don't have the numbers quite yet...am taking the measurements now.

Have any of you seen a rough idle or mild backfire exhaust noises associated with valve guide wear? I am trying to determine if I have two problems instead of one.

Cheers,

Mike


Thanks!

Mike

Laura

Loren/Steve

I have stayed out and let this play on, but you have interpreted something from a post wrong. Readiness flags were already set and ready for emissions testing when the car came to us. Diagnostics showed no codes in DME when the car was first brought to us. Car has 29K, no check engine light, no codes, no indication of SAI, had no previous paperwork showing any problems with SAI. Took car to test only station, passed smog. Completed PPI.

Previous paperwork and info from 1st owner has now been gathered and many things have come to light.

There has been so much discussion on this issue on this board without 100% of the information being presented in a clear concise manner. Bits and pieces, some items clearly out of context, assumptions being made without knowing the facts.... We didn't just fall off a turnip truck... Why would I say it was a good thing if the codes were cleared and readiness flags were not set? I know and understand the process with the PST, I am quite capable of using it in the shop and at the track, I know about readiness flags, short test, I understand the SAI and valve guide problem better than most, I have sat in on many conversations with techs from all over the US. There are some differences of opinion, but we are very confident in our repair method of these 2 seperate problems. We have been working on Porsche's only for over 25 years, my guys have over 90 years combined experience, and I know, for an independent, we see more 993's than anyone else in our area. I personally field 15 - 20 calls weeky regarding 993's from all over the US because of our success in this matter.

Trying to help someone diagnose a car over the phone without inspecting the car personally is very difficult, attempting it over the internet with words and phrases being misconstrued and misinterpreted (not intentionally) has just turned this into a nasty situation.

Laura
Hergesheimer MotorSports

Steve Weiner-Rennsport Systems

Laura:

Speaking only for myself, I've simply addressed this in a generic manner as indeed, I do NOT have this particular car here and no firsthand information about it.

My only intent is to offer some GENERAL constructive information, advice, and experience based on my 30+ years of working on these things.

Without question, I am no expert; I only offer my views based on personal, firsthand experience and that differs from shop to shop.

Once again speaking only for myself, no intent was ever made or implied that anyone involved was not qualified or competant to properly address the specific issues with this car so no words or erroneous conclusions should be drawn.....

My take on Loren's post (perhaps wrongly) was generic and informational in nature and I did NOT interpret it as specific advice for Jeff's car.

I reread this entire thread just now and I did not see anything that I wrote as off-base or "wrong". I meant no disrespect of any kind and I certainly hope you didn't read that as such.

That was NOT, by any stretch of the imagination, my intent.

Lorenfb

I agree with Steve. I only provided generic statements based on what the owner
and others had posted. In no way were my posts directed at any particular shop or
PPI.

Furthermore, if the PPI indicates that all the readiness states are set for
an emission test, i.e. the emission system is O.K. and there are no DTCs,
then the PPI was thorough from this aspect. Only when something appears
abnormal do further tests become necessary. A PPI is limited in scope and
the info it can provide, as is the shop performing the PPI.

Bottomline: These types of problems are inherent in the 964/993 cars. That's why
I own a 88 3.2. I have enough cars problems 5 days a week in my business and
don't need two more with my cars. A PPI can ONLY provide so much info on present
& potential problems for the prospective car buyer. Therefore, prospective car buyers
need to be aware of this and assume some responsibility. There's always a risk!

Additional comments are here ( www.systemsc.com/pictures.htm ).

Chuck W.

Laura....Steve Weiner-Rennsport Systems..... Lorenfb

I have NO mechanic ability. I know so little about 993 engines it is embarrassing. Because of my admitted limitations, I find these posts very important and educational. VERY VERY educational. The conversations that this type of post generates have done more to teach me about these engines than I could have ever hoped for.

For those of you that are well educated, please keep the professional and experienced lay opinions coming. I come to this board for them.