Steve Weiner-Rennsport Systems

[quote]Originally posted by RT7:
<strong>I only use Chevron super-premium w/Techron gas. Would this help?</strong><hr></blockquote>

Hi Ron:

Thats a good grade of fuel but it will not prevent this from happening, I'm afraid.

The best preventative is driving your car in the manner that Matt suggested,......take it to 6000 RPM twice a day and use a good fuel additive like Techron (large bottle) or LubroMoly.

LOL,...just because these engine's are well-mannered enough to poke around at low RPM, doesn't mean that its a good practice,.......

FWIW, a rough idle can be caused by excessive carbon buildup on the backs of the intake valves, fuel injectors, or a carboned up Idle Stabilizer Valve. The latter can be cleaned by removal and a thorough flush with carb cleaner.

Kevin Reilly

Curious what code the Hammer indicates when the light comes on from blocked air passages. My '96 suffered from frequent CE lights, almost always at idle when the engine was warm. Hammer always indicated random misfires, even after all plugs caps etc replaced after my 30k service. Car ran fine (no evidence of misfires).

But it hasn't happened in a couple of months now that I did a couple of Techron treatments and increased my daily drive to include highway level speeds.

Henry Graham

Arrrgh...

Carbon on the valves... It's always carbon on the valves!

My Ferrari Daytona is always breaking down and it has to be towed into my mechanic. My mechanic tells me that I need to really drive it hard, but I can't get it out of second gear in New York City.

My friends at the club all tell me that I should sell the Ferrari and get a Rolls Royce, but those are for old men. I'm a young playboy!

Dave Crellin

First off - I LOVED my car and still couldn't imagine not having some form of 911 after many years of ownership.

HOWEVER these engines are NOT bulletproof. I am looking down the barrel of $6000+ to have engine out, heads off, new valve guides, aux airways cleaned etc. I'm next on the list at my local specialist shop.

I bought the car with 28k on it, perfect running, have used Techron and Chevron all the time, use daily, rev high and take care of this machine. Now for the last 6-8k miles (now 42k) the noise of the valves and the burning of oil is getting worse and worse.

I did get the check engine light a while ago and had it checked and reset at said shop. It was the aux airway blockage. this was BEFORE I realized that I might have a claim against Porsche under the emmissions warranty.

Sorry to blab on about this, but carbon build up, valve guide wear etc can be somewhat prevented, but if a previous owner is shooting, these things are NOT bulletproof.

Steve Weiner-Rennsport Systems

Gentlemen:

Lots of good comments here & observations concerning carbon buildup, valve guides, and oil consumption!

Please let me just say that these carbon buildup issues are NOT indigenous to Porsche cars at all. These occur as result of burning unleaded fuels that contain MTBE, Zylene, Toluene, and other things that leave these residuals of combustion. Any other car you own suffers the same problems with this buildup on valves, injectors, and the internal passages in the head (if they use them).

Air-cooled 911's are as bullet-proof as human beings can manufacture, but one must keep everything here in proper context.

The only residual issues with 911's continues to be the material that Porsche chooses for their valve guides and frankly, its not too good. The 964 & 993 "fleet" has now aquired enough mileage that these problems are beginning to surface in the same fashion they did with their predecessors and the root cause is still the same. Even the latest and greatest GT-3 and GT-3R engines use that same material and these can stand replacement with a better alloy for this purpose. We have done a few of these engines and have noticed the same issues with premature guide wear.

Its just my opinion of course, but I would suggest that these two issues remain separate and one should not indict all 993's (or others) for the carbon issue. This is mostly fuel-related, and not really a design problem.

I would however, like to see and note how many European 993's have required decarbonization as their driving habits are different than ours.

tom_993

Hey Steve,
Would there be any value (or harm) to sustaining moderately high RPM, say 4,500 or 5,000, or even 5,500, for a few minutes? It’s not as high as redline, but it would last longer than a quick blip to 6,800 or so. Maintaining 4,500 or 5,000 would be pretty easy for those city bound cars that don’t get much of a chance to open up.

Thanks,
Tom

spinning disc

RennsportSteve:

your advice and comments are much appreciated.

thank you.

Mr Michael B

Its been on this forum a bunch of times...

Examples/Overview:

8-26-01 =This happened to my 96 993 c2 a couple of times and each time it was due to carbon deposits. My local shop had to do extensive and expensive cleaning on it. They happened around 60k and 80k. They think it might be because I don't let the revs go high enough and the gas brand I use. Even though I use brand name gas they told me to consistently use Mobil gas and to shift up at higher revs. It worked well for a while but now my check engine light at 97k is on again. I'll update you on what turned this on this time.

Nov-1-01 =...I've heard about the "carbon build-up" thing as well as an expensive dismantling and cleaning of the intake ports that MAY solve the problem...

Nov-4-01 =... Here is your problem. Your dealer is right it is carbon build up. The 993 has a port that adds air when you 1st start the car to offset it running rich. Thus the term "smog pump" This air port gets clogged with carbon. The dealer fix is to pull the heads and clean the carbon out. Expensive. I would not pull the heads on my car unless I had to. I'm not sure what the Ca. emissions test consist of but the car will probably pass any test when warm. The problem occurs when the car is cold. You may want to talk to a knowledgeable after-market guy about this...

Then there is this WHOLE thread from 4-27-02

<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=3&t=003261" target="_blank">Best one yet - click here</a>

etc., etc., etc.

Man, I feel like a real car geek now.

BTW... Hey 1995 owners... Lets hear it for the little $700 wire loom issue. I will take that anyday over this stuff!

Just kidding VarioRam boys

tom_993

[quote]Originally posted by Michael B.:
<strong>
BTW... Hey 1995 owners... Lets hear it for the little $700 wire loom issue. I will take that anyday over this stuff!
</strong><hr></blockquote>

Totally!

What I don’t understand is why the ’95’s are immune. They have a smog pump, just like all 993’s. I also don’t understand how a fuel additive can clean out the air passages that the smog pump uses. There should be no fuel in those passages. As for Steve’s comment about European cars, apparently (from all the other threads on this issue) they don’t have this smog pump.

Steve Weiner-Rennsport Systems

[quote]Originally posted by tom_993:
<strong>Hey Steve,
Would there be any value (or harm) to sustaining moderately high RPM, say 4,500 or 5,000, or even 5,500, for a few minutes? It’s not as high as redline, but it would last longer than a quick blip to 6,800 or so. Maintaining 4,500 or 5,000 would be pretty easy for those city bound cars that don’t get much of a chance to open up.

Thanks,
Tom</strong><hr></blockquote>

Hi Tom:

Go for it, Sir. Accelerating hard to 5500 RPM through 4th gear is good for it,..

RT7

[quote]Originally posted by Steve Weiner-Rennsport Systems:
<strong>

Hi Ron:

Thats a good grade of fuel but it will not prevent this from happening, I'm afraid.

The best preventative is driving your car in the manner that Matt suggested,......take it to 6000 RPM twice a day and use a good fuel additive like Techron (large bottle) or LubroMoly.
</strong><hr></blockquote>

Thanks Steve!! I guess it's time to exercise the beast. <img src="graemlins/xyxwave.gif" border="0" alt="[bigbye]" />

Steve Weiner-Rennsport Systems

[quote]Originally posted by tom_993:
<strong>

Totally!

What I don’t understand is why the ’95’s are immune. They have a smog pump, just like all 993’s. I also don’t understand how a fuel additive can clean out the air passages that the smog pump uses. There should be no fuel in those passages. As for Steve’s comment about European cars, apparently (from all the other threads on this issue) they don’t have this smog pump.</strong><hr></blockquote>

Hi Tom:

The 95's (USA & Euro) do not have those tiny air passages in the heads that the USA OBDII, '96 and later cars have.

You are correct, Techron and other additives will not loosen or remove any already baked-on carbon in those passages, all they do is help prevent it by reducing the amount of deposited carbon in the first place. Fuel additives are meant to clean the backs of the intake valves and injectors, they will not do much in the exhaust ports or in those air passages from the air pump to the exhaust port.

Now,.....that air pump on the OBDII cars is meant to help get the cat temperature up to normal as quickly as possible and if one drives the car moderately after a cold start, this will really help reduce how long the air pump needs to run (heats the cat quicker). This reduces the occurrances of carbon buildup.

In short, people ought NOT to idle these cars after a cold start and simply drive off being prudent to keep the RPM under 4000 until the oil temp guage has registered at the bottom of the normal range. This warms the engine quicker and also results in less fuel dilution.

Hope this helps,

Pete in DC

Wow this is a blockbuster thread, but having just had my ride diagnosd with some blockage, I am interested in why Porsche ate the labor on this fix in some cases (as posted above).

So I ask posters: was this under warranty, used car certification, or...? I think I'm covered on my two-month-old 96.

Thanks.

John S.

This is certainly an interesting thread, esp. to me as I just picked up my '96 a month ago. I've been away all the weekends so I haven't gotten to drive it much. It's funny because most Porsche people I talk to have said for years to just drive the things - and not baby them. It seems this carbon build-up would be helped by that as well. I'll certainly also use some additive before my next oil change.

The funny thing is that I'm sitting here at work worrying that carbon is building up as I type and I'd better get out and rev the engine as soon as possible (I guess I always feel like that) .

Tom T.

[quote]Originally posted by Steve Weiner-Rennsport Systems:
<strong>Air-cooled 911's are as bullet-proof as human beings can manufacture, but one must keep everything here in proper context.

The only residual issues with 911's continues to be the material that Porsche chooses for their valve guides and frankly, its not too good. The 964 & 993 "fleet" has now aquired enough mileage that these problems are beginning to surface
&lt;snip&gt;
</strong><hr></blockquote>


Hi Steve,

Is this why Porsche now recommends Mobil 1
0W/40?

Tom