g_murray

Ye velcum.
Do know, tho', that (and correct me if I'm wrong here folks) I read somewhere, that when the CEL goes 'ON' that the computer basically switches into "limp home mode" which, among other things, means that it enriches the mixture for starters (and with the price of gas nowadays....). Also, I also remember something about it 'ignoring' all the 'parameters' in its memory, that it has accumulated over the various drive cycles, and switches to a 'fixed known set of parameters' that is uses for such 'stand by' purposes.

Since your car is being (mainly) tracked, you probably have a bunch of engine/dme options installed that completely over-ride the 'backup' parameters that get invoked when the CEL is on ...so the standard 'limp home' mode may be moot -- since it's REALLY more applicable to street driving.

G.

tam993

Hi Mike,
Thanks for the post. I pretty much understand what's going on with the design now. I'm working on the last port passenger side forward. They didn't make it easy to clean without removing the cam towers.
I was using steel cable (different sizes) from the bottom of the car. They flex pretty good, you can get them to do a 90 degree if the bend is big enough. How ever I never got any of it past that mating surface between the cam tower and the heads. I thought may be I could get that last port from the top and be done with this.
From your pictures, I don't see how I actually could have done anything poking wire at it from the exhaust ports :-)) I suspect that crap I put down the gallerys freed things up, that and 125 psi.... I saw very little bit of carbon on the cables I was using to ream the ports from the cylinder head.
If I would have seen your pictures first I would have dropped the engine. I'm sure I could have been done a week ago.

Not much you can do with carbon that has hardened, except drill. I tried everything on the self.
I wonder what these shops use (chemical) to clean this stuff, or is it some trade secret... :-)
that berrymans chemtool b-12 was the only thing that seemed to work for me, all that other crap was a waste of money. Oh, one other thing worked! Carbon-off, $hits like paint remover! Safe on Aluminum. Washes off with water. That crap emulsified the carbon! Someone else needs to try that to make sure they get the same results. Took the slight build up off the exhaust ports and valves like new. Also made my jenair indoor grill top like new too :-))

The best tool suggestion was that blow gun thing someone suggested, I believe that worked the best.
After seeing your pictures I removed the feed tube and pressurized from the top. That way I was working on only 3 cylinders not having to deal with the exhaust valves open on the other bank and loosing air pressure (seemed to work well).
After doing all this, with my luck I'll have to drop the engine to do something else :-))
Then I'll go back to driving Ferrari :-)) just kidding....

Mike J

Maybe I will take another look at that interface between the heads and the cam towers to see how out of alignment the holes really are. If there is quite a displacement (and the carbon traces on my heads show that) then that could be a spot where the carbon can gather.....mabye two different teams worked on the problem at Porsche and they could only decided roughly where the holes should meet?

dutchcrunch

i have a question... seeing that the line are all the way in the back of the motor it is hard to see them unless you know what you are looking for. my point is whay cant you manufacture a line for the left and right side and plumb it down into the lower exhaust where the 3 pipes merge into one. all the computer cares is that the o2 sensor get a certain reading when its starts..... plumb it stealth like they run nitrious oxide. and be done with it. someone can make a kit and sell them for a resonable price. cant be that hard to do. all you would have to do is put a custom little end fitting in each exhaust header and run the lines. problem solved.

tam993

dutchcrunch.
exactly.
What kind of BS design did Porsche come up with.
We all would have been better off if you had been working at Porsche in the 90s.

Dan V

My MGB had the SAI ports in the engine at the exhaust valves. I believe the reason they aren't placed on the header is because the air needs the super-high heat in order to effectively burn off the left-over hydrocarbons.

tam993

the engine is cold when this thing runs for 60 seconds.
dumping the air into the begining of the exhaust would propbably work.
I think someone did a work around like that on this list

Mike J

Hmmm, I thought the idea was to introduce oxygen into the exhaust stream to help light up the cat's quicker than the lower oxygen content of exhaust. My understanding is the computer looks for a lean condition (i.e. low voltage) on the O2 sensors before the cat when the pump is going...that would signal that air was being pumped into the exhaust system. This is why the computer can only tell you which side of the engine is plugged because that particular o2 sensor is not running lean when the pump is running.

This is why the little circuit that was posted a few years ago works...it clamps the o2 sensor's output to ground when the pump is running. This fools the computer into thinking the signal from the o2 sensor is lean and the air is getting to the car just fine. From my point of view I would just wire up this circuit if I get into a SAI problem that I can't cleanout. But I like your idea but you would have to battle a bit on getting the air lines from the air distribution box in the rear of the engine through the side sheet metal down below the engine onto the exhaust system. But at least your idea does not violate and EPA regulations... ;-)

Cheers,

Mike

Luis A.

Mike,

I recall that circuit post but can't locate it through searching. Do you have a link to it?

Thanks.

Mike J

I don't have the thread but I do have the circuit...here you go..



I also posted this on the other SAI thread...

Cheers,

Mike

planeguy67

I was just talking to a mechanic yesterday who told me he knew someone that used OVEN CLEANER (you know, Easy-off) to clean the carbon deposits off a similar setup in a BMW!!!

I'm sure the highly caustic lye in Easy-off will do a number on carbon (after all, that's what's gunking up your oven), but I'm not sure how safe that stuff would be to use on aluminum engine parts.

And I agree with the rest of you, why the hell didn't Porsche just route the SAI tubing directly into the "cheap" heat exchangers vice snaking it through our very expensive engine castings???

jimwood

Anyone want to verify this statement or correct it. I would like to defer to someone who has definitive knowledge on the subject. Thanks.

Nonetheless, awesome job Mike. Don't know how you had the patience to do the job, let alone, take great pictures documenting it.

tam993

I used "carbon-off" to clean the build up. It worked, it's aluminium safe, and cheap.
It's used for cleaning burnt on grease and junk like that..... great stuff.
By the way the CEL SAI issue I had has been fixed now for a few months.
thanks, Mike J.

BrandonTR

This is a great thread and in my days of researching SAI P0140 code CEL light on my car the best visual of how these ports work on the car, so worthy of a bump. Man Rennlist is awesome.

Mike J

Jeeze - its been almost 7 years now - wow.

Interestingly enough, the Targa engine is still driving very strong. One small leak between the left cam carrier and the heads, but nothing else.

BTW, the whole rebuilding process is repeated on my web site http://www.pcarworkshop.com, its tighter with no comments...

Cheers,

Mike