CIS - Has anyone seen this before>

garmo · 11-20-2011, 10:02 AM

For some reason unknown to me I can't upload photos.

Last weekend I installed a new radio with Bluetooth and an Ipod connection into my '80SC in preparation for a road trip. I was having touble with the power antenae and blew a fuse a couple of times. After getting that sorted out and the radio working I went to move the car back into its space. It wanted to start, and did for about a second. Did that several times - no worky. With the blown fuse on my mind I figured something else got shorted. Checked the fuses and relays with no difference in problem.

Ran out of time to get it sorted out before my trip. Came back to it today after searching PP for a while. Went out to the garage and pulled the air cleaner off. The problem was immediately apparent. The pop-off valve has dislodged itself and positioned itself so that it jammed the air flow sensor. Pulled it out and the car started as usual.

Anyone else ever have this problem? Just one more thing to consider when having all of a sudden problems with CIS.

I am fairly certain I am following the correct procedures for uploading photos. Does anyone know of a link on how to do it? Maybe I just have a loose nut behind this keyboard.

garmo · 11-20-2011, 10:09 AM

Image for above post.

Vereeken · 11-20-2011, 10:49 AM

Your car started normal after you pulled the pop-off valve?

That would be one gigantic false air leak.

I pulled my CIs apart to rejuvenate it. I installed the pop-off valve about 6 years ago with epoxy.

It came out very easily. The epoxy had become hard and brittle. I am also guessing that the brittle epoxy created some smaller false air leaks.

I would think that way happend to you is not abnormal. In any case your airbox is still intact. I am guessing temps in Colorado have gone down so more chance of a backfire.

I have installed the pop-off again by using epoxy just to hold it in place and used a special hight temp silicone sealant to make sure I have no false air leaks.

Joe Bob · Joe Bob's Garage

Bad glue mix apparently....

garmo · 11-20-2011, 11:04 AM

Vereeken - once i pulled the pop off away from the air flow sensor, the car started. I just ran for a few seconds because I had the garage door closed. Put a heat lamp and heater near the air box and just glued it back on. Hopefully that will be that.

Yes temps are getting cold here - a few nights in the teens.

ossiblue · 11-20-2011, 02:59 PM

kind of hard to tell but does your pop-off valve sit flush on the bottom of the air box or do the ribs keep it a bit elevated? From the looks of the photo the lip of the valve doesn't appear to rest on the box. If so, it might be a good idea to remove the valve and carefully grind down the ends of the ribs to get a full seating of the valve.

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by ossiblue

does your pop-off valve sit flush on the bottom of the air box

Ossiblue - Is the design intended to have the larger step diameter sit on top of the flat plane of the box?

Mine does not, but I have an 81 with the added internal baffling that thwarts deep penetration. Mine is clearly elevated with only the smaller diameter going through the box.

Vereeken · 11-20-2011, 11:24 PM

I believe this pop-off valve sits too high. You need to cut away a good portion of the tabs so it can sink lower and rest completely on the bottom of the airbox.
Also make sure you can remove the spring from the valve by pushing it out. this means removing a tab all the way on the right hand side. You can the alos remove the top part of the valve which helps if you need to re-seal it after installation

The "internal baffling" you refer to does not intervene with that. The internal baffling are the channels for the Cold Start Valve. I am not sure when but somewhere in the 80s Porsche added some extra plumbing to the airbox which runs from the CSV to the six cilinders kind of like an octopus.

Michel

E Sully · E Sully's Garage

Bob,
Your valve is properly installed. It is not necessary to file away the ribs, just make sure it fits snuggly in the hole when glued.
Pelican Technical Article: CIS Pop Off Valve Installation
In my 1973.

ossiblue · 11-21-2011, 07:41 AM

Quote:

Originally Posted by Bob Kontak

Ossiblue - Is the design intended to have the larger step diameter sit on top of the flat plane of the box?

Mine does not, but I have an 81 with the added internal baffling that thwarts deep penetration. Mine is clearly elevated with only the smaller diameter going through the box.

As E Sully posted above, mounting the valve on the ribs is standard and if bonded well with a good epoxy, should not be a problem. However, many who have had valves blow off have taken the extra step to have the lip of the valve sit flush and since the PO had that problem, I suggested it. It's your choice and the rib-sitting valve should work just as well if the fit is tight and the adhesive is good.

Bob Kontak · Bob Kontak's Garage

Thanks guys. I do like the flush mount idea because of the larger surface for epoxy. The baffling in my 81 is pretty close to the bottom of the cylinder if you sank it in there on the 80-83 airbox. Too close from the standpoint of letting air out real fast.

In the link E Sully posted there is a comment way at the bottom about the interference in later CIS boxes.

I think if you went with the flush mount in these air boxes you would want to cut off a bit of the small diameter cylinder to allow air to flow out with ease

All of this said, my set up had been intact for the 16 years I have owned it so someone did a good epoxy job.