CIS Problem

[Red Fender]

I have a problem that I have created myself. My 2.7 was running perfectly from cold and would continue to run fine until I turned it off and left it for 10 minutes or so. It would restart fine, but backfired a little until it was fully warmed up again. I (wrongly) thought that I'd found the problem. Noticing that the allen head screws (with springs under them) that seem to mount the divider head etc were loose, I thought I should tighten them. I tightened the ones that were easily accessible, and strangely it improved the problem immensely. I should have left it at that, but when I had a bit more time, I removed the large rubber boot and tightened all the other screws. Then the car wouldn't start at all. I've now loosened them, but the car barely runs. I presume there is some sort of base setting of how tight the screws should be, but can't find any reference to those screws anywhere. Any knowledgable people have any advice please?

[tirwin]

What year?

US or RoW?

Can you post a pic of what allen head you’re talking about? Not following your description. I think you’re talking about the fuel distributor but not sure.

[boyt911sc]

Originally Posted by Red Fender

I have a problem that I have created myself. My 2.7 was running perfectly from cold and would continue to run fine until I turned it off and left it for 10 minutes or so. It would restart fine, but backfired a little until it was fully warmed up again. I (wrongly) thought that I'd found the problem. Noticing that the allen head screws (with springs under them) that seem to mount the divider head etc were loose, I thought I should tighten them. I tightened the ones that were easily accessible, and strangely it improved the problem immensely. I should have left it at that, but when I had a bit more time, I removed the large rubber boot and tightened all the other screws. Then the car wouldn't start at all. I've now loosened them, but the car barely runs. I presume there is some sort of base setting of how tight the screws should be, but can't find any reference to those screws anywhere. Any knowledgable people have any advice please?

Red Fender,

Inspect how the CIS rubber boot between the throttle body and air flow metering unit is mounted properly after you removed it. It is likely that you did not put it back correctly and causing a vacuum leak. Look closely that the edge or perimeter of the boot openings are completely over the lip specially the backside.

The Allen screws with springs that hold the air flow meter will not cause this problem. It is the CIS boot that is causing this problem. Go back and double check your work. Keep us posted.

Tony

[Red Fender]

Thanks for the replies. I am aware that the boot must be free of leaks and it is definitely tight. I have checked that.
In answer to tirwin's question, yes, I'm talking about the fuel distributor, however I can't find any pictures online of the screws I'm talking about so maybe there's something odd about it. I'll try to get pictures.
I believe it may be causing problems with the sensor plate height, but obviously, a little knowledge is dangerous and I've interfered with something that was 95% good before..

[T77911S]

^^^^^
the screws wont cause that problem.

also make sure you did not crack or tear the rubber boot.
there may be a hose connection on the back. make sure that is connected.

tony.
my memory is getting bad on the 911 stuff since I have gone 930.

[stlrj]

You likely do not have the boot on correctly. Seating the boot from behind is tricky since you have to do it blind. You'll know when you have it right soon as the engine fires right up.
It's not really a CIS problem more than a manual dexterity problem.

[E Sully]

The 6 allen screws with the springs under them should be tightened till snug, and backed off about 1 turn. There is a foam gasket between the plastic base and the air metering plate. If the foam has deteriorated it could cause an air leak. I have replaced it on mine.
It is also possible that one of the backfires damaged the plastic box creating an air leak.

[boyt911sc]

Originally Posted by E Sully

The 6 allen screws with the springs under them should be tightened till snug, and backed off about 1 turn. There is a foam gasket between the plastic base and the air metering plate. If the foam has deteriorated it could cause an air leak. I have replaced it on mine.
It is also possible that one of the backfires damaged the plastic box creating an air leak.

Ed,

Sorry to disagree with your post. Go over and inspect the CIS airbox. The cork or foam gasket between the air flow metering unit and the CIS airbox is not used to seal the air from entering the airbox. The underside of the metering unit is under at atmospheric pressure. Remove the air filter and do your investigation. The area behind the air filter area is at atmospheric condition and so is the bottom side of the air flow meter.

You can remove or eliminate the gasket without any adverse effect to the operation of the CIS. The gasket is simply for mounting and keeping dirt from entering the outer section of the airbox which under atmospheric condition. Backfire is not caused by the screws nor the gasket. You are barking at the wrong tree.

Tony

[stlrj]

Those spring loaded allen screws have nothing to do with vacuum leaks but the air boot does. If it helps, get a mirror and see what you can from behind.

[E Sully]

Sorry Tony, my quick answer seems to have caused a misunderstanding here. My response was meant as 2 separate items.
In my first line, since Red Fender had asked about it, I was just explaining the correct way to attach the air plate to the plastic air box And if you want to get picky, it is not atmospheric pressure but a vacuum. Also, yes it can cause a small amount of non-filtered air to leak if the foam is deteriorated. Since Porsche decided to use this method of foam and springs on screws, I would think they felt it necessary. Perhaps to prevent cracks in the plastic boxes mounts
I did not mean to confuse it with my second line, but to separately mention that since he has had quite a few backfires, this may have led to the possibility that there are cracks in the air box that can lead to un-metered air to enter the system.
On to the next part, which due to the backfires and possibly from age, there are a few areas that should be checked. The rubber sleeves under the airbox connecting to the runners, and gaskets to heads are a possible source, along with the rubber seals around the injectors. Leaks may have been existing already, leading to the backfires that may have caused bigger leaks.