Correct Air Box # for 1976 911S (CIS)

[Kansas 914]

I have seen two different part numbers for the air box for a 1976 911S (2.7L CIS) and am trying to confirm which one is correct.

I looked in PET (page 75/565) and am using my model identifier as 911.82

It lists 911.110.904.00 and 911.110.904.01

I had a big back fire when starting the car and it blew the pop off valve apart. Hopefully I haven't damaged the air box but want to be prepared.

It was a pretty big bang!

[Kansas 914]

[Jim2]

What's the status of your airbox, was it cracked?

[Kansas 914]

Originally Posted by Jim2

What's the status of your airbox, was it cracked?

Too early to tell. I managed to remove the old pop off valve. I might try to install a new first.

The screws in the air box (slot heads) are not lifted so I might get lucky.

I will update as things progress.

Thanks!

[Flat6pac]

Replace the pop off valve see. If you can get going. I have seen them blown out from lean ignition or mid fire.
I have a couple 80/83 s sitting on the shelf if needed.
Bruce

[Kansas 914]

Originally Posted by Flat6pac

Replace the pop off valve see. If you can get going. I have seen them blown out from lean ignition or mid fire.
I have a couple 80/83 s sitting on the shelf if needed.
Bruce

Thanks Bruce!

I got the old POV out this morning and will put the new one in (enroute).

The back fire was while attempting a cold start Saturday morning. The car runs great otherwise - oh yeah there is the idle surge when warm. I think it is a vacuum leak but haven't traced it down.

[Kansas 914]

Originally Posted by Flat6pac

Replace the pop off valve see. If you can get going. I have seen them blown out from lean ignition or mid fire.
I have a couple 80/83 s sitting on the shelf if needed.
Bruce

Hi Bruce,

I replaced the pop off valve and the car will "start" but not "run". Is this indicative of a blown air box or fuel delivery (which may have cause the lean back fire)?

Video here: https://youtu.be/vaA44-K30QA

[Flat6pac]

Check the air box seam around front and left side
Then check fuel pressure across the center of the fuel dist and the warm up regulator
Cold you need about 35 psi, just for info. The longer the ignition is on the more pressure will raise.
Suggest you U.N. plug the WUR to test.
Bruce

[Kansas 914]

Originally Posted by Flat6pac

Check the air box seam around front and left side
Then check fuel pressure across the center of the fuel dist and the warm up regulator
Cold you need about 35 psi, just for info. The longer the ignition is on the more pressure will raise.
Suggest you U.N. plug the WUR to test.
Bruce

Good advice - thanks!

[boyt911sc]

Test and confirm the integrity of your vacuum system. I have encountered several brand new URO pop-off valves that were defective right from the box. Vacuum test the POV before installation. Finally perform a smoke test to determine that the air box, intake runners, fuel injector sleeves, and o-rings are NOT leaking. Otherwise, you are hoping everything is OK and sometimes you get LUCKY. You can not rely on luck all the time specially when you are doing CIS diagnostics troubleshooting.

Test and confirm. Keep us posted.

Tony

[Kansas 914]

Originally Posted by boyt911sc

Test and confirm the integrity of your vacuum system. I have encountered several brand new URO pop-off valves that were defective right from the box. Vacuum test the POV before installation. Finally perform a smoke test to determine that the air box, intake runners, fuel injector sleeves, and o-rings are NOT leaking. Otherwise, you are hoping everything is OK and sometimes you get LUCKY. You can not rely on luck all the time specially when you are doing CIS diagnostics troubleshooting.

Test and confirm. Keep us posted.

Tony

Hi Tony,

Thanks for the advice. All great suggestions.

I think at this point I will remove the all CIS parts to inspect the air box and replace the injectors inserts and O-rings, the runner boots/clamps and replace the vacuum hoses to the components.

[7783911]

i am curious ad to how yu remove the cis airbox without dropping the engine? can you explain with a few photos too?

thanks

[rwest]

Originally Posted by 7783911

i am curious ad to how yu remove the cis airbox without dropping the engine? can you explain with a few photos too?

thanks

Many people do a partial drop by lowering the motor 4 to 6 inches. You don’t have to disconnect a lot and you get some extra clearance.

Tech article here https://www.pelicanparts.com/techarticles/911_partial_engine_drop/911_partial_engine_drop.htm

[Kansas 914]

Originally Posted by 7783911

i am curious ad to how yu remove the cis airbox without dropping the engine? can you explain with a few photos too?

thanks

The drivetrain is in a 914 and I have been told it is easier to do than a 911. I am not sure but will update here.

[Kansas 914]

Originally Posted by 7783911

i am curious ad to how yu remove the cis airbox without dropping the engine? can you explain with a few photos too?

thanks

Here is a well documented CIS removal with the engine in the 911 (no drop): Removing CIS with engine in the car - the writeup

[Kansas 914]

The CIS is out of the car. No engine drop or partial drop.

It took me about 3 hours. The air box was repaired in the past and I found several issues that may have contributed to the BIG BANG. The rear nuts on runners 5 & 6 were finger tight. When I lifted the air box the boots on 4-5-6 fell off the ports of the air box.

[UROParts]

Originally Posted by boyt911sc

Test and confirm the integrity of your vacuum system. I have encountered several brand new URO pop-off valves that were defective right from the box.

Tony

Hi Tony, thanks for letting us know about the issue (PM us anytime), our engineers investigated and found some valves in inventory that aren't sealing like they should. We're currently checking 100% of our inventory and scrapping any valves that don't pass the vacuum test, and will be making changes on the production line to address the issue going forward.

There are bound to be some valves on the shelf at retailers that have the issue, so if anyone receives a valve that doesn't seal properly, please contact us with your purchase details for a no-charge warranty replacement. (If you're outside the USA, please contact your local retailer where you purchased the valve for an exchange.)