3.0cis blow up airbox at workshop

[911ratlookRSR]

I needed to get my porsche lowered, and drove down to the local porsche workshop, delivered it yesterday in the morning, today i came down and got this message "You airbox is exploded, when we started this morning"???????

the airbox was broken so a little gap of air could slip in, pass the airfilter, and i have started it, and riding around 700km, without anything happend, i have been driving it, without giving it to the max, so what has happend in the workshop, any ideas why it suddenly explode there.........

could it be that he has been driving it very hard...fx

just think is weird that`s happend at the workshop.....$$$$$$$$$

[TRE Cup]

You cannot blame the shop when it was a faulty part to begin with ! Just because you were able to "get by" with it, does not lay the blame on them.
Un metered air in a cis box is just that; a crap shoot as to when it will fail completely, or worse yet- allow you to drive it for such a long time that one or more cylinders get lean burn damage

With over 35+ years of working on Porsche 911s, we have had our share of unusual situations when something failed as a client's car was in the shop. At best it is ackward calling a customer to tell them something just failed. But remember how old our cars are, how many miles they have enjoyed, and the sometimes unintentioned neglect of owners.

By no means is this oppinion meant as a absolution of all that goes wrong in a shop. Accidents or negligence can happen and the sign of a trusted, proven establishment is how they stand up if it is their responsibility

[Gunter]

911ratlook:
Do you have a pop-off valve in the box?
If not, install one.
Depending on where the crack is, you may be able to fix it with glue or JB-weld.
Airboxes do not blow from hard driving; they blow on start-up because of occasional back-fire, hence people install the pop-off valve.

[Fast Corners]

+1 on that. The best explaination I heard was from this one shop owner who said "every day you walk past a light switch, flip it and the light turns on...then one day you flip the switch and the light doesn't come on...what did you do wrong the last time?" Things break on cars and sometimes it happens at the shop. Sometimes you need to be glad that it happend there instead of somewhere out on the road miles from nowhere.

In my days when I was turning a wrench the customers that made me cringe the most were the ones that said "I only want you to fix this one problem". Invariably the car had other problems other than one you fixed and when you fixed that issue the car still wouldn't work right because of the other issues that were being masked by the problem you fixed.

My all time favorite was time honored request "Just give it a tune-up". The car won't idle correctly and stumbles on acceleration and stalls at traffic lights. Sure...all it needs are new filters, plugs and and a valve adjustment.

This is not to say that abuse does not happen at some shops and ignorance can often damage a car too. This is why it is so important with these cars to establish a good relationship with a good shop.

Last pearl of wisdom from an ex-wrench. Please, please, clean your car (inside, outside, engine bay and boot) before dropping it off at the shop. A clean car says to the mechanic, I care about my car and I appreciate you fixing it for me. This just provides that last bit of inspiration to the technician to do a great job for a person who appreciates their car.

As for your airbox problem. Exploded airboxes result from back firing up through the intake. The overpressure cracks the plastic intake. This becomes easier to do as the plastic gets older and brittler (due to the years of heat exposure on top of the motor). The best way to protect this from occuring is to install the popoff valve(we used to call it the toilet seat for obvious reasons - not a comment on CIS directly). I'm surprised that all CIS cars don't have this important modification. It has been around forever. Anyway, I recommend replacing the airbox as soon as possible to prevent further damage to the motor. You really don't want to lean out you motor to the point where you overheat or melt something.

[Mysterytrain]

FC, I can't agree with you more. I have always had that approach when I have had my car serviced..I prep it like is going to the Porsche Parade. I really want the guy that is working on the car to know that I care about the vehicle, so hopefully he will too! Great advice!

[JFairman]

When starting a cold fuel injected car you should not touch the gas pedal... especially a normally aspirated 911 with CIS.
Doing so will increase the chance of a backfire through the intake and this happening.
Let the cold start hardware do it's thing if it's still there and working.

[RWebb]

Yes, and you might ask if they used any gas when starting.

but it really is not their fault as per above.

I'll modify Dave B's comment slightly:
"it was a faulty part to begin with !"
"it was a faulty [design] to begin with !"

Porsche is at fault for this. It isn't that a part was made wrong or was not maintained properly, it is a design flaw.

If you have a long relation with the shop they might have told you to put in a pop-off valve; tho some don't like them. But they can save a LOT of money as you are now finding out.

YOu may want to join CIS-Haters, Inc.