How to remove a 911SC Airbox ??
 

Hello, I am new to this forum, and diligently trying to develop some mechanical skills. I am trying to remove the airbox on my 1983 911 SC to install a blowoff valve, get some real-estate to install a new engine compartment pad, and remove my throttle body that is in dire need of repair. I have purchased numerous books including "101 Projects for your Porsche" and been to the Pelican Parts technical site.

I have removed all of the screws on the bottom of the airbox and now confused as to what more I need to remove. It appears that the throttle body must come off with the airbox and furthermore, the fuel distributor (maybe wrong term) also appears to be attached. In the picture on the Pelican technical site, the airbox only seems to be attached to the throttle body.

I would greatly appreciate a step by step walk through to removing the airbox if anyone has one or can type one up without much trouble.

I must be missing something..
Thanks,
Matt

no need to remove anything...look at the articles on this webiste

Gotta drop the motor

Hi: Read the Pelican Tech. Article under Fuel Injection. It is not recommended to remove the airbox for pop-off valve installation. Why does the throttle body need repairing?
http://www.pelicanparts.com/techarticles/911_pop_off_valve/911_pop_off_valve.htm
SmileWavy

Thank you all so much for the quick responses. I am VERY inexperienced, so I appreciate your patience.

With regards to the throttle body, my car idles up frequently for no reason. That is to say, if I walk away from it while idling, I am afraid I'll come back to a blown engine. The local dealership diagnosed the problem as a worn throttle body. Apparently, their is way to much play where the plate sits inside the Throttle body. Furthermore, the microswitch that keeps the car at idle may also be faulty.
My intention is to remove the throttle body, examine it to better understand what they are talking about, and then decide a course of action.

As for the Pop off valve, I guess I am a more visual person. Since I saw the airbox out and on a bench I guess I assumed it had to come out.

Thanks again,
Matt

I think I would suspect a bunch of other parts before the throttle body for a wandering idle. Stuff like the deceleration valve, the aux air valve, distributor advance etc.

Whenever I hear the word "dealership", it makes me instinctively grab my ankles. Maybe you could find an independent Porsche mechanic in your area.

Bill's right, I'm also a novice on the CIS system, but the throttle-body is pretty simple and I've never heard of a problem unless it was "created". There are several items in the CIS system (also, better, known as Bosch K-Jetronic) that could cause the symptoms you describe. For an over-view of the system and brief description of how it works try these sites:

http://www.volvoclub.org.uk/k_jetronic.htm
http://www.students.tut.fi/~hezekiel/bosch.htm

As you can see, there are a number of possible reasons for an "erratic" idle. I would suggest you find a good (non-dealer) shop that is experienced in the K-Jetronic system (shouldn't be too difficult, it was used on virtually every european car of that era). As someone else said, there's no reason to remove the air-box to install a pop-off valve.

Good luck,

Jerry M
'78 SC

damn dealers. service writers know nothing, but won't hesitate to give advice, you usually can't talk to the mechanic who did the work, and as soon as the mechanics get some experience, they quit and go get a better job, or start their own shop.

You GO John!

Matt:

I am not sure what "idling up" means, but if you are finding that your engine speed increases for no particular reason you *may* be looking at the deceleration valve for adjustment. Pretty easy.

Find yourself a trustworthy local Pcar mechanic who sees you are interested and wants to learn about the car. Some items you will need to pay a pro. to work on, but then that's how all of us wormed our ways into the hearts of our favorite wrenches (that and donuts and beer anyway!).

This BBS will be a Godsend to you for certain. Right now most everything may seem strange and you will probably get many (seemingly) conflicting bits of advice. I would recommend that you purchase as many manuals on the car as you can (Bentley, Haynes, 101 Projects) and study, study, study. Make a list of what you think is wrong, what sounds off, what standard maint. items have to be performed, etc.

As a miminum, if the car is new to you, change out all filters and the oil.

John

Noah-
have you been able to remove the CIS system from an '80-83SC without dropping the engine? I'm asking because I'll be tackling the job this weekend, and most people are recommending that completely removing the engine will be the quickest & least frustrating way.

thanks,

Popoff valves are installed with everything still in the car. If you were to really NEED to remove the air bix, it is a tossup whether it's easier to just remove the engine. At a minimum, I would do a partical engine drop where you unhoold rear electrical, get a floor jack under the engine, remove rear motor mounts and just lower the engine a few inches. But I don't think you need to do that. I have never heard of a 911 throttle body problem, but if a throttle body had a problem, it would probably be wear where the throttle plate pivots. The shaft on which the throttle plate sits goes through holes in the throttle body. Just wiggle that, and see if there is play there. I doubt there is. My engine also has a high idle problem, particularly if it sits for a few minutes, engine off, while warm. It's a mystery, but I sure don't suspect the thottle body. More like decel valve or something. My decel valve is disconnected, as many are. I'd agree that sound pads do little more than add weight. I replaced mine, but will not do it again. Useless.

Welcome.

BTW, your car is probably the finest model and year of 911 ever produced.:D

Hey Matt,

I'm assuming your in Buffalo, NY. If you are actually around Buffalo, TX drop me a line cause we're practically neighbors. I will try and help you get the little dear out.

I also had the same issue with hunting idle on my '83. I disconnected the O2 sensor and the little dear idles just fine now. Thank you.

And Super is always right. The '83 (especially Targas with wide bodies) have to be some of the best Porsches ever built!!

Do not go back to that dealership again but ask around for a real Porsche mechanic. Put a request for one on this board, like: Anyone knows a good Porsche mechanic in or near Buffalo? Get a diagnosis before you play with the throttle body, it may be something very simple to fix the idle hunting. SmileWavy

as for removing the intake system as a unit, the 78 and 79 are fairly easy, and the 80-83 are a *****, due to all the extra crap for the frequency valve behind the intake. i highly recommend doing the 80-83 with the engine removed, or at least dropped down quite a bit. dropping it down quite a bit requires disconnecting just about everything that you would do to completely remove the engine, so why not just yank it.

Gunter, you make a really good point, I have tryed two local shops in the area who claimed they could work on Porsches. Neither knew what they were doing. A friend of mine has been helping me out but I don't want to monopolize his time.

Because none of the immediate upgrades or tune-ups are critical, I would prefer to do them myself under the direct or indirect supervision of someone who knows what they are doing. If there are any experienced individuals in the area, I am willing to compensate them for their time for some hands-on knowlege transfer on getting my car dialed in correctly.

There are a slew of other upgrades that I would prefer to have a shop do, so if any of you folks know of any experienced Porsche mechanics in the Buffalo area, I would appreciate an email.

Thanks,
Matt

Matt
 

Well, from my recent experiences, it may be something as simple as the idle speed set a whisker too fast.
I doubt the AAV is the culprit - plug that thing and say good riddance to it!
Could be the AAR though, maybe the Decel' Valve and/or the WUR - as was my issue, but now thankfully (hopefully) fixed.

Superman is very definitely NOT always right. It get "busted" regularly here. JW is the one who is always right. Matt, please post your plans here when you're considering taking the car to a shop. There are some things I take the car in for too, but they are very few. Some things you'd expect are difficult, are really not difficult. There are mechanics out there worth their weight in gold. But I'm 45 years old and I can count the ones I know on one hand.

Superman,

Sorry, I should have justified that remark. "Super's taste in cars is always right! At least, I think so..."

The Bentley manual has a pretty good description of how the CIS components work. There are other books that are good also, but they all pretty much say the same. If you understand them, you'll be doing yourself a favor.

The links that Jerry M listed were good info when I was learning (still learning, but not so clueless)

There is a Rennlister, Jim Williams, who has a good CIS website, and he was very helpful when I was learning the things I know about CIS (so was this board).


http://members.rennlist.com/jimwms/CIShome.html

I was completely convinced that CIS was more trouble than it's worth until I understood it. WE will help you learn. Ask a lot of questions.

Link didn't work. This show do it.

http://members.rennlist.com/jimwms/

Souk, thanks so much for the re-assurance. I was at a local bookstore and couldn't find the Bentley manual, but I did buy "How to Tune and Modify Bosch Fuel Injection."

I think I am beginning to get an understanding of whats going on with the K-Jetronic with Lambda Sensor.

Let me summarize and tell if I am getting close

1. Throttle body opens decreasing air pressure between throttle body and air distributor.
2. Plate in air distributor raises due to pressure change
3. plate is attached to lever that raises plate in fuel distributor
4. rate of fuel dumped to injectors is increased.

If this is right, I still don't understand how the lambda sensor controls anything or how the idle microswitch on the throttle body forces the engine to stay at idle.

Thanks everyone, I actually feel a little smarter
Matt

The lambda circuit will richen or lean the mixture. It senses a change in the air fuel ratio with the O2 sensor. It is not as exact as it should be as the change from rich to lean happens fairly quickly as detected by the oxygen sensor. There was recent discussion on Rennlist about the O2 sensor, and from what I gather, the resolution of an O2 sensor/circuit between rich and lean is not very good. I think the mixture swings back and forth between rich and lean, and the lambda circuit eventually finds a nice median where it thinks is a good A/F ratio, based on the frequency of the swing. Basically, the lambda circuit adjust the mixture as the O2 sensor voltage fluctuates until the frequency eventually it settles out. As I have learned from PID loop tuning on the pipeline, digital tuning of such a system (or the system that Bosch was aiming for) is not easily done at low cost, the lamba circuit is fairly simple and it works OK but it's not the the best (by cost efffective for the purpose it was developed), but it is a good case/arguement that anolog or pneumatic systems work very well for what they cost.

Anyways, I don't have a motor w/ lambda circuitry so I'm have avoid having to learn the system. So take the above for what it's worth (my $0.02). Most folks just disable the circuit by unplugging the O2 sensor. I think that fools the lambda circuit into thinking it has a stable O2 reading so it stops trying to adjust (thus no more surgin idle on those cars). You then adjust the mixture, at the fuel distributor/air flow sensor arm, to a level you want.

Do out rule all other features of your fuel or ignition system. I find that troubleshooting complex systems works best if you work on one part of the system at a time and by process of elimination, you should find your faulty part.

Others will chime in, so keep asking questions. That book you picked up is good, but I was a bit disappointed with its depth. You'll learn as you go along, but be patient and don't ruch into anything you are not sure of.

Good luck.

Try these as well:

http://www.volvoclub.org.uk/k_jetronic.htm

http://www.users.bigpond.com/INTERJECT/KSITEPLN.HTM#K-JETRONIC%20schooling

Also, keep in mind that the 450sl Mercedes used this system as did Volvos, etc. Lots of information in theory out there, so check out the Merc list or otherwise if you want to become a guru.

John