Newly acquired SC

[nealf2002]

Hi: I recently acquired a project '79SC. Car had been sitting for a long time. It starts, but takes a great effort to stay running. Once running, it runs pretty well. I drove it around the block on Sunday and seemed pretty responsive. I am reading tons of posts trying to figure out where my testing will begin and problem lies. One concern is the airbox. if it had been cracked in it's prior life, am I to understand that the car would not run at all, ever? Or, is my car symptomatic of a possible blown airbox. I do know whilke at the PO's house, he tried to start it and it threw some huge backfire explosions. The airbox and mounting does not seem too secure, nothing like my every day '82 SC which starts, runs, and drives perfectly. Please advise.

Thanks!

nf
'70 BMW 2800CS
'72 2002Tii
'79 SC coupe project
'82 SC Targa RoW

[theFONZ]

You probably have air leaks. Search for CIS vacuum leaks, and you will find a wealth of info. You'll need to find all the leaks and seal the system, then check and adjust your fuel pressures.

[dshepp806]

Can't speak specifically to these on your model but you are in good hands! CONGRATS and look for supporting interest from this Family of PP's.

Hold on, for sure.

Again: WELCOME!

BEST!

Doyle

[Norm Faustino]

Take the Fuel press accumulator off the other car and try that first to see if you have a head pressure problem.

[pete3799]

If no pop off valve i would look the air box over real good. They will run with a small vacuum leak.......but poorly.
A pressure test would be a good start as vacuum leaks are a major contributor to poor running.
Next would be a fuel pressure test. Got a fuel pressure gauge?

[blucille]

my '79 SC was similar, I found the vacuum port attached to the cold start valve was completely cracked, of course, I had to drop the motor to find this, but it has solved a host of starting, idling and running issues.

good luck.

[KiwiJohn]

"One concern is the airbox. if it had been cracked in it's prior life, am I to understand that the car would not run at all, ever?"
Not necessarily.
My 78 SC also "threw some huge backfire explosions" on startup.
Usually from cold when left idle for some time, but ran and performed well, and started fine hot. It had no pop-off valve so I thought I was dodging the bullet with a blown airbox after the explosions.
It was not until I dropped the engine for other work that I found the airbox was seriously cracked around the join. Since fixed. And pop-off valve fitted.

[Bob Kontak]

What pete says. Although, most all of 'em have small leaks, It's the medium leaks that will exhibit poor running.

Note that it is fundamentally necessary that you have no vacuum leaks and correct fuel pressures for the pressure/vacuum controlled CIS system to work as designed.

Focus on these two areas, get them flanged up per factory specs and you will have little to deal with afterwards.

I suggest you give me your 2800CS in exchange for my CIS fuel pressure gauge, cam nut crowsfoot wrench and my Charles Probst Bosch fuel injection book. I'll drive them over from Akron in the morning. Lemmie know.

[nealf2002]

So, check for leaks, leaks, and more leaks. Got it. I suppose I don't quite unterstand the whole air box thing. The part that can be damaged is really only the bottom, correct? If anyone wants to quickly explain how it works i'd appreciate it. Thanks.

[pete3799]

Correct.....air entering the top of the box (through the filter) is unmetered .
Once it goes up through the air flow metering plate it is (hence the name).
Any air introduced beyond that point ( false air ) will effect the mixture.

[ossiblue]

Welcome to the forum and, again, you are in good hands.

One thing to remember about dealing with CIS problems, or any other problems for that matter, is to have a systematic plan that eliminates possible causes and stick to that plan. The key here is the elimination of causes, one at a time. This requires a working knowledge of the system you are trying to fix--in this case, CIS. As you do more reading (start here: CIS Primer for the Porsche 911) and do more hands-on work, it will become familiar. You will absolutely need a fuel gauge pressure set before you can do any meaningful diagnoses. Your current problem may be vacuum leaks, may be fuel pressure problems, may be both but you'll never know until you test and confirm.

You have already been given good advice as to the possible cause of your problem but it will help greatly if you can be more detailed as to your symptoms. What exactly do you mean by "it takes a great deal of effort to remain running?" How long does this difficulty last? Are there any backfires heard? What do you mean by "it runs pretty good?" What you may not consider important can turn out to be very significant in pointing toward the cause(s) of your problem.

Your OP included your musing as where to begin. Personally, I would vary from the responses you've received in only one aspect. If I had a newly acquired project that had CIS issues like yours, my first step would be fuel pressure testing. It is easy to do and should be done as a routine on any newly purchased engine, IMO. You never know if a PO has fiddled with fuel mixtures to compensate for bad fuel pressures or air leaks. A properly functioning CIS requires fuel pressures within specs first. Then, air flow must be accurately metered. It is much easier to confirm your fuel pressures are in spec than to track down air leaks and since both factors need to be checked, you might as well do the easy one first. Just a thought and just my POV. If you choose to track down and fix any air leaks first, that's just as good but you still will need to confirm your fuel pressures at some time.

[nealf2002]

Here is how the story goes:

Car was sitting for the better part of 20 years, only started and driven every 6 to 12 months. I went to look at the car in February. The PO tried to start the car, and it would turn over but not stay running. After many, many attempts, including starter fluid down the airbox, and explosive backfires galore, he agve up and surmised it was a bad or buggered up fuel pump.

He replaced the pump with a new one and called me and said the car was now running. I went over a couple of days later and the car was already running and idling (albeit a bit low on rpm's) when I got to his house. Turned the car off and on a couple of times and it fired right back up and idled fine.

Fast forward to sunday when I went to acquire the car. Had a great deal of difficulty to keep running after it was started. Would turn over fine but takes a lot of feathering of gas pedal to keep idling. Cold start is a problem, warm or hot start does not seem so.

Each day since Sunday, I am trying to run the car to get rid of any excess junky old fuel and filter in the fresh fuel that is now in it. Same issues, have to start several times, it usually stalls, backfires, and all until I can finally get it to idle.


I have owned and currently own several old cars with either carb sor mechanical fuel injection, and my other SC runs perfectly so I am a bit of a disadvantage with experience on the CIS...

Thanks in advance.

nf

'70 BMW 2800CS
'72 BMW 2002Tii
'79 SC project
'82 SC Targa RoW

[ossiblue]

Your latest post helps. You have classic too-lean condition at start-up which may or may not be related to air leaks but certainly is related to fuel pressures. My advice is to first, get rid of the old gas and put in fresh. What the PO did to "solve" the starting problem besides replacing the fuel pump is unknown but you can certainly check the cold control pressure--too high will produce the exact symptoms you describe. Again, eliminate the easy potential problems first. Your lean condition can be a result of several malfunctions, as mentioned, but the most common and easiest to check is the fuel pressure. My suggestion, check the pressures--system, cold controlled, warm controlled, and residual--and report your results. From there, it will be much easier to track down the problem.

[nealf2002]

Fair enough> Next thing is to invest in a CIS-compatible fuel pressure testing kit?
I know our host sells one, are there any others that warrant a good look and I may be able to buy locally before the weekend, e.g. pep boys, harbor freight, autozone, etc. ?

thanks!

[timmy2]

Do a google search for Bosch CIS pressure kit, our host sells the ideal one for $ 100 or so, some others out there are cheaper but don't have the right connectors.

[GaryR]

I would load that fuel up with Techron and/or Seafoam to break down the crap i'm sure is in that fuel system also..

[nealf2002]

Hi: Ran the car again yesterday and wanted to let the group know the findings. I do plan on getting the fuel pressure gauges but in the meantime, it took me 10 starts and restarts to keep the car running. This included several backfires and lots of feathering the gas pedal. After all this, it is like a switch is flipped, it kicks right into a steady idle and is fine, albeit with a really low idle speed, like 500 or so.

Do you think it could be the cold start injector failing to work or something else to look for. I am trying to run the car at leas daily to cycle thru all bad gas that may be present, I tried to check the oil, and pulled the cap of to do so and idle dropped way down and stalled the car out...

Thanks.

[theFONZ]

No sense in changing, or worrying about, any parts until you have sealed the system for vacuum leaks and checked/adjusted fuel pressures. Lots of good info here, it's just going to take time to work through. There probably isn't a single fix, but several things are wrong. I can almost guarantee you have vacuum leaks, which may have led to someone fiddling with the fuel/idle to compensate, and lastly may have parts malfunctions. So work through it in that order. Check the system for leaks while you are waiting for the pressure tester, or check for leaks and order parts along with the tester. Common leaks are the pop-off valve, intake boots, injector seals, brake booster hose, airbox, and missing or disconnected lines below the throttle body. Do a search for homemade vacuum tester and go to town. After those are sealed up, the car possibly won't run at all due to the pressures. Hook up the tester, adjust to spec, and go from there. If it still acts up, them move on to parts troubleshooting.

Lucky for you, you have a great running SC right beside it to practice and learn from. The CIS systems on both are slightly different, however.

Keep working at it, it's not as bad as it sounds. And thanks for the updates, it's nice to have input from the OP's to help others in the future.

[theiceman]

cold start injector has nothing to do with cold running. once its started, to keep it running you are dependent on a few other cis components. read the primer. this is typical of a wur if you cant keep it running cold. go through and systematically check your cis components related to cold running.

i also saw a comment about a vacuum line on a cold start injector... huh..? a cold start injector is simply a 7th fuel injector connected to a timed circuit and squirts to help you start.

btw i replaced my airbox ( due to a infamous misprint in the bentley) and it runs flawlesly. starts and runs fine no matter what situation. personally i think a pop off valve is merely a cover up for a poorly tuned engine and causes more problems than it prevents. but that is a debate for another thread.

if this is a project car you want to work on you can reseal the cis for about a hundred bucks max of seals gaskets and rubber couplers.

the entire cis can be removed in about 90 minutes and you can refurb it on any bench. then you can do all your testing knowing you dont have a leak after you put it back.
but if you dont want to go this route get the tools. dont parts guess. you may create more issues

[boyt911sc]

Neal,

You know where to find me. With a young child in your family, I doubt if you could attend to this project and get it fixed. As you mentioned to me last week over the phone, this was a good buy (as is). Your problem is minor and won't take that much work to get this car to run like champ. Keep us posted.

Tony