911 sc starting issue

[boyt911sc]

Originally Posted by BMEPdoc

I wholeheartedly agree with Paul's post. Pay particularly close attention to the auxilliary air valve. These motors are set-up relatively lean and it doesn't take much of a vacuum leak to rob the sensor plate on the fuel distributor of the vacuum required to move the necessary amount in order to run properly. The AAR is notorious for causing the problem you describe making the motor either hunt up and down in RPM or simply die shortly after firing when cold, many times with a pop or backfire though not always.

In simple terms, the AAR is a temperature controlled (via the thermo-time switch) vacuum leak which, in conjunction with a richer, cold start mixture provided by a properly functioning FPR allows a marginally higher cold engine RPM until stabilizing to an even, lower, warm idle. If ANY component in the system is out of operational specification, a running issue exists. If, for example, your cold control pressure is too high (lean) then pops backfires are the result. On the other hand, IF you have a vacuum leak somewhere, control pressures are superfluous as a main component (air flow sensor) isn't receiving it's proper operating orders to begin with.

Also, by now, I'd imagine the majority of CIS cars out there have the toilet seat or backfire valve fitted. With the air filter cartridge removed you'll see what looks like a... well, spring loaded toilet seat epoxied to the floor of the housing. These were fitted specifically due to the propensity for the motors to cough or backfire as a result of their lean settings (particularly when ALL vacuum related components don't function as absolutely required), leading to warpage and in some cases just flat out blown up air boxes. You may want to check see that there aren't any issues there with a piece of debris or some such thing keeping the flap from sealing properly. There was even an outfit years ago which made cast aluminum air boxes to address this issue, though, I feel the toilet seat solution is more than adequate.

Also, it goes without saying. Your system control pressures MUST be with a given range of operation from cold to hot. If you don't have the gauges to verify the FPR or fuel pressure regulator is within specifcation, then you can very well be on a not-so-merry-go-round. Still:

Remember, air leaks are the enemy to a CIS system. That means anywhere a vacuum leak can occur. Injector seals, distributor vacuum diaphragms, etc. You can clamp a small pair of vice grips with which you can pinch off the vacuum line leading to the AAR to determine if it's the offender, or have a friend use pliers to selectively pinch off the lines. When you finally do get it to run, and once you get the motor up to operating temp, you can then use a can of carb cleaner and squirt a brief spray at the base of the manifold leading to the heads and check to verify the condition of the gaskets as well as where the injectors fit into manifold to determine the condition of the seals. Again, anywhere in the intake flow path. If you discover any notable change in RPM, address the seal or gasket or component.

Good luck

regards,
Jozef Schumann

Jozef,

AAR (auxiliary air regular) and TTS (thermo-time switch) are not even remotely related to each other. In fact they have nothing to do with others functionality and not even closely located in the same electrical circuit. Are you sure of this? Please inform us.

Tony

[BMEPdoc]

Originally Posted by boyt911sc

Jozef,

AAR (auxiliary air regular) and TTS (thermo-time switch) are not even remotely related to each other. In fact they have nothing to do with others functionality and not even closely located in the same electrical circuit. Are you sure of this? Please inform us.

Tony

Yes,
I'm guilty of thinking in one language and translating in my head to another then it does not come out right. I stand corrected in saying the TTS is responsible for powering the AAR when in fact thermo-time switch controls opening time of cold start valve.

It is affected by engine temperature and is powered through starter circuit and grounding through the thermo-time switch so it operates for only a short time while the engine is being cranked.
Depending on engine temperature the switch will take anywhere from a couple or more seconds to open. Injection through cold start valve will then stop.

Where-as the auxiliary air valve, or regulator, provides additional air to the engine to increase idle speed when the engine is cold. It allows air to by-pass the throttle valve which is closed at idle.
A heating coil in the valve is connected to the fuel pump circuit. As the coil warms up, it slowly closes the air passage.
The valve is measuring the proper amount of air to maintain a smooth idle without a large engine speed change as the engine is warming up.

I shall take more time to think out my responses in the future. I apologize for any confusion.

Jozef

[psalt]

Paul,

Precisely this is the reason why I purchased several '80 and '83 CIS units to evaluate and study them. Let's go directly to your '23' pins, this is exactly why I have some doubts about your knowledge about CIS and it its electrical system. For '80 SC's, only 10 pins are utilized while the '81-'83 SC's have 11 pins connected or used. The rest of the so called 2 dozens pins are not connected or in lay man's lingo 'open'. And some spaces are blank spots.

Tony,

Yes, I was right, hopeless. Your record of misreading and misinterpreting my posts and responding with incorrect personal attacks is intact. Anyone with actual experience diagnosing a running " later lambda system " would know there are two ECUs and a relay with 23 connected pins. But, I guess it is pretty clear that you have no experience with them. Have fun with your boxes, perhaps you can take a photo of them to add to your posts and pretend that you know what they do.

[T77911S]

paul, it would be helpfull if you used the "quote" feature. it makes a bit confusing at times when you quote someone.

[boyt911sc]

Originally Posted by psalt

Tony,

Yes, I was right, hopeless. Your record of misreading and misinterpreting my posts and responding with incorrect personal attacks is intact. Anyone with actual experience diagnosing a running " later lambda system " would know there are two ECUs and a relay with 23 connected pins. But, I guess it is pretty clear that you have no experience with them. Have fun with your boxes, perhaps you can take a photo of them to add to your posts and pretend that you know what they do.

Originally Posted by psalt

Paul, I have to confess I don't know what MY is and the other stuff makes even less sense to me.
Could you please elaborate?
Remember, mine is a 1982 911.


Warren

MY is model year, as in 1982. Your car's engine has the second version of CIS lambda. The first version in MY 1980 had a different calibration and several drivability issues, which were addressed in the later versions with band aid solutions until the EFI system arrived. If you think that your car has a cold acceleration problem and you are unaware that your engine has a separate cold acceleration control unit, my advice would be to take it to someone who understands the system or start studying until you understand the two dozen circuits of the control units. CIS lambda is very different than the basic system, corrects pressures are not "good enough" for good running. However, the system can be diagnosed with a dwell meter by someone who understands what they are doing. Swapping parts or altering pressures are a dead end until you know that all the system's functions are working as designed. My experience is most of the cold running issues on CIS lambda SC's have nothing to do with the WUR.

Paul,

I have attached a copy of your post to 'trojwl''s thread post #19 mentioning the so called 2 dozens circuits in the '82 OXS ECU. And additional documents to support the fact that there are only 13 existing electrical circuits and 11 active pins. You are an intelligent and smart guy so you should have no problem counting the electrical circuits but probably have difficulties admitting you made a simple blunder which most 'hopeless' people make every day.









Below is a picture of '80 OXS ECU with 14 pins and 10-wire plug. The later '81-'83 OXS ECU have 11-wire plug. Some of the pins are not used. So there are only 11 active wires/pins connected to the '81-'83 SC OXS ECU but has a total of 13 electrical circuits. (See wiring diagram above).



I did not fabricate these documents. All I did was collect them and use them for my show & tell to demonstrate that 'hopeless' people could still count. I have no problem admitting when I'm wrong because I make mistakes all the time. BTW, this is a technical forum and don't take the discussion personal. It is either you're correct and I'm wrong or we are both wrong! So let the facts decide.

Tony

[psalt]

Tony,

A word with an "s" on the end, as in control units is plural. If you can't see that, hopeless is correct.

Paul

[scott.k]

When I run the car, I start it and it goes into a 400rpm choppy idle, and dies out after about 5-10 seconds unless i hold thi little lever in the air box and move it up and down as necessary. When I do this, i can keep it running pretty smoothly for about two minutes. I did have the car running since I started this thread but since then, i put a bit too much oil in and thats when it started backfiring and couldnt stay running so I drained some oil and i havent got it running well since then. Could it be that I need to adjust the air/fuel ratio, or some adjustment like that?
Thanks
Scott

[scott.k]

Originally Posted by scott.k

When I run the car, I start it and it goes into a 400rpm choppy idle, and dies out after about 5-10 seconds unless i hold thi little lever in the air box and move it up and down as necessary. When I do this, i can keep it running pretty smoothly for about two minutes. I did have the car running since I started this thread but since then, i put a bit too much oil in and thats when it started backfiring and couldnt stay running so I drained some oil and i havent got it running well since then. Could it be that I need to adjust the air/fuel ratio, or some adjustment like that?
Thanks
Scott

I can get it to run great at about 1500 rpms if i hold the lever in the air box up.

[boyt911sc]

Originally Posted by scott.k

I can get it to run great at about 1500 rpms if i hold the lever in the air box up.

Scott,

By lifting the lever up, you are injecting extra fuel to compensate for the unmetered air!!!!! Pressure test your system to locate the air leak. Adjusting your fuel mixture without fixing the vacuum leak will make a bad situation worst. Problem like this will not go away and you need to approach it with a positive attitude. The vacuum leak might be right in front of your (my) nose but might not be obvious. In lieu of a smoke machine, a low pressurized air (5 to 8 psi) is sufficient to expose the leak/s.

If the test will show that there is no existing air leak in the system, then you have eliminated one critical variable in the equation. HTH.

Tony

[scott.k]

Originally Posted by boyt911sc

Scott,

By lifting the lever up, you are injecting extra fuel to compensate for the unmetered air!!!!! Pressure test your system to locate the air leak. Adjusting your fuel mixture without fixing the vacuum leak will make a bad situation worst. Problem like this will not go away and you need to approach it with a positive attitude. The vacuum leak might be right in front of your (my) nose but might not be obvious. In lieu of a smoke machine, a low pressurized air (5 to 8 psi) is sufficient to expose the leak/s.

If the test will show that there is no existing air leak in the system, then you have eliminated one critical variable in the equation. HTH.

Tony

Thanks for the help, im not sure I understand how you are recommending how I test it though. For the record, there is a diagram that is on the underside of rear decklid from the factory that shows how the vacuum hoses should be set up and it does not match up with that on my car. The line that comes out of the manifold vacuum limiter and branches into two lines, one that goes into the throttle housing, and the other leads to nothing so I taped it closed (it may have gone to the cruise control part located on the drivers side of the engine compartment but I cannot remember clearly. Should I try to match the hoses up with the factory setup, of should I just make sure that the one hose that connects to nothing is completely sealed?

Will I need to re-pressurize my vacuum air pressure?? (as you can probably tell, Im not too familiar with compression), but my neighbor does have a compression tool that he said I could borrow.

You mentioned that I was making a bad situation worse. Is this irreversible damage if I did indeed make it worse or can it be fixed?

Thanks for the help
Scott

[boyt911sc]

Scott,

If I'll be doing the troubleshooting, I would do the following:

1). Inspect and confirm that all the vacuum lines/hoses are attached or connected properly as per vacuum diagram for your engine. Check clamps, cracks on hoses, etc. You might have a vacuum line inadvertently connected to an atmospheric outlet.

2). Check your fuel pressures (control, system and residual). By doing this, you would know more about your WUR, FD, FP & fuel accumulator without even running the engine. This is a basic CIS troubleshooting procedure that you should implement. If you are not familiar with this specific procedure, let us know and we'll lay out the step by step procedures for you. If the fuel pressures are within spec, you have reduced the variables to be able to do a meaningful investigation.

3). Ignition timing & sparks including a fully charge battery must be checked and confirmed too.

In your earlier post, you mentioned that you were able to run the engine briefly for several seconds by manipulating the AFS (air flow sensor) lever. Unassisted, the motor failed to run at all as per your info. So it's time to stop guessing and do another test.

4). Perform a vacuum or air leak test. It would only take a minute or two to confirm and verify the integrity of your vacuum system. The test will show you whether it is leaking or not. It would most likely show some air leak/s!!!!! The big question is how severe is the leak to prevent complete engine combustion (????). If the test result is negative, which I doubt, re-direct the investigation to pin point the culprit/s.

Your problem is not difficult to fix. Keep us posted.

Tony

[Bob Kontak]

Tony - How do you perform the pressure test you speak (and have spoken) of? I have rigged maybe 10psi air pressure to the air box with duct tape and sealed off the exhaust and wet my hands feeling for air leaks. Only really find big leaks that way

What is your pressure test?

[Bob Kontak]

Also, my car runs better than it has in the last 15 years because of your and Paul's input. (and JW too, among others)

You guys kiss and make up.

Scott.k - Here is the CIS Primer link. It has a vacuum diagram.

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

[scott.k]

Originally Posted by boyt911sc

Scott,

If I'll be doing the troubleshooting, I would do the following:

1). Inspect and confirm that all the vacuum lines/hoses are attached or connected properly as per vacuum diagram for your engine. Check clamps, cracks on hoses, etc. You might have a vacuum line inadvertently connected to an atmospheric outlet.

2). Check your fuel pressures (control, system and residual). By doing this, you would know more about your WUR, FD, FP & fuel accumulator without even running the engine. This is a basic CIS troubleshooting procedure that you should implement. If you are not familiar with this specific procedure, let us know and we'll lay out the step by step procedures for you. If the fuel pressures are within spec, you have reduced the variables to be able to do a meaningful investigation.

3). Ignition timing & sparks including a fully charge battery must be checked and confirmed too.

In your earlier post, you mentioned that you were able to run the engine briefly for several seconds by manipulating the AFS (air flow sensor) lever. Unassisted, the motor failed to run at all as per your info. So it's time to stop guessing and do another test.

4). Perform a vacuum or air leak test. It would only take a minute or two to confirm and verify the integrity of your vacuum system. The test will show you whether it is leaking or not. It would most likely show some air leak/s!!!!! The big question is how severe is the leak to prevent complete engine combustion (????). If the test result is negative, which I doubt, re-direct the investigation to pin point the culprit/s.

Your problem is not difficult to fix. Keep us posted.

Tony

Thanks for the help.
I may need a brief description of how to do a few of those tests. (vacuum and fuel)

thanks
scott

[scott.k]

does anyone have the vacuum/ air hose diagram for a 1980 911 sc. I have one on the inside of my decklid (looks like its from the factory), and according to that the vacuum hoses in my engine are not set up correctly. And before I start to change hoses around, I would like to make sure that it is incorrectly setup in my engine, because my engine was running before with the current hose setup and I didnt seem to encounter any problems.
Thanks
Scott

[Bob Kontak]

If you can can post a pic these guys can set you straight. I have an 81 and can take pics of mine for you. They should be pretty close.

Edit - If the hoses have not been messed with my money is on your engine sucking big air somewhere.

[boyt911sc]

Originally Posted by Bob Kontak

Tony - How do you perform the pressure test you speak (and have spoken) of? I have rigged maybe 10psi air pressure to the air box with duct tape and sealed off the exhaust and wet my hands feeling for air leaks. Only really find big leaks that way

What is your pressure test.

Bob,

You have the right concept. There is really nothing special about this test. You could make or fabricate adaptors to fit your need. There are about half a dozen points where you could inject pressurized air (with smoke, optional) and locate the hard to find air leak/s. This is not a novel procedure!!!! This has been done by many mechanics way back as far as could remember.

At about 5-7 psi pressure, the pop off valve (generic brand) would lift up. So doing the pressure test with the air box installed on the engine is tricky. I have separated the pressure test into 2:
a). Air box installed
b). Without air box

Picture of air-box test:

A couple clamping devices to keep the rubber stoppers from popping out during test were used. Air pressure between 5 - 7 psi was sufficient to do the test. The best way to see and observed the test is placing the air box underwater. Every single tiny bubbles could be detected if you have an existing leak. Even a tiny pin hole will produce detectable air bubbles!!!!! Some of these miniscule or very tiny cracks in the air box may not even effect the air mixture.

Doing the air leak detection test on the engine is applying sufficient air pressure (less than 10 psi), plugging all orifices where air could leak out. Once you are able to maintain a positive pressure, spray soapy aqueous solution on suspected areas or spots. On the other hand, a more effective method is using a smoke machine and does not require using soapy water to detect the leak. HTH.

Tony

[Bob Kontak]

Cool. Thank you. I was on the right track. I should have used the soap. Just looked for a smoke machine on line. A professional set up costs over $1k US. You can buy a lot of dish soap for that. I have a halloween vapor maker but I don't think that is the ticket.

I bought the gaskets and o-ring for the air box a year ago but that is some real grunt work. The underwater test removes all doubt though.

[scott.k]

I have a vacuum leak somewhere.

Im guessing that there is a thread out there somewhere already of the procedure of how to go through the check list to find it. If anyone can link me to it that would be great.


THanks
Scott

[scott.k]

Does anyone know the hose size (inner diameter size) of the vacuum hoses in the '80 cis system?
Thanks
Scott