80 911 idle problem

[Porscheman912]

I am working on a friends 911 after a shop worked on it and charged him over $1000. The first thing I saw was one intake boot was torn. I replaced the boots, and found the boot on #6 was completely torn apart, so two huge leaks. I replaced all boots, found a plug in vac line to EGR so I cut that out, O2 was cut, and so on. He drove the car over, but it was popping and spitting. Anyways, after I fixed everything, the car started right up, but as it warmed up, the Idle went up to 2k. I tried the air bypass, and throttle stop, but no change. I had the car running, and pulled the flapper from air meter down a bit, easy, and the idle went down, but when I would let go, it would go right back. How to you adjust that flapper, to sit lower, and what do I need to adjust for CO2 adjustment? I have an exhaust analizer, just cannot find anywhere to adjust it. I am a carb guy, not injection, but trying to help out a friend.

[Bob Kontak]

CO and idle adjustment dials in easy when the air leaks are eliminated. You can spray starting fluid at your own risk on connection points to check for change in rpm. This works very well. Check the o-rings that hold the injectors in place. Given the condition of the boots the o-rings may be brittle and done for as well.

John Walker posted a thread about cracks in the vacuum line between the engine and the master cylinder - near the transmission - so there is another leak possibility that you would never find in the engine bay. Just some info to brighten your day.

The CO adjustment port is on the air sensor assembly. It is just to the right of the big rubber bellows that join the air sensor and throttle - and just to the left of the fuel distributor. Yes, way down in there. You need to slide a long 3mm allen key down in that hole. There may be a little rubber plug that seals the hole. I believe the hole is sealed from the factory.

To make life easy, cut off a 3mm allen wrench and drill a hole in the end of a larger sized allen head bolt and epoxy the 3mm into the hole. In this pic it looks like I ground some of the circumference off the bolt to slide down in between better.

I do adjustments in 1/8 turn increments.

FYI - You can always use the O2 sensor as a gauge. If the O2 sensor is delivering 0.450 volts then you are at the happy air fuel point (I can't spell that word - you know what I am talking about) Even if not connected the O2 sensor will deliver the voltage if it is functioning. Higher voltage = rich but the limit is just under one volt.

[boyt911sc]

Originally Posted by Porscheman912

I am working on a friends 911 after a shop worked on it and charged him over $1000. The first thing I saw was one intake boot was torn. I replaced the boots, and found the boot on #6 was completely torn apart, so two huge leaks. I replaced all boots, found a plug in vac line to EGR so I cut that out, O2 was cut, and so on. He drove the car over, but it was popping and spitting. Anyways, after I fixed everything, the car started right up, but as it warmed up, the Idle went up to 2k. I tried the air bypass, and throttle stop, but no change. I had the car running, and pulled the flapper from air meter down a bit, easy, and the idle went down, but when I would let go, it would go right back. How to you adjust that flapper, to sit lower, and what do I need to adjust for CO2 adjustment? I have an exhaust analizer, just cannot find anywhere to adjust it. I am a carb guy, not injection, but trying to help out a friend.

Porscheman,

The throttle valve stop is adjusted and set prior to running the motor and with visual inspection. Once this is set and calibrated leave it alone. This is not used to adjust the idle speed. The same with the air flow sensor plate, once calibrated and aligned, leave it alone.

The fact that the idle screw is not changing the idle speed means one or two things. There is unmetered air going in and/or the throttle valve rest position is out of spec. Since you have disturbed the previous setting for the throttle valve stop screw, do a visual inspection by removing the CIS intake rubber boot.

Do not change/alter the mixture setting with out confirming the absence of a vacuum leak. Otherwise, you'll be adding more variable to the problem. Not being able to locate a vacuum leak does not mean you don't have one!!!!!! One simple test to do: With engine fully warmed, let it idle. Remove the oil filler cap and observe for any change in idle RPM. If you don't get any significant drop in idle speed, you got a vacuum leak!!!! Keep us posted.

Tony

[Porscheman912]

All vac leaks have been fixed, and I replaced the rubber boots. A shop had worked on it, and set the injection without looking for vac leaks. I could see the #2 cylinder boot torn, and checked with carb clearing, safer than starting fluid. When I removed the plenum, that is when I found that #6 was completely torn apart. Someone had set the airflow meter with those big leaks, and now that they are fixed, it went right to 2k on the tach. I knew you could adjust the meter, but was not sure if it was that little hole on the top. Now that I know, I checked to see if one of my allen wrenches would fit, and it does. I did not have access to them, do to the owner of the car having my truck with the keys to our go-kart trailer, where my long allen wrenches where. I got my truck back, and left one of my Porsches at his house. Anyways, I will know here in a few minutes if this is it or not. Thank you all for the help.

[Porscheman912]

Special Thanks to Bob K. I got it warmed up, and check the O2. It was at .1 and Idling at 2K. I leaned it down, and now it is at .448-.456, and Idling at 900. The Idle is smooth, and thank you for the help. All you you have been a great help, and I love this site for that. Now I can go get my Porsche back, and give them theirs.

[boyt911sc]

Porscheman,

It is good to hear that you are helping your friend about his car. If I would be doing the troubleshooting, I would do the the following steps:
1). Check the ignition timing.
2). Check the control and system fuel pressures (cold & warm).
3). Check that the AAR (auxiliary air regulator) is partially open (cold) and fully closed when engine has warmed up.
4). Check the alignment of the air sensor plate and butterfly valve (throttle body).
5). A good method to use for locating vacuum leak in lieu of a smoke machine is the use of pressurized gas like air or nitrogen.

BTW, you need a fuel pressure gauge kit for CIS or any fuel injection system to do a meangingful investigation. Do you have a fuel gauge? Keep us posted.

Tony

[Flat6pac]

On an oxygen sensor car you need to do the changes to the CIS with the OX SEN unplugged to have the changes work without the lambda trying to compensate for the changes from its norm.
Bruce

[Porscheman912]

That is good to know. I was shutting the car off, making changes, and then restarting, and watching my meter until it would stop moving. I hope this works, and I am letting the car cool down so I can see if it will start cold, because that is why they originally asked me to fix, when I found the Vac leak from the #2 boot, then I started finding all kinds of other problems. A local shop worked on it, and charged over 1k and did not fix anything, but I think they were the ones that reset the airflow meter. It runs great right now.

[Bob Kontak]

PMan912 - Nice job.

Never ever say out loud that you have all the vacuum leaks fixed. Only think it. :-)

[T77911S]

i use a regular long allen to adjust the mixture. the advantage to that is you can see how much of an angle you have moved the mixture. this is very helpful if you do it by ear.

[Porscheman912]

Ok, now there is another issue. Now the car Idles great, but hesitaes off idle and then does not run very well when I drove the car. The only thing I am thinking, is the fuel filter, because it looks like it has been on there for awhile. I gets a mis for a second, and every once in awhile it will pop from the intake, which has pop off valve. Anyone have a clue with this?

[boyt911sc]

Originally Posted by Porscheman912

Ok, now there is another issue. Now the car Idles great, but hesitaes off idle and then does not run very well when I drove the car. The only thing I am thinking, is the fuel filter, because it looks like it has been on there for awhile. I gets a mis for a second, and every once in awhile it will pop from the intake, which has pop off valve. Anyone have a clue with this?

Porscheman,

Have you hooked up a pressure gauge? If not, then you are just doing quesswork!!!! Hope you get lucky and find the problem/s. Secondly, you need to pressure test the system (engine) to confirm the absence of air leak/s. Not being able to locate a vacuum leak does not mean you don't have one.

I'm glad you are not my mechanic (just a joke) because you'll be charging me so much man-hours for this troubleshooting work. I'm no expert but these tests could be done in a few mins. and avoid the quessing game.

Pressure tests (control & system pressures for cold/warm)..........20 mins.
Air leak test...........3 to 5 mins. The test will show presence or absence of any air leaks on a CIS engine (on a test stand). This is the most over-looked and neglected test by many investigators.

Correct me if I'm wrong in my assumption that you had adjusted or tweaked the mixture screw!!!! If you did and had not done the air leak test before the adjustment, you have made the situation worst by adding more variables to the problem. Without testing the integrity of your vacuum system, you are simply hoping that everything is OK.

Tony

[psalt]

Ok, now there is another issue. Now the car Idles great, but hesitaes off idle and then does not run very well when I drove the car. The only thing I am thinking, is the fuel filter, because it looks like it has been on there for awhile. I gets a mis for a second, and every once in awhile it will pop from the intake, which has pop off valve. Anyone have a clue with this?


The 80 SC has a test connector on the left side of the engine compartment. If you connect an old analog dwell meter to the green white stripe wire, the system will tell you if it is working properly and if the mixture is set correctly. Much better than guessing. You can find everything you need to know with the search button.

[flat6pilot]

Sounds like it's leaning out.

I think something has been compensated for to get it to idle.

I'm afraid I'd start over from the beginning.

I run with an AF/R gauge in my car, and I tell you the engine distinctly runs/sounds different when it's running 14+ AF/R (rough, backfire etc) compared to 12.7-13.7 or so.

[Bob Kontak]

He did run the O2 sensor output test that got the car in the ballpark. However, as he states in earlier posts the O2 system is not connected. The dwell meter test is therefore not an option. The frequency valve will only operate at 50% duty cycle.

He also states the CO was adjusted (previously) in a manner to compensate for substantial false air issues that he identified. I think he is doing pretty good considering his exposure to CIS with Lambda,

I would reconnect the O2 system and check the O2 relay under the passenger seat. Little $12 cube attached to the Lambda box. A failed relay will cause pathetic throttle response.

[Bob Kontak]

Flat6Pilot - where did you get the AF ratio gauge?

[Porscheman912]

Thank you, I will check the relay. I am going to put a fuel filter on in the morning, and then the car is going back to the owner. I told him he really needs to take it to a shop that knows this system, instead of a carb guy playing guessing games. Plus it is killing me on my machine work I am not doing due to trying to help someone out. I wish I was making money off of this, but I am not, plus I really do not like someone driving one of my Porsches. The owner has been burned by a few shops, who never did the stuff that mattered, like replase the intake boots that were screwed up. This is the very first time I have messed with the K-Jet system, and the L-Jet on my 928 is different. I have even called a few friend who work on these things, and they did not have an idea, only the start all over, and redo everything, do to some farm boy in Iowa replacing the engine before the grandfather giving this car to his granddaughter. I am just trying to help, do to the cost other shops have charged, and it did not look like anything was ever done, other than someone adjusting the heck out of the airflow meter to make the car run with a torn boot, and one the was split in half. The car runs great compare to what it was like when they brought it to my. I am just not an injection guy.

[psalt]

However, as he states in earlier posts the O2 system is not connected. The dwell meter test is therefore not an option. The frequency valve will only operate at 50% duty cycle.


No 911SC has a default duty cycle of 50%.

The default duty cycle for an 80 is 85%.

There is more to the test routine than O2 sensor output, since the lambda SC cannot run correctly without a pulsing FV, the dwell meter is the fastest way to isolate a fault.

[Bob Kontak]

Connect the O2 system. The male part is the wire from the O2 sensor. The female is the plug-in port that is located in the drivers side engine compartment near the #3 cylinder. On the left from the spark plug wire. The bracket that holds the female port in place often falls apart so look for a wire with a 1 1/2 inch by maybe 7/16 diameter on the end. Plug your O2 sensor into that - make it fit, even if you have to splice a wire and jam it into the port. In theory, your O2 system may now be armed and dangerous.

Check under the front trunk. Is the light working when you lift the lid? That is on the same circuit the O2 system is on. If not, check the third of forth fuse from the firewall in the front trunk.

If the O2 sensor is connected and the system is working there should be a change in behavior. IF not then get to the relay.

Check out post #14 in this thread. You can cheat and jumper the relay to see if it is working. Connect a wire between the 87 and 87b connectors and plug the relay back in. If engine operation improves you are on the right track. Do not forget to remove the jumper as the system will not shut off with the key. Only use this as a cheater test - not a fix.

911 SC running "flat" and no idle

[Bob Kontak]

PSALT - regardless of the default duty cycle, if the O2 system is not connected how can the dwell meter test be effective? I am not posting this to argue so please don't assume that.