911sc runs bad timing problem

[Porsche fan]

Hi I have a 911SC 1983 which I'm working on.
The car runs bad when warm between 900 and 4000 RPM. Maybe to lean?
- I checked the vacuum
- set the valves
- Idle is at 900 RPM
- checked the timing with a timing light.
- Timing is good at idle bud doesn't enhance enough in higher RPM
- checked the vacuum by sucking on it. Doing that the rotor enhances. So is good?
- CO is at 2,5% any lower it runs bad
- spark plugs are new

Can anybody help me with my problem. I have rad a whole lot of topics but I'm running out of suggestions.
Thanks in advance!

[timmy2]

Don't know the spec for CO for your car offhand but try bumping it up to 3 and see if it runs better. These cars love to run a little richer. My '78 liked 3.5 CO when I was running CiS.

[T77911S]

edscribe bad

is the O2 connected?
what about aire leaks?
you checked the vacuum advance. what about the mechanical advance?
dont be concerned with idle timing, its the full advance you are concerned about.
since i dont know what "bad" is, how are the cap, rotor and wires?
you can also use manifold vacuum to check the vacuum advance instead of sucking on it.
or buy a hand pump. very handy tool to have.
what about vacuum retard. is it connected and connected to the correct port on the TB?

before you change the mixture. check fuel pressures and verify no air leaks. otherwise, you are just compensating for a problem.

[ClickClickBoom]

Here are one or 2 of my discoveries:
Idle bounce/hunting

Jerry Woods dizzy install!

[Porsche fan]

Hi,

Thanks for the replies.
T77911s: - The Oxygen sensor is connected. I tried to read (3-4 ohm according to manual) the frequency valve but its very hard to reach.
- checked the rubbers on the intake for leaks, they seem good.
- Bad means bad pickup, small backfiring. Sometimes impossible to drive
- How do I check the mechanical advance?

Timmy2: tried 3% makes almost no difference

Clickclickboom: I'll read the post and let you know

[psalt]

Hook up a dwell meter to the lambda test port under the plastic cover at the left rear of the engine compartment. If you don't know what that is, try searching for "lambda CIS". If the FV is not pulsing, no amount of blind twiddling will make it run correctly. If you do not get the default value cold, start with the fuse and the relay.

[Porsche fan]

Originally Posted by psalt

Hook up a dwell meter to the lambda test port under the plastic cover at the left rear of the engine compartment. If you don't know what that is, try searching for "lambda CIS". If the FV is not pulsing, no amount of blind twiddling will make it run correctly. If you do not get the default value cold, start with the fuse and the relay.

Psalt I made a picture. Where can I hook up the dwell meter?

[psalt]

The test connector is a three wire plug, red , brown, green/white wires, usually inside a rubber boot with a hinged cap. Looks like yours is dangling under the CDI box. The dwell meter coil connection hooks up to the green/ white wire (isolated) , get +12v off the fuse nearby and ground to the engine. You should see around 58 dwell on the 4 cylinder scale on a cold start, then a fluctuating 40-55 dwell after it goes closed loop after a few minutes warmup. The frequency and range of the fluctuation will show the health of the O2 sensor. Most cars run best with the mixture adjusted to 30-40 dwell, with the vacuum retard disconnected and plugged. You should be checking for vacuum leaks at the injector sleeves and runner boots with propane and do not run the engine with the heater blower connection open.

[Porsche fan]

Originally Posted by psalt

The test connector is a three wire plug, red , brown, green/white wires, usually inside a rubber boot with a hinged cap. Looks like yours is dangling under the CDI box. The dwell meter coil connection hooks up to the green/ white wire (isolated) , get +12v off the fuse nearby and ground to the engine. You should see around 58 dwell on the 4 cylinder scale on a cold start, then a fluctuating 40-55 dwell after it goes closed loop after a few minutes warm up. The frequency and range of the fluctuation will show the health of the O2 sensor. Most cars run best with the mixture adjusted to 30-40 dwell, with the vacuum retard disconnected and plugged. You should be checking for vacuum leaks at the injector sleeves and runner boots with propane and do not run the engine with the heater blower connection open.

Psalt: Fond some time for the 911SC again. I don't have a dwell meter so I replaced the O2 sensor. That seemed to work but after warm up the car didn't have any idle anymore. rechecked today, first CO and idle good (without O connected) and reconnected the O2 sensor. The problem stays the same... I'll try to work on the car tomorrow. Maybe I can look at the other replies.

[Porsche fan]

Hi,
Psalt: I also checked for vacuum leakes again as you discribed. No leaks present...

[psalt]

Can't help you , you are operating blind without knowing if the lambda system is working and pulsing the FV in the correct range. Part swapping won't do it. Borrow or buy an analog dwell meter or you will never get the optimum tune on a lambda CIS SC. All those gray haired guys over 50 you see walking around have one and many will sell you one for $10. The O2 sensor is irrelevent on a cold start, but the FV is not. Does the dome light work and the relay click ?

[tirwin]

I just did this recently. I bought a timing light a couple of years ago that has a dwell function built in. Note that if you have the Bentley manual, it gives specs in terms of DUTY cycle, not dwell. You can convert with a little math.

Dwell angle divided by (360 divided by number of cylinders)= Duty cycle

So dwell of 30 on 6-cyl scale:

(30/(360/6)) = 50% duty cycle

I guess I am too young to remember the analog dwell meters. I don't think they typically have a 6-cyl scale, normally just 4/8 but I could be wrong. My digital one has 4/5/6/8/10/12.

[tirwin]

Quick and dirty vac leak test. With engine running and warmed up, take off the oil cap. Can you hear the RPMs change? If not, you still have a significant vac leak somewhere.

[psalt]

I guess I am too young to remember the analog dwell meters. I don't think they typically have a 6-cyl scale, normally just 4/8 but I could be wrong. My digital one has 4/5/6/8/10/12.

Too Young ? Nice problem to have. Most good analog dwell meters, even Sears (is that a real poncho ?) have a 6 cylinder scale, but that is for setting the points ignition. On lambda CIS, you are measuring the duty cycle of a single EFI injector that is used as a variable pressure regulator. Just multiply the 4 cyl scale by 90%, it is the closest value. An analog meter gives a better visual reading of the frequency of the dithering which is an indication of the health of the O2 sensor. They get real lazy with old age and you can see it right away if you have seen a healthy young one in operation.

[tirwin]

I guess I am too young to remember the analog dwell meters. I don't think they typically have a 6-cyl scale, normally just 4/8 but I could be wrong. My digital one has 4/5/6/8/10/12.



Too Young ? Nice problem to have. Most good analog dwell meters, even Sears (is that a real poncho ?) have a 6 cylinder scale, but that is for setting the points ignition. On lambda CIS, you are measuring the duty cycle of a single EFI injector that is used as a variable pressure regulator. Just multiply the 4 cyl scale by 90%, it is the closest value. An analog meter gives a better visual reading of the frequency of the dithering which is an indication of the health of the O2 sensor. They get real lazy with old age and you can see it right away if you have seen a healthy young one in operation.

I was 11 when my car rolled off the assembly line in Stuttgart. Some of you guys have forgotten more than I know about these old cars.

[Porsche fan]

Originally Posted by psalt

Can't help you , you are operating blind without knowing if the lambda system is working and pulsing the FV in the correct range. Part swapping won't do it. Borrow or buy an analog dwell meter or you will never get the optimum tune on a lambda CIS SC. All those gray haired guys over 50 you see walking around have one and many will sell you one for $10. The O2 sensor is irrelevent on a cold start, but the FV is not. Does the dome light work and the relay click ?

Psalt: I finally borrowed a analog Dwellmeter!!
i connected the black wire to the negative pole on the ignition coil and the red to the positive. I thought a saw the meter go but it hardly doesn't. It's 58 degrees. I first checked with a cold engine later a warm engine. I also checked to functionality on a 4 cylinder and the meter goes down in degrees when I throttle.
So I think we know that there is a big problem. Now what?

[psalt]

Yes, a big problem. What are you trying to test ? Reread my earlier post on where to hook up the dwell meter.

[fred cook]

Sounds like the plug wires could be cross firing. An easy way to check for this is to either put the car in a dark place or wait until night time. Start the engine and look in the engine bay while it is running. If the wires are cross firing, you will see little "lightning" bolts jumping from the plug wires to ground or even across to each other! You might need a complete set of wires or possibly just a new coil wire. A bad distributor cap that has carbon tracking on the inside can do the same thing, but you can't see it. Also, the little carbon button that contacts the center of the rotor could have worn out or broken! Good luck with your search!!

[T77911S]

why are you on the ignition coil?

[Porsche fan]

Originally Posted by psalt

Yes, a big problem. What are you trying to test ? Reread my earlier post on where to hook up the dwell meter.

Paul: My mistake, the guy told me the ignition coil. I tried to connect the + pole of the dwell meter to the red of the testconector red. And the - from the dwell meter to the brown of the testconnector. I also tried green white and brown.
All no response..
And what does FV stand for??

Greetz