911 SC - strange power loss - pls help
 

Hi guys,

my '81 911 SC is now since 4 weeks at the local mechanic and I (and he I guess) are getting increasingly frustrated not finding what causes the strange "power loss" of my car:
Symptoms:
Car is starting fine and seems to have good power. After 5 mins or so the idle is "shaky" and the car is running like a beetle. Barely goes 120 km/h and is not accelerating as it should. In addition CO is >7% and exhaust has blue smoke.
Strange: Sometimes for some few moments the car seems to have full power and then it flips back.

What was done already (with no positive effect :()
- Replacement of all rubber parts of the CIS (to eliminate false air)
- Replaced catalytic converter with a bypass (cat was partly clogged)
- ECU Lambda Computer replaced with a known-as-good one
- Replaced sparks and spark lines
- New air filter
- Checked pressure of the WUR
- Ignition Timing
- Valve timing (left bank)

All I could think of at the moment is the CDI and/or Ignition coil (and the wiring of that stuff).

Any other ideas? Thanks a million for any hints. I have kept reading this forum for many nights and I hope somebody can help me (and my old 911)

George

Check the rotor for melting or corrosion, or replace it with a known good one. Sometimes they go bad and you cant tell visibly.

Sometimes with intermittent problems such as yours it is a result of an electrical connection to one or more of the CIS components.

Check all electrical connections for loose connections, Cold start valve, Warm up Regulator.

Also it is posiible that your fuel system is dirty, perhaps the fuel ditributor or the fuel injectors are dirty. To test, you can simply take out all the injectors leaving them connected and check thier flow into glass jars.

Good Luck,

Shane

I really think this is ignition related, meaning your control box or distributor. Double check the wires to the distributor and make sure they aren't shorting and you have a good connection. Perhaps the connection is cracked or loose.

Make sure the distributor cap is on tight and not jiggling around, if it is loose, you can bend the clams back to their original configuration to make it tight again.

Injectors?

symptoms of CDI and /or coil. Swap for known good unit. Sounds like what often happens with a coil when it gets hot... also check cap, moisture can be intermittent too and will cause those symptoms..

"In addition CO is >7% and exhaust has blue smoke."

Hummm...Looks like your answer. I do not think a lambda system can operate at that level.

well, have you determined that the frequency valve is working yet? several things relate to that. the domelight fuse, which powers the oxygen sensor computer relay, which powers the oxy sensor computer, (both under the right seat). no function, and it feels like you're dragging an anchor, rough idle included. get it warm and unplug the relay or pop out the fuse and see if the engine runs a lot rougher. it should. usually the relay or it's connection in the plug.

Yah, the mechanic changes out the computer, but did he check the lambda computer relay or even the fuse for the inside light, which gives power to the lambda relay.

I'd honestly check those two things out.

Michael

Are you 100% sure there is blue smoke not BLACK smoke?

If it is BLUE smoke AND

If there is power lost when hot or occasionally,

than it is compression problem cause by head stud lenghtening, initially you will not hear the head banging noise. everything seems fine than the head stud snap.

It very very hard to check as the increse in length is marginal and you may NOt get oil leaks. if there is the leaks are very very little.

If you have black smoke the above anaylst is not valid.

Thanks so much for the hints!
FV is humming, so I guess the relay next to the ECU is OK

Compression was tested and found OK

Injectors have been cleaned
(at least he said so)

If it is down to the CDI Unit: Can These things wear out with high milage? My 911 has around 250k Miles

Is it possible to test the CDI (and) coil?

Thanks!

Hello !

I have the same symptom with my 930 and suspect that the sparks or something related to the CDI. Can you give me some news ? How did you resolve it ?

10 year old post....
 

Piatnik,

You just revived a 10 year old post (?). You would have a better luck by starting a fresh thread for your car.

Tony

DOn' ya just love it when they don't follow up with the cure?

Common behavior......
 

John,

This is becoming a trend these days. People seeking help and advise and don’t even have the courtesy to respond or share to what ever happened to the problem in question.

Tony