High Idle & Unsteady Acceleration

[SoCalJack]

I've got a problem with my 911. First of all it's a 1976 Porsche 911 with a 1983 3.0 transplant (I purchased it that way). Here are the symptoms hopefully you all can help me out. Car starts up with no problems. According to the tac it idles at start at 1,100 rpm. The car takes 15 minutes to fully warm up. If I drive it before full warm up the acceleration is unsteady/jerky and black smoke comes out of the tail pipe with moderate to hard acceleration. While warming up there is slight dark smoke coming out of the tail pipe. Once the car is at normal operating temp it runs good (strong good smooth acceleration and no smoke). however, the idle when warmed up will be at 1,600-1,800 rpm. The other thing is the gas mileage is not so good (not sure its a symptom or just the way I drive). I'll get approximately 175 mi on 3/4 of a tank of gas. The last piece of information and I'm not sure its related is that this all started after I changed out the fuel accumulator. I had a hot start problem and changed out the fuel accumulator which fixed the hot start prob. Any and all trouble shooting suggestions are welcome and appreciated.

OK the car won't start now crud! I crank over the motor but nothing starts no spudders or anything. I'm used to working on american cars. Typically I check to make sure I got fuel and spark.Is this what we do on our 911's. I'm pretty sure I've got fuel getting into the cylinders. I pulled the air filter off and while the key was in the ignition and fuel pump running i pushed up the valve thing and it made a high pitched whirling noise. Is this normal? I also smelled a little gas out of the tail pipe. I've read the CIS primer for Porsches so I've got a slight idea where the various parts for the CIS are. What would be your next steps for trouble shooting? Step 1 Step2 etc... Thanks

[longhornchris04]

Sounds to me like your CIS isn't tuned properly. There could be multiple causes.

1: control pressure is off
2: Vacuum leaks could be changing your air-fuel mix
3: Lambda system could be acting up
4: Lambda system is working just fine, but masking the poor tuning when active.

The lambda system only operates once the system is at full temperature to correct the AFRs. Since your sputtering problem appears to only happen during warm-up, I'd guess that the lambda system is compensating when active. The high idle sounds like a vacuum leak.

First thing to do is look for vacuum leaks - these would cause the high idle. After that, I'd look to adjust your AFR. I know there are some tricks using your O2 sensor, but I don't know what they are. My CIS is the older version without Lambda.

[SoCalJack]

My car won't start now. See original post I've updated the post with the latest. Any suggestions are very much appreciated. I've got Christmas to work on my car. Thanks

[ossiblue]

Since you now have a no-start, my first suggestion is to check for spark--very similar to American cars. Since you smell fuel and hear the injectors squeal, it's likely you are getting fuel but don't assume so. However, check for spark first in this case. If you find you don't have spark, post here and someone will help you through the procedure.

As far as your earlier problems go, it sounds like a CIS problem--possibly an overly rich mixture setting to compensate for air leaks or bad fuel accumulator or both. Once the accumulator was fixed, you are overly rich. Don't worry about that until you get the car to run again. Sounds like you have lots of testing to do. Not hard if you just ask for help.

[SoCalJack]

Ok had some time to look at the car. I checked for spark and there is no spark. The prior owner had a spare coil so I changed out the coil and still not spark. I also have a multimeter and I'm not getting 12V to the coil with the ignition in the start position.. What should I check for next? Thanks for the help.

[boyt911sc]

Originally Posted by SoCalJack

Ok had some time to look at the car. I checked for spark and there is no spark. The prior owner had a spare coil so I changed out the coil and still not spark. I also have a multimeter and I'm not getting 12V to the coil with the ignition in the start position.. What should I check for next? Thanks for the help.

What kind of CDI do have in the car now? Bosch or Permatune? A simple way to test your CDI is install a known good one. Unless you have a good electronic background to look for the defect in a CDI, substitution is a good course of action.
Double check the plugs and connections for your ignition system. Keep us posted.

Tony

[Bob Kontak]

Listen to Tony. There was a recent thread where someone could not get spark and finally found the wire harness was not plugged into the CD box.

[SoCalJack]

I took a photo (photo is upside down) of the CDI box I'm not sure which one I have. I don't have an extra one. Is there a way to test it? If it is broken can I send it out to get repaired or do I need to buy a new one?

[ossiblue]

You have a Bosch CDI box, which is stock for the car. Some simple things you can do--first, turn on the ignition and listen to see if you can hear the box "whine." Typically, if they don't make a sound there is a problem, but that's not always the case. Second, unplug the three plug connector from the bottom. Now, I don't know what kind of CDI you have--three pin or six pin--since the car has a newer engine. If it is a three pin, the middle connector on the plug is terminal B, and you should have 12 volts there with the ignition on. Test that with a multimeter. If it is a six pin, I don't know the terminal for 12 volts, but someone will post. Report what you find from the above two checks.

[boyt911sc]

That got to be a 6-pin CDI for '83 SC engine. If you would need to have the CDI checked and tested, send it to Ingo Schmidt (ischmidt). You could PM him and inquire. For the meantime, turn the ignition switch and listen very closely for the 'whinning' noise it makes. There is this distinctive faint sound it makes when it is working!!!!! Check and double check all the electrical ignition connections and plugs. I had few unexpected CDI failure caused by loose electrical connection.

Tony

[SoCalJack]

I turned on the ignition on and listened to the CDI Box and hear nothing. I've pulled the cdi box out of the car and it seems like it has been rebuilt before. I also opened up the back to see if there are any visible burnt circuits or wires. Everything seems to look ok. What to do next? Send in the CDI to get rebuilt again or buy a new one????? Thanks

[T77911S]

i dont mean to through you off track, but it seems very strange that he seemed to have a VERY rich condtion and then the CD went bad. also, i have never checked mine, but should there be 12v on the coil?
can i ask how you checked for spark? if you used one of the plugs out of the engine, it may be fouled. if you used a plug out of the engine, i would suggest trying a known good plug or even a new one.

[SoCalJack]

Still no spark. This is what I've done so far. I bought a new spark plug, pulled out one of the spark plug wires grounded it against the engine and still no spark. Next I replaced the green wire off of the distributor still no spark. I sent my CDI off to get tested (thanks Loren) results was CDI is good. Went to permatune web site for trouble shooting guide and did the following "To quickly test the triggering circuit without the use of an oscilloscope: Unplug the harness connector from the ignition box. Refer to the 911SC902 Installation Instructions diagram; connect an Ohmmeter between pins 3 and 6 of the harness connector. To prevent the possibility of misdiagnosis, tug on the green triggering signal wire located at the base of the distributor while viewing the meter. The published specification for the magnetic pulse generator is 600 Ohms +- 100. Our experience has shown that a variation of +- 25 Ohm indicates a need to repair defective connections or to replace the magnetic pulse generator windings." See attached pic my analog ohm meter is reading 100 Ohm. What does this mean? Also there are two circular receptors nearby the CDI box. Are those for relays? Can those be causing my ignition problems (if they are relays none are plugged in)?

[kodioneill]

Possibly the pick up coil in the distributor?