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attention all CIS experts....

hello all.

Well I got my idle CO set last night, set the timing, dwell and idle speed. When I drive it, the car stumbles and sputters untill about 3k RPM and then accelerates normally. I just got to figure out this part throttle stumble. It pops sometimes trying to get past this part throttle range of the off idle RPM.

Any ideas or suggestions? I guess I might order the fuel pressure testing rig for CIS and check the fuel pressure etc.

Any help is always appreciated!!!!


Chris

Old 04-10-2002, 05:38 PM
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any ideas?

Thanks,

Chris
Old 04-10-2002, 07:07 PM
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Cool Sputter, Pop!

With the engine running in a dark place (like your driveway on a moonless night), check the coil wire for arcing. If the ignition is grounding out you will see mini lightning bolts. A good test is to replace the coil wire, go for a drive and see if the problem is gone. Sometimes a defective coil wire will short to ground at low rpms but not at higher engine speeds.

Good luck

Fred Cook
'80 911SC
Old 04-10-2002, 07:25 PM
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I have almost the same problem, but mine stumble happens regardless of RPM, just seems to be throttle opening dependent.

I can't figure it out yet. I've tried just about everything I know to do.

I hope someone figures this out for you (and maybe me too).
Old 04-10-2002, 07:55 PM
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I second the advice to check wires

No CIS expert, suggest you check the electrical side before going wild on the CIS diagnostics.

First, make sure the wires are good -as recommended earlier- by checking on a dark night. I spent a lot of time with mixture adjustments refusing to believe my wires were bad. Same stumble with partial throttle/load conditions. The problem was arcing at the coil-distributor cap.

Points, if you have them, can cause major confusion too. Been there.
Old 04-10-2002, 08:09 PM
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Pull the injectors off the manifolds, check the spray pattern with the ignition on and a slight push up on the sensor plate. You might find that some of them will be pissing to the side instead of delivering a fine mist. They all need to spray evenly if you have any hope of solving your driveablity problems.

Joe Garcia
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Old 04-10-2002, 11:04 PM
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Check this site out http://www.permatune.com/Technical%20Support/Porsche/911.htm. Lots of info whether you are using a Permatune or not.
Old 04-11-2002, 04:04 AM
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post the year of the car and what specs you set it at, and then we will have something to go by.
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Old 04-11-2002, 07:38 AM
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Chris,

Before you spend another dime, change your plugs!

Joe
Old 04-11-2002, 07:55 AM
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I second John Walker's suggestion. Would also be helpful to know some history. Was the car already stumbling at low rpm, and that's what prompted you to check the CO setting?
Old 04-11-2002, 08:19 AM
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Sorry guys that I didn't include the vital info in my original post. The car is a 74 911 2.7. Just completed full engine rebuild. The CIS system was disassembled, completely cleaned, reassembled with all new gaskets and o-rings etc.

I found my uneven idle to be very high CO reading of about 7%. I adjusted it to about 2% and it does idle better. However, when trying to drive, it sputters and stumbles at about 2k to 3k rpm and then wants to clear up and accelerate normally.

The car ran pretty smoothly before the total rebuild. I have set the timing, dwell and idle speed together "rocking" them into the best compromise adjustment.

If efforts to clean up the wiring to and from the engine, I did wrap the shielded wires from the + side of the coil into the main harness with electrical tape. Maybe I am getting some "crosstalk" within the harness? I will un tape these and test when I get a chance.


I did bench test all the injectors. They seem fine with a good spray pattern and all seemed to open at the same pressure.

Thanks for all your help thus far!

Chris
Old 04-13-2002, 08:52 PM
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If it is a stumble and a miss at higher rpms only when the throttle is open, I would check the gap on your plugs. If they are too wide the spark will not make the jump. Try reducing the gap before you do other things.
Old 04-14-2002, 01:56 AM
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Hi- I had the ame symptoms in my 75. Turned out to be the mechanical advance was siezed. Pull your distributor cap and twist your rotor to see if it moves and kind of springs back. If not pull the rotor and remove the felt pad in center of distributor shaft. Fill it with penetrating oil and let it sit over night. Then try to wiggle the rotor. It mght take a while but eventurally it will free up.

Old 04-14-2002, 04:42 AM
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