Running rough after Cruise Control removed
 

Hello all,

I finally removed my non fuctioning cruise control yesterday from my 81 911sc after a weekend autcross incident with a stuck throttle caused by the CC cable cover.
I plugged the 2 vacuum lines, and now have a car that stumbles, pops and runs rough generally. Once the RPM's come up it seems to be okay, but when starting from an idle pops and backfires, including from airbox.
Any ideas? Or do I stick that CC back in.

Kirk

you still have an air leak

Reply
 

It is possible that your vacuum cannister was leaking badly. So basically you had a significant amount of air that is not going through throttle plate. Your engine was "tuned" to run best at that condition.
With the leak now gone, the excess air is no longer there. Now you are running rich (same fuel flow - less air flow).
Try retuning.

http://forums.pelicanparts.com/uploa...1282669858.jpg

You say you plugged 2 lines? Could be that one line had the vacuum and the other feed from the first. So if you simply plug them both then the 2nd now has no vacuum. I'd trace those 2 lines to see where they go. It could be you now have a line that needs vacuum but no longer has it?

Just my thoughts.

Removing the oil filler cap will let in extra air, causing it to go more lean.

If you pull the cap and it stalls it was prolly too lean already (vacuum leak) iffn it smooths out and idles fine without the cap, it was prolly too rich and trojwl was right.

Clear as mother's milk, right?

If plugging both lines isn't the problem then you may have dislodged another vac line while you were back there. If all your lines are original then just moving them around could cause one to crack and begin to leak. See if there is a leak with a small amount of starting fluid.
Also, found this:

Originally Posted by 81white911
Does this brake booster vacuum hose connect to a Y fitting that goes to injection body?
I took a good look in the engine bay and I still cant figure out where it finally connects to the intake.
Yes, on US 1980-83 SC's the vacuum line connects with a "Y" to the throttle body and the airbox.
On US 1978-79 the vacuum line connects straight to the airbox.
Inspect the hose itself but also tighten all clamps.
And NO, there is no "T" to the Cruise Control Servo from the Brake Booster vacuum line; the Cruise Servo gets vacuum from a "T' in the line between Decel. Valve and Throttle Body.

This is an SC not a Carrera, I think the SC cars vented the oil tank before the Air Meter Funnel (not 100% certain) if they did vent before the funnel then removing the oil cap will not change the mixture.

The 84-89 Carrera cars vented the oil tank into the rubber boot between the AFM and the TB, in this case when you open the oil cap you allow un-metered air to enter after the AFM and this is why it effects mixture.

Can someone confirm where the SC cars vent the oil tank/system?

Oil filler cap
 

On my '82 SC, when I remove the cap (like to check oil level with engine running), the engine will stumble somewhat but it won't cut off.

Thank you all for your comments and ideas.
I replaced a few of the vacuum lines which were connected to the CC, this was after hooking the vacuum lines back up to the CC thinking it may fix the problem by inducing the original air leak, didn't.
When I did open oil cap it ran rougher and died out, it used to start chugging but continue to run as most responders had said.
After replacing the vacuum lines and leaving the larger of the 2 vacuum lines from CC open it seems to be running "normal" again, no popping, backfires, and a steady idle. Will update again tomorrow as this was with a somewhat warm engine, I will see how it runs after sitting for the night.
Popping today on way home was happening when lifting off of throttle.

Reply
 

Don't leave any vacuum lines "open". You are allowing unfiltered air to enter your engine.
Basically by leaving line open you are simulating the badly leaking cruise control vacuum cannister that you removed.
You need to plug line and maybe play with idle mixture.

Trojwl, thanks for your insight and also from the other contributors to my vacuum leak.
I have leaned out the mixture as per suggestions and it seems to be running as it was prior to the CC being removed, no pops or backfires.
The test will be tomorrow morning with it being stone cold, or maybe later tonight.
Thanks again.