o2 removed = running smoother

[nene]

My 86 has some "FLat Spots" when accelerating with the o2 (newer) is connected, but runs much smoother when I disconnect it. Is it fair to say that there may be an air-leak?

I have checked most of the engine bay hoses for leaks, and any other areas that may have then as well, but only one that may be the culprit is the brake booster hose. Is this hose hidden in between the cabin, or does it run underneath the pans?


Thanx,

[bpu699]

Search out my very recent thread labelled "WUR... argh..." in the 930 section. May have your solution in the last several posts...

Mine was a weak ground.

Good luck...

[yelcab1]

the 86 has no WUR. My guess is you need a new O2 sensor

[bpu699]

Didn't know that... My 930 is an 87 and does... Just learned something .

[Daves911L]

Normally aspirated 911 from 84-89 used DME, hence no WUR. 930 continued to use CIS through 89. OP (at least in the photo) does not have a 930. You guys are both right.

[Quicksilver]

Originally Posted by bpu699

Didn't know that... My 930 is an 87 and does... Just learned something .

The Turbos retained CIS through the 80s so they are kind of a hold out.

[T77911S]

the brake booster hose can be tested with a hand vacuum pump.
great tool to have if you dont have one.
pull a vacuum on it at engine bay. if it holds the hose and booster are good.

check the throttle switch and make sure it is set correctly. not sure if it is open or closed at idle. with engine off you may hear it click as you operate the throttle, in engine bay of course.

[Quicksilver]

Originally Posted by nene

My 86 has some "FLat Spots" when accelerating with the o2 (newer) is connected, but runs much smoother when I disconnect it. Is it fair to say that there may be an air-leak?

I have checked most of the engine bay hoses for leaks, and any other areas that may have then as well, but only one that may be the culprit is the brake booster hose. Is this hose hidden in between the cabin, or does it run underneath the pans?


Thanx,

Are the "flat spots" during full throttle acceleration? I ask because the O2 sensor shouldn't be in play at full throttle. If it is I would suspect you have a sensor issue plus a full throttle switch issue.

For the basic issue you are having I would guess the 2 most likely causes would be the O2 sensor and the AFM "wiper track".

Test before replacing!!!

[gliding_serpent]

I have a true euro dme in a north american car. Love it. I put a wide band 02 sensor in the place of the original lamda sensor. Best thing i did.

[Bob Kontak]

Originally Posted by Daves911L

Normally aspirated 911 from 84-89 used DME, hence no WUR. 930 continued to use CIS through 89. OP (at least in the photo) does not have a 930. You guys are both right.

FWIW, I believe CIS was used in the 91-93 3.3 turbos. If I remember correctly, without validating, the '94 3.6 Turbo did not have CIS. Just factoid info, nothing more.

Here is a 91 3.3 Turbo (per the website I pulled it from)

[nene]

Thank you all for the responses,

This is the second o2 that I have used, and very new.

QuickSilver - The initial "flat spots" are at low and mid-range and the Track on the AFM are barely visible, which I verified.

At this point, I will work on "smoking" the Brake Booster hose and see if any remnants of smoke come about.

*To clarify, I don't have a 930.

Serge

[Quicksilver]

With low to mid range driveability issues I would look at vacuum leaks around the intake manifold and all the rubber hoses around the rear of the engine.

Remember as you add throttle the intake vacuum goes away so the effect of vacuum leaks becomes less and less. At full throttle a vacuum leak really makes no difference because it is inconsequential compared to the wide open throttle. (On a car with a 'learning' ECU that may not be the case but the DME does not learn.)

The engine goes back to open loop at full throttle so the O2 sensor isn't in the equation.