bnen911

Hello everyone. I have an 86 911 that bucks on occasion. It does it a bit at around 2100 2300 rpm, when just running at that engine speed or about 100k. Runs great spinning up to redline past that rpm, idle's great. It does get better when warm but still does it on sporadically.

Temp sensor on cylinder head? Love to hear you thoughts.

Cheers..

Dubbin'

Hey man,

Seems to be a very very common issue on the 3.2 and the resolutions are very diverse... Injectors, O2 sensor, speed /flywheel sensor, CHT, exhaust leaks, DME relay, fuel relay or pump, fuel filter, AFM, etc...

I am having a similar issue with my 87 3.2 which has 52 k miles. I'd advise that you search the pelican forums and read up.

If I were you, start with the easy checks. First, unplug your O2 and see if your car runs better. If it does, then your problem is related to your O2 sensor. If there is not change rule out the O2 sensor. Even though the CHT is often a culprit it might not be yours... To rule out the CHT, drive the car until it is up to operation temperature and bypass the CHT. What you need to do is unplug the CHT sensor and insert a U shaped paper clip in the female section of the plug-this will default the system to the warm engine setting which is correct. If that doesn't help you will have to continue diagnosing.

I'll let you know if I find anything while diagnosing my car.

Thanks,
Mark

Dubbin'

Also, make sure to re-torque your intake manifold bolts to 18ft/lbs. a lot of people have experienced bucking from vacuum leaks which is another area you might need to check. Worn intake manifold gasket would also create vacuum leaks... Good maintenance to change them but it's a good amount of work.

Thanks,
Mark

bnen911

Okay thanks for that.

I have a new O2 sensor, plugs wires cap and rotor and fuel filter. It has been running great by the way, this is new. I will check that idea out with the paper clip.

Cheers..

Dubbin'

Mine was also running fine and then just started bucking one day. It's slightly different then you though. Mine hesitates/bucks at higher RPM and more when at WOT.

On a really hot day when the oil temps get around the middle mark of the temp gauge, the bucking completely stops. I am hoping my issue is the CHT. It would be an easy fix. I've seen others hunt for a while before finding any kind of relief.

I also just put in a new rotor, dist cap, magnecore wires, plugs and air filter. Will be changing the fuel filter shortly .

Don't rule out the O2 sensor only because it's recently been changed. Unplug it and see if the issue gets resolved. Your better off going through the entire process from the get go.

If you are handy with a Multimeter, you can also use the O2 sensor values to diagnose if it is a rich or lean condition... It might eventually pin point what is going on.

Thanks,
Mark

bnen911

Okay cool, I will get on that o2 sensor as well. I will keep you posted.

Thanks,
Ian.

oldskewel

I had similar problems (to bnen911, NOT to Dubbin, which I think are different) a long time ago on my '85 and it was the AFM - search up on that and there is a lot of info. It is a common problem, not too hard to diagnose and fix.

Dubbin'

I have not really ventured through the AFM threads. Can you enlighten us on how you did it? Where you using a CO2 meter?

What worries me about playing with the AFM is that both our cars where running fine and the condition appeared from one day to another. Adjusting the AFM in my opinion would mean that something mechanically has changed? Vacuum or air leak somewhere requiring added or reduced amount of fuel?

Thanks,
Mark

bnen911

Hello again. I just finished the AFM cleanup and wiper adjustment, car started and sounds good but I better be patient and wait for the silicone to dry before I road test it. Keep you posted. Search Youtube Porsche AFM repair Dubbin, it was easy and why not try it. I did not add the ground wire btw.

Cheers!!

bnen911

Hello Oldskewel, thanks very much for that info. Could not wait any longer, I just had to do a road test. So now l am driving one sweet 911 (again) thanks to you. I do appreciate your thoughts too Dubbin but that AFM repair was easy and fixed my problem very well.

Thanks Again,
CheeRS,
Ian..

Dubbin'

Good job brother! I'm happy it was that simple!

I have been going crazy reading through the forums. I have to get down and dirty and take the time to get through my diagnostics to find my issue.

I'll take a look at Youtube and rebuild the AFM while I'm at it. Just like you said, it obviously can't hurt.

Thanks,
Mark

bnen911

Hey, good luck and keep me posted.

CheeRS..

Dubbin'

Hey Ian,

Did you use the videos showing how to rebuild the AFM on the 944 or 924? Didn't find one for the 911...

Thanks,
Mark

oldskewel

Bnen911, I'm glad my quick comment was able to help you out. Your careful description matched my previous experience fairly exactly, which helped.

Dubbin, It sounds like you've got a different problem. I would not assume that you've got nothing to lose by repairing the AFM, even if that is not the source of your problems. At the least, I would do the tests on it before opening it up. I checked my saved links from this, and here are the ones that still work. I did this fix in the days before youtube, so none are from there.

https://rennlist.com/forums/911-foru...-on-3-2-a.html

http://www.the944.com/afm.htm
I think the 944 versions are basically the same (size, design form), but the numbers (angles, resistance, voltage values) will be different, so keep that in mind when following instructions for 944 vs 911.

http://www.systemsc.com/tests.htm
Towards the bottom of the page, he shows values for voltage output vs. angle

https://rennlist.com/forums/911-foru...idle-only.html
Real AFM stuff starts on page 2, so read on.

https://rennlist.com/forums/911-foru...tment-etc.html

Here's my summary on how to test it, after digesting all the info:
remove AFM, connect 9V battery where 5V should be.
Door closed ==> 0.45V
Wide open ==> 8.0V (assuming 9V battery, adjust accordingly)
linear in between
Measuring resistance only, it will be smooth but not monotonic - low-high-low

I've got more complete notes and a copy of someone's Dissertation on the topic that is no longer on the interwebs too, in case there is interest.

bnen911

Hi Dubbin, yes, oldskewel is right, the 911 is the same as the 944, or close enough. When you open it you'll see. The link from the 944 forum explained it very well I might add.

Just got in from a great drive and it's working great.

CheeRTS All!!