running problem with 89 3.2 carrera
 

Hello Porsche people,
I have an 89 911 with a rough running idle and surging at steady speed.All tune up parts are new,fuel pressure and delivery good and no vacuum leaks.Car is appearing to run lean,cannot get above .5 volts at 02 sensor,adjusted fuel trim at motronic ecm and no difference.Removed air flow vane meter and tested sweep.It starts out at 550 ohms,doesn't move past that for the first 1/8 to 1/4 inch.then moves to 1000 ohms around 1/2,then starts to degrade down to 336 ohms at full open.Anyone know if this sounds incorrect?Seems to me it should graduate smoothly and evenly as per shop manual.Anyone know what spec is,thanks,Hort.

Hey Rick,

Are you sure you have no vacuum leaks? Have you tried the oil cap test?

Mike

This car is starting to get under my skin. We have swapped about every part I can think of.
We have a "Leak Tamer". It's a $1400 tool that tee's into where ever you want to go and injects smoke into the system. It there is the smallest leak, you will see smoke. Grrrrrrr.... This is a 60K 89 carrera. I'm about to go to square one and do a leak down test and go forward from there.

Did you replace the O2?

New, O2 sensor,plugs,wires,cap,rotor,fuel filter, air filter. We tried another air vane sensor, it ran the same.

Fuel injectors... Ask me how I know...
Plug rough running 3.2 in the search, and see how many threads I've started...
Been there done that, and replaced just about every external part with either new, or testing with a working part from another car.
Send your injectors out to someone like WitchHunter, and have them overhauled.
At the time, my 3.2 was my one and only car. I didn't have a ride for the down time, so I ended up buying new injectors from our host. The car ran like it had a new motor! Also increased mpg's as well! Just my humble opinion...

We are on the same page. I have the Bosch pump cleaner for the old CIS injectors, but these are a differant deal. That's my next test.

If you're a DIY guy, and this isn't your primary car, I would strongly recommend sending those injectors out for a rebuild! Check out there site - www.witchhunter.com
$18 per injector and a 3 day turn a round. It's kind of odd, as in the old days with carb'd cars, no one ever gave it a second thought to the importance of rebuilding an old carb. Many folks have the misconception that injectors last forever, or can be made brand new by pouring a bottle of injector cleaner into the fuel tank. Your car is nearing 20 years old. If this hasn't been done, it will likely need it soon enough!

I would also check the gap on the idle switch - put an ohm meter across and see how far you have to move the throttle shaft until it changes state... if it is a hair trigger.. then adding a bit of gap may help with reducing unwanted and unneeded signals to the ECU.

Can you swap around the engine timing sensors with a different set (as opposed to buying new ones at $145 each-or something like that).

Check out this link for info on AFMs: http://www.frwilk.com/944dme/afm.htm

Based on the write up in the link; Looks like Ohms won't tell you much. Need to feed power through it and check the output voltage.

Hope this helps....

Just FYI, Rick is a master mechanic and restoration specialist with Eurotech in VT. For him to ask here is a compliment to the brain trust.

How was I supposed to know?:o
No disrespect intended Rick!!

Surging, hesitation, and rough running can mean SO many different things on a 3.2!
Just thought I'd share my experience with what took me the better part of a year and a half to finally figure out!

Rick is a very well known asset to the guys over at the "S" registry maybe not as recognized
on the Pelican boards...
I've recently been expeirencing the same difficulties on my '97 Chevy dually and replaced
almost as many components.
Once the ETC and '02 sensors were switched out it really started running like crap.My last
bet has been the ECU and my nigling suspicion has been one or more injectors for some time.
It is running so rich it looks like a deisel going down the road...Way Rich!
Once the reflashed control unit arrives the injectors are coming out,sometimes the hunting
calms on the 3.2's but it could take some time ,maybe it'e remapping?
just a thought,Bert

Thanks for reminding me Budge! Mine too was running WAY rich to compensate for the poorly performing injectors. 2 were really bad. That was a definite symptom that was steady... HORRIBLE gas mileage! Also, the surging and flat spots were all over the place, extremely inconsistent and intermittent at best. With bad injectors, mileage was 15 city, 19 highway. New injectors - 19 city, 28/30 highway.

Rick,

Ohm reading on the AFM is not going to tell you much. Rather than put all the details on howto test this AFM please see my doc on the AFM testing and operation, you can get it here:
http://members.cox.net/widebody/AFM/AFM3.2LCalibration.doc
I have done extensive testing and work on these AFMs and compiled what I've learned into this doc. One RED flag with the AFM is if it has ever been opened before, may folks simply try to adjust the spring tension to achieve more fuel but after you read my doc you will quickly learn why this approach does NOT work.

In the front of the doc (page 3) is a section that covers bench testing of the AFM with specific output voltages for each section of the AFM.

Also, your approach of using the car's NarrowBand O2 sensor for estimating AirFuelRatio will get you in the ballpark and the way I do it is to first unplug the sensor signal wire from the car then set the Base Idle first then crank the CO screw on the bottom of the AFM all the way in, this should cause rich mixture and drive the O2 signal to a value well above 0.5v more like 0.75v on a good new sensor. If you can not achieve this rich mixture with the screw all the way in then something is wrong:
1. Be sure your O2 sensor works, spray starter fluid into the intake and you should see the O2 signal drive to 0.75v if it does not replace the sensor
2. Air Leak in the intake
3. Be sure idle switch and WOT switches are functioning properly
4. Finally, the AFM is out of calibration. Does it appear to have been tampered with? If not you can try moving the Adjustment 'A' (see my doc) wiper arm further up the track to achieve richer mixture or down the track for leaner. DO NOT touch Adjustment 'B' (spring tention). Please read the doc carefully as it has instructions on howto record the settings you currently have so that you can put things right back to the way they are now.

One last thing: using the NarrowBand O2 will get you in the ballpark but the final adjustment for CO should be done with a CO monitor and set CO to 0.8% or the method I prefer is a WideBandO2 monitor and simply set the AirFuelRatio to 14.2AFR wich is about equal to 0.8% CO level. The idea is to set the AFR slightly rich at 14.2 then when you plug the O2 sensor back in it will bring the AFR to 14.7

Good luck