sweet jesus ,it is you Loren alias dave still after all these years , big PITA and arrogant ..why do you even posts your brain tumors here??beats me..

Ivan

live is about communication and you do not have those skills ,ever ..if you have nothing good to say why do you talk --write...

An english reading comprehension problem, right?

Yes, that's good advice. I've been semi-reluctant to remove the AFM because there was a previous vacuum leak here (small) that I patched with some sealant (now no leaks), and also because all the tests I performed on the output of the air flow meter seemed to reveal no issues. BUT, at this point, I'm close to getting ready to pull it to take a look.

-Wayne

Whatever electrical testing was done on the AFM does not take into account the spring tension on the door of the AFM. Output voltage will show normal, but the amount of air its actually metering will not match what the DME thinks its getting. Spring tension on the barn door of the AFM can only be truly tested using a flow bench and knowing whatever correlation between voltage output and CFM.

One can reasonably adjust the AFM spring tension by checking AFR with the engine under load at various throttle positions. As i mentioned on page 1 of this thread, this is a dangerous way to do it. Also like i mentioned, this is how i figured out what was wrong with my car.

Jon,

good points. Also, the bypass screw on the AFM essentially influences where the barn door ends up under idle conditions. So at a given idle with the screw all the way tight and the passage blocked the door deflects more -> mixture richer. If you back out the screw air can go through that bypass and the door is closer to its mechanical rest position -> mixture leaner. The DME only sees the electric output equivalent to the door position. This is how idle mixture is set on the 3.2

I don't know how much you'd have to mess up the spring or how much impact that has relative to this adjustment. On a virgin AFM the rule of thumb is to tighten that screw all the way and then back out 4 - 5 turns.

ischmitz, i looked at some old pictures from when i was messing around with this. The clock spring on my AFM was adjusted aproximately 8 teeth from where i believe it was 'factory' set. There was a scribe mark on the wheel that was probably only smart thing the person that adjusted the AFM in the first place did. Car ran incredibly lean, to the point of audible knock. Despite fixing this, i think the damage was done, i have no idea how long the car was driven like this. End result, i foot the bill to make it a 3.4L "while i was in there".

I also think knowing what the true cold start AFR is will be a helpful clue to determine what is going on. As Wayne mentioned many times, it runs fine at cold idle. If cold idle is at 15:1; its going to idle ok, but will lean out even further as the car warms up; probably beyond what the O2 sensor and DME can correct for. I looked a few times to see if that question was ever answered, but too much stuff to sift through.

Yes - makes a lot of sense. Fact is that messing with the spring tension in the AFM is the WORST way to affect mixture. Completely uncontrolled and no way of knowing what you end up with. It may cover another issue (e.g. vacuum leak) well only to destroy the engine with this hack-fix. Your damaged engine is living proof of that. The O2 sensor system can only do so much before it gets to the end of it's rope. It was never designed to account for this kind of issue.

I am surprised the AFM bypass screw for setting idle mixture hasn't been discussed in more detail. Or maybe it was covered and I missed it in the flood of messages. I still think that is the single most impactful way to shift the idle signal from the AFM at running temps. At cold the CHT richens the mixture to the point of condensation on the intake runners and your engine runs essentially from that stuff. But as you get to operating temps that is going away.

Also as you go higher in load (barn door opens wider) that adjustment even if completely wrong becomes less and less meaningful in the overall picture. It just tweaks the response of the AFM at idle and running temperature and that is where he seems to have issues....

Correct!


Actually, you missed the point being made, i.e. using the AFM is a valid approach for troubleshooting fuel running problems,
once the initial spring setting is marked. The AFM is unique versus other load sensing devices, e.g. MAF/MAP sensor,
in that one can easily change the fuel mixture and determine how the engine responds and always revert to the original setting.
If the engine seems to be missing once it's warm or too rich, use one's finger to reduce the wiper position (no need to actually
change the spring setting). That will provide insight as to whether the rough running is air/fuel mixture related.

With regard to the air bypass screw on the AFM, it has little to no effect once the flap begins to move.
The only real effect it has is at idle! That should be obvious, once you relate the air flow from the flap
to the air bypass hole size.

Isn't idle where Wayne has issues? SmileWavy

Okay, I have some updates from today, but I’m headed out for a bike ride very shortly, so I will briefly document them.

ISSUE #1:

I think I may have missed something obvious the other day – something that Steve W commented on back on Sunday. The cylinder head temperature sensor. I measured them after moments of running – I did not actually get under the car with my laser thermometer and *actually* measure the temperature of the exact sensor. This was a mistake, as I found some discrepancies. Kenny @ AutoWerkstatt loaned me a brand new Porsche head temperature sensor today, and I took it out and dropped it in (not fully submerged) into some hot / near boiling water, and I tested the resistance. Here are the findings:

NEW:
22 degrees C – 2062 ohm13.8
51 degrees C – 900 ohm
67 degrees C – 434 ohm
77 degrees C – 308 ohm

OLD (in car):
26 degrees C – 792 ohm
32 degrees C – 1023 ohm
36 degrees C - 365 ohm
43 degrees C - 421 ohm
47 degrees C - 154 ohm
50 degrees C - 185 ohm

Porsche spec:

0 degrees C – 4,400 to 6,800 ohms
15-20 degrees C – 1,400 to 3,600 ohms
40 degrees C – 1,000 to 1,300 ohms
80 degrees C – 250 to 390 ohms
100 degrees C – 160 to 210 ohms
130 degrees C – 90 ohms

So, the bottomline is that the sensor that is in the car is out of spec, by quite a bit. I made this mistake by not directly measuring the sensor temperature on the engine (one has to remove the large grommet covering the hole). Tonight I will replace the sensor. I think this is contributing to the problem, but not 100% the problem.

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ISSUE #2:

When I saw Steve W. today (he lent me a 3.2 fuel rail setup), he specifically mentioned the airflow meter and wanted to make sure if I had checked to see if it had been “messed with”. Since I recently sealed all of the vacuum leaks up, I didn’t really want to remove it, but I think I will tonight to take a look. I found something odd with the air flow meter today. Reminder – I checked the flapper to make sure there were no flat spots on it – I’ve now checked it multiple times, and I still think it’s okay. However…

I read this today, and thought, “I wonder if the air flow meter flap is opening at idle”:

Indeed. But I found that when running the car at idle, the air flow meter flap is opening. I confirmed this through my oscilloscope which shows the flapper moving when we start the car. Here’s the video:

<iframe width="560" height="315" src="https://www.youtube.com/embed/7Hc0CeVMFgw" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

I didn’t even think to check the air flow meter to see if it was opening at idle. There’s no test for that listed in the factory manuals. It may be opening incorrectly because it's been "messed with", or it may have something to do with the airflow in the altered boot in the manifold (technically/theoretically it should not, but with fluid laminar flow, odd duck things tend to happen sometimes!).

Thoughts?

-Wayne

At the danger of sounding like a broken record:

The amount of air needed to idle is the sum of what passes through the adjustable bypass channel around the barn door and what has to pass through the barn door thereby deflecting it. By adjusting the cross-section of that bypass with the allen set screw you effectively vary the position of the barn door at idle. At idle the total amount of air ingested into the engine is comparatively small to when the engine is under load at elevated RPM. That's why this adjustment mostly impacts idle mixture.

This is also why i asked if the silver plug that covers the adjustment screw was still on the airflow meter. The plug has to be drilled out to be removed.

Another waste of time and parts! As was mentioned before, once the sensor gets below 300-400 ohms it has basically NO EFFECT!
When the engine is warm, just bypass it with a paper clip if you're concerned. The only problem with the original sensor is that it's on the
low side affecting the cold running mode. You don't have that problem. The ONLY function of the temp sensor is for cold starting and running!

So what! It still may have the spring adjusted incorrectly, causing a too lean condition when warm, your problem (remember).


Right, it always moves when there's intake vacuum. Hardly any great news.


Then move the wiper when running the engine and see what happens!

Bottom line: The 911 3.2 system is not that complicated!!!!

The thread has gotten so long, who knows what the real problem is now, given all the parts changes.
It's never been stated, or I missed it, what happens above 1500-3000 RPM.

From the 1st post:

It doesn't help when all the running modes aren't fully indicated (posted).

Yes, the car idles terribly after about two minutes, and then also misses in the 1500-3000 range...

-Wayne

Idle is really bad. But also missing in the 1500-3000 rpm range...

-Wayne

Took off the air flow meter - someone definitely has been messing with it, and it doesn't appear that the wiper has been placed into another position. Is the only way to have this checked / fixed is to send it off to a rebuilder that will be able to calibrate it? I've heard that Bavarian Restorations in the Bay Area has a decent reputation?

I knew getting this thing running again would be a major pain.

-Wayne

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http://forums.pelicanparts.com/uploa...1589517986.jpg

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Yes, I've been using the screw to adjust the air bypass valve...

-Wayne

The wiper track is heavily worn around the idle location for the AFM. Have you adjusted the wiper arm so it touches a good spot yet?

Personally, i would find / borrow a known good AFM and retest.

So here's probably the major cause of your problems. On a scale of 1-10, with 10 being the worst I've ever seen yours is probably a 9, maybe even a 10. The carbon has worn down to the substrate, and you can also see a shadow of it at 15% in, where it may be the cause of the miss around 2-3000. There's almost no V out there which would cause the mixture to go very lean, while ignition timing would also be thrown out of wack because the DME would think there is little to no load on the motor. You can try and renew it by repositioning the wiper tip inward on fresh material, but you also face the need to check and probably recalibrate the spring tension as I previously described to you. I would not go to any aftermarket 'recalibrator' or source any aftermarket 'rebuilt' unit. Those have all been nothing but problems and severely miscalibrated, usually so rich the car ends up with a different problem that is insolvable. Or you can try and source a good used one, do an exchange with Porsche, or get a used one from a 964, from where Singer sends all their take off parts.

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