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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... |
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-Wayne |
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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.... |
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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. |
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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. http://forums.pelicanparts.com/uploa...1589508756.JPG 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”: Quote:
<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.
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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! Quote:
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Then move the wiper when running the engine and see what happens! Bottom line: The 911 3.2 system is not that complicated!!!! |
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It's never been stated, or I missed it, what happens above 1500-3000 RPM. From the 1st post: Quote:
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-Wayne |
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-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 http://forums.pelicanparts.com/uploa...1589517986.jpg http://forums.pelicanparts.com/uploa...1589517986.jpg http://forums.pelicanparts.com/uploa...1589517986.jpg http://forums.pelicanparts.com/uploa...1589517986.jpg |
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-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.
http://forums.pelicanparts.com/uploa...1589522386.jpg |
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http://forums.pelicanparts.com/uploa...1589530663.jpg Your suggestion regarding the Singer take-offs is a good one. I'm assuming that the guy with all of the Singer parts is this guy? http://forums.pelicanparts.com/uploa...1589530792.JPG I mean, who really has 76 of these units, unless you've been buying them off of Singer? He's also located right here in SoCal -> two pretty big clues there. Tomorrow I will readjust the wiper on there and button the unit back up. Pretty disappointing, as I'm quite sure that this unit is not the one that I gave with the engine (that only had 65,000 or so miles on it). In the meantime, I will try to source a new AFM that hasn't been messed with. -Wayne |
Wayne i`m a little too far but i can give you a unit for free -i have 4 - but it will take a little time with the post....let me know if you like it later ,problem ,you would just pay for the postage....i guess it would take a week with DHL?
Ivan |
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-Wayne |
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I have the same issue : AFM tracks worn to substrate. I have tried retracking them and it 'looks' Ok on the scope but with the engine running there are dips and peaks (even on idle) resulting in a small hesitation. Due to COVID, I am unable to do a test drive (it is still forbidden to drive classic cars in BE 'for leisure'). If the retracking doesn't work out, I will be looking for a replacement unit soon. If you decide to sell any of the units, plz contact me. @SteveW : I see that the output of the AFM (pin 7 ECU) goes straight into the multiplexer and then the A/D converter. So somewhere in the EEPROM there must be a mapping table for the input ? Can this be used/remapped to make the ECU work with the 'aliexpress' replacement boards for the AFM ? Or is it impossible to recalibrate perfectly ? Kind regards, FrankM from Belgium |
I might have one also. Did mention that in post #8.
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Yes, it can be re-coded if you disassemble the original Bosch EPROM code and re-write it in 8051 assembly language. Also not that difficult if you have the Intel 8051 compiler and can write C code. If you have access to an old PC with DOS, there's an assembler in it you can use to write the code in assembly language. Good luck! |
Steve, I was not aware that the 964 unit is a drop-in replacement? Is this really the case? And yes, Autobahn in LA is where all the Singer take-offs go, I bought some 964 calipers from them. Nice guys and they are willing to deal on the prices somewhat
Bill |
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really that important. Had the cover off my 964 AFM and noticed it has a set of three contacts on the copper wiper unit instead just two on your 3.2 AFM. I know the two units are interchangeable, but there is that subtle difference. Three contacts surely offer better redundancy than two. |
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Thx, Wayne |
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<iframe width="560" height="315" src="https://www.youtube.com/embed/Tx-ElHkZVGo" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe> I'm not sure how susceptible the ECU would be to noise in the AFM? I've never seen another scope trace of an AFM while the engine is running, so I don't know if this is typical / normal, or if this is an issue? Thoughts? -Wayne |
Wayne, this thread will be a gold mine to future trouble shooters. And somehow it makes me feel a little better as a guy scratching his head when my 3.2 runs a little or a lot funny. After 25 years of driving my 911 I have come across most issues and helped fund your hobby with a lot of parts buying.
You are way more experienced than most of the other guys posting on Pelican. And some of the top experts have chimed in. I am following along to see just what is the culprit. My coil caused me some real headaches, and until I replaced it with a old black Bosch coil did that issue go away. You have replaced the coil and tried all the logical things. Good luck finding that gremlin, and I look forward to seeing the solution and your cool 914 back on the road. |
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Mine has spikes too, but also slight hesitations in idle... https://youtu.be/C2qnNGzoXrs Sent from my iPhone using Tapatalk |
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http://forums.pelicanparts.com/uploa...1589567673.jpg |
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http://forums.pelicanparts.com/uploa...1589570027.GIF Move the tip inward maybe about 1mm, and angle the wiper tip to maintain the same angle it had originally to the carbon track. Also adjust the wiper pressure so it has just enough pressure to maintain contact, so as when it just makes contact give just enough pressure for the wiper to deflect another 1 to 1.5mm of pressure. Too much pressure accelerates wear of the carbon, which you don't want. The arm should be positioned a couple of mm higher up on the pivot hinge than before in order to allow the tip to come inward. If you have a contact enhancer, lube and treat the track with it. I always use a DeoxIT pen on those. But your meter could be at the point of no return. It's also a bit questionable that half your wiper tip is off track completely, as if someone loosened that philips screw and repositioned the angle more clockwise to address a rich issue. They usually should not be that far off track, and most of the time are usually all on the carbon track when parked. Porsche superceded the AFMs on the 3.2s to a 964 part number. A few years ago, Porsche offered replacement AFMs on an exchange basis for something like $700. No idea who redoes them for Porsche. The 964 units do all have a triple tip wiper tip, along with a reduntant wire from the wiper arm to the copper wiper bridge contact above it to reduce noise and resistance. The triple tip AFM can be found on some of the later 89 3.2s. These units do seem for some reason to exhibit less wear over time then seen on the 3.2 units, most of the time they look really good. Whether the calibration is the same, I'm not absolutely sure. The last 964 unit I tested seemed to have noticeably tighter spring tension than the one on my 86, and the throttle response also seems to be not as sharp. I ended up recalibrating it, loosening the tension to be the same as on my 3.2, I forget but I think by about 4 or 5 teeth, which brought the response to where it was equal. Autobahn is where a lot of the Singer parts get sold to. You could contact them directly and speak to Mike who's in charge of those parts. |
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Actually, here is the video: <iframe width="560" height="315" src="https://www.youtube.com/embed/Z-QlPtsjh7g" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe> -Wayne |
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I will try to move it to a new section and see if that makes a difference, while moving to get one of those 964 Singer take-off units. It is interesting that there was an original 930 part number that then got superseded to a 964 part number, but the internal BOSCH number remained the same on both of those units. Something is a bit odd about that - I'm quite familiar with the way Porsche performs supersessions, but not so much on BOSCH. The 3-contact 964 unit *should* be a separate part number if done "the Porsche way", as it's an updated (and presumably more reliable design). Also, in the back of my mind, I would think that the displacement increase of the 3.6 versus the 3.2 (more than 10% difference) would mean that the airflow would be greater through the 3.6 engine than the 3.2. That would mean that the effective range of the unit would be less for the 3.6 if the two AFM units were exactly the same (the flapper box would max out opening / pushing against the barn door screen sooner than on the 3.2, resulting in a more limited range of the box). If BOSCH increased the spring tension on the door to compensate, that would make sense, although technically that *should* not be the same part number. Who knows, it could be either one... -Wayne |
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My AFM came from a 10k mi unmolested 964 3.6 and was sealed as new. |
BTW if you ever fix this thing, the next thing you should address is the clusterfuch of elbows om your intake. From dyno testing every 90 degree bend kills power by 4 hp to the wheels, and the one from your air filter to the AFM is horrible, at least a 10hp killer!
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http://forums.pelicanparts.com/uploa...1589572135.JPG Gosh, things are so much easier these days with libraries, and modules, and apps, and graphical user interfaces, etc. And compilers! As expected, *none* of the high school girls were ever impressed with *any* of this stuff... -Wayne |
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