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gatorjos
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Joined: April 19, 2003
Posts: 406
Location: San Francisco
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 Posted: Thu Oct 11, 2012 4:40 pm Post subject: Air flow sensor swaps, rebuild guide, sources |
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So, by swapping parts I learned my airflow sensor is bad. I ohmed it out and sure enough the resistance between pin 6 and 9 is very odd. I can sort of get a reading for a split second of ~100 Ohms or so, and then nothing (open circuit). My bus is currently running with a borrowed part, so I need a fix.
I haven't dug deeper into my sensor yet, and was hoping to find a used or rebuilt replacement, but it is proving hard to do. A few questions:
- has anyone tried swapping different years? Mine is a 1977 Bosch 0 280 200 020 (Yes I've been to http://www.ratwell.com/technical/FISwap.html
- is there a rebuild guide available online? Blogpost?
Thanks!
I will just log really quickly what I have found so far:
- Page 18 of this was more complete than the Bentley http://www.thesamba.com/vw/archives/manuals/afc_fi...Manual.pdf
- These guys want $300 to rebuild my core: http://www.fuelinjectioncorp.com
- Both busboys and Busdepot list them at $150-180 or so plus a core charge.
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1977 Westfalia Weekender Berlin "The Kitebus" aka " Colonel Mustard"
Previous romances:
1972 Ghia cabriolet (full body-off restoration -- stolen after five years of ownership)
2004 Passat 1.8T (manual)
http://21stcenturyhobo.com |
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merlinj79
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Joined: December 05, 2008
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Location: SOCAL
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| Posted: Thu Oct 11, 2012 4:57 pm Post subject: |
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I bought a "rebuilt" unit from Bus Depot a couple years ago. It had been cleaned up real nice, but the resistor strip that the wiper arm rides on was worn. Not worn through, but obviously used.
In my book a rebuild has all wearable items replaced. I'm sure those boards are NLA, maybe it's impossible to recoat them without the OEM mfg equipment.
I'd ask and find out what you are getting for your rebuild $. It might be worth $300 if they can really refresh the resistor coating. Otherwise the AFM is still used, and is still on borrowed time...they only have so many lifetime wiper arm movements (throttle position changes) before it wears through.
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Rick
"Pumpkin II"
Stock 2L FI '77 Westy
CA Smog Stuff |
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gatorjos
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Joined: April 19, 2003
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Location: San Francisco
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| Posted: Thu Oct 11, 2012 5:15 pm Post subject: |
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| merlinj79 wrote: |
In my book a rebuild has all wearable items replaced. I'm sure those boards are NLA, maybe it's impossible to recoat them without the OEM mfg equipment.
I'd ask and find out what you are getting for your rebuild $. It might be worth $300 if they can really refresh the resistor coating. Otherwise the AFM is still used, and is still on borrowed time...they only have so many lifetime wiper arm movements (throttle position changes) before it wears through. |
That's a good point -- I will ask though I don't think anybody has those PCBs new. Here's a shot of what mine looks like on the inside:
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1977 Westfalia Weekender Berlin "The Kitebus" aka " Colonel Mustard"
Previous romances:
1972 Ghia cabriolet (full body-off restoration -- stolen after five years of ownership)
2004 Passat 1.8T (manual)
http://21stcenturyhobo.com |
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gatorjos
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| Posted: Thu Oct 11, 2012 5:37 pm Post subject: |
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with regard to swapping parts around, I forgot to mention my bus has a 2.0 with stock cam but big AMC heads -- 42x36 I believe.
_________________
1977 Westfalia Weekender Berlin "The Kitebus" aka " Colonel Mustard"
Previous romances:
1972 Ghia cabriolet (full body-off restoration -- stolen after five years of ownership)
2004 Passat 1.8T (manual)
http://21stcenturyhobo.com |
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Tcash
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Joined: July 20, 2011
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Location: San Jose, California, USA
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SGKent 
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Joined: October 30, 2007
Posts: 42464
Location: at the beach
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| Posted: Thu Oct 11, 2012 9:26 pm Post subject: |
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you can't swap the PCB. If you move it you will screw it up. It reads in a two dimensional plane and each one was separately calibrated by Bosch with a laser after the PCB was mounted. If you watch Fleabay you can find a NOS 020 for about $200 but you have to actively watch. I've bought several there NOS in the original unopened box. You would be smarter to do that then tweak it than buy a re-manufactured unit. I went through I think 3 or 4 before I got one that worked right.
Good luck.
If you give up here is link to one for sale right now for $500. 018 and 020 are the same device internally and externally.The price is high and you can find them for less but not every day. Be sure to set it up with an air to fuel gauge before any extensive driving. They come way lean. http://www.ebay.com/itm/Bosch-0280200018-New-Air-F...mp;vxp=mtr
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gatorjos
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| Posted: Fri Oct 12, 2012 7:39 am Post subject: |
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So it looks to me like the PCB was glued onto a metal base -- that's probably where the "laser" aligning comes into play (jeez -- didn't think anything was laser aligned on my bus). If I'm careful, I should be able to remove the metal bas to at least take a look under the wiper board assembly and measure around a little with my meter right? Not much to loose at this point -- it's an unusable part.
thanks for the links. If I find a NOS for $200 I will jump on it. Not shelling out anything over that though...crazy
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1977 Westfalia Weekender Berlin "The Kitebus" aka " Colonel Mustard"
Previous romances:
1972 Ghia cabriolet (full body-off restoration -- stolen after five years of ownership)
2004 Passat 1.8T (manual)
http://21stcenturyhobo.com |
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asbug
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Joined: January 01, 2008
Posts: 287
Location: N.W. Ga.
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| Posted: Fri Oct 12, 2012 1:04 pm Post subject: |
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Try this, loosen the three screws on the PCB and see if there is any free play.
There will not be alot, (the hard wires limit travel), but what you need is to move the board closer to or farther away from the pivot of the wiper arm.
This will open up a new path for the wiper arm to travel on.
As you can see the contact area of the wiper is very small and you do not need much movement.
I had a '76 that had dead spots on acceleration that was caused by a worm board.
I was able to move the board around enough that I never had any more problems with it for a year or so till I sold it.
It's free to try and might work.
You have nothing to loose but some time.
KC
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SGKent
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| Posted: Fri Oct 12, 2012 2:55 pm Post subject: |
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stop it and listen. Bosch used a new PCB and mounted it on each one of those AFM's. Then they went into a special machine for calibration. A technician used a laser to burn little traces (you can see them) in the resistors on the PCB to get the curve to be right. When the wiper goes across that board it DOES NOT just measure linear from point A to point Z. It reads in two planes from A-B, A-C, A-D, A-E, A-F, B-A, B-C, B-D, B-E, B-F, C-A, C-B, C-E, C-F etc. Each of the pins out give a reading to the ECU. When you replace the board or move it in any dimension it screws up all the readings. You cannot undo what you have done once you loosen those screws. It will NEVER work right again. In fact it may even end up JUNK. Ask me how I found all this out. I replaced a worn PCB with a new one FIC gave me because I was stubborn and didn't listen like y'all aren't listening. That AFM is somewhere in an aluminum scrap heap now. ANYTHING you do that moves where that wiper sits on that board changes ALL of the values and the ECU needs ALL of them to properly calculate fuel flow and acceleration or deceleration. It isn't just WHERE the door is. It is where it is and how fast it is moving between all the points. There is also differences in how it handles flow at low rpm vs higher rpm. But you do what you want.
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raygreenwood
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Joined: November 24, 2008
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Location: Oklahoma City
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| Posted: Fri Oct 12, 2012 5:08 pm Post subject: |
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| SGKent wrote: |
| stop it and listen. Bosch used a new PCB and mounted it on each one of those AFM's. Then they went into a special machine for calibration. A technician used a laser to burn little traces (you can see them) in the resistors on the PCB to get the curve to be right. When the wiper goes across that board it DOES NOT just measure linear from point A to point Z. It reads in two planes from A-B, A-C, A-D, A-E, A-F, B-A, B-C, B-D, B-E, B-F, C-A, C-B, C-E, C-F etc. Each of the pins out give a reading to the ECU. When you replace the board or move it in any dimension it screws up all the readings. You cannot undo what you have done once you loosen those screws. It will NEVER work right again. In fact it may even end up JUNK. Ask me how I found all this out. I replaced a worn PCB with a new one FIC gave me because I was stubborn and didn't listen like y'all aren't listening. That AFM is somewhere in an aluminum scrap heap now. ANYTHING you do that moves where that wiper sits on that board changes ALL of the values and the ECU needs ALL of them to properly calculate fuel flow and acceleration or deceleration. It isn't just WHERE the door is. It is where it is and how fast it is moving between all the points. There is also differences in how it handles flow at low rpm vs higher rpm. But you do what you want. |
Actually its nothing special. Its called laser trimming. Virtually any PCB shop can do this. The equipment used is a fairly simple X-axis laser (basically the equivalent of a flatbed plotter with a low wattage CO2 laser). They sell for about $20,000. Most membrane switch, PCB shops and flex circuit shops that do surface mount or PTF printing do this every day.
The object is you print a generic circuit path (in this case carbon)....and you get resistance that varies with ink deposit thickness. I can control in my shop to about 2-3 microns....but its tough. So they make the circuit path and measure the resistance....usually at pads for this purpose that are printed out of the circuit area. If the resistance is high...you ablate some of the mass of the strip away with a laser..... in the right location (especially if its a rheostatic strip)...or you can etch it away........or you can scribe it away. But you have to do it a little at a time...with the measuring equipment hooked up while you are doing it...using a true RMS multimeter
Not everyone has a laser...not everyone has the time to program the the cad file or DWG to make the cut shape just for a few circuits....so virtually every shop occasionaly scribes away carbon by hand. Takes just a few minutes...and some practice. If you scribe away too much....its toast. If you slip and scribe in the wrong area its toast.
From what I have seen some of most of these boards are ceramic. Some of the carbon ...especially hard carbon that must be smooth and operate with a wiper switch...is a high fire temperature. i spent a few days in one of Bosch anti-lock brake circuit board plants back in the 90's.
It would not be a big deal to find a shop to print a batch of these for a group. Someone would have to do the engineering print and tell them what resistance you want to start with.
The printing and firing of the board is the easy part. They can probably also laser trim the parts for you to give teh required performance. Otherwise...whoever makes teh order could sell them raw and you guys could scribe them yourselves if you are adventurous.
There is nothing special about mounting the board. It just must be flat to the wiper plane. I work in the fringe of this industry by the way....we print carbon in my shop on a regular basis....but ours are mainly flexible medical sensors.
By the way....this was relatively new back when Bosch originally made these boards in 1974....but this is everyday stuff now for any SMT (surface mount technology) printed circuit shop (there are somewhere north of 1800 shops that do this in the USA). This is how virtually all printed resistors in telecommunications devices, computers and appliance control panels are made. Gold or silver conductive traces with a pinch area are printed. Carbon or any number of resistive metal elements are printed between the two traces. They are oven dried (some are even UV cured)....then before the dielectric is printed over the top to encapsulate....the board is mounted on pins and the laser trims all of the resistors. If you can control your deposit thickness well enough...you can just batch trim the resistors without mesuring in situ.
If you want to know more.....here is an OLd article from 2002. Its even more advanced now.
http://aept.ncms.org/0203%20ESI%20CircuiTreeFeature.pdf
Ive got lots of arcticles on this but not close to me. Here is another from 2007
http://electronicdesign.com/article/power/resistor-trimming17261
That article states that the equipment is fairly capital intensive....not entirely true. It is if you are working at the integrated circuit level...but on standard SMT type3 PCB's....which the AFM board fits squarely into....the features are fairly big. $50k would buy a spankin nice flatbed laser with pick-and-place and laminating capability. Even some 20k lasers can do this board. For IC work....a very fine pitch laser (a semi-conductor stepper unit)...costs about $1 million new...$500K used.
for the finest none IC PCB board work about $185,000 buys a nice highly controllable Galvo laser (our shop should have one by January). Decide what you need a look around. Lots of people in my industry need your business.
Ray |
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gatorjos
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| Posted: Sun Oct 14, 2012 11:41 pm Post subject: |
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Well I tried with all my might to get those three Philips head screws loose, but no way. Whatever thread locker they used is amazing, so don't worry SGKent.  I still don't see what I have to lose though. It's a dead part right now. I don't have all my tools right now, but a little heat will probably get those screws loose .
Very interesting stuff about the pcb. I can see the little scribed char marks of the laser now.
I may have found a used replacement to the used loaner after all...waiting to hear back...
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1977 Westfalia Weekender Berlin "The Kitebus" aka " Colonel Mustard"
Previous romances:
1972 Ghia cabriolet (full body-off restoration -- stolen after five years of ownership)
2004 Passat 1.8T (manual)
http://21stcenturyhobo.com |
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gatorjos
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Joined: April 19, 2003
Posts: 406
Location: San Francisco
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| Posted: Wed Oct 31, 2012 6:17 pm Post subject: |
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So I got the new (i.e. different) AFM installed. The mixture was way off, so I turned the little wheel until the the RPMs would decrease if I held the arm slightly to left or right. It's running pretty well but after several hundred miles my plugs are looking a little darker than I would like.
How many tooth sprockets is a reasonable adjustment for now? I just turned the black wheel three teeth leaner, so clockwise according to the picture provided by a fine Samba member a few posts up.
I will check my plugs again in another 300 miles or so. Reasonable? Can't think of another way to adjust the high rpm mixture without a gas analyzer.
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1977 Westfalia Weekender Berlin "The Kitebus" aka " Colonel Mustard"
Previous romances:
1972 Ghia cabriolet (full body-off restoration -- stolen after five years of ownership)
2004 Passat 1.8T (manual)
http://21stcenturyhobo.com |
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