Newly rebuilt M20 AFM - $70 (Standard MF20040) NOT a forsale thread

[Gregs///M]

They interchange. The Motronic 1.0 uses 5v, 1.3 uses 12v and they are a direct swap for each other (153 ECU is plug and play for a 173).

I have been hacking the OBD1 ECU's for years.

This is another incorrect statement regarding Air Fuel Meters. Feeding a 12V reference into a Motronic AFM would damage the AFM, ECM, or both.

Motronic 1.0 systems utilize a reference voltage of 12V DC.
Motronic 1.1 - 1.3 utilize a reference voltage of a highly regulated 5V DC.

This is a result of my findings through AFM research from the many that I've tested over time.

[E30-325iS]

At what rate does the ECU sample the AFM signal?

[Gregs///M]

Here is another bad AFM that I tested for a customer.


Notice now the voltage spans from 0 volts to almost 5 volts. This is 14 cycles from fully closed to fully open. Noticed the short duration drops to zero. This occurs in the microseconds and cannot be captured by a DVM/DMM. Only an oscillocope or data acquisition software will have the resolution to capture these drops to zero.

A DVM/DMM would only show the average as you move the wiper arm from fully closed to fully open. It would appear the AFM is good, when indeed it is bad.

[Gregs///M]

I see the same thing when emulating an eeprom in the ECU as well, during data tracing.

Perhaps I should have said DMM not DVM, Fluke, whatever you want to call it. You are posting a pic of a worn wiper track, ok, but the wiper arm can just be bent.

I see your finding, and don't disagree that you can show a graph, but to open an AFM, bend the arm and verify an AFM is working. Do you take them completely apart and soda blast the cases, check door spring tension, anything other than moving the wiper and testing with your service?

DMM=digital multi meter
DVM=digital volt meter

Same thing and these two terms are used interchangeably in the industry.

Have you even read my ad on AFM rebuilds? Have you even read this thread?

Again my process is this:
1. Test intake air temperature resistance over the heat range via Bentley repair manual.
2. Test spring tension vs. a known recently calibrated AFM using Newton scale meter. (Fuel Injection Corp. unit)
3. Disassemble wiper arm and connector assembly. Clean incoming, and outgoing contacts and bend them to contact fresh material. Clean wiper arm contacts and primary grounding post. Adjust wiper arm to contact fresh material.
4. Reassemble wiper arm and connector.
5. Measure voltage output with oscilloscope and adjust if necessary. I run a variety of tests including quality repeatability, linearity testing (or non linear for eta AFM's,) quality repeatability in the idle genre and the fully open genre.
6. I provide my customers with physical photos of the entire process and my oscilloscope print outs of their individual AFM being tested.

I do not perform any cleaning or sand blasting of the AFM casing. However, I am working with a forum vendor to begin these services soon. Unfortunately, my AFM's might arrive a little dirty but electrically they are 100% working again. I've had zero negative feedback and only 100% positive feedback in the 20+ units that I've sold this year. I have yet to hear any negative feedback on my AFM refurbs.

Again let me state...Do not trust ForcedFirebird or anyone else's advice of using a DVM or DMM to test AFM's. I think this thread clearly identifies the difference and reason for my statement.

Additionally ForcedFirebird, you have failed to prove my previous post incorrect or inaccurate. So either I am right or you are right, if so, we are waiting for your proof.

[ForcedFirebird]

I see the same thing when emulating an eeprom in the ECU as well, during data tracing.

Perhaps I should have said DMM not DVM, Fluke, whatever you want to call it. You are posting a pic of a worn wiper track, ok, but the wiper arm can just be bent.

I see your finding, and don't disagree that you can show a graph, but to open an AFM, bend the arm and verify an AFM is working. Do you take them completely apart and soda blast the cases, check door spring tension, anything other than moving the wiper and testing with your service?

[Gregs///M]

You're the electrical engineer that wants to charge kids $120 to bend a wiper track and hook up an AFM to an o-scope, you should already know the answer.

The AFM testing procedure I linked works just fine using a DVM.

I'm afraid you are the one who incorrect. But hey, here is your opportunity to prove me wrong in front of everyone in this forum.

A DVM does not nearly acquire voltage signal as fast as a oscilloscope. Let me explain this the best that I can.

Let's say we want to test for bad AFM. Customer reports they have severe "bogging" at idle speeds. So let's test with a DVM vs an oscilloscope.

DVM:
Measure voltage output while the wiper arm is moved from fully closed to half open. The DVM does not have the resolution of an oscilloscope so its averages the voltage over the time acquired. BTW, in general, DVM acquire voltage using three methods...max volts, minimum volts, and average volts. The DVM is going to provide you an average of the voltage acquired.

Therefore, with a DVM, the voltage feedback would appear to be within spec and you pass the AFM and return to the customer. Customer spends hundreds of dollars replacing other items and troubleshooting, etc.

Oscilloscope:
Measuring voltage output while the wiper arm is moved from fully closed to half open and displays this voltage difference over a time scale of say...10 seconds.

This graphs shows myself opening and closing the AFM from 0% to 10% nine times in a period of 10 seconds.

Notice the "dips" to zero volts. This is known as voltage drop out and is the reason why there is a sudden loss of power near a specific RPM range, which correlates to a certain speed range or air input to the AFM.

Also notice on the second curve that voltage drop out occurs near the beginning of travel and near the end of travel. It happens several times more over the period of 10 seconds.

But note: these drops to zero occur and only last a few milliseconds and even microseconds! A DVM CANNOT ACQUIRE NOR DOES IT HAVE THE RESOLUTION TO CAPTURE THESE MILLISECOND DROPS TO ZERO VOLTS.

I would fail this AFM and the customer would rest assured that he has found the problem to the solution.

So please, anyone reading this. Please understand a DVM is not sufficient to test a AFM. At bare minimum, a oscilloscope or data acquisition software must be used which has a resolution of microseconds or better. My oscilloscope can acquire data at a rate of Pico-seconds so it is more than sufficient to test accurately.


ForcedFirebird, you're welcome to dispute my research and findings. Please enlighten us.

[ForcedFirebird]

Elaborate?

You're the electrical engineer that wants to charge kids $120 to bend a wiper track and hook up an AFM to an o-scope, you should already know the answer.

The AFM testing procedure I linked works just fine using a DVM.

[noid]

"Nowhere did I downplay the value of an oscilloscope. Actually what I said was that oscilloscopes are dime a dozen and is not something special.".....

"For the record oscilloscopes are great devices."

It appears you are contradicting yourself.

How so? Can't something be great, readily available and accessible?

[Cha Ching]

"Nowhere did I downplay the value of an oscilloscope. Actually what I said was that oscilloscopes are dime a dozen and is not something special.".....

"For the record oscilloscopes are great devices."

It appears you are contradicting yourself.

[SmokeE30]

i dont think he is talking shit on your electrical knowledge or doubting the importance of the o-scope, but rather he like most people who have done electrical work themselves see that checking an afm to ensure its working and doing a quick refresh of it are not difficult things to do. i personally feel what you do to referb afm's is not much work at all, but would i buy one from you over a unknown reman place of course, i dont have a o-scope sitting around anymore as it didnt get much use, you a fellow enthusiast that has a reputable background, the proper tools ad experience i fixing these electrical items that make the cars we all love tic. is it something we must all rely on somebody else to do, well no, but would i fell more comfortable buying a unit from somebody like you over the cheapest no name place i can find of course. i think noid just wants to know how the afms i question compare to a good quality unit

[noid]

Bosch does not supply just the resistor board, you cannot buy parts for these AFM's anymore. You cannot buy it, that's it. If you want "everything new" AFM...buy a new one from Bosch.

Providing valuable information is hardly scaring anyone. I simply stated using 12V on a 5V circuit could damage the electronics, which is true. The article states you must use a "highly regulated 5V power source" so using a 12V or 9V won't work accurately.

If you are going to talk s**t on here, at least provide some valuable, intelligent technical information instead of blasting someone like me, who actually provides technical info instead of asking for someone else to do it. I actually help the community by providing technical information and provide electrical assistance. All you seem to be doing is talking s**t, even downplaying the value of an oscilloscope. Perhaps you should ask your dad if an oscilloscope is a trustworthy tool.

Calm yourself pal, no need to get your panties in a bunch. I didn't go out looking for trouble, I started this thread and I am keeping my opinions in this thread. As I said, I appreciate the fact that you provide the community a service, and members see value in that. Not everyone wants to DIY and some people are willing to pay for your service, nothing wrong with that.

If Bosch is still producing and offering brand new AFM units then that means the parts within those units are still in production. PERHAPS (hence this thread) BWD has used their muscle and solidified a deal with Bosch for new boards, perhaps not, perhaps they are using a Chinese POS board, perhaps they bend the arm.

Nowhere did I downplay the value of an oscilloscope. Actually what I said was that oscilloscopes are dime a dozen and is not something special. Any even remotely respectable company will test their units after rebuilding. They can be had for under $100 used on kijiji. I know exactly what an oscilloscope does and I have seen it in action as we had one in my house growing up. For the record oscilloscopes are great devices.

You also admitted that bending the arm higher or lower on a curve results in longer/shorter travel. Your opinion is that it is not a big enough difference to care, my opinion is that it makes a difference. Opinions are great they are like assholes, everyone's got one.

[devon.818]

tldr

standard auto parts is quality, use them daily, sometimes their core charge is more than the price of the part but thats just commical.

[Gregs///M]

You don't need an o-scope to test a potentiometer.

Elaborate?

[ForcedFirebird]

Perhaps you should ask your dad if an oscilloscope is a trustworthy tool.

You don't need an o-scope to test a potentiometer.

[Gregs///M]

Two wrongs don't make a right. Just because they do it improperly doesn't mean that is the way everyone else should be doing it. Generally speaking that is the most profitable way to do it (at the expense of the customer) since it requires no new parts and hardly any labour.


There is no need to scare DIY'ers. Its a simple process, that virtually anyone can do. I love that you provide a service to the community and people see value in that. However, there is no reason to scare people into not doing it themselves.

Bosch does not supply just the resistor board, you cannot buy parts for these AFM's anymore. You cannot buy it, that's it. If you want "everything new" AFM...buy a new one from Bosch.

Providing valuable information is hardly scaring anyone. I simply stated using 12V on a 5V circuit could damage the electronics, which is true. The article states you must use a "highly regulated 5V power source" so using a 12V or 9V won't work accurately.

If you are going to talk s**t on here, at least provide some valuable, intelligent technical information instead of blasting someone like me, who actually provides technical info instead of asking for someone else to do it. I actually help the community by providing technical information and provide electrical assistance. All you seem to be doing is talking s**t, even downplaying the value of an oscilloscope. Perhaps you should ask your dad if an oscilloscope is a trustworthy tool.