Ditching AFM in favour of a MAP sensor.
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  1. #1
    Cal
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    Default Ditching AFM in favour of a MAP sensor.

    Is there any disadvantage to doing this? Anyone here tried it?

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    Cal.
    1995 Mazda MX5 - 2F Race Car
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  2. #2
    Moderator Alan S's Avatar
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    Cal,

    Why don't you give that son of mine you spoke to at the FCD in Brisbane a call as I think he's doing that to his 16V before Pittsworth.
    I'm sure he's done a few and as he gets access to a dyno to check out his work, he could possibly quote facts & figures as well as possibly pointing you in the right direction to get the best part at the best price.

    Alan S
    If it ain't broke, use a 12" shifter.....that usually does the trick!!

  3. #3
    1000+ Posts tekkie's Avatar
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    I was under the impression that AFM's are inferior to MAF's and MAP systems. It has mainly to do with a mechanical way that AFM's monitor the airflow through the vane system.

    There are few units on the market that allow the change of the incoming signal from AFM to MAF or to MAP.
    Have a look at www.splitsec.com.
    .
    1300cc's of jap buzzbox delivered the times below.

    EC 1:54.6 , Wakefield 1:13.15 , OP (short) 52.00 , OP GP 1:24.40


  4. #4
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    Quote Originally Posted by Cal
    Is there any disadvantage to doing this? Anyone here tried it?

    Cal.
    I am building a Megasquirt ECU to allow me to do this on either my 505 or 205 GTI. Let you know how it goes.

    Graham Wallis

  5. #5
    1000+ Posts PeterT's Avatar
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    The AFM is quite a restriction on the 405 and 205 engines. I've fitted Haltech systems to both, which uses a GM MAP sensor, and they both show impressive gains, particularly in low-mid range torque. The main problem with the AFM is its sensitivity at low RPM, particularly with wilder cam timing.

    The AFM is just a potentiometer, the resistance changing with air speed. A MAP sensor works the same way, in that it's resistance changes with manifold vacuum. If you're handy enough with electronics, there's no reason why you shouldn't be able to make a MAP sensor appear electrically the same as the Peugeot AFM. The Haltech system uses the 1 Bar GM MAP sensor. I'd imagine wreckers would have heaps of them. Certainly the Nissan Pulsar/Holden Astra of '90-'91 vintage and the Camira used the same sensor.

    It's good project. I might have a fiddle and see what I come up with.

    '92 205 Mi16
    '90 Mi16x4

  6. #6
    1000+ Posts tekkie's Avatar
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    Peter, my understanding is that the response times of those units may be different throughout the rev range. Whilst most AFM,MAP,MAF sensors operate at 0v~5V range their instaneous responses differ wildly. Hence finding a unit that gives precisely same reading at same airflow/pressure range is like finding a needle in a haystack.
    Your tunable Haltech gets programmed to learn the sender response at number of RPM spots.
    .
    1300cc's of jap buzzbox delivered the times below.

    EC 1:54.6 , Wakefield 1:13.15 , OP (short) 52.00 , OP GP 1:24.40


  7. #7
    Cal
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    It's for the MX5 which already has Motec.

    Cal.
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  8. #8
    1000+ Posts PeterT's Avatar
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    Quote Originally Posted by tekkie
    Your tunable Haltech gets programmed to learn the sender response at number of RPM spots.
    No way. It's just a straight linear voltage divider.

    '92 205 Mi16
    '90 Mi16x4

  9. #9
    1000+ Posts tekkie's Avatar
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    Cal,

    I think you should part company with the AFM then.
    .
    1300cc's of jap buzzbox delivered the times below.

    EC 1:54.6 , Wakefield 1:13.15 , OP (short) 52.00 , OP GP 1:24.40


  10. #10
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    always thought a hot wire AFM is superior to a MAP. Isn't the MAP less precice as the engine wears?
    JoBo

  11. #11
    1000+ Posts tekkie's Avatar
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    Jobo, you mean MAF?

    AFM has a vane system that moves and changes the resistance indicating the relative vacum on the manifold side. MAF uses the said hotwire. And yes some argue it is more precise as it takes the air temperature into consideration of its readings.
    .
    1300cc's of jap buzzbox delivered the times below.

    EC 1:54.6 , Wakefield 1:13.15 , OP (short) 52.00 , OP GP 1:24.40


  12. #12
    1000+ Posts PeterT's Avatar
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    Quote Originally Posted by Cal
    It's for the MX5 which already has Motec.

    Cal.
    So are you saying the Motec current senses engine load via the std. AFM? If so, I'd definitely change to a MAP sensor.

    '92 205 Mi16
    '90 Mi16x4

  13. #13
    Moderator Alan S's Avatar
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    Cal,

    Just asked (my) Brad as he passed through re: this project.
    He tells me the MAP sensor you need is a Delco and costs about $86.
    The better option is to buy one from a Holden dealer to suit a V6 or V8 Commode as they are identical to those supplied by MoTec even down to using the same part number which he thinks (off the top of his head without checking his MoTec books) a 53001.
    If you check it out & the number doesn't line up, I can get him to confirm it but he's pretty sure that's it.

    Alan S
    If it ain't broke, use a 12" shifter.....that usually does the trick!!

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    Quote Originally Posted by Alan S
    Cal,

    Just asked (my) Brad as he passed through re: this project.
    He tells me the MAP sensor you need is a Delco and costs about $86.
    The better option is to buy one from a Holden dealer to suit a V6 or V8 Commode as they are identical to those supplied by MoTec even down to using the same part number which he thinks (off the top of his head without checking his MoTec books) a 53001.
    If you check it out & the number doesn't line up, I can get him to confirm it but he's pretty sure that's it.

    Alan S
    I got one as part of my Megasquirt kit which cost a total of $200 dollars including postage, Motorola part no MPX4250A

    Graham Wallis

  15. #15
    1000+ Posts alan moore's Avatar
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    My MAP sensor that came with the Motec was a GM product No.039 7341, but this is for N/A engines and so would be unsuitable for your supercharged set up. Ring Staffordtune (Motec dealer) and see what they want for the correct sensor.
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  16. #16
    Cal
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    Thanks guys. My tuner is around tonight. I'll ask him which he recommends too. I asked him for a ball park figure the other night and he said $200.

    Cal.
    1995 Mazda MX5 - 2F Race Car
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    1977 Jaguar XJS V12
    1971 Morris Mini 1100K
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  17. #17
    Fellow Frogger! MondeoST24's Avatar
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    You can get a GM 2 bar MAP sensors to suit turbo/ supercharged applications. I was using one on my old Charade with Delco (GM) injection. The normal GM MAP sensor isn't suitable as it won't register positive pressure (or at least that was the case back in '95 .)

    It may be the same item as used on the Supercharged V6 Commodes? I got mine before they were sold here and only know they were used on some USA model vehicle that GM made???

    You'd have to get all your Motec retuned though... $$$$$ ... And most likely the results of switching from a AFM to a MAP sensor won't be as noticeable on a forced induction set up as a N/A engine.
    David
    Former 306 S16 owner- now own a Mondeo ST24 V6

  18. #18
    Cal
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    Mr Motec guru was around last night. It is running a MAP sensor. Some tosser left the AFM there doing nothing but restrict airflow. It is a GM one of some sort. Next step is to remove the AFM and get a pipe made to put a pod filter in a cold air box further from the engine.

    Cal.
    Last edited by Cal; 20th August 2004 at 01:34 PM.
    1995 Mazda MX5 - 2F Race Car
    1990 Mercedes 300TE
    1990 Mercedes 230E
    1977 Jaguar XJS V12
    1971 Morris Mini 1100K
    1967 Porsche 911S
    1957 Porsche 356A Speedster Replica

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