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Thread: Getting Correct Knock Sensor

  1. #1
    Electronic Ignition!
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    Getting Correct Knock Sensor

    I am adapting a complete TBI system out of a 1991 chevy 350 truck to a Pontiac 350

    I pulled all the wiring, 1227747 ECU with ARJU chip, throttle body, a 454 spreadbore adaptor , and all the sensors including the knock sensor

    According to the chevy/gmc Haynes manual (pg 6-18) the resistance for 1988- 1995 knock sensors should be 1.5K-10K ohms while 1996-2000 should be 90k-110k ohms

    Now, my junkyard 1991 KS measured about 100k ohms. I went ahead and measured a couple other pre '96 KS's in the yard and they were about 100k as well.

    I bought a new KS for a 1991 truck (BWD P/N S8011) and it measure about 4k ohms (agrees with the book)

    So what's the deal? How critical is it?

    Also I think I read somewhere that the bore size dictates the KS spec. True? My Pontiac is bored to 3.915" vs a Chevy 4.00"

  2. #2
    Super Moderator dave w's Avatar
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    I'm wondering if Manual Transmission vs. Automatic Transmission might explain the 4K vs. 100K knock sensors. The 1227747 ECU has a knock filter module mounted near the throttle body. 1991 also used the 16147060 TBI ECU / PCM with 4L80E transmissions. The 1991 16147060 PCM uses a Memcal inside the PCM that has the knock filter instead of a knock filter mounted near the throttle body. Maybe the knock filter specs you posted was for the knock sensor used with the 16147060 PCM?

    I'm thinking the bore size is how the knock sensor frequency is determined.

    I would first try the 100K knock sensor on the Pontiac 350, provided the external knock filter is being used. I'm thinking the 4K knock sensor would NOT be the correct knock sensor for the 1227747 ECU.

    dave w

  3. #3
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    I grabbed everything including the throttle body and didn't see anything else besides the ESC. what does that filter look like? The donor had a 700r4.

    and thanks for the quick reply

  4. #4
    Fuel Injected!
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    You've got it then. It's the ESC - flat squarish box with a 5-pin connector that has 4 wires connected.

    I've always though it was odd they called it the Electronic Spark Control module when it was a knock sensor filter that provides the knock detected signal to the ECM. It doesn't have any direct control over the spark.

    I was thinking the 7747 was a 4k sensor. There was a post about that here a couple of days ago.

    Found it - it appears the 7747 would use a 100k sensor.

    http://www.gearhead-efi.com/Fuel-Inj...ll=1#post34353
    Last edited by lionelhutz; 01-30-2014 at 08:20 AM.

  5. #5
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    lionellutz: do you have link? I was searching for the topic here.

    So one vote 4k and one for 100k? (for Pontiac) Also I was looking up sensors on Oreilly Auto Parts and 1995 is TBI ( manual says 1.5-10K through 1995) and 1996 (~100K) is MFI not TBI

  6. #6
    RIP EagleMark's Avatar
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    100k with eternal knock filter (ESC) like on your 1227747.

    4K with a Memcal PCM where knock filter is in Memcal.

    The ESC has to match the knock sensor from same cubic inch vehicle.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  7. #7
    Electronic Ignition!
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    from my original post: my 1991 1227747 with ESC came with 100K and others in the yard

    several mechanics screwed up then?

  8. #8
    RIP EagleMark's Avatar
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    Sorry no, I reversed my post to be correct.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  9. #9
    Fuel Injected!
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    It's what Mark posted, generally the external filtered ECM's used a 100k, the internal OBD1 PCM's used 4k and then the OBD2 switched back to 100k. There were some 4.3L trucks in that era that used 2 x 8k sensors in series which probably explains the manual you're reading.

  10. #10
    Super Moderator dave w's Avatar
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    Quote Originally Posted by alsalp View Post
    I grabbed everything including the throttle body and didn't see anything else besides the ESC. what does that filter look like? The donor had a 700r4.

    and thanks for the quick reply
    http://www.autosparepartsmart.com/es..._module_7.html

    dave w

  11. #11
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    Quote Originally Posted by dave w View Post
    thats what i got, thanks. Looks like I'll try the 100K with my Pontiac (All concur? ) Hopefully the 3.915" bore is close enough

    thanks everyone

  12. #12
    Super Moderator dave w's Avatar
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    Quote Originally Posted by alsalp View Post
    ...Looks like I'll try the 100K with my Pontiac...
    That is a good plan.

    dave w

  13. #13
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    So while I got your attention what does everyone think about using the factory 454 spread bore adapter and the water jacket feature vs a simple plate adapter

  14. #14
    Super Moderator dave w's Avatar
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    Quote Originally Posted by alsalp View Post
    So while I got your attention what does everyone think about using the factory 454 spread bore adapter and the water jacket feature vs a simple plate adapter
    I've used the 454 adapter without plumbing the engine coolant through the adapter without problems, but I live in an area that does not see real cold weather. The 454 adapter can sometimes be a bargain for a budget, but might have hood clearance problems. Seeing you have the 454 adapter already, and have the hood clearance, I'd say use it. I don't think there is any real noticeable difference in performance between the 454 adapter and an aftermarket adapter.

    The only caution I would mention is the TBI fuel air mixture does not like flowing over the primary / secondary dividers of a quadrajet intake manifold.

    Many of the aftermarket TBI adapters position the TBI throttle body above the quadrajet secondary openings.

    dave w

  15. #15
    RIP EagleMark's Avatar
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    Quote Originally Posted by alsalp View Post
    So while I got your attention what does everyone think about using the factory 454 spread bore adapter and the water jacket feature vs a simple plate adapter
    Besides being UGLY? They are prone to vacuum leaks and the also mentioned hood clearance...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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