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308 Flywheel Sensor Questions

Discussion in 'Technical Q&A' started by Doc, Mar 11, 2004.

  1. Doc

    Doc Formula Junior

    Sep 13, 2001
    886
    Latham, New York
    Full Name:
    Bill Van Dyne
    I have a couple of general Q's re: the 3 flywheel sensors on a 308. First of all, which of the 3 sensors are related to the 2 banks and the tach--location- wise ? Also, how does one test these sensors, if there is Q of a problem? In using an ohmeter what values would one expect to see on each of these sensors? Just curious.
     
  2. Verell

    Verell F1 Veteran
    Consultant Owner

    May 5, 2001
    6,992
    Groton, MA
    Full Name:
    Verell Boaen
    Search the old FerrariChat 'Tech Q&A' and also 'Tech Q&A Archives'.

    I remember a thread or 2 a couple of years ago, pretty sure some resistance meas'ts were reported, along with a fair amount of other info about the sensors.
     
  3. carlrose

    carlrose Formula Junior

    Nov 25, 2003
    295
    Hi Doc,

    Just so happens had reason to remove these to test in past month. My 328 only uses two - a TDC sensor & an RPM sensor (tachometric). Resistance values as follows:

    TDC: 0.728 ohms
    RPM: 0.692 ohms

    One can read the resistances form either the multi-connector harness under LR fender, at junction of intermediate harness (from bracket to top of bellhousing) and sensors, or directly from sensors. These numbers are directly from sensor on bench. Advantage is ability to manipulate lead to confirm consistent reading (i.e. no hidden wiring fractures). Should you get an erronous reading, on my 328 the oil cooler line required removal (to pull sensor); the front bank one was extremely challenging (remove 5-8 dist cap) recessed into bellhousing iwth two 8mm nuts & lock washers. Would suggest for time & effort if multimeter check is suspicious to simply remove with intent to replace.

    :) Carl
     
  4. Doc

    Doc Formula Junior

    Sep 13, 2001
    886
    Latham, New York
    Full Name:
    Bill Van Dyne
    Thanks, Verel and Carl. Now , which sensors are attached to which functions? That is , does the one at the top of the bellhousing control the tach, the one at the engine rear control the rear bank, etc?

    Thanks.
     
  5. carlrose

    carlrose Formula Junior

    Nov 25, 2003
    295
    Doc, can only adress 328:

    Front (5-8 bank) TDC controls ignition
    Rear (1-4 bank) RPM controls tach

    Seem to recall the 308 has TDC sensors for each bank?

    :) Carl
     
  6. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    19,255
    Texas
    Full Name:
    Steve Magnusson
    Doc -- Check the schematic in Section 3, sub-section "ignition system componets" of your model/year/version 308 OM. Often these diagrams include "spatial" information pictorially that you can match-up to your F to figure out who's who. Even if the pictograms in the schematic don't match up exactly, you can follow the electrical connections to figure out who's who.

    Each bank on a 308QV does have it's own "TDC sensor", and since they show the flywheel using 2 "marks" this means that the two TDC sensors must be ones mounted 90 deg apart to get the desired result (i.e., 4 pulses per 2 revolutions coming out of each TDC sensor, and the two TDC signals separated in phase by 90 deg of crankshaft rotation).

    The 307/84 OM ignition schematic shows the TDC sensors connecting to plugs with 4 wires each; the RPM sensor connects to a plug with only 2 wires.

    PS -- Carl -- should those be "K Ohm" resistance values? (I can't believe you're measuring to the milliOhm ;))

    PPS -- Looks like they made a small mistake and copied/used parts of the TR ignition schematic in the 328 OM ignition schematic because it only shows 3 "marks" on the flywheel for the TDC sensor rather than the (I think) needed 4 -- anyone got a 328 flywheel to confirm/deny?
     
  7. carlrose

    carlrose Formula Junior

    Nov 25, 2003
    295
    Somedays I'm good, just not that good....doh!

    Carl (making Homer Simpson noises right now)
     

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