How to tell a fuel distributor needs rebuilding | FerrariChat

How to tell a fuel distributor needs rebuilding

Discussion in '308/328' started by yelcab, Mar 3, 2021.

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  1. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    12,661
    San Carlos, CA
    Full Name:
    Mitchell Le
    I have an 85-308QV (US) that was running well and then just acted up. Symptoms are:

    1. Start Relay began clicking during starting
    2. Fuel pump relay turns on and off in synch with start relay clicking
    3. The purple-white wire coming from the blue switch at the fuel distributor blue connector (this wire is the air flow switch signal and should be solid ground or 12V) is jumping around causing the Start Relay to click and turns the fuel pump on and off.

    While the engine is off and cold, System Pressure is 72 psi, so it seems the fuel pump is good
    Cold Control pressure is 22 psi, slowly rising to 45 psi after a few minutes, so it seems the WUR is good.

    Car idles high then low and then dies

    Are there other tests can be done on the Fuel Distributor before I pull it for a rebuild?
     
  2. mike32

    mike32 F1 Veteran

    May 13, 2016
    5,827
    Isle of man- uk
    Sounds more like the 12 volt supply is not constant . If start relay and fuel pump relay are not staying in it make me think volts on/ volts off. Cannot see how fuel distributor is doing this. Fuel in the sump oil plus misfiring, loss of power are signs of distributor failure.
    Rig a multi meter up to the signal wire on the starter solenoid, see if you get a steady 12 volts. The Mondials are known to have a problem with loss of volts to the starter solenoid and you can buy a kit consisting of a relay to sort this out.
     
    mike996 likes this.
  3. mwr4440

    mwr4440 Five Time F1 World Champ
    Rossa Subscribed

    Jun 8, 2007
    55,828
    Bavaria, The 'Other' Germany
    Full Name:
    Mark W.R.
    An FYI.

    THE FDs are easy to rebuild.

    The amount of fuel turned to varnish I got out of mine was HORRENDOUS.

    That said, it still ran and reved OK.

    I 'break' them in-half C-A-R-E-F-U-L-L-Y and soak each half in a sonic cleaner for 30 minutes to an hour. That usually cleans them right up.

    I put EVERY PART BACK in its original location. Sans the dirt, it is in its EXACT original configuration.

    There are 8 little white ceramic disks which are wafer-thin on the inside. DO NOT BREAK one of those when taking it apart or putting it back together. It is REAL EASY TO DO. Replacements are near IMPOSSIBLE to find.

    Replacement (black) gasket and o-ring kits can be found on eBay.

    The fuel filter/fuel line connector (after-market) that screws into the FD can be found on Amazon for about $4.00. Or just sonic clean the crap outta the OEM one.

    The hard part is tuning or balancing it.

    I don't have nor do I wish to fab the testing equipment necessary to do so.

    I send them halfway around the world and pay to have that colossal headache done.

    When you send it off, send about 12 new brass Bosch injectors* with it so that all 8 FD ports and 8 injectors can be balanced and matched as a complete system to a very specific and equivilant output over time port to port, cylinder to cylinder.


    * - 12 for an 8 cylinder car? Yep. Its a Good Idea as there are lots of 'Dud' (for our purposes) brand new Bosch brass injectors out there. They will work just fine in a BMW or MB but NOT in a Ferrari.
     
    JL350 likes this.
  4. Lawrence Coppari

    Lawrence Coppari Formula 3

    Apr 29, 2002
    2,149
    Kingsport, TN
    Full Name:
    Lawrence A. Coppari
    Check you battery terminals and ground. Connections may not support high current draw during starting causing a large voltage drop that affects relays. Once relays open reducing current draw, voltage rises, relays close, etc.,....
     
  5. smg2

    smg2 F1 World Champ
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    Apr 1, 2004
    15,475
    Dumpster Fire #31
    Full Name:
    SMG
    The absolute hands down guy to talk to about anything CIS related is Larry... He lurks about here sometimes... And on the Porsche groups...
    http://www.cisflowtech.com/

    Parts, rebuilds,etc... He's the guy.

    There's some ferrari CIS manuals out there, scant info though. Find the Mercedes stuff to be far more informative. Bosch books are decent.

    Honestly, if you want it to run like it should... Call and talk to Larry.
     
    JL350 likes this.
  6. mwr4440

    mwr4440 Five Time F1 World Champ
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    Jun 8, 2007
    55,828
    Bavaria, The 'Other' Germany
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    Mark W.R.
    IIRC his wife is German and while she was visiting family, he'd head-off to the Bosch Referb Plant and see what was new in Tips and Techniques on the 'Old-Timer' front.
     
  7. yelcab

    yelcab F1 World Champ
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    Nov 29, 2001
    12,661
    San Carlos, CA
    Full Name:
    Mitchell Le
    Well, as it turned out, I did not need a rebuild. The old AAV hose blew off its mounting and caused a massive air leak which caused the idle to be radically bouncing around, which caused the FD circuit to cut power to the fuel pump in synch with the idle bounce.

    Who would have thunk?
     
    2cam and smg2 like this.
  8. SeattleM5

    SeattleM5 Formula 3
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    Jul 9, 2006
    1,203
    Kirkland, Washington
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    Ettore Palazzo
    #8 SeattleM5, Mar 28, 2021
    Last edited: Mar 28, 2021
    I thought I would add to this thread as folks might find it interesting. I just got done rebuilding a fuel distributor for a very close friend. This cast iron distributor was off of a 308QV but is the same distributor shared by the 3x8/Mondial lines with 3.2 engines and Kjet with lambda (Bosch 0438100139). This car had travelled just short of 100k miles, however, the distributor had reportedly been rebuilt in the not too distant past by a well known rebuilder. Pre rebuild testing found that flow variances between the 8 ports were widely out of spec. Bosch allows for a 16% flow variance at idle, and 10% flow variance at part load and full load. This one had over twice that. Once the distributor was apart I found white chalky debris throughout that was clogging many of the output ports. It looked like someone had tried to compensate for irregular flows by manipulating the port adjustment screws as their depths were significantly different from one another. I've rebuilt many distributors and I'm accustomed to seeing fuel deposits and varnish particularly on cars that sit for long periods but I've never encountered this white chalky stuff. Anyway, after multiple rounds of ultrasonic cleaning, new O-rings, and a new diaphragm the unit is back together and calibrated to flow variances of 5% or less at idle/part load/full load. For those sending their fuel distributors off for rebuilding I would absolutely insist that the rebuilder document pre/post rebuild flow variances as as well as system/residual pressures to ensure that the internal pressure regulator is set appropriately.

    Please note, I include this post for information only and am not trying to sell any services. After acquiring my 328 many years ago I became particularly interested in the Bosch CIS system and have acquired/built all the necessary test equipment to evaluate these systems. Everyone worries about being bored after they retire. I know exactly what I'll be doing :)

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  9. mike32

    mike32 F1 Veteran

    May 13, 2016
    5,827
    Isle of man- uk
    AAV hose, you better educate me as not up on this
     
  10. lopena

    lopena Formula Junior
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    Nov 3, 2003
    692
    The AAV is the Auxiliary Air Valve. On a 328 it sits directly underneath the coolant tank. The AAV sends extra ‘auxiliary’ air into the intake plenum when the engine is cold (thus raising the idle speed). As the coolant heats up the heat transfers to the AAV and the air valve, controlled by a bi-metal spring, slowly closes. This shuts off the auxiliary airflow and lowers the idle speed. It’s a simple, purely mechanical way of controlling the idle speed as the engine warms up.

    When Mitchell’s air hose blew off the AAV this had the effect of allowing an uncontrolled amount of air to enter the intake plenum.

    Alan
    N.J.
     
  11. dave80gtsi

    dave80gtsi Formula 3
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    Nov 3, 2003
    1,813
    Ohio
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    Dave Meredith
    As a PSA, would you be willing to share the name of this 'well known' firm?
     
  12. SeattleM5

    SeattleM5 Formula 3
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    Jul 9, 2006
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    Ettore Palazzo
    Dave, without formal documentation confirming the rebuild I don't feel it would be appropriate to do so.

    As far as a PSA, I will reiterate what I stated in my prior post. If you are considering having your CIS fuel distributor rebuilt by a professional first ask if the rebuilder has the appropriate equipment to test flow variances and ask that they confirm pre-rebuild flow variances, system pressure, and residual pressures to determine if the unit is out of spec before embarking on an expensive rebuild. These distributors are quite robust and hold their calibration well provided fuel is regularly flowing through them. For reference, I have tested 150k+ mile Mercedes distributors that are perfectly within spec. If a rebuild is determined to be necessary, the same equipment will be required to calibrate the distributor post rebuild. Ask that the rebuilder document the post rebuild flow variances and at a minimum they should be <=16% at idle and <=10% at part/full load. It takes a lot of time but these units can be calibrated to within 5% flow variance and it is my opinion that the difference in drivability is noticeable.
     
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