308gtbi us spec. ignition timing issues (digiplex) | FerrariChat
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308gtbi us spec. ignition timing issues (digiplex)

Discussion in '308/328' started by c.bridge, Oct 6, 2015.

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  1. c.bridge

    c.bridge Rookie

    Oct 6, 2015
    1
    london england
    #1 c.bridge, Oct 6, 2015
    Last edited by a moderator: Oct 6, 2015
    Hi, i've been having many issues with my 308gtbi (us spec) car. It's recently been imported but hasnt been ran for quite some time. First issue, it was a non runner. That was resolved was a sticking fuel head, cleaned and unseized which it now starts and runs. However;

    The ignition timing is very retarded. The front bank is more retarded than the rear bank. (So much infact the rear bank wont run atall) (Front bank 20 deg, rear bank 10 deg roughly.) I have changed the crank trigger sensors (digiplex) to which the problem is still apparent.

    I was thinking maybe the pegs on the flywheel could be bent but surely how would the rear bank run better than the front if that was the case? The both read the same sensors? I have noticed that one of the old sensors had a scrape mark on the tip of the magnet. To which i cant remember if it were 1-4 or 5-8 sensor. Where would the individual problem be with the ignition timing on the front bank?

    compression test, 150 ish across Ok

    Timing check found front bank exhaust cam 2 teeth advanced. (Always known for flicking forward when belts removed) i have corrected the timing.

    Obviously the digiplex system has its set timing, (unable to adjust) - i'm not used to working on these us spec cars which have extra coolant temp sensors/egr/vac systems. I have removed all of the us spec vac system, air pump, cannistor and blanked off all exposed fittings.

    i thought about bridging the coolant expansion bottle thermoswitch to which it advanced the timing some 6 degrees. Now the front bank runs with the rear because the timing is now within the window. Is there any other sensors on the us system which contribute to the ignition timing? I tested the vac on both digiplex units. They both hold vac. I disconected the main vac feed to both units and put a vac to the line.

    This actually retarded the ignition, i thought it would have advanced it.

    Maybe the vac advance boxes are stuck? With the vac line perminantly disconnected the engine runs much better and the timing is much closer to what it should be but still not right! The front bank is still more retarded than the rear. How confusing. Maybe i should remove the flywheel and inspect the pegs as its impossible in situ.

    What should the timing be at idle on a us? Are they more retarded than the uk spec?

    Is there a wire input to change the ign timing.

    Any help really is greatly appreciated.

    Sorry for the essay introduction!
     
  2. jon s

    jon s Formula Junior

    Mar 9, 2005
    509
    pocasset ma
    Full Name:
    jon shoukimas MD
    #2 jon s, Oct 10, 2015
    sorry your having trouble. i gave up on mr marelli and put an aftermarket ign in my us spec 81 gtbsi. all the info you need is in a manual titled "engine operation checking procedure" - in english so i assume us spec. if you get desperate i can copy the ignition section and mail it.
    anyway advance curves for idle (0-`1200 rpm) CYLS3,4,5,6,7,8(warm ENGINE)=minus 3 deg. cyl 2=0 deg, cyl 1=6deg. in same cyl order above for cold engine minus8, minus 5,1. hope this helps. cheers, jon s good luck - check the usual manual sources and see if you can find a copy-good section on the jetronic fi
     
  3. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,935
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #3 Steve Magnusson, Oct 10, 2015
    Having the Atlantic Ocean in between might be an additional obstacle, but Ferrari Service of Bedford:

    Ferrari Service of Bedford Products - Ferrari Service of Bedford

    rebuilds DigiPlex ECUs with modern internal components.

    For the ignition "specs", go to All Ferraris and download the Mondial8/QV Workshop Manual 281/83 -- it has all the information on both US version and Standard (euro) version 3.0L-2Vi DigiPlex ignition systems.
     
  4. Tire Fryer

    Tire Fryer Karting

    Feb 18, 2013
    154
    Farmers Branch, TX
    Full Name:
    Christopher Williams
    #4 Tire Fryer, Oct 12, 2015
    I know it doesnt help your current situation, but I also became tired of the multiple failures from the Digiplex system on my 1980 GTBi, and I removed the complete system and replaced with Electromotive's set up. It really transformed the car in terms of drivability and acceleration.
     
  5. MNExotics

    MNExotics F1 Rookie
    BANNED

    Dec 13, 2010
    2,631
    Good Thunder
    Full Name:
    Ben Gruenzner
    #5 MNExotics, Oct 12, 2015
    U.S. Boxes, med 801a, are horrible. Stock timing at idle is 3 deg atdc so extremely retarded. The ignition is triggered by crank position so for ignition the boxes don't care where the the cams are. Check the pickups for signal and clean the distributor caps and rotors. The engines also tend to be a little sensitive to spark plug condition. These engine run low vacuum so small leaks in the system can hide well.

    The euro spec boxes 802a I believe had base timing of 10 deg btdc. But that is from memory. You can swap in the euro boxes without additional mods.
     
  6. Badman

    Badman Formula 3

    Mar 4, 2007
    1,116
    Gotham City
    Full Name:
    Bruce Wayne
    #6 Badman, Oct 14, 2015
    Switch the connections between the two digiplex boxes. If the timing problem switches banks, then you've got a bad digiplex box. Ferrari Service of Bedford can test your boxes for function, and if bad they can rebuild them with either the US curve or the Euro curve. As long as your local laws allow you to alter the emission systems in the car you can get the advantage of the Euro curve as well as new internal circuitry.

    A rebuild to Euro specs is a much better solution than the XDI system for the injected cars, as it's a drop in replacement that doesn't require hacking up the wiring, and it keeps the more modern ignition curves vs the XDI which copies an older two spring distributor advance system. The folks I know who have switched to the Ferrari Service of Bedford Euro curve rebuilds are amazed at the difference, even more so than QV folks who have done it. (I've got the Ferrari Service of Bedford QV boxes in my car and they're great).
     

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