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Interesting Problem...

Discussion in '308/328' started by jcinflorida, Feb 1, 2010.

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  1. jcinflorida

    jcinflorida Formula Junior

    Oct 24, 2009
    331
    Melbourne Florida
    Full Name:
    John
    #1 jcinflorida, Feb 1, 2010
    I have put about 200 miles on my 83 308 QV in the last week and yesterday something interesting happened. About 30 minutes into the drive it backfired and started running rough at medium - high RPMs. I had been on a straight road for about 3 minutes keeping about 4K RPM when it happend. The tachometer became very erratic and read about TWICE what the actual RPMs were. All temps & pressures were fine. I stopped, checked for leaks and let it sit for 10 min. I got back in and it still did the same thing until a few minutes later it backfired again and started running fine. I am guessing its something ignition related - as in the tach sensor or ECU / wiring or coils. I am really hoping that something just rattled loose but I am prepared for the worst. This car just had a major service 300 miles ago including belts, plugs, seals, distributors. Tonight I will check & clean all connections, verify ECU grounds, and maybe test the sensors / coils with an Ohmmeter. Any suggestions fellow F-chatters? Any help is greatly appreciated!
     
  2. FamilyCar

    FamilyCar Formula Junior
    Rossa Subscribed

    Sep 26, 2007
    787
    Seattle, Wa
    Full Name:
    Peter Goodall
    #2 FamilyCar, Feb 1, 2010
    It sounds as if you're on the right path, although that is a really strange situation. I believe that the sensors for the ignition and the tachometer are entirely independent, so while a bad TDC sensor or connection could create poor running, it would not affect operation of the tach. Conversely, the tach could go wild without affecting the engine. What they have in common is the magnet on the flywheel, which I suppose could have picked up some crud then thrown it off, but the issue starting and stopping with a backfire is weird unless it's just chance.

    Hopefully someone that knows more than I will chime in. My car is not an '83-type, so it could also be somewhat different, perhaps they do share a sensor. There are a number of threads on TDC sensors. Good luck.
     
  3. Paul_308

    Paul_308 Formula 3

    Mar 12, 2004
    2,345
    #3 Paul_308, Feb 1, 2010
    1983 qv cars have same electricals as the 2v cars, including the dual dupliplex ignition modules. The tach signal comes from the digiplex and errant tach readings have not implications to the tach sensor but tdc sensors are suspect. You will first have to learn if you are loosing a complete bank or not. Start with diagnosis of sensors including resistance. IIRC two should be 750 ohms and one 719 ohms (or tother way around). But first refresh grounds, especially those on the digiplex ignition units.
     
  4. ClydeM

    ClydeM F1 World Champ
    Owner Rossa Subscribed

    Nov 4, 2003
    11,908
    Wayne, NJ
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    Clyde E. McMurdy
    #4 ClydeM, Feb 2, 2010
    I have an 83 qv. I second cleaning the grounds & reseating. Esp. if the tach became erratic.
     
  5. jcinflorida

    jcinflorida Formula Junior

    Oct 24, 2009
    331
    Melbourne Florida
    Full Name:
    John
    #5 jcinflorida, Feb 2, 2010
    Thanks for the tips!
    I openned up the trunk and checked the digiplexes. There were no ground wires to the boxes and the mounting bracket looks like it was not making good contact (it was painted so no bare metal - metal contact. So I added a ground wire to each box and made sure the chassis ground contact was clean. The car started normally and after its warm-up I ran it for another 5 minutes (it was raining so I did not drive it). It revved strong. I won't be
    convinced I have fixed anything until I drive it for 45 minutes (maybe tonight). I will check
    the TDC sensor resistances and connections as well tonight to be sure they are OK. If I
    have an intermittent problem with them I won't know until trouble strikes again. I am
    convinced I lost a bank of cylinders though when it was running rough before. I will keep
    you posted on what else I find. Thanks everyone for your help so far!
     
  6. Dr Tommy Cosgrove

    Dr Tommy Cosgrove Three Time F1 World Champ
    Owner Rossa Subscribed

    May 4, 2001
    36,435
    Birmingham, AL
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    Tommy
    #6 Dr Tommy Cosgrove, Feb 2, 2010
    My money is on the crank position sensors
     
  7. dwhite

    dwhite F1 Rookie

    May 30, 2003
    3,511
    Bklyn, NY/Vero Beach
    #7 dwhite, Feb 2, 2010
    I agree it could be the culprit and it would be an easy fix.

    However you need to check all components of ignition system. There is a port to check all the components of the system, if you just had service it might be beneficial to take car back and ask them to do a check for you. Once you know what part is problematic it will be an easy fix.
     
  8. Paul_308

    Paul_308 Formula 3

    Mar 12, 2004
    2,345
    #8 Paul_308, Feb 2, 2010
    Each digiplex ignition module has a black wire at pin #9 which goes to a proper ground.

    _________________________
    http://www.FerrariWiring.com
     
  9. jcinflorida

    jcinflorida Formula Junior

    Oct 24, 2009
    331
    Melbourne Florida
    Full Name:
    John
    #9 jcinflorida, Feb 10, 2010
    I drove the car last week for about 1.5 hours and did not have any power-loss issues so I am hoping that the additional grounding wires fixed it. But if it comes back I will check the sensors. Unfortunately near the end of the drive another issue arose: smoke from the engine compartment. It smelled like buring oil. When I got home it was smoking pretty bad so I openned the engine compartment and did a quick inspection. There is an oil splatter down around the main pulley and oil dripped onto the frame and exhaust pipe below it.
    Until I get the tire and wheel well out I won't know for sure but I'm thinking its the front
    engine seal. Hopefully its not a cam seal. All the seals just got replaced and only 300 miles
    later one has already gone bad. Arrrgghhh!!!
     
  10. CliffBeer

    CliffBeer Formula 3

    Apr 3, 2005
    2,198
    Seattle, Washington
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    Cliff
    #10 CliffBeer, Feb 11, 2010
    I would bet you fixed your problem with adding the grounding wires to the digiplex boxes. I had exactly the same symptoms...took a look at ole' f-chat here, saw the suggested fix (separate ground wire for the digi boxes) et viola! She runs great now.

    I bet a lot of guys have replaced digiplex boxes or caps/rotors/extenders or TDC sensors trying to fix this same problem....

    Great to hear she's running well now.
     
  11. ClydeM

    ClydeM F1 World Champ
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    Nov 4, 2003
    11,908
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    Clyde E. McMurdy
    #11 ClydeM, Feb 11, 2010
    Get use to the cam seals going. They're a stinker to put in right even by seasoned mechanics.
     
  12. jcinflorida

    jcinflorida Formula Junior

    Oct 24, 2009
    331
    Melbourne Florida
    Full Name:
    John
    #12 jcinflorida, Feb 11, 2010
    Thanks for the input so far guys! Now on to the oil leak...
    I checked things out visually while the car was running and
    found my oil leak problem: the rear cam drive pulley is wobbling
    and making a chattering noise. So I'm betting the bearing
    failed and took the seal with it. At least its the easier one
    to get at but as I understand it, removing the bearing without
    removing the engine is next-to-impossible. Sucks since I've
    only had the car 2 weeks! Good thing I found it before the
    pulley failed and took 16 valves with it. Ugh... so far, excluding
    the purchase price, the maintenance on this car has cost me about $50 per mile.
    If I did not like it so much I would call it a lemon at this point.
     
  13. fastradio

    fastradio F1 Rookie
    BANNED Professional Ferrari Technician

    Apr 26, 2006
    3,664
    New England
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    David Feinberg
    #13 fastradio, Feb 11, 2010
    The outer lower cam drive bearings can be done relatively easily with a "Sykes-Type" bearing puller.

    Best,
    David
     
  14. CliffBeer

    CliffBeer Formula 3

    Apr 3, 2005
    2,198
    Seattle, Washington
    Full Name:
    Cliff
    #14 CliffBeer, Feb 11, 2010
    Last edited: Feb 11, 2010
    John, yup, even a lemon with some sugar sprinkled on it tastes pretty good....

    Fact is, most 308s that are driving around have a ton of deferred maintenance problems, despite what the owner thinks. Why? Because if you can't turn wrenches yourself then a) it's hard to know what needs to be serviced, and b) the average non-mechanical guy is faced with writing pretty large checks to get all these service items handled. Consequently, the car sits in the garage going nowhere (getting worse) most of the time, coming out for the occasional Sunday drive in the summer at which point a few of the problems exhibit themselves. The owner decides to sell (not understanding the full scope of what needs to get fixed) instead of fixing, New Guy buys the car and then inherits all the deferred maintenance issues. If New Guy knows how to turn wrenches (like you) then he pretty quickly starts to realize the full extent of what needs to be fixed....

    Perhaps in some situations Ignorance Is Bliss but I just can't stand to own and drive around in cars that have obvious (to me) needed fixes. So, I do what you're doing - take it one thing at a time and fix it all. In the end you've got a really good and reliable car that's fun to drive.

    Good luck and hang in there, there's light at the end of the tunnel.
     
  15. PV Dirk

    PV Dirk F1 Veteran

    Jul 26, 2009
    5,401
    Ahwatukee, AZ
    #15 PV Dirk, Feb 11, 2010
    JC, sorry to hear about the problems. I hope you are having an experience similar to mine in that for some reason I still have a smile on my face when I pull out the credit card for my car. When it's back together you'll have to do what I do about the $/mile issues. I control what I can by driving the car as much as possible. Best of luck.
     
  16. jcinflorida

    jcinflorida Formula Junior

    Oct 24, 2009
    331
    Melbourne Florida
    Full Name:
    John
    #16 jcinflorida, Feb 11, 2010
    Thanks guys for your support. It really helps to know that others out there have gone
    through similar trials and it was worth the effort. I hate defeat and I will fight for my dream
    as long as I can. I got new jack stands and a nice floor jack today so I'm ready to
    "hike her up" and get at it. It looks like I will be looking for a Sikes-type bearing puller. I am a little nervous about messing with the timing belt but the Birdman Ferrari procedure looks simple enough. As long as I mark everything's position and clamp things down then nothing should get out of alignment. I really hope nothing happened on the INSIDE bearing or drive gear but I guess I will find out. Hopefully I can get this done in a short amount
    of time because the Florida driving weather is pretty good right now. It is true that I
    have a growing list of maintenance items that I have found just in chasing this problem.
    Almost everywhere I look its "oh, that needs fixing too". Sound familiar? Ugh!
     

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