85 QV intermittent stalling issue | FerrariChat

85 QV intermittent stalling issue

Discussion in '308/328' started by Cuddy K, May 18, 2019.

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  1. Cuddy K

    Cuddy K Karting

    Oct 30, 2017
    181
    Full Name:
    Ian Karr
    #1 Cuddy K, May 18, 2019
    Last edited: May 18, 2019
    Hi Guys,

    My 85 QV starts up easy, revs well, idles smoothly and rock-solid at 1K, and pulls great under power. It's perfect...for about 15 minutes. After that I've developed an intermittent problem where the engine wants to stall when coming to a stop...or even just coasting. I sometjmes also notice a larger than normal dip in RPM between shifts, too. After it stalls, it re-starts fine (maybe an extra few seconds of cranking).

    I don't suspect the booster vacuum since I'm seeing symptoms without my foot on the brake. The intermittent nature has me baffled. The only constant is that it seems to happen only after the car is fully warm. It's never stalled within the first 15 mins of driving. I've narrowed the suspects down to the WUR, EGR, fuel filter and accumulator. Before I start messing with parts that are perfectly fine, I thought I'd ask the experts here...

    Thoughts? Tests I can run? Thanks!
     
  2. thorn

    thorn F1 Rookie
    Silver Subscribed

    Aug 7, 2012
    3,322
    Tallahassee, FL
    #2 thorn, May 18, 2019
    Last edited: May 18, 2019
    Things I'd start with:

    1) Battery/Alternator connections
    2) Bad grounds for the engine or ECU
    3) Fuel pump - confirm the pressure AND the current draw
    4) Vacuum leaks

    In that order. If all those check out, then move towards things like crank sensors and ignition stuff.

    (FWIW, #2 AND #4 caused serious issues with my car. #2 was completely heat-related... the car would just completely shut off as I was driving down the road. Were a bit tricky to find, but each was about a $5 fix.)
     
  3. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,040
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    What version 1985 308QV? US, euro, euro converted to US legal, euro converted to US legal and then unconverted, something else?
     
  4. Cuddy K

    Cuddy K Karting

    Oct 30, 2017
    181
    Full Name:
    Ian Karr
    Thanks guys. It's a US version.
     
  5. Ferraridoc

    Ferraridoc F1 World Champ
    Owner Silver Subscribed

    Jun 20, 2012
    16,070
    Gold Coast, Aust.
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    Patrick
    You've really got to work your way through the system. I rebuilt the WUR, checked the AAV, replaced the pump and accumulator, and had the exact same problem. It turned out to be running too rich. I leaned it out a bit, which required adjusting the air bypass to suit, and that fixed the problem. Stick a gas analyser up it's bum and see what your CO is
     
  6. Brian Harper

    Brian Harper F1 Rookie
    Owner Silver Subscribed

    Feb 17, 2006
    4,078
    San Jose area
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    Brian Harper
    US version with oxygen sensor? And does it have sample ports still? I'm asking because I suspect another Fchatter's rough running when warm was rotten sample tubes that throw off the lambda sensor by admitting ambient air into the exhaust. The system doesn't use the lambda sensor until it is warmed up.
     
  7. Cuddy K

    Cuddy K Karting

    Oct 30, 2017
    181
    Full Name:
    Ian Karr
    99% sure it's US without sensor. BUT...I think I found the smoking gun. One lead to the thermal valve on the expansion tank was just barely resting on its terminal, making intermittent contact. This being part of the EGR system, I'm pretty sure this is the culprit. Gonna drive as soon as I have a free afternoon (in case this isn't it and I break down). Will report back...
    Image Unavailable, Please Login
     
  8. Cuddy K

    Cuddy K Karting

    Oct 30, 2017
    181
    Full Name:
    Ian Karr
    Unfortunately that didn’t solve the issue. It does seem better though. Gonna continue running through your suggestions.
     
  9. paul01

    paul01 Karting

    Jul 31, 2011
    92
    Hi Cuddy,
    if you search for the reason one of the first things imay be to look if only one bank is problematic. Then the ignition may be the problem, e.g. one coil because you mentioned heat and "intermittent".
    Maybe you see that on the spark plugs. So you could also see if only one cylinder is affected.
    Paul
     
  10. miketuason

    miketuason F1 World Champ
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    Feb 24, 2006
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    Cerritos, CA.
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    Mike
    Digiplex box can also cause the same intermittent problem.
     
  11. thorn

    thorn F1 Rookie
    Silver Subscribed

    Aug 7, 2012
    3,322
    Tallahassee, FL
    One bad cylinder, or possibly even a full bank, is not going to take the whole engine down and stall the car... run like hell, yes... but probably not cause a full stall and shutdown. The car WILL run will at idle, with a bank completely disconnected. At least, based on my experience.

    There's a process here to find the problem; don't just spitball it.
     
  12. Cuddy K

    Cuddy K Karting

    Oct 30, 2017
    181
    Full Name:
    Ian Karr
    Agreed. The checklist approach is usually best for intermittent problems with several possible causes. The engine either runs amazingly great....or loses power / stalls when taking your foot off the gas. Given the on-off nature of the problem, I'm suspecting it's ignition (or the electrical triggers), but I'll work methodically through the systems to make sure there aren't multiple things conspiring.
     
  13. Dr Tommy Cosgrove

    Dr Tommy Cosgrove Three Time F1 World Champ
    Owner Rossa Subscribed

    May 4, 2001
    35,288
    Birmingham, AL
    Full Name:
    Tommy
    I had this issue two years ago. Ran like a top - but would stall. Start it and it would run perfectly, then it would stall.

    It was the spade connector on the fuel pump on the fuse panel. That's all it was. Apparently it loosened up/got hot/etc over the course of 33 years and just was not making a good contact any longer.

    Check it first. Sometimes you just have to go back to the basics first before overthinking something.
     
  14. Cuddy K

    Cuddy K Karting

    Oct 30, 2017
    181
    Full Name:
    Ian Karr
    Success! I've driven 150 miles of backroads, stop signs and lights without stalling. Either the problem is solved, or it has gone underground, just waiting to frustrate me again ;).
    What I think happened...Over the winter, I removed the plenum and throttle body to strip and restore (video link below).


    When I put everything back, I adjusted the air bypass, throttle plate adjustment screw and throttle position sensor to achieve proper 1K idle. I suppose the engine may not have been fully warm when I did this, as I needed to do some fine tuning of the adjustment screw after a few drives. It seems that adjustment caused a situation where the switch on the throttle position sensor wasn't actuating when the the lever was on the stop. I adjusted the TPS in a quiet garage so that I could hear the "un-click" of the switch as the throttle opened, and "click" again as it returned back to the stop. No more stalling.

    Does this make sense to the gurus? Or did I just get lucky for a while?

    Thanks!
     

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