Jerky feel and lumpy idle in 91 Testarossa | FerrariChat
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Jerky feel and lumpy idle in 91 Testarossa

Discussion in 'Technical Q&A' started by Shamile, Dec 5, 2004.

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  1. Shamile

    Shamile F1 Veteran

    Dec 31, 2002
    6,712
    Lakeland FL
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    Shamile
    #1 Shamile, Dec 5, 2004
    Dear Ferraristi,

    It's me again.

    Ever since I changed my coolant, the TR has just not felt right. Now when I accelerate, I can feel a sort of jerkyness and a slight jerkyness while running at a constant speed. ( All speeds )

    I have changed plugs, fuel filters and now I'm looking into wires. Everything before the coolant change was fine. One thing I did is that I had the run the car for 6 hours for the flush kit I was using. Since I didn't have the time to run the car that much, I would let it idle in the garage for a 1/2 hour at a time of the course of a few days.

    I just don't understand what it could be, it ran perfect before. One thing I noticed is that I no longer get that "clank" ( some relay or selonoid ) when turning the key to position 2 before starting. I don't know if that has any bearing but I noticed that was different. I also get a vibration at 1800rpm now, no where else in the rev range. I can run the car up to 6800 per shift and it pulls fine. I do feel that jerkyness though...not violent but noticible.

    If I stick my head between the exhaust pipes, the sound is even and when it sounds like it is "missing", both exhausts register the change in pitch.

    After changing the plugs , the car sounded better. I still get the vibration at 1800 and at idle ( at traffic light ) I pulled the new plugs and all have the same look....dry with some slight grey color. I put my timing light and all registered at the same point. ( per bank only)

    Please help me out on this. I'm really bummed out. :(


    Shamile

    Freeze...Miami Vice!
     
  2. tbakowsky

    tbakowsky Two Time F1 World Champ
    Consultant Professional Ferrari Technician

    Sep 18, 2002
    20,034
    The Cold North
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    Tom
    #2 tbakowsky, Dec 5, 2004
    Sounds like you may need a slight tweek of the co adjustment, one one or both of the fuel distributors. If you are not familiar with this proccedure do not attempt it. The screw is VERY sensitive. You need a 4 gas analyzer or a dwel meter to do this correctly.

    Having said that..there are a few things to check first before turning any screws. Many issues on the TR are electrical related. The first hing I would check would be the fuse panel. With the car running..wiggel the wires and relays around. See if you notice any change in the running of the enigne. If this does not revel anything, a visual check of the connectors is in order.

    Also..double check any area that you were working in. You may have inadvertantly knocked a connector out of place. Check the connections under the expantion tank(were you add the coolant) and the large round connection on the passenger side..just forward of the muffler..under the fender..also check the smaller one beside it. Make sure that coolant did not spill on any electrical connections during the flush. Of you find damp connection dry as needed.

    Hope this helpd out a bit,,it may not solve the issue but it is a start before turning any screws
     
  3. TOM B

    TOM B Formula 3

    Jul 24, 2003
    1,038
    Orange County, NY
    Full Name:
    Thomas Buckley
    #3 TOM B, Dec 6, 2004
    It may be the sparkplug wires. The original wires weren't very good. Similar symptoms to what you describe started on my Mondial a few days ago. While pullind the wires to check my extenders, one snapped in half in my hands. I ordered a set from Magnecor and will put them in on Tuesday. Stay tuned for an update.

    Tom
     
  4. parkerfe

    parkerfe F1 World Champ

    Sep 4, 2001
    12,887
    Cumming, Georgia
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    Franklin E. Parker
    #4 parkerfe, Dec 6, 2004
    Could be a vaccum leak. You may have knocked a vacuum hose off while servicing the coolant.
     
  5. Smiles

    Smiles F1 World Champ
    Lifetime Rossa Owner

    Nov 20, 2003
    16,675
    Pittsburgh, PA
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    Matt F
    #5 Smiles, Dec 6, 2004
    I'd also double check the throttle linkage for smooth operation first.
     
  6. Shamile

    Shamile F1 Veteran

    Dec 31, 2002
    6,712
    Lakeland FL
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    Shamile
    #6 Shamile, Dec 7, 2004
    Dear Ferraristi,

    Thank you very much for your advice. I'm really dumbfounded why this would happen after a coolant change. I didn't spill any as Ferrari electrical connections are like Italian politics...iffy at best.

    I took my multimeter and did a resistance test from each point in the distributor cap to the end wire. All extenders registered the same at .03 Ohms

    I noticed on one, (#6 ) I wasn't getting any reading at all. I unscrewed the wire at the cap and found the end burned. I snipped the end back, reattached and got a reading. Obviously I wasn't getting any spark. The thing is my timing light registered spark...go figure. Anyway, I test drove the car and the jerkyness at speed and acceleration is gone. NO CIGAR YET !

    I still have a miss or slightly rough feel at idle. I then took a reading from every cable and found a couple in the M Ohm range. OK, I unscrewed all wires and snipped a bit off and reattached. All reading were now from 8.31 K Ohms to 14.03 K Ohms. I started the car....it sounded better but still a sort of roughness. I mean the car will rev freely and smoothly but at idle it will be smooth then go rough (jiggle side to side very lightly ) then smooth. I haven't test driven the car since the full "snip and reattach" I will give you the results soon.

    I've changed everything execpt the plug wires and based on all your advice, I've ordered a set from Magnacor. I suppose if I had a burn spot in the wire at the cap, the wires can't be all that good.

    I'll let y'all know what transpires after I install them.

    BUT... if you do have a sort of miss, try snipping a piece off at the cap and reinstalling. I mentioned this to Magnacor and they said the the Ferrari cap was a bad design with the screw going throught the cable. It leads to burns. Hmmm...it's what I've found so far.

    BTW, the engine was balanced with new O2 sensors in June of this year. Everything was smooth before the coolant change.


    Shamile

    Freeze...Miami Vice !
     
  7. f355spider

    f355spider F1 World Champ
    Owner Rossa Subscribed

    May 29, 2001
    18,055
    USA
    #7 f355spider, Dec 7, 2004
    Great news, and sounds like you are making progress on this. It sounds like you tested all the extenders and the resistance is consistant? Did you also carefully inspect each extender for damage or burn through spots on the extender body. This would be a sign the voltage is going to ground through the extender exterior, to the inside of the spark plug hole, causing a miss. Also, the #6 cylinder plug may be fouled from not firing...and may now need to be replaced (been there, done that). Same with those other plugs that had the bad reading...You might be able to take those plugs out, wire brush them or something, and they will work fine, maybe not. When I fouled a plug, I just replaced it.

    Dave
     
  8. Shamile

    Shamile F1 Veteran

    Dec 31, 2002
    6,712
    Lakeland FL
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    Shamile
    #8 Shamile, Dec 11, 2004
    Dear Ferraristi,


    After snipping each plug wire at the distributor and reinstalling, the car runs as it was when at speed or accelerating. This was an amazing transformation. I haven't installed the new wires yet but I think that is not where the issue is now. I'm now thinking a air leak at the manafold or injectors.
    My Ferrari mechanic told me that if I was experiencing a miss, it would be very noticible at high revs. He also said at idle, a perceived miss is usually a sign of a bad or gummed injector. As I have said, the TR is now very smooth except at idle.

    Upon inspection, I noticed a ring of wetness around two intakes...#1 & #3. If retorqueing the manafold doesn't do it, I'm going to replace all the intake manafold gaskets and the injectors. I'm leaning this way after many posts dealing with a rough idle let to an injector replacement.

    I'll keep y'all informed !

    Shamile

    Freeze....Miami Vice !
     
  9. Shamile

    Shamile F1 Veteran

    Dec 31, 2002
    6,712
    Lakeland FL
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    Shamile
    #9 Shamile, Dec 12, 2004
    Dear Ferraristi,

    Dear David,

    I actually check the extenders first for "pin=hole" burns. That was a common problem in my 308 days.

    Regarding the plugs, I just changed them and since my problems started, I've only been using the car in "test" mode. After every run, I've been pulling plugs to see what if any changes.

    Shamile

    Freeze...Miami Vice!
     

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