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308 acceleration "fluttering" when warm

Discussion in 'Technical Q&A' started by climb, Oct 8, 2012.

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  1. climb

    climb F1 Rookie

    Sep 19, 2006
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    Stuart K. Hicks
    #1 climb, Oct 8, 2012
    Last edited: Oct 8, 2012
    Been trying to solve this problem I've had with my 308 for four years now. Took to Ferrari mechanic and he said it needed A/F mixture adjustment which he did. Thought problem was solved but it isn't.

    Don't know if it's fuel or spark or grounding problem.

    1980 USA spec 308 GTSi fuel injection.

    Here is the problem:

    Car starts and idles fine and pulls through the entire rev range for about 12 minutes. THEN once she fully warms up If I peg the gas pedal to the floor it flutters like it's either getting an intermittent spark or fuel. Hard to describe but similar to a boat that has had the engine trimmed too high out of the water and you get that cavitation sound (kind of wha wha wha pulses of sound) if I go at the throttle halfway it will climb through the rev range fine with no fluttering. Seems it's when the oil comes up to temp too as I usually catch a waft of warm oil smell from the weeping connection around the oil cooler before the fluttering starts. The next stab of the throttle after I smell that warm oil is when the condition will manifest.

    What I've done:

    New plugs, wires, extenders and fuel injectors.

    Took a new crank sensor and moved it to all three positions

    added grounds to digi boxes

    reversed coils

    New fuel pump relay

    reversed digi connections from bank to bank

    cleaned and checked rotors and caps

    unplugged cold start valve

    Had A/F mixture adjusted by Ferrari mechanic.

    Any ideas?

    Thanks
     
  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #2 Steve Magnusson, Oct 8, 2012
    Along this idea, you could physically block the air lines passing thru the AAV and the VLV (simulating a fully closed condition for each -- which they both should be when warm and under load). I give it about a 20% probabilty, but, it's easy to do, and would eliminate the AAV and VLV from any further doubt if there's no effect on the problem.
     
  3. climb

    climb F1 Rookie

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    #3 climb, Oct 8, 2012
    Last edited: Oct 8, 2012
    Thanks for the idea.

    So under your 20% scenario if the AAV isn't closing the car is running too rich when warm? Or lean I guess.
     
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #4 Steve Magnusson, Oct 8, 2012
    No, based on your "fluttering" description, I was thinking maybe the sealing element in either might be bouncing/flutterinmg around (or something else strange) so the airflow entering the engine is bouncing around. More a suggestion to eliminate them as suspects rather than to get a conviction ;)

    By "fluttering" do you mean it's missing and losing power or just sort of an odd acoustic behavior, but still have good power?
     
  5. climb

    climb F1 Rookie

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    #5 climb, Oct 8, 2012
    This has been the hardest to describe. Everyone I tell is like WTF? Have you ever gotten a boat up on a plane then trimmed the motor out of the water to reduce drag for top speed? If you trim it too far it cavitates and makes a fluttering noise. It's the sound of either the spark cutting in and out a hundred times a second or the sound and engine makes when not getting enough gas.

    The power is down when this happens. Nail the gas and it makes the sound. Sounds like when your a kid and you make a fast motor sound to try and sound like a car but your lips start bouncing against one another. If I go halfway on the throttle it doesn't do it. Never gets to the point where the car surges back and forth but it sounds like it should. It's a very very fast pulsing sound that gets a rhythm to it similar to a boat cavitation when trimming the engine is the closest I can get to the sound.
     
  6. climb

    climb F1 Rookie

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    #6 climb, Oct 8, 2012
    Sounds very similar to this: Dosen't do it a low speed though. Usually around 2000 to 4000 rpms. Is fine 'till then and smooths out around 4500 but the most HP (what little there is) is in this range it seems.

    [ame]http://www.youtube.com/watch?v=wRZZMcf3lzE[/ame]
     
  7. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    9,634
    #7 Mitch Alsup, Oct 8, 2012
    Any chance the cold start carbeuretors (on the backs of the DCNFs) are not closing after warmup. If they do not close all the way, they will overly richen up the mixture.

    Generally, when the fuel mixture goes rich the car will sound "fat" (whaaaaa without much go) whereas when it goes lean it will go pop-pop-pop (also without much go).
     
  8. climb

    climb F1 Rookie

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    #8 climb, Oct 8, 2012
    Last edited: Oct 8, 2012
    I see. So it sounds rich?

    It's a fuel injection. Bosch CIS. Running test pipes. Just thinking maybe the AAV wasn't closing which was fine for cold running but too much air for warm. Just a hunch. Can't say I hear popping but my exhaust is not very loud (stock) so I may not hear it.
     
  9. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #9 Steve Magnusson, Oct 8, 2012
    Last edited by a moderator: Sep 7, 2017
    One other thing that you might check is the warm control pressure both with vacuum applied at idle (i.e., the normal condition) = should be ~3.5 bar; and without vacuum at idle (by unplugging the vacuum line going to the WUR) = should decrease the control pressure to ~2.7 bar. When you go to WOT, that is also is a "no vacuum" condition, and, if the control pressure is (wrongly) dropping to a very low value that would add excessive enrichment -- just a(nother) thought:
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  10. climb

    climb F1 Rookie

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    #10 climb, Oct 8, 2012
    Thanks. Guess I'll have to break down and buy the equipment to test.
     
  11. finnerty

    finnerty F1 World Champ

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    #11 finnerty, Oct 8, 2012
    Last edited: Oct 8, 2012
    The engine parameter that changes most dramatically (both in value and in rapidity) when you suddenly open the throttle wide is load, or to be more precise in terms of engine management functionality, vacuum.

    So, if I had no other information other than what you have stated (and I don't, because you haven't investigated any operational specs of any components yet ;)).........I would be tempted to begin by looking for vacuum / air leaks. Many of engine management devices on this car (both for fuel delivery and for ignition supply) rely on intake manifold vacuum for inputs. I'd inspect all the vacuum hoses and connections that you can easily access --- especially, the small hose running to the digiplexes (notorious for getting pinched off and developing leaky cracks) :)

    ....also....small vacuum leaks can tend to be affected by changes in temperatures........so.....it fits. (Although so do many other things, the majority of which Steve M. has already pointed out) :).
     
  12. climb

    climb F1 Rookie

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    #12 climb, Oct 8, 2012
    I've thought about vacuum leaks a lot. The hose from the plenum to the digiplex boxes seems fine. I do hear a slight hissing sound but I can't pin point it. On My Z a vacuum hose broke and the sound was so loud I could find it in a second. But on this car it may be slight. Guess I'd have to have it fogged.
     
  13. 335s

    335s Formula Junior

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    #13 335s, Oct 9, 2012
    the cavitation you descibe is actually surging-yes?
    there is a set up which requires a vaccuum guage, as I recall it is a 1 inch and no more-or else it surges....its in the FI section in the WSM, the adjustment screw made of brass on the TB is the screw in item here-as I recall...been 20 years.....or more...
    I've seen heads removed to fix this!
    it was a 1/4 turn and all was good!
    2V injected cars use lots of vaccuum-ck EVERY SINGLE LINE AND READING AGAINST SPEC....
     
  14. climb

    climb F1 Rookie

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    #14 climb, Oct 9, 2012
    I'll look into that.

    Surging? I guess you could describe it that way. A back and forth cavitating sound and half power while it's happening. I run my hand down the hose from plenum to digiboxes and don't feel any leaks though. The little T and the boxes have silicone hoses and look newer than the braided one going to plenum.

    Thanks for the responses guys.
     
  15. finnerty

    finnerty F1 World Champ

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    #15 finnerty, Oct 9, 2012
    Isn't that adjustment just for idle settings ? Does it affect open throttle conditions ?
     
  16. 335s

    335s Formula Junior

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    #16 335s, Oct 11, 2012
    I checked some decade old notes and was reminded that 2v injected cars ALSO have a convoluted hi idle speed compensation cuircuit with a couple of other items I can't recall...a frequent CA re-direction of vac lines included these items, so.... how much was interconnected is frankly had to recall after 20-25 years...but if hooked up non-stock, you get faulty readings and therefore potentially false diagnosis...(this is why a head was unnneccessarily removed!)
    moral of story is make certain all of the baseline factory settings are in spec before getting into the deep end of the pool........this adjustment was a big deal as I remember however....
     
  17. climb

    climb F1 Rookie

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    #17 climb, Oct 11, 2012
    Thank you for taking the time to go back to the ten year old documents.

    Let me get what your saying straight so your efforts aren't in vain.

    Your saying that the sprind loaded brass screw connected to the throttle body is the culprit and it has to be properly adjusted using a vacuum tester and this procedure is in the WSM manual? Also your seconding the point that it may be a vac hose gone bad. The only vac tube I see is the one from the plenum to the digiplex boxes and they seem fine as do the little silicone ones coming to the T and then to the individual boxes. What are the other ones I can check?
     

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