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1982 MONDIAL 2 VALVE ENGINE RUNS ON...ANY SUGGESTIONS

Discussion in 'Technical Q&A' started by lbanez, May 11, 2004.

  1. lbanez

    lbanez Rookie

    May 11, 2004
    38
    Hello Everyone.....I lately developed a disturbing problem with my Mondial 8, it's driving me crazy.......at times when I shut off the engine ,it will run on.....these are the steps I have taken,,,,,,Idle speed is 900 RPM, CO is at 1 %, HC at 100ppm, vacuum at throttle plate is less than 1"Hg, sensor plate height is right on the money, no vacuum leaks, cold start injector does not leak,the motor runs perfect and strong, I even tried a different set of Ignition Moduals,all the injectors are new, warm up regulator is new, fuel distributor is smooth with no binding,......any other suggestions??.....thanks in advance...Angelo
     
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  3. tbakowsky

    tbakowsky F1 World Champ
    Professional Ferrari Technician Consultant

    Sep 18, 2002
    15,117
    The Cold North
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    leaking injectors? Take them out and hava them checked at a good place that has a propper test bench. Also check your fuel pressures warm control pressure inparticular.

    Normaly a run-on probelm is caused by a high idle. But with C.I.S this is not a common problem. I fact I don't think I have ever seen a rn-on problem on any C.I.S equiped car. Keep us updated as to what you find.

    What else has been done to car service wise before this problem occured?
     
  4. theunissenguido

    theunissenguido Formula 3
    Silver Subscribed Owner

    Jan 21, 2004
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    In what country you live ??
    The fuel changes here in Europe caused also this problem...
    Guido
     
  5. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
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    Angelo -- Please describe "run on" better. Do you mean that it hacks and coughs on a few cylinder for a few seconds or that it continues to just idle normally with the ignition key removed?
     
  6. lbanez

    lbanez Rookie

    May 11, 2004
    38
    THE MOTOR DIESELS ON FOR ABOUT 3-5 SECONDS WITH THE KEY REMOVED
     
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  8. lbanez

    lbanez Rookie

    May 11, 2004
    38
    LIVE IN CANADA......I ALWAY USE SUPER 91-94 OCTANE
     
  9. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,220
    TN
    I would think that it would be a timing issue or a problem in the ignition. This isn't a common problem that I have seen. Keep us posted.
     
  10. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
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    One thing you might do is verify that the ignition actually shuts off when you turn the key off (i.e., with a timing light on a coil wire, does it still flash during the unwanted dieseling period?).

    Unfortunately, they don't include the schematics in the Mondial 8 OM so I can't really say if this is important for sure, but something easy to try would be to swap the "U - relay for ignition key controlled services" with another relay of the same PN.

    One hears stories of old British sports cars with enough glowing carbon deposited on the piston tops to make shutting off difficult, but that doesn't seem consistent with a well-running injected car -- but you've got to go this direction if the ignition is truly shutting off properly yet the engine diesels.
     
  11. lbanez

    lbanez Rookie

    May 11, 2004
    38
    THAT WAS ONE OF THE FIRST THINGS I tried, no power to the coils when the ignition is off, I have 2 sets of ignition moduals, MED 801A .....checked the timing, its at 3 deg atdc as stated in my manual.....anyone need a modual ?.....I have the original wiring diagrams for the car..I must have all the manuals on the Mondial 8.......... I'll keep pluging away
    Please keep the Idea's coming in......thanks
     
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  13. peterp

    peterp F1 Veteran

    Aug 31, 2002
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    Since the ignition is off, dieseling can only be caused by one of two things: 1) too low an octane; or 2) by carbon deposits. Somewhat contrary to what you would think, low octane is actually easier to ignite than high octane fuel and this is why the engine with will continue to run with low octane after the ignition is off because combustion occurs from the internal heat -- spark is not needed (this is how a diesel engine works and is why diesel fuel is very low octane). If octane is sufficient, then carbon deposits are usually the problem because they raise the internal temperatures such that heat-based combustion occurs even with high octane fuel. Even though fuel injection is very efficient, carbon deposits will still occur if the car is used for short trips because the cylinder head never reaches sufficient temperature to burn the carbon and it ends up accumulating inside the engine. The best solution is to add two bottles of Techron fuel additive and fill the tank. Then give it an Italian tune-up -- drive it at least one hour at slightly elevated RPMs to keep the cylinder head temperature elevated. The extended drive is very, very important because the fuel additives are only effective at removing carbon deposits when the cylinder head is held at sustained high temperatures. If your car is frequently used for short trips, chances are very good its carbon deposits -- you may have to run fuel additives for several tankfulls if they have really built up. Another possibility is that the valve timing is off, but this seems less likely (it should be checked if the fuel additives don't work because you don't want to break a timing belt). I'm not an expert, but I think carbon deposits are likely the cause.
     
  14. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,220
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    Good info. Thanks for sharing. I would have never thought that carbon build up could cause this or low octane for that matter. Thanks Again.
     
  15. lbanez

    lbanez Rookie

    May 11, 2004
    38

    I ran a can of GM combustion chamber cleaner in thru the egr port, used a control valve , and kept the revs up, took out a rear plug before and after, sure cleaned the top of the pistons, I woulld imagine the heads recieved a good cleaning in the process...I always use high octain fuel as recomended........I doubt that its carbon causing this...I think is has somthing to do with the throttle plate.......still plugging away.......thanks
     
  16. AR!

    AR! Formula Junior

    Apr 8, 2004
    974
    Berlin, Germany
    Ibajaps guitars suck!

    :)

    Just kidding, keep on rocking ...!
     
  17. peterp

    peterp F1 Veteran

    Aug 31, 2002
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    I would not think that the throttle plate is likely this given that your car idles fine -- the fuel should not ignite once you turn off the key, so something is causing it to ignite. If it is fuel-related, then it is probably caused by a lean condition rather than rich because a lean mixture is easier to burn. It seems less likely that it's caused by continued fuel delivery -- fuel injection should stop delivering fuel when you turn off the key, but even carbureted engines that don't stop the fuel supply normally don't diesel. If it isn't carbon, improper valve timing may be the cause because I think a delay in the exhaust valve opening can also cause internal temperatures to be higher than normal so that sparkless combustion occurs.

    Does this ever occur when the engine is not fully warmed up? If so, it may suggest that it is valve timing. Carbon build-up or a lean mixture shouldn't cause run-on if you've only run it for a few minutes -- because, in the case of lean mixture, there won't be enough temperature to ignite and, in the case of carbon, the temperature must be high enough for it to glow like a glow/spark plug.

    The EGR based cleaning sounds like an interesting technique. How long did you run it for and was the engine already very hot when you started? I read that deep carbon deposits can only be removed when the cylinder head temperature is held at very high temperatures for an hour or more.
     
  18. lbanez

    lbanez Rookie

    May 11, 2004
    38

    When I ran the combustion chamber cleaner , I warmed the engine up to operating temp....let me tell you....you should have seen the flakes of carbon coming out the exhaust.......the run on will happen warm or cold.......to add an interesting twist to this.....this happened only after it came back from the dealer........I thought this was a coincedence........they had just finnished valve adjustment and timing belts........I thought that the exhaust headers were too cherry red when the engine was running........I noticed it a night , had them have a look at it to see if it was normal.......when I got it back,,.....I had this runon........do you think, they may have changed the timing?.........it sure runs smooth.......I can't see the timing to be off ?...could it be possible?
     
  19. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,220
    TN
    Sounds like cam timing.
     
  20. cinquevalvole

    cinquevalvole Formula 3

    Feb 6, 2004
    1,149
    Germany, Bayern
    not the JEM!
     
  21. peterp

    peterp F1 Veteran

    Aug 31, 2002
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    NJ
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    I do think it is the cam timing -- I discounted that possibility initially only because the belt would have to slip to be off, but since you just had the belts serviced, this becomes much more likely. I am not an expert, but I think that if the timing is off, delayed valve opening can cause the effective compression ratio to be higher than normal even though the cylinder head geometry hasn't changed. The higher the compression, the higher the octane required to prevent sparkless combustion. Premium is fine for the standard timing but may not be enough when the valve timing is off. It seems even more likely to be the cause given that it happens when the engine is cold because carbon deposits would only be a factor when the engine is hot. You've already proven that it doesn't have spark and therefore I don't think it can be a fuel problem since it shouldn't ignite, so valve timing is really the only variable. The EGR cleaning technique sounds quite effective, I may give this a try.
     

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