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QV acting weird

Discussion in 'Mondial' started by srephwed, Mar 1, 2020.

  1. srephwed

    srephwed F1 Rookie
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    Apr 29, 2012
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    fred brown
    Out for a spin the other day. Stopped for lunch and when I restarted it as soon as I touched the throttle it shut off like turning the key. Restarted and the same thing. Third try it ran and we got out on the road. Shifted into second and I could feel it die. let off and it ran. touch the throttle and felt it die. It repeated this several times and since I was going down hill it finally kept going. Ran fine the rest of the day. I have experienced this a couple times at a red light before. I don't know where to start with this one. Thanks in advance for any help.
     
  2. mike32

    mike32 Formula 3

    May 13, 2016
    2,430
    Uk
    Chuck a bottle of injector cleaner in the fuel tank, just with a couple gallons on fuel.
    Do u find as soon as you take your foot off the accelerator the engine dies and you lose the brake servo. Do this every year and should be fine
     
  3. Wade

    Wade Two Time F1 World Champ
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    Mar 31, 2006
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    My initial thoughts are a vacuum leak. Check all of your hoses, especially those that are attached to the intake plenum and etc.
     
  4. FerrariJB

    FerrariJB Rookie

    Jun 8, 2019
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    FerrariJB
    My thoughts. It seems that the fuel pressure drops. The warmup valve might play a role here, there is also a vacuum connection for acceleration enrichment. This changes the fuel pressure. You could disconnect the vacuum line so that you exclude it.
     
  5. moysiuan

    moysiuan Formula 3
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    Nov 1, 2005
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    My bet is a clogged fuel filter. Marvel Mystery Oil is a good fuel system cleaner to try, these old injection systems respond well to the MMO and it can sometimes declog a filter. Also make sure your air filter is clean.

    Another item to check is the throttle position sensor. At the intake, when the engine is off, put your ear close to the TPS and then open the throttle a tiny bit. You should hear the TPS make a click. If not it needs adjustment (you loosen the attchment bolts on the TPS and adjust so it clicks just as the throtle opens), or has failed. There are voltage checks to see if it is working as it is supposed to. Probably not the problem, based on the intermittent aspect of what you described, but does not cost anything to check.

    Also check for the "burnt white connector" in the fuse box. This can affect the fuel pump and maybe there is some poor connection here.
     
  6. srephwed

    srephwed F1 Rookie
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    Apr 29, 2012
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    Couple things mine is the K jetronic fuel injection so no tps. Also it dies when I push the throttle not when I leave off. I regularly add injector cleaner and replaced fuel filter not many miles ago. Also I added a relay for the fuel pump to eliminate the burnt connector at the fuse box. Once it decided to run it ran great. Just seems funny that it idles and just the slightest pressure on pedal and it stops like you pulled the key. If I let off quick enough it picks back up and idles
     
  7. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
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    Are you saying this issues comes and goes? Also, please confirm/deny if a US version 1985 Mondial QV.
     
  8. mike32

    mike32 Formula 3

    May 13, 2016
    2,430
    Uk
    Any sign of fuel contamination on the engine oil dip stick, or has the sump oil level increased ?
     
  9. srephwed

    srephwed F1 Rookie
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    Euro version. No smog stuff.Had done this a couple times the last year. strange how it acted this day. Oil level okay
     
  10. mike32

    mike32 Formula 3

    May 13, 2016
    2,430
    Uk
    There is a way to check the fuel pressure as a thread on here very recently, also non return valve on outlet side of fuel pump which might be sticking. Check fuse and relay for fuel pump, in case pump is cutting out. I have wiring diagrams if u get stuck
     
  11. sidtx

    sidtx F1 Rookie
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    Feb 9, 2014
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    I have an 85 QV US spec version.

    Last year, I was having a ton of fuel related engine problems. It got to the point where one entire bank quit working.

    Tried everything -- Accumulator was ok, fuel pump was working great, fuel pressure into the Distributor was right on spec. We replaced the entire ignition system (plugs, wires, caps, rotors, coils -- everything except the digiplexs). We even took apart and cleaned the warm-up regulator, and the valve that is attached to the bottom of coolant reservoir. Nothing worked. Even after we fixed a couple of small vacuum leaks -- still had the issue.

    Nothing worked until we installed a rebuilt fuel distributor.

    After the installation -- the car ran sort of like what you are describing. We then adjusted the fuel air mixture screw (the little allen bolt that is hiding under the press-on cap, on top of the fuel distributor).

    Check for vacuum leaks first. Then, try adjusting the fuel-air mixture -- it's fairly easy, turn the allen bolt counter-clockwise until the engine starts running rough -- then turn it back clockwise about a 1/4 turn. Or, if you have access to an exhaust gas analyzer -- you can get a much more precise adjustment.

    Sid
     
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  12. mike32

    mike32 Formula 3

    May 13, 2016
    2,430
    Uk
    #12 mike32, Mar 2, 2020
    Last edited: Mar 2, 2020
    I was asking about oil level or fuel in the sump due to thinking the fuel distributor needed an overhaul. You can get a repair kit for about £50 as used in a volvo and other cars. The diaphragm splits and some cylinders go full fuel with spiting and back firing, also some fuel pours past the piston unburnt into the sump oil and the level comes up
    Try letting car go cold, then start up and go for a drive- as soon as it starts playing up, get into engine bay and put your hands on both coils, should both be cool. If one is hotter than the other then hot one is breaking down. I dont think this is your problem but worth a try. Mine had one go but big misfires after a few miles
     
  13. srephwed

    srephwed F1 Rookie
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    Mine has XDI ignition so no stock coils. Rebuilt fuel distributor this winter. Strange how it seems to correct itself then run fine the rest of the day. Awful hard to fix when it ain't broke.
     
  14. Albert Penello

    Albert Penello Karting

    Jul 21, 2019
    140
    Woodinviille, WA
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    Albert J Penello, Jr.
    This is classic fuel pressure problem. Car is starting off the cold idle valve, but not enough pressure to fire the mechanical injectors.

    So it's your fuel pump or accumulator. Do a pressure test. I had the same problem and it was the accumulator.
     
  15. mike32

    mike32 Formula 3

    May 13, 2016
    2,430
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    He has done the pump and accumulator. I think the power supply to the pump might be an idea as it has a relay etc
     
  16. Albert Penello

    Albert Penello Karting

    Jul 21, 2019
    140
    Woodinviille, WA
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    Albert J Penello, Jr.
    Agree it could also be power for sure. Bad relay (if they are the originals) or bad ground or connection at the pump also super easy to check.

    I would still want to see it get hooked up to a FP gauge and see what's going on. Super easy to do - even Harbor Freight has a fuel pressure kit that has the right fittings and it's like 5min to set it up - just run on the line going to the WUR.

    Fuel Pressure test will allow you to see pump, accumulator, and leaking injectors.

    I doubt it's vacuum related since it's intermittent. If it's idling smoothly, then while possible it's unlikely to be spark esp. if the car won't rev up in neutral.
     
  17. srephwed

    srephwed F1 Rookie
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    Still grappling with why it runs till the throttle is touched and I mean just touched. Let off and it keeps running then eventually took off and ran fine
     
  18. Albert Penello

    Albert Penello Karting

    Jul 21, 2019
    140
    Woodinviille, WA
    Full Name:
    Albert J Penello, Jr.
    It makes sense if you know how the mechanical injection system works. It's a really good and reliable system so long as the injectors are clean and you can hold good pressure.

    First, the mechanical injectors REQUIRE over 50psi to release. This is not like a modern electronic fuel injector (or even the cold start injector) where the firing pulse is electrical, and even with weak pressure SOME fuel will come out. Unless you are maintaining a consistent fuel pressure over 55 PSI, the injector simply will not fire. Your cold start injector WILL fire, so you can keep restarting the car running from the gas from the cold start, then die.

    The second you touch the throttle, you transition airflow from the idle screw to the butterfly, which signals flow over the CIS airflow plate. Take your airbox off and see how fast touching the throttle opens the butterfly.

    What happens is with the car at idle, the CIS air flow plate is closed. This allows all the fuel pressure to stay inside the fuel distributor (no transfer or metering is happening). However, once you open the fuel distributor, you bleed off pressure to the WUR to allow metering to the engine in anticipation of higher RPM and delivering the right amount of fuel.

    So what I believe is happening in your case (and is super common) is that you system can provide enough pressure to fire the injectors at idle because you are keeping enough pressure inside the distributor. So you're making over 55 PSI. However, once the air flow plate opens, you bleed off enough pressure that the system cannot keep up. This is either a problem with the pump, with the accumulator, or something is going on with your WUR that is not allowing enough pressure to pass back to the distributor. This is why you need to hook up a fuel pressure gauge and see what's going on.

    To see how the injector works, check this video out on things that can go wrong.

     
  19. spicedriver

    spicedriver Formula 3

    Feb 1, 2011
    1,738
    I would remove the air cleaner assembly. When the problem shows up, get out and open the throttle at the motor. Look at the air flow plate, and see if it's getting stuck. Try pressing it down at the same time you're opening the throttle.

    I'm thinking the plunger inside the FD is getting stuck, and the motor isn't getting enough fuel.
     
  20. mike32

    mike32 Formula 3

    May 13, 2016
    2,430
    Uk
    Might be an idea to check the throttle cable where it attaches in the engine bay, the spring loaded lever needs a squirt of wd 40 @ times. Just be sure it is free to return
     

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