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hot-start issue, cold-starts great! 85 308qv

Discussion in 'Mondial' started by sipes216, Sep 9, 2019.

  1. sipes216

    sipes216 Karting

    May 9, 2015
    116
    hey guys, me and my father (also on the boards here) have been going through an extensive repair-a-thon on our vehicle. we've been having quite a show out of fixing one thing, and then finding another age related coincidental failure along the way.

    at this moment, our issue is largely a hot-starting problem. we found a failed thermo-time switch recently, and replaced this sucker down in the valley as we were getting a terrible starting delay, and no signs the cold valve had been working. as it is, cold-start is working great.
    we can take the car around the block, have a blast, get her really heated up, and pull her back on the drive and kill the engine (or stall... ) and then we're SOL, you can turn the motor over until you're as blue in the face as the car's paint color.

    as per "use the search function" policies, we have repaired or verified the following:
    -new dizzy caps/rotors/wires/plugs and gapped from the box correctly. plugs are OEM PN, no variance here with this.
    -spark plug extenders? yea, those are new too.
    -new injectors. i posted a bit ago here about rockauto having the matching PN for dirt cheap compared to other places :) yes, they're bosch.
    -the fuel accumulator - no leaks, verified holds pressure. is OK. we would have more cold-start symptoms as well. no fuel comes from the drain pipe.
    -fuel dizzy, works great when running, appears adjusted correctly, haven't screwed with the adjustment on the airbox EVER.
    -cold start system -thank-god, doesn't exist on this car. there is no cold start air valve like birdman has details about.
    -replaced any/all gaskets around the intake plenum and the hoses to the aux-air valve
    -we smoke-tested the intake system. pulled off the driver side, farthest forwards vacuum hose, and plugged our smoke injector right to the nipple. only place we had smoke come out of is the line coming from the oil separator. if the smoke is passing through the manifold, and through the engine, it should be normal i imagine to see this after a little bit.

    when we hot-start the vehicle, when it refuses to start, we have examined the engine compartment and the cis unit's metering plate. it does slightly pull down the metering plate enough, but the system does not buzz like the car does when cold-starting.
    -even when we disconnect the safety-switch on the metering module, we get the buzz, but the vehicle still refuses to start.
    -we are getting fuel. with a line disconnected, we have a strong-steady flow rate, even after the accumulator has spent it's load with the open line. we aren't talking just cracking a line, i'm talking with line off. we are getting a consistent flow and rate. this is further backed up by the vehicle being super responsive before the ignition is cut. it has a great power and tone as it did prior to these issues occuring.

    we have spark (verified all cylinders via inductive tool)
    we have air, with no detectable leaks via evap smoke system testing
    we have fuel operating as should.

    i would imagine any flywheel sensors wouldn't be the case here as the vehicle runs great prior to shutdown. faulty crank sensors would result in intermittent road operation i would imagine, by cutting the spark.

    anyone got an idea?
    maybe a batman spotlight with a bird image instead?
    any insight would help at this point.
     
  2. AndruL

    AndruL Karting

    Apr 4, 2018
    136
    Full Name:
    AndruL
    Check Valve?
     
  3. Subito Grigio

    Subito Grigio Karting

    Jun 2, 2009
    162
    The many details you provide are super-human. Lots of us have been where you are. If you have a leaking banjo fitting (I think there are about 17) - that leak will allow zero pressure in fuel system when engine is hot. [[Please note: my QV has always started when cold, regardless!]]. Look for a leaking banjo fitting. SG


    Sent from my iPhone using FerrariChat.com mobile app
     
  4. Subito Grigio

    Subito Grigio Karting

    Jun 2, 2009
    162
    Secondly: if no leaking banjo is found try this approach -- when engine is hot and everything is set perfectly on the car - did you know it takes a DIFFERENT approach to start the engine?

    Cold start: don't touch accelerator and it will usually start. If not, wait 4-5 seconds then flutter the accelerator.

    Warm/Hot start --

    1. I know everything is correct, repaired, etc., on this engine.

    2. I know the engine is warm or hotter.

    3. Turn key to start the engine (don't touch accelerator at all) and try starting about two seconds at most then flutter the accelerator a little. It will usually catch and start. All things must be correct though, accumulator, fuel pump, banjos, etc.

    4. I Never, never, push accelerator to the floor because the engine will refuse to start. Period.

    Hope something I shared helps!

    Good Luck




    Sent from my iPhone using FerrariChat.com mobile app
     
  5. sipes216

    sipes216 Karting

    May 9, 2015
    116
    No leaking banjos on the entirety of the fuel system. I've been over, beneath, and inside of this engine compartment pretty thoroughly. Lol.

    By check valve, are we talking about the one atop The fuel pump?
     
  6. mike32

    mike32 Formula 3

    May 13, 2016
    2,048
    Uk
    Is your car with the fuel pipes in between the engine and the passenger space. We had someone on here had problems with the pipes picking up heat from the exhaust- with the fuel static, it was heating up if i remember correctly.
     
  7. sipes216

    sipes216 Karting

    May 9, 2015
    116
    No, not that I'm aware of. Pipes come up the passenger side of the car around the quarter cheese grater, and under the air box to the fuel dizzy. No heat exposure there I could see being bad enough. It's all well spaced off from the engine.
     
  8. mike32

    mike32 Formula 3

    May 13, 2016
    2,048
    Uk
    Only other thing i can think off which is fuel related is the fuel distributor head- the block with all the small injector pipes coming out of it- someone i know had problems with his, in that the rubber diaphragm split . His problems were different to yours in that he had fuel build up in the sump and bad misfires. The split was causing it to overfuel some injectors and the fuel was spilling past the pistons.
    Point is the repair kit is about £50 and easy to fit. Look on the side of the housing for a bosch number, then on e bay. Used in volvo etc so available
     
  9. sipes216

    sipes216 Karting

    May 9, 2015
    116
    We tried the repair kit first, one of the center piston rings was bad in the appropriate kit and bound it up. We ended up getting a tested and certified refurb. It's operating as it should, and we actually have pictures of it's rebuild internally as well as received the video of it passing a flow test with the old proper kdje bosch tools.
     
  10. AndruL

    AndruL Karting

    Apr 4, 2018
    136
    Full Name:
    AndruL
    Yes.
     
  11. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    18,249
    Texas
    Full Name:
    Steve Magnusson
    If you have confirmed that the supply fuel pressure has not dropped below spec after warm-shutoff, do have spark, and the fuel pump is running, but no warm restart, we have had cases of the mixture just being set way too rich causing this symptom - for example:

    https://www.ferrarichat.com/forum/threads/hot-no-start-issue-need-a-new-direction.602834/

    Of course, these cars had no cats -- otherwise, they would have been on fire ;) Do you have cat(s)?
     
  12. spicedriver

    spicedriver Formula 3

    Feb 1, 2011
    1,519
    No hot start - press the sensor plate down and spray some starting fluid into the intake.

    If the motor starts and runs, then you know you're not getting enough fuel from the injection system.

    If the motor doesn't start, you're either getting flooded, or the ignition system isn't working.
     
  13. sipes216

    sipes216 Karting

    May 9, 2015
    116
    I had been directly avoiding starting fluid due to fear of backblow as can sometimes occur. Don't want to knock an adjuster or something out! I've only caught one car on fire in my life and I'd like to keep it that way :D
     
  14. sipes216

    sipes216 Karting

    May 9, 2015
    116
    Also, Steve, my dad found a post of yours going into detail about the expansion tank coolant temp sensor having an influence on the digiplex retarding the ignition under different conditions. We have had it unplugged as well as jumpered via high tech paperclip, no difference there.
     
  15. spicedriver

    spicedriver Formula 3

    Feb 1, 2011
    1,519
    Other Tests:

    Remove and examine the plugs when getting the hot no-start symptom. A wet plug will not fire.

    Lay a spare plug on an engine ground, and attach a plug wire. Have someone else crank the starter so you can examine the spark.
    There is a also a spark tester you can get that attaches between the plug wire and the extender to see the spark.

    A cold engine needs a richer mixture. You can try leaning out the mixture with the mixture screw. Just keep a written log of your adjustments. This is not a fix, just a test to see if the hot start mixture is too rich. Keep in mind that the plugs need to be dry in order for the car to start. One incident of flooding can foul the plugs.
     
  16. sipes216

    sipes216 Karting

    May 9, 2015
    116
    Previous to replacing some intake gaskets and hoses, it was definitely fowling up the plugs. I'll pull the set of new plugs, and blast/clean them later. I've got equipment for that. Laying a plug on engine ground or with spark testers does yield a spark impulse. Regularly I use an inductive tester instead of having to pull a plug out. After running for a bit, it should defoul the plugs though, you'd imagine ... I'll go at them all anyways
     
  17. spicedriver

    spicedriver Formula 3

    Feb 1, 2011
    1,519
    Fuel fouled plugs only need to dry out. This will happen after letting the car sit overnight. Check them with the engine hot after trying to start it.

    Also, with the engine running, lift the sensor plate slightly with your fingers. If the RPM increases, that would indicate an overly rich mixture.
     
  18. sipes216

    sipes216 Karting

    May 9, 2015
    116
    I'll check the plate.
    After the car sits for approx one or two hours, the vehicle will crank to life just as strong as a newer modern car. So then I do t think I'll be pulling plugs with that in mind.
     
  19. sipes216

    sipes216 Karting

    May 9, 2015
    116
    Updates!
    I checked the metering plate. It is centered well, and moves correctly safely.
    Per one of the recommendations, after the car was warmed up, I sprayed some accelerant under the plate, this had no affect to restarting.
    From there, I disconnected the cold start valve and put my fuel pressure gauge inline.
    Pressures after running are 70 PSI when pump active, holds no less than 40 PSI after 20 minutes, as per the workshop manual.

    I had a hair rained thought earlier yesterday about the metering airbox. The car was a lot better to start after I replaced the hoses for the aux air device, and resealed around the cold-start valve. When I get home I'm removing the metering box and I'm going to re-seal the box halves. There was a slight difference in difficulty with the air filter off the car versus air filter in its box, I stalled correctly. I'm stepping closer and closer towards an over-lean issue where on hot start, it's just not building vacuum to successfully draw the metering plate to kick on the fuel pump and fuel accessories. The second you touch the metering plate, she whirrs and hums, same as removing the safety switch connector.
     
  20. spicedriver

    spicedriver Formula 3

    Feb 1, 2011
    1,519
    It's odd that a car won't start with starting fluid. You could be getting flooded from the K-Jet system, or you've got an ignition problem. You can eliminate the possibility of flooding by pulling out the fuse for the fuel pump. It's easy to test if the fuel pump is running by removing the safety switch jumper. If the car still won't start with starting fluid, and the plugs are dry, then you must have an ignition problem.

    Also, whenever you replace a major component in the injection system, you must readjust the mixture screw. The manual calls for a CO analyzer, but you can get air/fuel mixture meters fairly cheap these days. The mixture screw is very sensitive. One turn out of whack, and the car won't start at all. You could try starting the car cold, then adjust the mixture screw while the motor is running until you get a lean stumble. Then get up to temperature, and try a hot start at the new settting. Make sure to keep track of your adjustments.
     
  21. sipes216

    sipes216 Karting

    May 9, 2015
    116
    I have an analyzer at my house I've never used, for this purpose on a vw fox GL, also a CIS. sold the wreck before I ever tuned with it. I was trying to tell my father we should consider doing g that, but he's stuck on the paranoia of "it should be fine how it is!!! Do t mess with it!" But here we are. Lol

    What results or ratios should I expect at cold or hot? Is there a specified chart to reference?

    And since I'm at the airbox anywho right at this point, I think I'll confirm good metering unit seal by examining it. Couldn't hurt.
     
  22. spicedriver

    spicedriver Formula 3

    Feb 1, 2011
    1,519
    The low emission ratio is 14.7 -1. A full power ratio is 12.5 - 1. With a full power ratio, you will have some unburned fuel going into the exhaust. This will destroy your cat. So if you have cats, you need to set it to the lean number.

    The proper method to adjust a K-jet is to adjust the fuel pressures to the factory specs. Then adjust the mixture screw to the specified CO level. Eg:

    Note: I wouldn't drill a hole in the WUR . You adjust it by moving the fuel cell position. It's a pita, but that's the right way to do it.

     
  23. sipes216

    sipes216 Karting

    May 9, 2015
    116
    we have a fuel gauge at the line that goes straight out to the cold-start fuel injector. the measurements above were taken there, with the vehicle warmed up. i feel that with what the video goes into some detail of, we atleast have that correct.

    earlier today, for the majority of the evening, until i just a little bit ago got cleaned up, i was "refurbishing" the metering unit the fuel dizzy sits atop. i removed the original seal between the box halves, the damn thing was just rock hard, no real sealing qualities to itself. scraped the f*er off, polished my surfaces, and created a custom-fit gasket out of the appropriate felpro gasket material. i've been doing a lot of custom gasket creation in a few air channel places lol

    tomorrow i'll put the airbox back in the vehicle, and we'll give her a crank up to see how the ol' gal operates.

    what are the preferred methods to remove the adjustment hole blockage? driling it out? is it a special threading, or just normal rightie tightie?

    also, i'm not sure what you mean by moving the fuel cell's position. fuel cells in my book refer to the gas-tank, and that's only got one spot :p

    so far this thread has been amazing. i feel definite progress with our repairs. gotta have this car operational by the 21'st, so that me and the then wifey can escape from our wedding reception! :)
     
  24. spicedriver

    spicedriver Formula 3

    Feb 1, 2011
    1,519
    The tamper proof cover is a plug. Not threaded. Try working it out with a pair of needle nose pliars. For the adjustment, use a 3mm allen wrench. Attach a vacuum gauge to manifold vacuum. Adjust counterclockwise until you get a lean stumble. This will be about 1/2 turn. Then slowly adjust clockwise until you get maximum vacuum on the gauge.

    The cold start valve is at system pressure. Should be 5 bar or 72.5 PSI. You need to find your control pressure. You measure this at the WUR. Control pressure should be 3.5 bar or 50 PSI. If your control pressure is correct, there is no need to adjust the WUR fuel cell.

    You might have to buy a K-jet gauge kit to get the right fittings to test control pressure.

    https://www.thetoolwarehouse.net/s-g-tool-aid-33865-P223535.aspx?gclid=Cj0KCQjw2efrBRD3ARIsAEnt0eiwnDufuUWh7fhKE05EujKX_cUharovWz3y62_zm9ACkqg79c1c15QaAtaQEALw_wcB


    This article describes the fuel cell in the WUR. This thing is not easy to adjust, so if you have the correct control pressure, there is no need to mess with it.

    https://k-jet.biz/wp-content/uploads/2019/06/double_diaphragm_wur_rebuild.pdf
     
  25. sipes216

    sipes216 Karting

    May 9, 2015
    116
    I do have a cis compatible fuel gauge set. So what's the ideal position to install correctly for control? Between wur intake "ingress" port and the dizzy?

    Also, it may be worth noting, we have a single diaphragm wur on this car. We do not have a vacuum port on the bottom or side of the unit
     

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