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512 bbi hot start issue

Discussion in 'Boxers/TR/M' started by pshoejberg, Jun 20, 2020.

  1. pshoejberg

    pshoejberg Formula 3
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    Dec 22, 2007
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    Peter H
    I need some expert help here on a hot start issue. The story is following:

    I spent yesterday adjusting and setting up my newly serviced 512 bbi engine. I checked and fine adjusted the ignition timing and balanced the two banks perfectly while adjusting the idle to +-1000 rpm. The engine is running very smooth and responsive. After the fine tuning I noticed that starting the hot engine was troublesome and needed cranking for many seconds and to some extent also a heavy foot on the speeder. Based on these symptoms I decided to checked the injection system. Following pressure data was recorded:

    Fuel pump pressure (Primary pressure) = 5.4 bar both sides.

    Control pressure (with WUR connected to power supply) = 2.0 bar start (at 20 deg ambient temp), 3.4 bar and stable after approximately 3 minutes (WUR fully heated). Same figures in both sides.

    Upon completion of control pressure test I shut down the pumps and observed system pressure immediately drop to 0.7 bar and 2 minutes later drop to 0 bar over 2-3 seconds. Same behavior both sides.

    I have limited knowledge about the CIS system, but I believe all measured values above are correct except from the system pressure after pump shut down. I would have expected the system pressure to remain around 3 to 2 bar for 15-20 minutes in order to facilitate efficient hot start conditions.

    Are there anyone that knows what is going on here, why do the system pressure drop like a stone when the pumps are shut down?

    I'm puzzled by the fact that both sides behave similar...One failure can happen but It is rare that a failure is doubled?

    I believe that following issues could cause lack of pressure accumulation in the system:

    1. Defect back pressure valve in fuel pump(s) (Can these valves be inspected and cleaned?)

    2. Defect fuel accumulator (hole in diaphragm): I see no fuel coming out of the spring chamber breather outlet.

    Any input or theories are received with much appreciation.

    Best; Peter

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  2. Steve Magnusson

    Steve Magnusson F1 World Champ
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    +1 -- you need to correct this problem for good hot restart behavior.

    Three possibilities:
    1. Bad check valve on fuel pump outlet.
    2. Bad Accumulator (since you report no fuel leaking out the vent nipples of the Accumulators, this is not the problem).
    3. Bad O-ring inside pressure regulator section of the fuel distributor.

    I believe on the V-12s with K-Jet CIS injection, Ferrari learned that it was better to connect the control pressure sections of both banks together to give an exactly equal "average" control pressure on both banks; however, this also gives the result that, if one bank loses system shut-off pressure for some reason, then both banks lose system shut-off pressure. Do you have a fuel line connecting the top of one WUR to the top of the other WUR? Can you post photos of the top of your WURs? This interconnecting line for the control pressure is usually "double-stacked" on one of the banjo bolts on each WUR -- Fuel line 59 here:

    https://www.ricambiamerica.com/car-diagrams/ferrari/v12/boxer-group/512-bbi/fuel-injection-system.html
     
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  3. pshoejberg

    pshoejberg Formula 3
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    Thanks a lot for the comprehensive and logical response Steve. I have a couple of comments:

    1. I ruled out your failure suggestion #3 due to having correct fuel pump pressure at 5,4 bar, but i guess the regulator could still leak at lower pressure and potential bleed off the system pressure to the fuel tank.

    2. You are right with the interconnected WUR's. There is a line between those and I see now why I have so equal measurements on both sides.

    I just inspected the fuel accumulators and the fuel pumps and it strikes me that my fuel pump setup doesn't look like the setup I can find on google. Please have a look on the fuel pump picture below. It doesn't look like there is a check valve in the nipple. Can the check valve be integrated in the pump?

    Best, Peter

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  4. Steve Magnusson

    Steve Magnusson F1 World Champ
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    #4 Steve Magnusson, Jun 20, 2020
    Last edited: Jun 20, 2020
    No, the fuel pump(s) being able to deliver good pressure when "on" has nothing to do with the check valve sealing well when the pump is turned "off".

    It looks like you have the wrong style (newer) fuel pump installed -- have they been replaced recently?

    Your model originally came with the older style CIS fuel pumps (now Bosch 69523 here in the US):
    BB512i assembly with original style Bosch 69523:

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    with the check valve built into the pump head itself -- this check valve is not replaceable nor serviceable. Later on, Bosch got smarter, and made the check valve a replaceable part -- so a still good motor and roller pump head could be reused when the check valve went bad (this style pump is now Bosch 69532). It is possible to update a system to use the later style fuel pump but this also requires plumbing/fitting changes.:

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    Unfortunately, it is also possible to use the older plumbing on a new pump, but this has no check valve at all. If you do a search here using "69523 69532" that will get you a lot of threads discussing these fuel pumps and showing the differences and the difference in their plumbing.
     

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  5. Steve Magnusson

    Steve Magnusson F1 World Champ
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    #5 Steve Magnusson, Jun 20, 2020
    Last edited: Jun 20, 2020
    I ran out of time to edit my prior post (so it's a little mangled), but here are the two full pump types:

    The early Bosch 69523 with built-in check valve (note the long output "snout") that uses a threaded coupling to connect to the plumbing:
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    The laler Bosch 69532 with replaceable check valve that uses a banjo bolt to connect to the plumbing:
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    What you have is the 69532 pump with the check valve (wrongly) removed and the threaded coupling (wrongly) installed.
     
  6. pshoejberg

    pshoejberg Formula 3
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    Thanks again Steve. The problem is hereby identified. My car must have had the fuel pumps changed recently by the previous owner and he apparently did a half job. I now have a small project ahead of me. I need to source a set of check valve nipples with end caps and Cohline fittings for new lines between pumps and accumulators. I just read an old Newman thread where he did exactly this and he was well supported by you and Larry Fletcher.

    If anyone knows a good source for Cohline fittings specifically for Polyamide hose in Europe please speak up. I know it is produced in Germany, but it seems impossible to source for normal private persons.

    Best, Peter
     
  7. Steve Magnusson

    Steve Magnusson F1 World Champ
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    #7 Steve Magnusson, Jun 20, 2020
    Last edited: Jun 20, 2020
    You may actually have the easier option of just getting the correct Bosch 69523 fuel pumps. What happened was that the Bosch 69523 was not available at all for a while a few years ago so people were forced to upgrade to the new Bosch 69532 and adapt the plumbing; however, the Bosch 69523 has recently become available again.

    If you do want to get the necessary fittings and Cohline plumbing (and check valves) to keep using the Bosch 69532, contact Larry Fletcher at www.CISFlowTech.com (but, IMO, doing this is way more hassle than just getting the Bosch 69523 pumps -- especially for someone not in the US).
     
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  8. turbo-joe

    turbo-joe F1 Veteran

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    romano schwabel
    you may go to a mercedes dealer and try to find an old technician who knows about the older cars. they also had those valves and could be ordered without a pump. or go to a bosch dealer. problem today is nearly no store guy can find anymore something without a VIN and bosch not listed this valve for BBi.
     
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  9. Ludwig

    Ludwig Formula Junior
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    I just replaced one of my pumps and the accumulator. the check valve is indeed the original fitting that can be screwed directly into the new pump. Both pump and bosch accumulator were from e bay.
    I believe it is normal behavior for all cis systems when warm to require some cranking and throttle to restart as the pressures are not maintained for long.
     
  10. turbo-joe

    turbo-joe F1 Veteran

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    #10 turbo-joe, Jun 23, 2020
    Last edited: Jun 23, 2020
    you may try the following when next time starting warm engine:
    as soon as you turn the ignition on the fuel pumps will run for a short time. when you just go on with starting the battery needs the most power for the starter and the pumps getting slower a little. so you may turn on the ignition 3 -5 times that the pumps will always run this short time several times and can deliver fuel and then you may start.
    let me know please if this helps

    I once had this problem with a mercedes 300 SEL 3,5 ltr ( but this car had a D-jetronic, not a CIS ) and I put in a buttom switch to let the fuel pump run when pressing this buttom. it takes mostly minimum 30 seconds until the fuel pressed all the air out. had this problem I had only when the engine was warm and about 5 minutes after turning off the engine and 45 minutes after. so directly starting again and after those 45 minutes never had a problem. unfortunately never tested the fuel pressure, had not gauge, too expensive at that time for me ( have been 22 ;) )
     
  11. pshoejberg

    pshoejberg Formula 3
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    Thanks for the good hints Romano. I have basically started the hot car by turning the ignition on and off a few times as you describe and it works. But I hate to make difficult starts in the public, a super car must start immediately if you know what I mean. I have now disconnected the micro switch in the CIS airmeter to keep the pumps running constantly when the key is turned (I know the risk here). I have ordered two check valves and plumbing equipment to rectify the issue so hopefully the car is back in business in a few weeks. I will update this thread on the progress. On another note I'm also planning to convert the ignition system into a MSD system. I'm tired of the high whine from the original ignition Dinoplex and I suspect that it will break down at any point in time. I use my cars regularly and wants full confidence. I have a programmable MSD unit in my Dino and it's the greatest (And only) upgrade I've ever made. The MSD unit is on order, more of this rebuild will follow later.

    Best, Peter
     
  12. dwhite

    dwhite F1 Rookie

    I have been driving my car alot the last 6 years -10K+. Hot start is not an issue. Something is not right. I have MSD box, but I doubt that is the difference.
     
  13. turbo-joe

    turbo-joe F1 Veteran

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    don´t think so. except you modified also the injection. the MSD is for ignition and the hot start problem is a fuel problem
     
  14. pshoejberg

    pshoejberg Formula 3
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    Slight progress in the hot start issue rectification; Spare parts arrived from UK and the States. With this setup it should be possible to keep the original steel piping and still having external back pressure valves that can be serviced. Next up is installation and re-test of system pressure.

    Best, Peter

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  15. DonB

    DonB Formula Junior
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    I had the same problem. Having the WUR's rebuilt and putting new check valves on the fuel distributors solved the problem. Note, I had the correct/recent fuel pumps ans accumulators.
     
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