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Help needed 400i, left bank cuts out at high temperatures

Discussion in '365 GT4 2+2/400/412' started by sebackman, Jun 30, 2019.

  1. sebackman

    sebackman Karting

    May 19, 2010
    62
    Dear all,

    I have an odd problem on my 400i. When the outdoor temperature is high and after a few hours driving (3 hours today at roughly 60-70mph, ambient temp about 27C/ 81F) the left bank starts to stutter and then stops. After some cooling down its all fine again for 20-40 minutes and then same happens again. Adding cold fuel has the same effect as cooling down. Up to the stuttering she spinns like a kitten and runs very even on all cylinders.

    Engine temp and oil temp is solid at 80-85C. Oil pressure is good. All fluids changed end of last season. CO2 set to 1,7% and vacuum set on both banks with gauge. Idling at 800rpm. A little valve cluttering around 1000rpm but not bad. Engine has done just over 30k miles. Fans are working and she runs an MSD ignition box.

    Can it be that the left fuel pump is intermittent faulty? Both relays changed last year.

    Ignition is probably unlikely as there is only one distributor? Why would only one back suffer if faulty.

    Many things are recently exchanged or calibrated so it is probably not;
    Injectors, new
    Fuel lines in engine bay, new
    Fuel distributor, newly serviced and calibrated
    Fuel pressure regulator, newly serviced and calibrated

    I will change the fuel lines at the tanks but cannot see that they could cause this albeit that they are old and should be exchanged. I have asked for advise on length and dimensions in a separate thread.

    I also need to figure out what the different hoses do in the rear. There is a crossover hose between the tanks that is joined in a square metal box, what is that. I sits on the front wall in the trunk. I do have the work shop manuals but the page with the different tank parts are all in Italian.

    One observation is also that the tanks themselves becomes rather warm after a few hours driving when hot outside. When I got back today and when the left bank cut I measured with an IR gauge and they were about 47C/117F on the surface with the cover taken off. They do probably get warm from the fuel return from the engine. Is that normal? Had about 50 liters in the tanks at the end, so a decent amount.

    At what temperature does vapor locks become a problem? Can it bee that a vapor lock only affects one bank?

    And I guess the final question is, can a fuel pump stop working at high temperaturs or do you think it is an electrical problem. As all is perfectly normal when cooled down it is a bit odd.

    Not very easy to trouble shoot as this only happens after long driving stints in warm weather when everything is very warm, including the fuel in the tanks.

    All input much appreciated

    //Rob

    Can this be due to back fuel accumulators?
     
  2. Highmiler

    Highmiler Formula Junior

    Dec 8, 2010
    414
    Missouri
    Full Name:
    Greg
    I had exactly the same problem and chased all the things you mentioned.
    The Bosche fuel pumps require 30 amps to run and this power comes through the fuse board under the passenger side floor board. When the fuse board heats up it causes the amperage to drop cutting off the affected pump. Cooling down fixes this temporarily. The permanent fix is to run wire capable of 30 amps direct from the battery to each fuel pump. Install relays in each line and turn them on and off with the existing wiring. This relieves the fuse board of all that heat and keeps Mr. Bosche's pumps happy. There is a thread on this and I'll post it if I can find it.
    Greg
     
  3. sebackman

    sebackman Karting

    May 19, 2010
    62
    Hi Greg,

    Thank you for the input, I will check on the fuse/relay plate later this week. It is pretty cramped down there so it does probably get warm when driving and after 40 years the connections may need some cleaning.

    Does the pump draw much more current when the fuel is warm in the tanks as I can mitigate the problem by adding cold fuel from the tap? This only happens once the fuel in the tanks get warm and goes away totally once the fuel are cooled down. No problem with warm engine, it just occurs when the fuel in the tanks get warm due to return fuel.

    Maybe if the current is enough for cold fuel but it takes more power to pump warm fuel and then it cuts out?

    Are these sensitive on choice of pump or would any Bosch 044 type do if the fitting are correct?

    Can it be a problem in the return line so that the pump pumps against high pressure resistance and hence overheats?

    If you do find the link, please post here.

    Kind regards
    //Rob
     
  4. SouthJersey400i

    SouthJersey400i Formula 3

    Mar 14, 2007
    1,202
    Romulus, NY (Finger Lakes)
    Full Name:
    Ken Battle
    Rob
    Look at the terminals on the right side of the fuse/relay board. One of the plugs contains the two wires to the fuel pumps. Mine were toasty.

    The pumps have a high current draw when they start and less once running. the only link to hot day / long runs is look at where the fuse panel is located, right above eh passenger side exhaust manifold! Your heat shield my have lost some of its insulating material.

    I think I started the link with the modification to run 12 gauge wires to relays located under the rear seats (just above pumps) with separate relays controlled by the original power signal. It works and several others on this site have done the same.
    Ken
     
  5. Highmiler

    Highmiler Formula Junior

    Dec 8, 2010
    414
    Missouri
    Full Name:
    Greg
    Ken is the guy who put me on to the fix.
    Last night I ran this by a neighbor who is an Electrical Engineer. He says for every .1 Ohm resistance the Voltage drops 1.2 volts. Consequently bad grounds, fur on terminals and heat in the wiring will all cause the pump pressure to drop. It takes those 30 amps to generate the pressure required to run the Bosche mechanical fuel injection. Nowhere in the Bosche fuel injection books is this mentioned. Ken told me what to do and it fixed the problem.
    Greg
     
  6. sebackman

    sebackman Karting

    May 19, 2010
    62
    Excellent. I will try to re-wire come the weekend. It’s not on the lift yet.

    Can you please give some insight to how the wires normally go. Are they under the car or drawn in the console and down to the pumps under the rear seat?

    kind regards
    Rob
     
  7. SouthJersey400i

    SouthJersey400i Formula 3

    Mar 14, 2007
    1,202
    Romulus, NY (Finger Lakes)
    Full Name:
    Ken Battle
    Rob
    Remove the back seats and center cushion. If I remember the original wires come down the left side sill and go thru the floor to the pumps. I think the hole is under the rear seats or just in front of them. If you use the original wire for the last run from the new relays to the pumps, the whole job can be done inside the car (no work needed under car). There is plenty of room to mount relays under the rear seats. Trick is finding a good power source in front of car. I used one of the two main feeds from the battery to the fuse/relay panel. I ran my new heavy guage wire down right side of center console. You will use the original wires to the pumps as the control wires to the relays.
    Ken
     
  8. Al Campbell

    Al Campbell Formula Junior
    Silver Subscribed Owner

    Nov 22, 2013
    411
    Australia
    Your neighbour is correct.

    To calculate the voltage drop across a connection multiply the resistance of the connection x the current flowing. So in your example it would be 1.2V drop is 0.1 Ohm resistance X 12 Amps.

    Of more importance is the power dissipated in the connection which is -
    Power = Current x Voltage.
    As Voltage = Current x Resistance.
    Power also = Current x Current x Resistance.

    In your example Power dissipated in the 0.1 Ohm connection would be 12 x 12 x 0.1 = 14.4 Watts
    This power dissipated is in the form of heat which oxidises the metal in the connection which can increase the resistance meaning more and more power will be dissipated in the joint until it fails.

    Therefore it is very important to keep the resistance of each joint in a high current circuit (and the earth path) to a minimum.
    To do this I use silver conductive grease as it lowers the resistance & helps dissipate heat from the connection surface. Use this sparingly as it can bridge out between conductors if not careful.

    Cheers,
    Al



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  9. sebackman

    sebackman Karting

    May 19, 2010
    62
    Hi again,

    Thank you for all the good ideas.

    I have now run a new separate fused cable (single 9 gauage / 6mm2) from the battery to the fuel pumps. I use the old pump feeds to drive two new relays mounted just behind the center console above the pumps. The last feet of wires to the pumps are not changed. -Just as described above.

    I still get rough running on the right bank. It gets better when warm. The car blew a 15amps fuse for the feed to the pumps after a while when idling. Is that normal or an indication of a bad pump. How much current do they draw at operation? I now use a 25 amp fuse.

    I have a fuel pressure gauge on each bank and the pressure is equal between the banks and good. The system also holds pressure quite some time after turned off the fuel accumulators are probably ok.

    However that does not say anything about the flows. And the banks are connected so I will have to block that to get a proper reading.

    The filters are changed maybe 10 years ago and the car has only covered a couple of thousand miles since then. Can they be clogged due to age and preventing flow ?

    I will change the distributor cap and the rotor this winter. I have checked spark and that is good on all cylinders. She is running an MSD box.

    My plan is to clean the fuel system over the winter. Is there anyone having a description how clean the fuel system and what hoses are needed to replace the old ones in the rear.

    There seem to be a small black box/connector between the tanks in the trunk from which the fules is fed to the pumps. Can that clogg? I have changed the fuel level sensor at the top in the right hand tank as that was corroded. Maybe that stuff lays on the bottom of the tank outlet and blocks the flow?

    The car is a 1980 400i with 30k miles on the clock.

    What fuel filter is recommended? Original?

    If I do need to replace the pumps what would you recommend?

    The reason for asking is that these cars were made 40 years ago with no ethanol in the fuel, now we have about 10-15% mixed in. At least over here. Maybe that creates some problems with OEM parts?

    Kind regards
    //Rob
     
  10. jacques

    jacques Formula Junior

    May 23, 2006
    830
    Los Angeles/Florida
    It would be veery nice to see a diagram or picture. This sound like a very good fix. Thank you so very much. Jq.
     
  11. SouthJersey400i

    SouthJersey400i Formula 3

    Mar 14, 2007
    1,202
    Romulus, NY (Finger Lakes)
    Full Name:
    Ken Battle
    Rob
    One 25 Amp fuse should be okay but 30 Amp better for both pumps, but the individual pumps would use 15 Amp fuse each. At normal running I think the pumps pull less than 10 Amps but I've been told the starting draw is over 15 Amps but for a very short duration, not enough to blow the fuse but high enough to burn the connectors in the fuse panel. You have avoided that latter problem by by-passing the current from that panel.

    The correct Bosch fuel filter is #0-450-905-021, sometimes listed by a stock # 71020. There is a whole series of "identical" filters but different end connections to match the plumbing. Numbers given are correct for 400i. These filters will handle 15% ethanol, better than some parts of system. I suggest changing them both but after letting sit for a few days I would cut open the one on the right side and see what is inside. You will either have a "Got IT" moment or you will know to keep looking. There should be very little pressure drop thru it.

    If one or both filters are full of junk, I think you know where to look, our fuel tanks are not fans of drinking ethanol.

    Keep us informed what you find.
    Ken
     
  12. Part Time

    Part Time Formula Junior
    Silver Subscribed

    Dec 16, 2013
    471
    Port St. Lucie, Fl
    Full Name:
    Gary Shore
    Rob.....here are some Bosch part numbers.....do you have the Ferrari Fuel Inj Manual ?

    400 F101 V12 4.8L K-Jetronic

    Injector Valve 0 437 502 047
    Fuel Pump 0 580 254 975
    Air Flow/Mass Sensor 0 438 120 098
    Fuel Filter F5021
    Thermo-Time Switch 0 280 130 220
    Fuel Distributor 0 438 100 055
    Cold Start Valve 0 280 170 412
    Fuel Accumulator 0 438 170 004
    Warm Up Regulator 0 438 140 033
    Auxiliary Air Valve 0 280 140 104

    Gary
     
  13. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    18,732
    Texas
    Full Name:
    Steve Magnusson
    #13 Steve Magnusson, Dec 19, 2019
    Last edited: Dec 19, 2019
    It's not a good sign for that fuel pump. Although the inrush current at start-up is much higher, IME the steady-state current of the Bosch CIS fuel pump is more in the range of 9~11A. (The fuse doesn't blow at start up just because the very high current only occurs for a very short time, and the fusible element doesn't heat up enough to melt.)

    Only the control pressure areas of the two banks are connected together (so each bank "sees" the same average control pressure). The regulated fuel supply pressure for each bank from each fuel pump are completely separate. If you can measure the regulated fuel supply pressure on the offending bank during good running and during bad running, that will tell you if the fuel pump (or perhaps fuel filter) is the issue -- i.e., if different = could cause problem; if not different = runability problem is not caused by the fuel pump (even if it is blowing fuses).

    Of course, once you have the pressure gauge out for use, it wouldn't hurt to measure the control pressure during good running and bad running just to make sure that it isn't doing something weird.

    Good Hunting!
     

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