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

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

 

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

 

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

 

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

 

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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It would be veery nice to see a diagram or picture. This sound like a very good fix. Thank you so very much. Jq.

 

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

 

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

 

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!