Gang, I'm still trying to diagnose my engine dying problem on my 88 740 GLE B230F... you know, the one where if you push in the brake or hit the turn signal, the engine will die.

The power comes in from the battery through the firewall to the ECU... This much is clear.

1. DOes the ECU have anything to do with the
a. turn signals
b. brake lights
c. stereo
or, are these items stand-alone?

2. Where is the main fuse box grounded to???

3. Where do the alternator wires connect to?

4. Is the fuel pump relay supposed to engage when the brake pedal is pressed?

your answers/suggestions would be greatly appreciated.

thanks.

nm

1. No, no, no, yes -- although they ALL draw their power through fuses in the fuse panel.
2. The fuse box is not grounded. Why would you ground it? That would blow fuses and start fires.
3. The fat red wire goes to the battery, a small wire connects back to the idiot light, and the ground wire connects to the engine block.
4. No.

Hi, I can't answer all, but I will try to help.

1. ECU controlls engine only (Fuel input duration and spark timing) depending on several sensors in the engine / air / exhaust-circuit. Not possible to disturb from inside the car without pulling wires/fuses.

2. Don't know 740, but are there any need for grounding in fuse box? No high voltage and whole chassis is ground. Grounding points are everywhere.

3. Battery/ground? These heavy gauge wires might need a check somtimes.

4. No, fuel pump relay is controlled by ignition switch and ECU only. Switch with new / known good relay.

Braking/turning should not trouble the engine, but the brake servo is using wacuum from engine and can change the rpm for some seconds.

Sounds like you having wiring/grounding trouble. Check all wires/connectors/earthing from battery via engine to dashboard.

Relays need a ground. There is a ground bus bar under the fusebox. It grounds at the body in front of the door, behind the kickpanel. Not sure which side is for the bus bar, but there are multiple grounds on both sides.

Which side of the car is this kickpanel at?? By the computer on the passenger side??

ok, so now I have two that say no ground and one that says ground... Does the fusebox have a ground? IF yes, where exactly does it go?

Hi, found a drawing of a 740, and saw that the fuses were mounted in a box together with the relays. All relays need ground, if one pin is missing it may try to draw power from other sources. Try to find a manual for the fuse/relay box and check all relays.
Sorry for answering without knowledge of the rest of your fuse box.
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Frodo 240GL 89 LH2.4