Fuel pump relay bypassed on my 308

There almost has to be a relay somewhere as the current to run the CIS fuel pump (~10A) is too high to pass thru the ignition switch. The relay panel has 3 large "keyhole" openings along the top edge -- shifting the relay panel upwards about ~6mm then allows you to pull it forward over the nailhead studs (but look to see if there are any screws that need to be removed first before the relay panel can be shifted upwards). You might also have a look behind the passenger footrest panel as that's a common place to hide electrical additions/modifications.

 

Section 5 of your OM.

 

I had to replace my 328s fuel pump relay, they are easily obtainable , with that being said, my fuse board had to be rebuilt as well. This after 100,000 miles on the clock.

Thank you

 

Another possibility entirely is that the air-metering plate in your CIS unit is misaligned. Open up the airbox, remove the filter and take a very close look. The fuel pump cut-off "safety switch" works via a circuit that incorporates the level that the metering plat pivots on. It is supposed to open the circuit whenever the plate is fully closed, to prevent fuel from being injected into an engine that is not drawing any air. It doesn't take much to disrupt the connection. A slight warp in the plate will do it. Or a tiny piece of debris, caught on the edge of the plate. If you mechanic messed loosened the center nut on the plate while trouble-shooting, it may not be in alignment.

By the way, if you ever need to prime your engine have a complete loss of fuel pressure (or if the car has sat for a long time) pushing down that plate (gently!) for a few seconds with the power applied to the car will cause the fuel pump to run. Listen to the sound--you will hear a change in the sound when all the air is purged (takes just a second or three) and then the sound will change. STOP. You can easily over do this and flood the engine. (Note: other people suggest disconnecting the blue safety plug to do this instead, but I personally try to minimize fussing with 37-year old plastic connectors when alternatives exist.)

Anyway, good luck.

 

Where does the green wire go? There may not be power on the green wire unless the key is "on" (and some other conditions).

Is the black plastic piece in your fingers: 1) a relay, or 2) a relay socket that you've already removed the relay from?

Does the black plastic piece only have two wires (the brown and green) connected, or are there more wires connected to it?

 

That is very bad as that will put all of the high CIS fuel pump current thru the ignition switch Pos II contacts -- it won't survive for long. You've got some serious hackery in your electrical system -- can only suggest that you restore your fuel pump wiring back to matching the wiring of your OM schematic which uses two relays and the safety switch to control the fuel pump operation:

(If a euro 308i 2-valve)
Relay F -- Start electro-valve control relay -- based on the starter command signal and safety switch signal coming into this relay, it controls the fuel pump relay
Relay N -- Fuel pump relay

My guess would be that your relay F had a fault, and your Mechanic didn't know that it is what operates relay N. (If you have a US version, the fuel pump electrical system is the same, but the relays may have different letters and/or slightly different names).

 

If you've got ALL of the wiring for relays F and N back to matching your OM schematic, try a different ...101 relay in the relay F position.

Also, please confirm that you have a euro version 308i.

 

For a 1981-82 US version 308i, the correct schematic reference is in OM 216/81 (send a shout if you don't have a copy, and I'll post a Dropbox link):

Relay P (item 90 on the 216/81 schematic) -- Relay for start injector -- based on the starter command signal and safety switch signal coming into this relay, it controls the fuel pump relay H
Relay H (item 91 on the 216/81 schematic) -- Fuel pump relay

Things you should do to get started:

1. Confirm the top and bottom of fuse #3 are +12V all the time (even key "off).

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2. Confirm the large P beige wire leaving the bottom of fuse #3 goes to terminal 87 of the fuel pump relay H (item 91 on the 216/81 schematic).

3. On terminal 30 of the fuel pump relay H there should be two P beige wires -- a small one (that goes to things like the AAV heater, etc.) and a large P wire that goes to the fuel pump motor.

4. If you remove the fuel pump relay H and touch a jumper wire from the female metal terminal 87 in the relay socket to the female metal terminal 30 in the relay socket = the fuel pump should run (even with the key "off").

If you can get this far, plug the ...113 fuel pump relay H back in and try a different ...101 relay in the relay P location. With the engine not running, see if the fuel pump will correctly not run with the key in Pos II (run) and the safety switch plugged in, but will correctly run with the key in Pos II and the safety switch unplugged. If all that works, the car should start and run fine. If not, you'll just have to keep comparing your existing wiring for relays H and P to the 216/81 schematic wiring for relays H (91) and P (90) and see if anything else is different. Good Hunting!

 

Very good! Your ignition switch will thank you. Did you ever find out why someone decided that this needed such a serious modification to "fix"? Was it just a bad relay P?

 

Here's the part I don't get with his thought process: the car DID leave the factory with power to the fuel pump. Therefore, no cutting and splicing of new circuit pathways was ever going to be the correct solution. You fix the circuit path - you don't invent a new one.

My own car had a mechanic at some point who took a similar approach to the slow power windows (which of course, didn't fix the core issue). So maddening to have to un-frack it, just to have a normal baseline to troubleshoot from. Glad you got it worked out.