3.2 conversion - fuel pump

[chrisf]

I'm wiring up my 3.2 into my '76.

I came across something over the weekend and I'm looking for some guidance/info.

on the '76, there is a switch that is triggered by the CIS "metering" plate. When the engine is not running this switch is in the "closed" position, and the circuit has continuity. This causes the fuel pump relay to go from a closed (primary) circuit to the starting circuit, waiting for power from the starting position of the ignition switch. What this means is that when the ignition is on, but the engine is not running (metering plate closed) the fuel pump does not run.

So.....ignition on, relay switch to starting circuit (no fuel pump). Ignition is switched to "starting" position, and current flows through relay and on to the fuel pump. Engine starts up, metering plate opens (switch is now open, meaning there is no current through this circuit), and the fuel pump relay goes back to its primary position, which passes current to the fuel pump. Ignition switch is released back into the "on" position and the car continues to run. If the engine dies, the metering plate closes, which closes the switch, and the relay is brought back into the "starting" circuit, and the fuel pump shuts off.

When I first got my car, this switch was disconnected in the back of the car, and the fuel pump ran whenever the ignition was on. I connected it, and did the metering plate test, can confirmed everything was performing as designed.

Now, with the 3.2l, this circuit is open again, and I don't want the condition of the fuel pump running while the engine is not.

Any one have a solution or fix for what I'm talking about.

and for reference here is my other wiring thread: 3.2 conversion, DME wiring to fuse panel

Thanks,

~Chris

[porwolf]

This is the fuel pump relay function as I understand it for late 70's and 80's cars: The fuel pump gets power from relay terminal 30. Terminal 30 is internally connected to terminal 87A in normal run position of the ignition switch. The relay in normal engine run mode is not powered and the relay switch is in the normal closed position that internally bridges terminals 87A with 30. The relay does get powered in the ignition start engine position. Then the fuel pump gets its power through terminal 30 from terminal 87. Terminal 87 is connected to terminal 30 in the relay powered position. The relay powered position happens when terminal 85 is pulled to ground because the other relay coil terminal 86 is always powered with +12V.
Now terminal 85 is pulled to ground by the air flow sensor switch which shorts to ground when the CIS air flow sensor plate is in the rest position (engine not running). Actually the relay also gets powered when the RPM limiter circuit pulls the terminal 85 to ground, cutting off the fuel pump when the engine is running.

[MikeD]

I don't recall the details right now, but 1/2 of the DME relay is a fuel pump relay. The DME has a provision for running the fuel pump during cranking. Somewhere in Marc's 3.2 conversion write up it explains where to connect the yellow wire that makes this work. It can be done.

[chrisf]

I would say that with the relay in the normal run position (ignition on), is powered, or at least getting current flow. It is getting current thru S21 (which I can't find in my car btw) but ultimately from being bridge with S12. Below is a shot of my current flow diagram (which matches very closely with what you have above). If you follow up from S21, it is bridged with the top of S12




When the ignition is switched to the normal run mode, the relay is powered, but the circuit switches from 87a-30 to 87-30. This happens because (as you have mentioned) 87a-86 are internally bridged. So the instant you insert the key and switch to ignition on (normal run) the current flows from 86-85 because the air flow sensor switch is closed. This pulls the relay into the start position (87-30) on opens 87a-30 cutting the fuel pump off.

It is this function that is going to give me trouble. If I no longer have the air flow sensor switch connected, when I provide power to the relay (ignition on, normal run positon) there will not be continuity thru 86-85, and the relay will remain in the 87a-30 position, which will run the fuel pump.

MikeD: I've been following Marc's thread for most of this install. He does mention a yellow wire within a 4 wire bundle: 2 black, 1 yellow, and a black/vio. He only mentions using 1 of the black, and the black/vio.

As far as I have found there is no other wiring mod that I am missing. If that is the case, then I haven't affected how my fuel pump will be run except for eliminating the 86-85 cicuit, which doesn't seem good to me at this point. The car will start and run, but so will the pump when the engine is not given that the ignition is on.

[Flat6pac]

The relay is out of the Carrera system with the power to the fuse being controlled by the brain and the feed wire to the pump from the 3.2 harness connects to the top of the fuse and the wire from the relay is removed and taped off.
This takes the relay completely out of the system.
Bruce

[chrisf]

Originally Posted by Flat6pac

The relay is out of the Carrera system with the power to the fuse

o.k., the black 6pin DME relay? and which fuse: S21 (or for the '77 in Marc's thread, S16)?

Originally Posted by Flat6pac

being controlled by the brain and the feed wire

which wire? In Marc's thread he mentions connection of (3) wires from the DME relay: thick Red (in black sheath) to (+) terminal, black, and a black & violet (this is in the (4) wire bundle running from the DME relay, which consist of, yellow, two blacks, and the black & violet). The black wire connects to the bottom of S11, and the black& violet connects to the tach. so:

DME relay pins (according to Marc's thread):

1=87 goes to 6 pin FI in engine bay
2=87b red/green wire to front, taped back/no used
3=85 brown wire, reading ground/0 ohms
4=85b goes to 6 pin FI in engine bay
5=86 black wire, connected to bottom of S11
6=30 Red wire to (+)

There is also a black wire (bundled with the red/green, which is taped back) to the bottom of S16 (which in the '77, this connection runs to J16 (fuel pump relay), but he states this wire is run with the red/green wire, but I'm not sure is this black wire connects with the red/green wire on DME pin2, 87b

The only connections to the fuse panel up front are specified as being made to the bottom of the fuses.

Originally Posted by Flat6pac

being controlled by the brain and the feed wire to the pump from the 3.2 harness connects to the top of the fuse and the wire from the relay is removed and taped off.
This takes the relay completely out of the system.
Bruce

Bruce, are you saying here that the wire running from (in the '76 current flow diagram) the top of S12 to S21 is removed, taped off and a wire from the DME is then substituted into the top of S21? Or are you saying that if I wire this up correctly, the 5pin relay currently in my car is not even used?

I'm think I'm totally lost now.

help.

[chrisf]

bump for help/advice.

[Flat6pac]

You have an e mail
Bruce

[E Sully]

This is a quick sketch of my '86 DME harness. In the upper right you can see the R/Grn wire. This is from the dme relay to the fuel pump. It will need a 25 amp fuse in line before connecting to the fuel pump.

[1SIK930]

Forgive me if I don't know what I'm talking about here, because I don't.

You want to be able to turn your key to the "Ignition" position, without the fuel pumps being turned on right?

1) I'm pretty sure all cars fuel pumps turn on when the key is turned to the "Ignition" position. That's one of the ways that they diagnosis fuel pump problems. Turn the key to "Ignition" and listen for the fuel pump. My 930 had CIS, but pumps came on when you turned the key to the "Ignition" position. Now with the CIS, you actually had something (meter plate) that moved and you could put a switch on, for the fuel pump to turn on with. You don't have anything like that with the 3.2.

2) The only way I can think of to make the fuel pumps do what your asking for, is to find an RPM switch that turns on at 100 RPM. That way when the starter engages the engine and starts to turn the motor over, it will activate and turn the fuel pump on. I haven't found one that activates that low yet, but maybe some here knows of one or can find one.

3) Just curious, but why do you want to be able to do this?

[1SIK930]

One other way, would be to put a hidden switch somewhere in the cockpit. Wire it up to the control side of the relay. You could leave it on most of the time and turn it off when you needed to. Or, you could also use it as an additional "anti-theft" switch.

[boyt911sc]

Chris,

Have you already figured out how to connect the FP with the DME relay? See pages 970-26 to 31 (911 Carrera service manual by Bentley). The original FP relay set-up for the CIS is omitted or by-passed. PM me and I'll walk you through the process.

Tony

[chrisf]

E Sully....exactly what I was looking for, thank you so much! So...to confirm I will run the red/green wire into the top of an empty fuse location.....I will run remove the black wiring running from the fuel pump up to the original relay (terminal 30 shown way above) and run that into the bottom of the terminal/fuse (25A) for the red green wire.

Tony....thanks for your help too, with this and the oil thermostat thing. When I spoke to Bruce, Flat6pac. He said the same thing: The original FP relay will now be totally bypassed.
I'll shoot you a PM in a second.

1sik930....I'm pretty sure that beginning with the midyear cars (maybe earlier, I'm too sure) the system was designed to run the fuel pump in only (2) conditions: when the ignition switch is in the "start engine" position (running the starter) and when the engine is actually running. Its a safety consideration. You are right about the meter switch. If the car is running, the plate is open, which opens the switch, breaking the continuity the relay is looking for, so the relay runs the pump. if the engine stalls, the CIS meter plate closes, switch close, which tells the relay to shut off the fuel pump. This evolution happens without touching the ignition key.

Again, thanks for the help guys!