Fuel Pump and Tachometer issue in unison

[whyismybmwbroke]

Car is a 1978 BMW 320i M10B20.

It runs without no issue. Idle, blimps, full throttle. Cold or hot, doesn't matter.

But, over night (16 hours) something has happened. The fuel pump will not turn when key is in ON position. But will turn on without an issue when jumped. It used to do what it is supposed to do, turn on for 2 seconds then shut off. Also, the tachometer has went out with the fuel pump not turning on.

I have checked all connections, and related fuses. I have all normal dash lights on, and my fuel and temperature gauge is working with no issue.

I have also tested the fuel pump relay with a guide I found on here by EPMEDIA.
I have also changed out the old fuel pump relay with one I had laying around, still to no avail.
I have proper voltage at the positive coil terminal (+) 9.0 volts, but jumps around A LOT when car is running. Normal?

The wire in my hand in the first picture is typically hooked up to the positive side of the coil also, it comes out of the loom from the fuse box with the other wires.

This car has had pertronix points for almost a year now and has worked fine with them, only reason I mention this is due to the second picture I uploaded. The two cut wires are the old ignition wires that used to run to the distributor condensor and the positive terminal on the coil. Just wanted to be sure these two are not the issue because those two should be obsolete.

I don’t understand where this “pulse” wire is. Is this the black wire connected to the bottom negative post on my distributor, or is it the one that ends in the loom?

Of course, all the naked wires you see are from me working on it, they were not like that when it was operating correctly.




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[epmedia]

Both the fuel pump relay and tachometer rely on a pulse from the negative side of the ignition coil.

* the actual 'pulse' comes from an ignition system that is at least strong enough to trigger the fuel pump relay, importantly while turning the starter motor, or just blipping the starter motor to - for example: proper ignition points slightly going from closed to open, assuming the other ignition components are also proper... I'm not sure how the Petronix is wired.

Here's a wire diagram pdf file for the '78.
http://www.findmymerchant.com/images...l/ETM_1978.pdf

[GDAus]

Hi ....

By the look of it, your major problem is a dodgy instal of the Pertronix ignitor.

Looks like you are using the OEM coil with the ballast resistor in the line connecting to the +ve coil terminal. Having 9 volts there is consistent with that. Going to make the assumption you are using the Ignitor 1 (if you are you are using an Ignitor 2 with a standard coil you are wasting a lot of it's capabilities).
In the attachment I've added a bit to the section in the Pertronix Installation notes to show how a Ignitor 1 should be for a 2.0 litre M10.

Having the red wire from the Pertronix connected to the +ve Coil terminal means you have been running it off 9 volts instead of 12!
The Black Pertronix wire to the -ve is right, but is that another Black or Black/red wire on the +ve coil terminal?
If it's a Black /red, then it can be disconnected .. that's the bypass for the Ballast resistor during starting. If it's another Black ... where does it go ?

As for the long bit of bare wire .. I can only assume is the end of the green wire with the ballast resistor in it. The ballast resistor has to dissipate about about 12~14 watts of power and long term, it cooks the PVC insulation and it falls off and possibly melts the insulation in the guts of the wiring loom.
If it is the green wire , that is connected back to the Start/Run Bus and battery through the ignition switch WITHOUT ANY FUSES!

Short that to ground and it will get very exciting very quickly. And pretty crispy/melty as well.

Personally, I'd forget the the existing Green wire, cut it back at the fuse box end and splice a new wire to the coil area and use an external ceramic ballast resistor. That would give you a +ve 12 volt end for the Pertronix and a 9 volt end for the Coil +ve. The green wire goes back to the big flat plug on the front-right side of the fuse box.


Cheers

[whyismybmwbroke]

You guys are godsent. I have been looking for wiring diagrams like that because mine are so blurry I cannot even read them!

I have fixed the issue. Keep in mind I didn't even touch the car prior to this happening. It did it all on its own. The wire you are talking about with the sheathing baked off of it had gotten so hot that it had arced over to the negative side of the coil (-) wire in side of the loom. I am guessing this could have been interrupting the "pulse" from the ignition system?
I trimmed the loom very far back to find this. IT COULD HAVE CAUGHT ON FIRE! LOL

Only thing that could have caused that wire to get hot is a short, or a key left on without the car running, correct?

The car would run without an issue though, this one really threw me for a loop.

Thank you for you help, both of you!

As for the pertronix system, yes this is the Igniter 1. I will be doing this set up because right now, it is totally running on 9 volts and has been for a year now.. LOL!!!