So as the title says every time I hit my brakes it causes the fuel pump to stop pumping. The car in question is a 79 with the original 12a motor and about 60k miles on it. I just replaced the fuel pump, fuel filter and ignition switch on it and have also pulled the tank out and cleaned it. I have looked at the wiring harness for issues but have not found any exposed wires or bad fuses that could be causing this.

 

Put a voltmeter on the fuel pump and measure the voltage while pressing the brakes and see what the voltage is. I bet it's an issue with the alternator.

 

I will give that a try. I forgot to mention that I cant get it to start because of that issue.

 

It's not the alt then. Work on getting it started first. Pressing the brakes is not a requirement for starting it.

 

Possibly bad battery but it may have already killed the alternator. You need to get it started by jumping it and then check the charging voltage to the battery at idle and with a load an higher rpm to see if the alternator is doing its job. You may want to charge the battery before doing this as well, that way you know you are starting with a full charge or a possibly weak/dead battery if it won't take a charge. If the battery is more than 4 years old and it has drain down to nothing, it will most likely be toast and you need a new one.

 

I'm not laughing at you, I'm definitely laughing with you.
I'd be interested to hearing what the solution was, though my instincts would be to check for shorts first... but definitely record the voltage to the pump when this occurs.

I love these cars, although I have an FD, there are still moments just like your problem, when it happens it makes makes me go: "Well... that's cute."

 

Figured out the alternator is going out and got a new one ordered. Will let ya know if that's the fix.

 

If that doesn't do it, check the ground back at the hatch latch (it goes on one of the 10mm bolts that holds the hatch latch to the body). That is the common ground for the fuel pump and all rear lights. If that has excessive corrosion, or is just plain unhooked the pump will run until the brakes are pushed.

I had this exact problem years ago. Was doing some body work and had that hatch latch removed (and the ground removed) and went to start and move the car and it was doing exactly what you're describing. Didn't realize at the time it was the ground for both and I assume the pump was grounding out through the pump housing or something, which is why it ran... Ground issues can drive you nuts for sure...

 

+1 to 82transam's suggestion. It sounds a bit "ground loopy" to me.

 

Don't forget the ground strap from the rear of the muffler up to the mounting bolts for the chassis hangers for the muffler.

 

when the alternator was going bad, I had to keep the rpms up, and at a stop sign the engine would sputter when I braked. What was happenning was the car was mostly drawing on the battery because of the flakey alternator. As the battery drew down the higher rpm was required for the alternator to do its job.

All was corrected when I replaced the alternator......23 years ago

 

I've always wondered what in the world this was for, seems to serve almost no purpose other than to barely ground the engine at the rear of the car?