Engine Dies When Brakes Applied

[DieselSpider]

The Franken Diesel Spider has started cutting out occasionally when the brakes are applied. Occasionally a fuse blows but not always. There is an intermittent short that causes the fuel valve on the Bosch Diesel Kiki pump to close.

I am not finding any shorts going to the stop lights so it has to be in the maze of cut wires the previous owner left under the hood. Are there any signal wires on a 78 Spider that go to the master cylinder or possible some pollution control device that's potentially been cut out of the system when the simple computer free diesel was put in?

The engine only has a temperature gauge, starter signal wire, oil pressure wire, fuel valve solenoid, tach feed from the Kiki pump and a 2 wire alternator aside from the separate circuit with its own fuse and relay for the glow plugs so its requires much less wiring than the gasoline engine to run it as the Kiki injection is all mechanical.

The low brake fluid switch is just hanging from its wires right now too.

I really need to spend some quality time pulling and getting rid of a literal spider web of unused wires many of which were left uncapped and live.

My temptation is to just run a new feed wire from the brake switch to the stop lights and bypass everything that's there in that circuit.

[klweimer]

Vacuum booster for brakes?

[DieselSpider]

Vacuum booster for brakes?

Its a Diesel so there is no intake vacuum going to the booster but rather a separate vacuum pump driven off the back of the alternator and the fuel injection is a completely mechanical distributor pump driven by a belt. It appears to be electrical so its some wire that went to a sensor or solenoid related to the gasoline engines ignition or carb to activate an idle stop or other device when you hit the brake to prevent pollution or stalling that has been cut off and shorting. If I unplug the brake light switch on the brake pedal it does not stall. Eventually if you hold down the brake pedal long enough it will blow the fuse. If there was obvious snapping, popping or sparking it would be easy.

I will have to spend some quality time with the wiring diagram and car since when they put the Diesel engine in they repurposed a good bit of wiring so it no longer powers what it was originally intended for. On this one it may be time to just dig in and correct the rest of the sloppy work they did when they converted it to a Turbo Diesel.

[Ragno124]

You might want to check your voltage regulator on the alternator. High variations in voltage can cause you problems when the regulator starts to fail. Another classic symptom is noticeable fluctuations in headlight intensity with engine speed when driving at night.

[spider2081]

If unplugging the brake light switch eliminates the car stalling I would think the problem is in the wiring from the brake light switch to the brake light bulbs. I would start by removing the bulbs and inspecting the sockets and then visually inspecting the bulbs. It is sort of common for the brake light switch wires to gets pinched by the brake and clutch peddle assembly. You might look to be sure the wires are clear of the peddles moving parts. If anything has been done with the seat belt attachment point near the drivers door that is where the brake light wire passes before entering the fender wheel.

[DieselSpider]

You might want to check your voltage regulator on the alternator. High variations in voltage can cause you problems when the regulator starts to fail. Another classic symptom is noticeable fluctuations in headlight intensity with engine speed when driving at night.

No alternator issues even when turning on a high amperage electrical heater/defroster which I use since I have not yet hooked up the heater core to the Diesel engine. Only dies when the brake lights activate and only some times.

[DieselSpider]

If unplugging the brake light switch eliminates the car stalling I would think the problem is in the wiring from the brake light switch to the brake light bulbs. I would start by removing the bulbs and inspecting the sockets and then visually inspecting the bulbs. It is sort of common for the brake light switch wires to gets pinched by the brake and clutch peddle assembly. You might look to be sure the wires are clear of the peddles moving parts. If anything has been done with the seat belt attachment point near the drivers door that is where the brake light wire passes before entering the fender wheel.

Seat belts and seats have been replaced and that is where I put my cane while I am driving so there is a possibility that its shorting depending on how my cane is shifted. When I am trouble shooting the cane is outside the car since I am walking around so definitely something to consider.

[DieselSpider]

For some reason it has stopped doing it and I really wish I knew why. I may just go back to my original thought of eliminate anything that goes anywhere from the brake light switch to other than the brake lights. On this car none of that is used and we know its only going to behave until I am in some really bad stop and go traffic.

Oh the joy of the intermittent problem that won't happen when your trouble shooting it.

[81SPIDERMATT]

I seem to remember reading once that a worn clutch cable going thru the firewall would make contact and ground out the whole pedal assembly and anything attached to it ... just a thought ...Matt

[DieselSpider]

If I feed power to the brake switch from another circuit all is well so I am not sure what is going on there. I even ran a new line going from the brake light switch to the brake lights with no improvement however when I removed the power feed going into the new brake light switch and ran a line in from the courtesy light feed as a test all has been well.

It being an intermittent problem makes it more fun to nail down. There was no connector in the wiring harness until the back corner of the left rear of the car so the one that's been spoken of by the side of the drivers seat does not exist on my 78.

[spider2081]

however when I removed the power feed going into the new brake light switch and ran a line in from the courtesy light feed as a test all has been well.

I think courtesy light power is on the "hot all the time" circuit of the car. The brake light switches original power was from a "hot in start and run" power connection in the car. In other words originally the power passed through the ignition switch and the fuse 1 connections. The ignition coil is powered from the same contacts in the ignition switch as the brake light switch. Possible intermittent contacts in the ignition switch could be part of your problem. Adding the brake lights current to the ignition switch contacts might be causing a voltage decrease to the coil.

Another point you mentioned is the fuse blows sometimes if the brake pedal is depress for a while. This makes me wonder if something has been added to Fuse 1's circuit that brings its operating current close to the fuses 8 amp rating. Then when you hold the brake pedal down eventually the fuse blows.

Hope this is some help

[DieselSpider]

however when I removed the power feed going into the new brake light switch and ran a line in from the courtesy light feed as a test all has been well.

I think courtesy light power is on the "hot all the time" circuit of the car. The brake light switches original power was from a "hot in start and run" power connection in the car. In other words originally the power passed through the ignition switch and the fuse 1 connections. The ignition coil is powered from the same contacts in the ignition switch as the brake light switch. Possible intermittent contacts in the ignition switch could be part of your problem. Adding the brake lights current to the ignition switch contacts might be causing a voltage decrease to the coil.

Another point you mentioned is the fuse blows sometimes if the brake pedal is depress for a while. This makes me wonder if something has been added to Fuse 1's circuit that brings its operating current close to the fuses 8 amp rating. Then when you hold the brake pedal down eventually the fuse blows.

Hope this is some help

It would have to be something that does not run all the time though and not manually switched since its intermittent and I have not been able to force it to do so.

Brown wire fix was done, all ignition components have been removed since its a mechanical Kiki Pump Diesel, Diesel Fuel Valve and lift pump are switched by a small relay that draws milli-amps and powers everything from a fused line directly from the main battery cable. The car does not even have a radio installed in it. On reflection though it could be a weak connection with some resistance that only acts up when the weather changes.

[spider2081]

Why do I keep forgetting its a "Diesel"

I think your ignition switch has an unused "int" terminal on it. I would install an inline fuse holder with something like a 5 amp fuse to this terminal and power the brake light switch with it. If the newly installed fuse blows the intermittent would seem to be in the brake light system.

[DieselSpider]

Its been trouble free for a few days now powered off the dome light circuit. Its really amazing that the car is as reliable as it has been considering the maze of cut wires they left behind under the hood and dash when the pulled out all the stuff required to keep the gasoline engine running. Really need to do an inventory and eliminate what's not needed. He/They did some things pretty nicely sliding in the diesel while others leave me feeling that that lone mosquito at a nudist colony - Where do I begin..... ;^)