Engine dies when brake pedal pressed

Stevehose

Stevehose

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I have my friend's beautiful Verona CS in my garage so I can get my e9 on while mine is in the shop getting the towers welded.

When the brake pedal is pressed, the engine dies, it's not vacuum leak type dying, it's an electrical issue. What would cause a short that would have this effect? I think I will pull the under dash piece to see if a bare wire is hitting the pedal. Any other ideas?

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hi Steve
you sure is not vaccuum ?
electrical ?
humm,
what year is it ?
i recall seing relays fixed on top of brake booster beam in some versions (not in mine so i am being a bit imprecise), so if a cable is there wandering in the way of the brake pedal rod, who knows what is doing,...
 
1973. I am going to verify the vacuum, but usually vacuum leak will cause a rise in rpm but will see.

deQuincey said:
hi Steve
you sure is not vaccuum ?
electrical ?
humm,
what year is it ?
i recall seing relays fixed on top of brake booster beam in some versions (not in mine so i am being a bit imprecise), so if a cable is there wandering in the way of the brake pedal rod, who knows what is doing,...
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The only intended electrical action is the brake light switch. It is a long shot if there is a short on that circuit downstream of the switch and somehow the fuse is not doing its thing, but you would see that voltage drops to many other systems. If you remove fuse #7 the circuit would be isolated and any short in that circuit would be immaterial.

There could be a loose wire, does it happen even when stationary? Or could be the car braking forces that move a wire. I had one of those and it took many trips on HWY 85 at 60-80mph to diagnose it. Now the only electrical way of killing the engine would be through the coil I believe, so how about checking that.

The other thing you can do while you have that car is to steal a good shock tower and replace it with one made of Verona painted cardboard. If the owner blames you, then he wasn't a real friend so you gain that knowledge plus the shock tower.
 
Bad brake servo check valve or it's installed backwards?

When the car is running does the coil get hot?
Had a similar problem with a friends car, took a while to figure out the coil had gone bad. It would stall under braking.
 
I think you've hit on something here, when I followed him to my house I noticed his brake lights and blinkers were not working. The car did not die when the brakes were used on the drive home. When I replaced the red fuse to get the brake lights working, the problem started but the fuse does not blow...

I didn't hold the brake pedal down very long (in order to keep the engine from stalling), so maybe held long enough it would blow the fuse but doubtful.

So what is down stream of the fuse which could be suspect? The battery is charging so I am waiting on that before I can start it again-the car has been sitting a while.

And thanks for the shock tower idea, I'm on it.





Arde said:
The only intended electrical action is the brake light switch. It is a long shot if there is a short on that circuit downstream of the switch and somehow the fuse is not doing its thing, but you would see that voltage drops to many other systems. If you remove fuse #7 the circuit would be isolated and any short in that circuit would be immaterial.

There could be a loose wire, does it happen even when stationary? Or could be the car braking forces that move a wire. I had one of those and it took many trips on HWY 85 at 60-80mph to diagnose it. Now the only electrical way of killing the engine would be through the coil I believe, so how about checking that.

The other thing you can do while you have that car is to steal a good shock tower and replace it with one made of Verona painted cardboard. If the owner blames you, then he wasn't a real friend so you gain that knowledge plus the shock tower.
Click to expand...
 
Not to change the subject- because it's important- but Steve, that is an awesome garage! I love the wood everywhere, a true classic "man cave".
 
Thanks but it's still full of junk, and I just recently cleaned it out! Our house was built in 1927 and the garage added probably late '40's so it is defintiely old and drafty, but it's enough to keep the coupe dry. And it can hold two cars as I often remind my wife...

Peter Coomaraswamy said:
Not to change the subject- because it's important- but Steve, that is an awesome garage! I love the wood everywhere, a true classic "man cave".
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Yeah, Lee here. And the luckiest e9coupe owner around because I live in the same town as Steve, the most generous and knowledgeable coupe owner around. Thanks man.
 
modshop said:
Yeah, Lee here. And the luckiest e9coupe owner around because I live in the same town as Steve, the most generous and knowledgeable coupe owner around. Thanks man.
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and always a willing participant to sit down and drink a beer with you ... oh, and talk about coupes. looking forward to having a beer with him in 6 weeks at Amelia
 
Stevehose said:
...
So what is down stream of the fuse which could be suspect? The battery is charging so I am waiting on that before I can start it again-the car has been sitting a while.
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Not much, so either the bulb socket got wet or shorted, maybe a faulty bulb, or the wires got crimped. Good news is you can check all that with an ohmmeter.

I see your replacing of fuse #7 started the whole thing, using a 100A fuse and melting some wire harness would have been another friendship test that beer cannot fix.
 
Update

Charged the battery and started her up. Unplugged the brake light switch. Activated the other circuits on this fuse - the wipers, wiper washer, blinkers, horn, reverse lights - none blew the fuse.

Plugged the brake light switch in - blew the fuse.

Unplugged the switch and jumperd the wires - blew the fuse.

Any suggestions?

Trace the wires to the brake switch?

This is driving me to drink alone!
 
Thanks, will check bulb sockets next.

I have a feeling that since the car was running soley on alternator power when exhibited the dying symptom, there wasn't enough amperage to blow the fuse but the current draw drained the ignition system somehow. Now that the battery is fully charged - kaboom - instant blown fuse.

What color is the 100 amp fuse? Black?

Good thing I have s pile of red ones lying around.


Arde said:
Not much, so either the bulb socket got wet or shorted, maybe a faulty bulb, or the wires got crimped. Good news is you can check all that with an ohmmeter.

I see your replacing of fuse #7 started the whole thing, using a 100A fuse and melting some wire harness would have been another friendship test that beer cannot fix.
Click to expand...
 
Steve,

start by looking at the simple things, are any of the brake light wires grounding out? look at the connections and the wires around the lights?

get a big pile of fuses ...

if it blows the fuse when you plug in the stop light switch, it has to be something downstream of that switch.
1st - check all of the grounds
2nd - unplug the brake lights, then plug in the stop light switch and see if that blows the fuse. if the fuse blows, its something between the two ... and there is only wiring.
 
Yes - that's tomorrow's game plan. Too much cab consumed at this point to be working on someone else's car.

rsporsche said:
Steve,

start by looking at the simple things, are any of the brake light wires grounding out? look at the connections and the wires around the lights?

get a big pile of fuses ...

if it blows the fuse when you plug in the stop light switch, it has to be something downstream of that switch.
1st - check all of the grounds
2nd - unplug the brake lights, then plug in the stop light switch and see if that blows the fuse. if the fuse blows, its something between the two ... and there is only wiring.
Click to expand...
 
I would check the two brake light housings in the trunk for corrosion in the light sockets and on that strap that connects the grounds together. Also check the trunk ground for all of the rear lights, which in my car is on the fender near the jack.
 
The problem has stopped. But not because I found anything definitive, I diconnected the rear brake light wires and the fuse doesn't blow. Then I reconnected the tail lights one by one, no problems. So perhaps by moving the wire harness or something...

I am going to closely inspect the wires and harness in the trunk, they look a little crusty. The grounds for the lights are in the center of the rear section, not by the spare and they look good.

I will also clean out the connections of the light housings.



Ohmess said:
I would check the two brake light housings in the trunk for corrosion in the light sockets and on that strap that connects the grounds together. Also check the trunk ground for all of the rear lights, which in my car is on the fender near the jack.
Click to expand...
 
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