Engine dies when I apply the brakes

[greenjeep]

So a fun new thing started on my Commando the last couple days, If I put on the brakes, especially when going slow, it sputters for a second then dies. I lose all power, no lights, stereo, gauges, nothing. It stays like that for up to 30-45 seconds before I can start it again, then it's back to normal even starting my music again where it left off.

My turn signals have been being weird since my unplanned trip down Kenny's Climb backwards, so I was thinking it might be tied to that, but that was 3 weeks ago and this just started Thursday. A friend suggested it might have something to do with vacuum pressure, but didn't explain it so I understood what he meant.

It seems to me it should be something simple and easily fixable. I checked all my wires on battery, alternator, sillinoid, and nothing was loose or obviously weird.

My setup: 68 Commando, EFI 4.3, 700R4, 241, 44s w/discs. Normally runs great.


Any ideas?

 

[rollover]

My first thought would be vacuum like your friend (power booster?), but that still doesn't explain the electrical problem.

Check your elect wiring from your brake pedal switch to your tail lights and turn signals to your rear lights. Brake lights and turn signals are the same wire at the bulb. Next you might want to check your grounds on the ECU that you added when you did your swap.

Just some thoughts.

 

[DOSS]

I would lean towards a Vacuum leak somewhere in the system. When you press the breaks you use the vacuum from the engine to assist with your power booster. anyhow go through your vacuum system line by line fitting by fitting and see if you can find something loose in the system..

Also check that electrical stuff too

 

[Bart]

My first guess would be a ground. Seems like you've lost one and it's trying to ground back to through the system.

 

[greenjeep]

Ok, good suggestions, but I need more help on the vacuum stuff, I understand the vacuum theory but need more specific details.

Check the wiring back at the tail lights or under the hood?

 

[jeepspeedtj]

Ok, good suggestions, but I need more help on the vacuum stuff, I understand the vacuum theory but need more specific details.

Check the wiring back at the tail lights or under the hood?

First thing i would do would be to disconnect the vacuum line to the brake booster and cap it off. Start the jeep and press the brakes. Does the jeep die? If so that eliminates the brake booster. and you have an electrical problem.
Check all of the wiring in the brake light system first.

 

[DOSS]

First thing i would do would be to disconnect the vacuum line to the brake booster and cap it off. Start the jeep and press the brakes. Does the jeep die? If so that eliminates the brake booster. and you have an electrical problem.
Check all of the wiring in the brake light system first.

Umm ya X2 that is a good way to go about it..

if it doesn't die then it is the Vacuum if it is read through this and it will give you a good grounding for checking the vacuum system http://www.aa1car.com/library/vacleak.htm

 

[Jared]

Have you tried pressing the clutch pedal when you press the brake pedal? Or just taking it out of gear when stopping? My sister had those issues a lot on her first car.

Hope this helps.



Okay, okay. I'm going with the ground problem. Check all grounds on your brake lights first thing... or try unplugging your brake light system and see if the problem goes away.

I'd be on the vacuum bandwagon if it weren't for the electrical gremlins that occur when the motor dies. Sure sounds like you'll have fun finding this one!

Jared

 

[cheepin]

First thing i would do would be to disconnect the vacuum line to the brake booster and cap it off. Start the jeep and press the brakes. Does the jeep die? If so that eliminates the brake booster. and you have an electrical problem.
Check all of the wiring in the brake light system first.

Do this first.Then check for loose wires around the brake pedal.I believe you have a loose ground that is hitting your pedal and shorting out.

 

[jp008]

Try pushing the clutch pedal in before stepping on the brakes. (kidding)

 

[UNSTUCK]

Does it do this sitting in the driveway or is it while driving, you step on the brakes and it dies? Does it die when you come to a complete stop or while coasting?

If the above problems don't fix it, make sure the torque converter is unlocking. IIRC, the factory wiring set up unlocks the TC when you step on the brake pedal. If you wired it this way, check your switch. If you used a stand alone TCC system, then you may not have wired it this way, and wouldn't have to worry about this.

 

[greenjeep]

First thing i would do would be to disconnect the vacuum line to the brake booster and cap it off. Start the jeep and press the brakes. Does the jeep die? If so that eliminates the brake booster. and you have an electrical problem.
Check all of the wiring in the brake light system first.

That sounds easy enough, I'll try that first.

Umm ya X2 that is a good way to go about it..

if it doesn't die then it is the Vacuum if it is read through this and it will give you a good grounding for checking the vacuum system http://www.aa1car.com/library/vacleak.htm

Thanks

Have you tried pressing the clutch pedal when you press the brake pedal? Or just taking it out of gear when stopping? My sister had those issues a lot on her first car.

Hope this helps.



Okay, okay. I'm going with the ground problem. Check all grounds on your brake lights first thing... or try unplugging your brake light system and see if the problem goes away.

I'd be on the vacuum bandwagon if it weren't for the electrical gremlins that occur when the motor dies. Sure sounds like you'll have fun finding this one!

Jared

No clutch. Unplug the brake lights from where? I'm electrically retarded so use small words.

Do this first.Then check for loose wires around the brake pedal.I believe you have a loose ground that is hitting your pedal and shorting out.

Like under the dash?

Does it do this sitting in the driveway or is it while driving, you step on the brakes and it dies? Does it die when you come to a complete stop or while coasting?

If the above problems don't fix it, make sure the torque converter is unlocking. IIRC, the factory wiring set up unlocks the TC when you step on the brake pedal. If you wired it this way, check your switch. If you used a stand alone TCC system, then you may not have wired it this way, and wouldn't have to worry about this.

Yes to all your first paragraph. Why would the torque converter just all of a sudden stop unlocking?

 

[DOSS]

Ok I am not sure where the brake switch is 100% on a Commando but it should either be under the dash - Follow your break pedal and it should at some point come in contact with a little button switch (that would be it).. or it will be on the Master cylinder itself just look for little wires coming off it somewhere and that should be your switch.

As for the TC not unlocking it could be part of your electrical gremlins if it does it while in park I wouldn't think it is the TC but don't rule it out..

Go through the disconnecting the vacuum from the brake booster and see what it does before letting too many other tangents come into play

 

[UNSTUCK]

So it dies in driveway AND while driving? You step on the pedal and it dies? And it dies while coasting AND once stopped? Is it really yes to all of them?

How does the engine run the rest of the time? While idleing, does it sound like it has a miss? (that could be from vaccum loss)

Does it die anyother way or do you have to step on the brake pedal? If you have to step on the brake pedal to make it die, you can nerrow it down to wires.

Look and see if your ignition switch wire is being pulled by your brake pedal when you push it. Could be causing a bad connection.

Next unplug the brake switch from the pedal assembly. Now step on the pedal. What happens? Now push the brake switch with your finger, does the engine die?

If none of that helps, just hook me up with some room and board and I'll be right there. Well, I'll need a truck and trailer for my Jeep to come along too.

 

[greenjeep]

So it dies in driveway AND while driving? You step on the pedal and it dies? And it dies while coasting AND once stopped? Is it really yes to all of them?

How does the engine run the rest of the time? While idleing, does it sound like it has a miss? (that could be from vaccum loss)

Does it die anyother way or do you have to step on the brake pedal? If you have to step on the brake pedal to make it die, you can nerrow it down to wires.

Look and see if your ignition switch wire is being pulled by your brake pedal when you push it. Could be causing a bad connection.

Next unplug the brake switch from the pedal assembly. Now step on the pedal. What happens? Now push the brake switch with your finger, does the engine die?

If none of that helps, just hook me up with some room and board and I'll be right there. Well, I'll need a truck and trailer for my Jeep to come along too.

I haven't driven it much since this started happening, but during that time it died as I slowed to a stop, and it also died in the garage when I put the brake on to pull it out of the driveway. I'm no engine expert, but other than dieing, it seems to run as good as always. Only ever died when I stepped on the brake.

I haven't had time to play with it yet, but hopefully in the next day or two, I'll try to isolate whether it's vacuum or electric. You are welcome down anytime! I have 2 guest bedrooms with room for a truck and trailer.

 

[UNSTUCK]

You are welcome down anytime! I have 2 guest bedrooms with room for a truck and trailer.

I'll hold you to that!

These engines are also known to die when braking to a stop when there is no VSS. Do you have one? If not, was it turned off in the ECU? Even if it was turned off, you can still have problems with it. From what I can gather, it's pretty random. Some people have it happen all the time, yet it has never happened to me.

 

[jeepspeedtj]

Hey Greenjeep. Is your 4.3 TBI or CPFI? If it is the later it could be a fuel pressure regulator. I had a 94 s10 come into the shop with a simmilar problem and that is what it ended up being. Also are you using a painless or howell or a stock engine harness. since you are running a transplanted drivetrain i am doubt full the problem has to do with the brake wiring. But it is to soon to rule out a bad ground.

 

[jeepspeedtj]

It is doubtful that he has a vss But the dieing issue that you are refering to was mostly on the LT1 with a 4L60E. It was a software issue in the ecu that would not allow the IAC to compinsate the lack of throttle. The ground speed is erelevant to the running of the engine. (I know that people are going to challange me. But think about it due to diffrent gear ratios and such the motor does not need speed to run properly.) Is your tach working properly?

I'll hold you to that!

These engines are also known to die when braking to a stop when there is no VSS. Do you have one? If not, was it turned off in the ECU? Even if it was turned off, you can still have problems with it. From what I can gather, it's pretty random. Some people have it happen all the time, yet it has never happened to me.

 

[greenjeep]

I'll hold you to that!

These engines are also known to die when braking to a stop when there is no VSS. Do you have one? If not, was it turned off in the ECU? Even if it was turned off, you can still have problems with it. From what I can gather, it's pretty random. Some people have it happen all the time, yet it has never happened to me.

Way over my knowledge base for electrical!!

Hey Greenjeep. Is your 4.3 TBI or CPFI? If it is the later it could be a fuel pressure regulator. I had a 94 s10 come into the shop with a simmilar problem and that is what it ended up being. Also are you using a painless or howell or a stock engine harness. since you are running a transplanted drivetrain i am doubt full the problem has to do with the brake wiring. But it is to soon to rule out a bad ground.

I think TBI, how do I verify? Stock harness as far as I know, was there when I bought it.

It is doubtful that he has a vss But the dieing issue that you are refering to was mostly on the LT1 with a 4L60E. It was a software issue in the ecu that would not allow the IAC to compinsate the lack of throttle. The ground speed is erelevant to the running of the engine. (I know that people are going to challange me. But think about it due to diffrent gear ratios and such the motor does not need speed to run properly.) Is your tach working properly?

No tach.

 

[jeepspeedtj]

Does it look like a carburetor?