Paddiee

I have an 87 firebird, recently converted to a 5.7. Out of nowhere, my car started dying when braking. Slow or fast doesn't matter. It never happened before and I'm confused. I have no idea what it could be. Alternator is new fuel pump is new. Any ideas?

TreeFiddy

Maybe brake booster leaking vacuum. Do the brakes work less well too?

Or maybe IAC valve if u are TPI.

Paddiee

The brakes work just as well as they always have. It's a carbureted engine (Holley 600 cfm)

Paddiee

Oh and my electrical doesn't cut out. When I go to start the car up again, it's almost like it isn't getting fuel or spark. It takes a while to get it started after it's been running and dies. I hear brake booster vacuum leak is a common problem as well as wiring. The funny thing is, when I had my V6 in it, the car shut off one time but started right up. I'm thinking perhaps what was once a minor leak has turned into a huge vacuum leak?

TreeFiddy

Any sustained hissing from the booster with the brake pedal held down (apart from the 'whoosh' you might get initially)? If you can get a vac gauge on the intake and watch what happens, that may help.

Paddiee

no there's no noises at all. it's almost like the car isn't getting any fuel. it started after we jetted the carb and I'm thinking the float got messed up and might be caught on something.

TreeFiddy

Does your Holley have a dashpot - might be broken, maybe snapping the throttle closed when you lift to brake and causing the stall. To test, can you set the idle up a little so the butterflies don't close quite as far, see if that helps?

TreeFiddy

Also having just re-read this - yeah, I know my Holley's are extremely susceptible to bad behaviour following work, if you end up with an internal gasket leak or a stripped screw, very easy to do and not notice.

Paddiee

I'll definitely look into that. The carb is new so I hope it isn't broken.

Base91

iTrader: (1)

Try disconnecting and plugging the vac line to the booster and go brake somewhere with plenty of room. If you get the same thing happen it's not the brake booster.

edspring1

How about driving the car until it does it {cuts off}. Then before cranking see if the carb has any fuel in it by operating the thottle by hand while looking down the carb ?
If it has fuel, have a good insulated screwdriver handy and unplug the easiest plug wire and stick the screwdriver into the plug end of the wire, holding onto nothing more than a well insulated handle hold the shaft of the driver close to a ground and have a buddy crank the engine over. You need to find out what system isn't functioning or you'll spend a lot of time, money and trouble going back and forth from system to system. {gas, vac, electrical, etc}
You mentioned it did it once b4 with the V6. I have seen fuel pumps do exactly the samething. Once or twice the car would stop running then 3-4 days it would be fine, then one day it won't even start anymore. Maybe its just a clogged fuel filter? Is your gas cap vented ? If not the pump can and will create a vacuum so strong in your tank that the tank will actually start to collapse. I have seen that 2 times. Bad pump ? Not to be disruptive to anyones suggestions, but a vacuum leak at the booster bad enough to cut an engine off would certainlly make it idle higher, brake pedal would get hard , etc. I am thinking he is keeping the engine running while applying gas to it. But I know what you mean. We are all just trying to help. Maybe your loosing spark ? Does it shut off imediatley or slowly looses power and then shut off ? If it cuts off after loss of power and you have cats on it, maybe see if it is clogged. A cat usually needs to get hot before it clogs up enough to restrict the exhaust to the point the engine shuts off, but they do it all the time. Then you have to sit and wait for the cat to cool off b4 it will start again. I think we all need more info than whats been offered. Like does it do this all the time ? How long does it take for it to stop running ? How long do you have to wait for it to re-start and once it does restart how does it run ? When it re-starts is it kicking out any BLACK smoke ? Ever pull the plugs and see what they look like ? Are the ECM sensors still being used ? Crank sensor etc, No problem with the insulation thats on the engine side of the hood ? Air filter ?

Paddiee

I'll check the spark that way. When the car is dying, it sputters and slows down until it dies. I've had the carb on the engine for months now and it just started. My fuel pump is working and we've already checked the brake booster for any vacuum leaks but there are none. No sensors on the car have been used in years. It runs in the simplest way possible: fuel, spark, go. The car only kicks out smoke on start ups after it's been off for a while because it burns a teeny tiny bit of oil. It was explained to me but not a big deal. The plugs are brand new, wires are brand new, points are brand new. There's no insulation on the hood. I try to restart it right away and it takes forever to start up again. The issue started once we jetted the carb and had to remove the front bowl. Perhaps the float got knocked around or is sticking at a low level? I have to get time to dig around and see what the issue is as far as that goes. I just put a cat on it for inspection but it was dying before that. The air filter is clean as well. I had 3/4 tank when it first died; only when coming to a stop and took a while to start up again with pumping the pedal.

AJHECK95

just puting this out there on my buddies jeep his choke spring broke and every time he braked his car died from closing the choke. he put a new spring on and it never did it again

Paddiee

Hmmmm very interesting. Never once thought of that. I'll check that out as well. Thank you!

edspring1

I would lean towards a fuel issue. Sounds to me like you may have a defective needle & seat, float adjustment, etc. I don't think when you slow down or utilize the brake has anything to do with it shutting off. Sounds to me like at that point its just running out og momentum anyway. It sounds like it's running out of gas for whatever reason. I do not mean the amount of gas in the tank, rather the amount of gas the carb is being supplied or being allowed to enter the primairy bowl. If you have those little filters inside the fuel inlet adaptor at the fuel bowl, replace them or if you have a GOOD 10 micron inline filter installed elsewhere, throw them away its just overkill. A sticking needle can shut the fuel off before it enters the carb. {dirt, defects, etc} The float may be set incorrectly as well. Float too low and you can empty the bowl as you cruise along and if the flow of gas isn't strong enough to keep the bowl filled the engine will run out of gas. Sputtering etc right before it cuts off. This would happen everytime you drive it. I assume your useing a Holley 4150 style carb ? 1st thing I would do because its easy, and doesn't cost anything I would pull the level screw from the primairy fuel bowl and see where the level is. If you have gas barely dribbling out, thats a good thing. If nothing dribbles out, its a bad thing. If nothing dribbles out leave the screw out, put a few rags under that area and start the engine. If still nothing dribbles out while running bump the fender slightly. You should have a small amount of gas dribbling out. If NOT, adjust the needle and seat assy until you do. If the float setting appears to be correct I would then remove the needle and seat assy from the primairy bowl and inspect it carefully. NOTE HOW MUCH OF THE NEEDLE ASSY. IS STICKING OUT OF THE BOWL BEFORE YOU REMOVE IT ! If yours has the rubber O ring on it take your time and CAREFULLY inspect it for any knicks, cuts, scraps, gouges. Flip the assy over to make sure the needle is moving freely up and down several times. Make sure the point on the needle is not defective, as well as the seat is clean and none defective. If all that cks out re-install. Reset float level with engine running and level. 3rd Make sure you have no kinks, or obstructions of any type in your fuel line. Also make sure its not too close to any heat. {vapor lock} Are you useing the OEM pump in the tank ? If so I assume your also useing a adjustable regulator. Is it set between 4 1/2 - 6 lbs at idle ? I hate to mention this but....Sometimes the sock filter on the pick up tube in the tank gets clogged. That would def restrict flow as well as pressure. Also but rarely I have seen it more than once, the plastic OEM sloush baffle in the tank break loose and gets sloushed around with the gas in the tank and restrict/crack/break the pick up tube/sock. In order to see this, you have to use a wire coat hanger or something like it and see if it is loose by attempting to move it threw the fuel sender/pump hole. Those things can be completely broke loose or one or 2 rivets are broken allowing the baffle to float around with the gas or just swivel occassionally.
Can you install a fuel pressure guage where you can see it while driving ? If the problem persist, I would install one. Just install the feed line end as close to the carb as possible, next time the engine shuts down note the amount {if any} pressure you have at that time. If its up to 5-6 lbs you would know that the fuel pressure is OK all the way up too the carb. I just can't think of any electrical componet that would do give you this type of problem. Now a days everything is printed circut, and if a printed circut overheats they are broke that simple. Not like the old stuff with points, condensors relays etc where if they overheated sometimes letting them sit and cool off they could and would function again. Printed circuts don't and can't do that. It seems to be you have a fuel or air flow issue. From your description "sputtering before it shuts off" and "waiting before it can restart" sounds like your running out of fuel, and then possibly have to wait before the fuel is available again. If your running a manual fuel pump does the 'waiting' thing mean your cranking the engine but it won't start ? Does 'waiting' mean that you have to leave it alone for a certain amount of time ? How long ? How often does it shut down ? Is this all the time or occasionally? Does it do it within a certain milage or type of use ?

Paddiee

Taking everything you said into consideration, the problem started 2 months after just putting the engine in the car. The carb is barely 3 months old. I had the front bowl off because it's the only one I've ever removed and the float was fine. There was a good amount of fuel in there. Waiting to start the car means that I'm cranking it but it won't fire as if there's no fuel in the engine which is strange because the fuel pump works. I had to lean everything out to help it with inspection. I don't know if leaning it out like that would screw things up. It will sputter every single time I go to stop. The tranny I have is built to handle a certain amount of hp and I was thinking maybe it's putting too much pull on the engine in the slow-down process. I have no idea but it seems like a fuel issue to me. After I do manage to get it running, I shut it off and go to start it back up and it takes a few seconds to get going again; roughly 5 seconds with pumping the pedal. Again, we leaned it out so maybe that's why that happens? I've never had an issue like this before. Pumping the brake pedal when it's in drive with the e-brake on doesn't stall the car at all and there are no noises nor does the pedal get rock solid so I'm ruling out a brake booster vacuum leak.

TreeFiddy

Is this a Holley 4bbl? Check for fuel sloshing up out of the rear bowl vent tube under deceleration, and flooding the motor. Would explain the hard re-start too.

Paddiee

Yeah it's a 4 barrel. That's a great point. Never thought of that. I'll check it out tomorrow for sure.

Paddiee

Also, how would I go about solving that problem if it is the cause?

TreeFiddy

Rear float level may be too high.

If it's ok, I've read of a trick where you run a piece of rubber hose between the vents, with a few small vent holes in the top of that. If fuel sloshes out the vent, the hose prevents it falling down into the carb and flooding the engine.

Paddiee

Well I took the rear bowl off the car and reattached the fuel delivery tube, the opened the choke flap all the way and it stopped stalling on me. I'm not sure if that was the real solution but it worked.