stalling only on highway but every time

[choprsam]

Anyone know why my 427 crate engine (351w) stalls out every time going a constant 75mph on flat highway then won't restart for 20 min. til cool? but drives around town at red lights in HOT sunny south Fl fine.
Changed carb (and brand) and put carbon fiber between engine and carb.
Distributor problem?
P.S. Car was built by one of the local cobra importers!

[Bonos]

vapor lock???? is gas tank vented???
bonos

[RallySnake]

Are you using an electric fuel pump or mechanical? Have you checked your fuel pressure? Which carburetor (or FI) are you running? Are the fuel lines made with steel tubing or rubber hoses? Did you route the fuel lines near the exhaust headers? Did you use rubber insulated clamps to secure the fuel lines to the chassis?

It sounds like your fuel line is getting so hot the fuel is vaporizing. Have you tried the silver heat insulated tubing over your fuel lines near the engine? like this: Amazon.com: HeatShield 274012 Thermaflect Sleeve 1/2" ID x 3' Heat Shield Sleeve: Automotive

RS

[RICK LAKE]

choprsam Easy thing to do, roadtest car until stalls out on highway, Open gas cap and see of car starts. Open cap slowly, if you get an air sound it's vapor lock and you need a vent to allow air into the gas tank.
If you get no air sound, I am going with a spark problem. Would start with a coil issue. Where's the coil mounted on the car? If it's on the motor and is an oil filled one, it's possible it is over heating and you loose spark. After the winding cool down you have spark again. Does your car have an MSD igition module, same problem. Need to see if you have spark when car stalls. If the coil is mounted on the motor in a horizontal position, move and change to vertical. Could also be too much voltage going to coil from charging system. Might need to add a resistor to drop voltage to coil and keep around 9-12 volts to it. Rest of system can run charging voltage. You didn't say what the voltage is on the car at highway speed. Quick test, get a cheap test light and go drive, need 2 people. When problem happens, pull spark plug wire and use test light to see if you have spark and light turns on. If it does, looking at possible fuel issue. Get back to us after doing these 2 tests. I think we will have an answer for your problem. MSD 6AL boxes fail from poor or no air getting to cool them also. Have guys on here that distributor modules failing in housing. lets stay with basics. Check cap first, than check spark. Rick L.

[lnfletcher]

I agree with RL, I've had a coil do that.
Also ignition module.

[TXBLU]

Great advice, guys. If you do the gas cap test, take a spare ignition coil with you. Be sure to try to start the car right away if you hear air venting into the tank when you crak the cap. If it still won't start, swap the coil out and try again. If you're running an MSD box, you could try swapping that out, too. If all of that fails, look for a hot spot on your fuel supply line.

If the car used to run fine all the time, I'd lean toward some kind of electrical (ignition) issue. If it's always run like that, I'd bet on fuel delivery problems. There's an answer somewhere for you. Someone will come up with the solution, I'm sure. These guys always do!!!

What kind of fuel pump/plumbing are you running? Mechanical pump? Electric (in-tank or external)? Dead head system, or return-style?


Eric

[Great Asp]

Originally Posted by lnfletcher

I agree with RL, I've had a coil do that.
Also ignition module.

Check the coil to see if it is cracked. The oil could have drained and the resistance will build up in the coil the hotter it gets, kill the engine, and the engine will re-start (once cooled) in say....20 minutes....

E

[Clois Harlan]

My first engine in my Cobra did that as well, turned out to be vapor locking. I didn't have my fuel tank vented properly. Actually, the way I had it set up it wasnt' vented at all.

[Ron61]

Does it stall when you drive at a constant speed of less than 75 MPH or if you drive faster than that? It would seem to me that at say 65/70 MPH you would be getting about the same amount of heat to your gas lines as at 75 MPH. If you go above 75 do you feel any loss of power? What you describe sounds more like an electrical issue to me as the faster you go the more you are working the electric system. Good luck and I hope that you find the problem soon.

Ron

[CHANMADD]

My boat used to do that.......Halfway to Catalina .......stop...........the tank breather had corroded closed.....

[Gaz64]

The phenonomen known as "vapour lock" and inadequate or no fuel tank venting are completely separate issues.

You can suffer from either one on it's own.

Air has to be able to enter the tank as fast as instantaneous fuel consumption is occurring.

[Blas]

Or try not fully tightening the cap from the start of the ride..... What position is your coil mounted in? Horizontal or vertical....Any oil leaking from the coil?
Did you or someone replace the original fuel cap lately?

[TXBLU]

Man, I'm really hoping to hear what the fix is on your car...

Eric

[Rick Parker]

When this occurs does it abrubtly "Shut off" or begin to lose power (while still running roughly) and refuse to respond to the throttle pedal?

[Marc Wulf]

Please tell us what the problem was!

[Blas]

FYI: Had another person with a similar problem. I think his charging system was pumping our +15.8 Volts on a regular basis. Seeing that the MSD box is usually hooked up directly to the hot side of the starter solenoid, the MSD was seeing high voltage and was probably overheating internally. Stalling out allowed the box to cool off, and the car restarted again. for a while, then died again. Just something to check into if you have this issue. Contact me off-line if you like regarding this. I'd like to collect some data on this from people having this problem - Seeing if they are experiencing high charging rates.

[stallion112]

If you install a filter on the inlet side to the pump make sure it is 100 microns. A typical fuel filter is either 10 or 35 microns (intended for placement after the pump on the pressure side) and they are way too restrictive for the inlet side. The restriction can cause a vacuum to form just after the filter, especially on a hot day. You may then find yourself under the car removing the fuel line to purge the air pocket. Been there.

[Marc Wulf]

Blas,
I had the same thing going on with my car. I wound up replacing the coil,magnetic pick up,and now, finally the MSD box.I just recently took it for a ride and it did not stall.But I'm not completely convinced I have the problem cured because of what you just described has always been in the back of my mind. When and how is the easiest way to assure I'm not having the same thing going on (High voltage heating up the box)?I would love to take the car for a long trip. I just don't completely trust It right now.

[Blas]

Do a charging voltage check with the car running.
Contact me offline and I'll send my phone number....

[Shootnride]

I had virtually the same situation with a vehicle years ago. After about the third time it quit running on the highway, I pulled over, disconnected the fuel line at my in-line fuel filter and jammed a Phillips screwdriver through the fuel filter. Problem solved. Put a new filter on when I got home.

Ted