Nothing i like more than having to call AAA to get a tow home from the gym in town. thought i might describe whats going on and see if someone on here has had it happen to them before.

drove to gym, its like 100 degrees here. came out and hour later and started it up, sounds like its running on 5 cylinders, really rough, wont idle unless i keep my foot in it. so i ran over to napa and grabbed new spark plug wires and new spark plugs, no change, still running rough as hell.

it doesnt do this very often but when its done it before i kinda just sit in it and keep tapping the gas and it eventually snaps itself back into a smooth idle.

i am completely stumped. any advice would be wonderful. thanks.

-Jon

 

Does this happen in hot weather only?

Where or should I say how is your fuel like routed? Are you running headers? Make sure your line is at least 3" away from any exhaust component or any high spot where heat will rise and collect.

 

Yes it seems to only happen when its quite hot outside. The fuel lines are nowhere near any source of heat like the headers. ive swapped coils now and still no change, so that's 3 ignition components that have been ruled out. perhaps there is some sort of blockage in the carb...

 

How long does it last before normalizing?

 

You checked all the way back to the tank? You sure one of your pipes isn't too close somewhere?

 

Also pull the top off the carb and check the bowl for any debris. You know what else...and this is probably the simplest...have you changed your fuel filter?

This new gas does not fair well and you may have some corrosion in your system. I always run a little 2 cycle in my vehicles (injected and carburetted) every other tank to help slicken things up and provide some corrosion protection. Just enough to give it a slight blueish hue, never full strength.
With FI it keeps the injectors lubricated and provides some top end lubrication.
For carbs it keeps float needles and valves from sticking, lubricates the valve guides, and provides a little top end lube.

 

The inside of the bowl looked good, the fuel filter is about 1 month old. while its running i see two good squirts of fuel when i blip the throttle, it just idles very rough and wont stay idling unless i keep giving it gas. some members of another mustang board seem to think the pertronix unit is the cause.

 

Again, how long does it do this before normalizing?

 

+1, how long before she comes good? Once running is it ok?

you can get heat soak all along the fuel system from tank to carb from both the car's own heat and the road surface too. it causes the fuel to prematurely vaporise.

does she blow sorta black smoke before coming good?

 

It varies, sometimes within 30 seconds, sometimes ive waited 5 minutes before it regained its smooth idle. once it gets its smooth idle back all is well. this only happens on start up. it has never happened pulling up to a light or in the middle of cruising. only after the engine is off for a period of time and restarted. if it was heat related i would expect it to not continue to be acting up right now considering its been sitting in my garage for a day.