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Steve, Service Manager
Category: Ford
Satisfied Customers: 5494
Experience:  25+ years experience as a professional technician ; ASE L1 master Technician
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Have a 1978 Ford f150 4x4. 6.6liter 400 eng.

Resolved Question:

have a 1978 Ford f150 4x4. 6.6liter 400 eng. Just had a rebuilt engine installed. since then, the engine has been cutting out on me ). 99% of the time it happens after a long drive (45+ min.) after I stop, and then try to accelerate again (for example, today i drove 1hr 15min on the hwy, got to the offramp and when I got to the light to accelerate harder, that's when it cut out. It sputters, and with some speed, sometimes I can get it going again, otherwise, it dies & won't start again for at least another 10 min.) Always been able to get it going after 10 or 15 min. Sometimes it happens when I accelerate hard to get on to the highways (less frequent). Mechanics tried the following: Found cracks in some fuel lines and said it was probably taking in air. They replaced all cracked lines. Problem still exists. Cleaned/light service of carb. Prob. still exists. Asked if it was fuel pump-they said no. Debris in fuel tanks? Said filters were clean. Why pattern with long drive?
Submitted: 7 years ago.
Category: Ford
Expert:  Steve replied 7 years ago.
You may not have a fuel system problem. On Ford vehicles in the 70's and 80's it was far more common to lose spark whe you have a heat related stalling condition like youa re experiencing.
There were 2 common faults that could cause this to happen on this design of ignition system. The most common was a failing ignition control module; this is an aluminum box usually located on the inner fender under the hood with either 2 or 3 electrical plugs attached (depending on the exact module used in that year). The other common cause of a heat related problem like you ahve there was a failing ignition pickup coil inside the distributor. What happens is the small coil of wire in the ignition cpickup would develop a break in the wire; it would work OK untill it got hot, at which time the thermal expansion of the coil would pull the ends of the broken wire apart slightly. When it cools it contracts and the break touches again, restoring normal operation.
What I would do is the next time the truck shuts off, use a spark checker tool or a spare spark plug to see if the ignition system is the cause of the problem. If you have no spark, replace the ignition module; that usually cures the problem. If it does it again, replace the ignition pickup in the distributor.
Also, a good test is to take a heat gun and warm up the module and/ or the distributor base with the engine running. If you can make the engine shut off by heating either of these components, that component is faulty.
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Customer: replied 7 years ago.
One more thing. The ignition control module was just replaced when they put the new engine in. Could it still be that or does it probably mean that it's the pickup coil?
Expert:  Steve replied 7 years ago.
It could be either; although if the module is new it is less of a possibility. However, this design of Duraspark module was well known for having problems. Back in the 80's when I drove Fords with this type of ignition system I always carried a spare one in my glove box and had to use it a few times.
I was also just thinking that the ignition coil (the one the distributor coil wire runs to) can also cause this type of symptom.
Take a logical diagnostic approach; first verify that youa re losing spark when the problem happens. If so, take a heat gun or a high powered hair dryer and try heating the parts under the hood that could cause this one at a time to see if you can cause it to happen sitting in the driveway.
Another thing you can try is to use an ohmmeter to see if the pickup coil is going open circuit (infinite resistance) when the engien stalls. If so, it is bad and needs to be replaced.
Customer: replied 7 years ago.
thanks again!!
Expert:  Steve replied 7 years ago.
Thaks for using Just Answer!
Customer: replied 7 years ago. more thing I just thought's never cut out on me while I was just driving (cruising hwy speed) it only happens after I stop, and THEN accelerate again. In other words. do your heat tests still apply? That's why I kept thinking fuel since its always on acceleration. Gladly pay more for more advice.
Expert:  Steve replied 7 years ago.
Well, you mentioned it only happens after a long drive; generally this is an indication that a component is becoming hot from all of the heat generated by the engien. Not much else changes between startup and after aXXXXXexcept things get hot.
This may possibly be another indication of a failing pickup coil in the distributor; when you accelerate the vacuum advance mechanism is causing the base plate inside the distributor to move.
Take a spare spark plug along with you the next time it is likely that you might have a problem. When it dies, unplug a spark plug wireh and plug in the spare plug, lay it on the metal engine surface and crank the engien over to see if it sparks. If not, then that confirms it is an ignition system problem.
If you suspect you may have a fuel system problem (I suspect you don't but it never hurts to check), carry a can of starting fluid spray with you. When it is not starting, spray a little down the carburetor throat and see if the engine fires up for a moment. If it does, then it is a fuel system problem; if it does not that is another indication that the ignition system is the likely source of the problem. By spraying some starting fluid into the carburetor throat youa re basically bypassing the entire fuel system, including the carburetor.
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