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'96 F150 ignition problem

B

bradley martin

Well-known Member
1996 F150 w/4.9 (300) engine. Occasionally, when slightly warm, engine will not start. Seems to happen more frequently in cold weather. Never occurs when engine hot or cold .....go in a store for 20 minutes and come out, engine won't fire. Removing and reinserting key multiple times( 6 to maybe 20) times and fires right up. Switching fuel tanks or using spare key does not overcome issue.Being an intermittent problem, I am having difficulty narrowing this down. Acts like not getting fuel, but with EFI, I suppose it could be lack of spark. Key and cylinder are worn, but why would issue only occur intermittently when warm, never on a cold start or hot restart? Thanks in advance for all suggestions.
 
A little troubleshooting should be able to tell you if it's the ignition switch located slightly forward of your tumblers in the steering column or ignition parts located under the hood. Of course, because none of us are there, all posts will be a guess. Start by checking for spark and fuel pressure when you crank it. Also, I've seen fuel shut-off inertia switches (shuts fuel off if you should have a crash) go bad.
 
Sounds like a fuel-pump problem to me. I have a 98 Dodge van that does exactly the same. Starts great or does not fire at all. No in between. I had hold my finger down on the top of the fuel-pump relay and then it starts fine.

Can you hear the fuel pump run when you first turn the key on and it won't start?

I have a 1995 F150 4WD with the 300 six and 47K original miles. Great truck except for the crooked front wheels when the weight of a plow is on it.

That said, the ignition modules on the distributor were known to fail. New one is $30. I carry a spare but so far, have never needed it.
 
This is an issue with fuel pressure. With a slightly warm engine the temp sensor, thru the computer, will not turn on the fuel pump. The pressure regulator and check valves in the pumps should hold approx 40# of fuel pressure for 24 hours or so. Your pressure is bleeding off, hence no fuel, and no pump to build up. You can by pass the whole system by just shorting the fuel pump circuit to ground thru the ECCIV test plug. Put a pressure gauge on the fuel and leave it there. I think you will find, that the no start condition when slightly warm, is do to no fuel pressure. For years I had a momentary switch (like a door bell) hooked to my test port, and would just hold it down for a couple of seconds. This used to be most irritating when buying fuel and then be dead by the pumps with guys in line. You have a check valve system in with the fuel pressure regulator and then in ea pump, on the pressure and return sides.
 
Why would the fuel leak back warm (sometimes) and yet always fire on the first spin when cold? I would think that if the fuel pressure leaked off, that it would require extended cranking on occasion when cold.
 
Usually when it happens, I am not expecting it so have not listened for the fuel pump to pressurize. Also, it generally happens on a city street or busy parking lot so even if paying attention, I can't hear the fuel pump. It is so intermittent that I suspect I will be a while tracking it down.
 
"Thanks in advance for all suggestions."

Instead of GUESSING/speculating lack of spark vs. lack of fuel, why not connect up a spark tester and and a fuel pressure gauge and narrow it down to one or the other?
 
Because the cold temp turns on the fuel pump. The pumps don't come on when you turn the key on a warm engine, to avoid flooding possibilities I suppose. The solution, turn on the fuel pumps, the fuel rail will re-pressurize and away we go......
 
All vehicles that I know with electronic fuel injection have a timer or safety over-ride so every time you turn on the key to IGN position - the pump runs for 5-6 seconds and then shuts off if the engine is not started. This is when to listen (before you try to start the engine). Very easy check.
 
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