Engine Won't Start Sometimes
 

This is a strange problem

My truck is a 1998 4.6 l engine with 150,000 miles

I drove to the Bronx and back today, full throttle for 1.5 hours, with no drivability problems. I stopped at a store, the truck started fine, drove locally with no problems, then I stopped at the firehouse and the truck would not start. It cranks, but will not start, it acts as if it is flooded. It wants to start as it coughs, but will not keep running. I waited a hour and half then tried to start it and it fired as nothing was ever wrong.

When it was not working
I checked the fuel rail pressure at the valve, and had pressure.
I listened for the fuel pump running at the filler neck when the key is turned, fuel pump is running.
I checked the fuel inertia switch, all was good.
Checked all fuses, all is good.
There were no CEL's, checked with my own scanner.
I have no PATS system

The previous (and only other time it happened), I changed the fuel filter and IAC, even though both looked good.

I am stumped and hoping you can steer me in the right direction.

maybe one or both coil packs are overheating?

Thanks Matt but I changed those this summer as a precaution, not because they needed it. Didn't want to be stuck because of old coil packs

Friend of mine had a similar sounding problem. Someone shoved a piece of paper into his gas tank. When it got down there it opened up flat. e could usually get it start but when he would take off down the road it would get sucked into the fuel pump and stall the car. He would wait and the paper would float to the top. He could then start again and get going down the road for the same thing to happen again.

so theres no codes, good fuel pressure, newer coil packs, and i'm going to assume theres new plugs and wires? what brand coil packs did you get? also do you have a tach? and is it reading properly? and does the ect read normal on the scanner and on the dash?

:lol: what year was the truck? theres no way you could get a piece of paper through the filler neck of the newer trucks. at least without taking the filler hose off and sliding it straight into the tank.

Motorcraft coil packs, wires, plugs. All new this summer

Could the injectors be leaking? I kinda ruled that out because all the injectors would have to leak. At least one cylinder would have to fire.

What could cause it to flood? As I stated, I wait an hour and if fires right off

the only thing i can think of is something getting hot. the injectors could be a possibility but i would think they would leak down at all times. when you tried to start it and it didnt did you push the throttle to the floor? how does it run?
when it sits and starts does the rpm shoot up to what it normally does?

Did you use a pressure gauge to check the fuel pressure? I cant remember the exact specification but the fuel pressure has to be over like 35 lbs. Any less and it wont start. You can have what seems like enough pressure but if its not high enogh the injectors wont work. If not enough its pump or regulator.
Use a gauge and make sure it within specification...

started without pushing the gas, started normal, normal RPMs. Its like it never had the problem.

Like I said, weird problem

Jethat

I did not measure the pressure, if the pressure was at fault, the truck would have constant starting problems. This is intermittent and rare, and from what I could tell, after I do a long hard run

You could have a failing fuel pump or pressure regulator intermittent failure. Could be the pump gets hot or the regulator is old and sometime it doesn't work. Bottom line is I would rule it out with a fuel pressure gauge.. What your having sound like a low fuel pressure problem to me.

Someone should take your license away and lock you up! Your going to kill someone!! - Trucks prolly spent, their not made to run that way.

I suspect the camshaft position sensor or the crankshaft position sensor. Does seem like it would throw a code though. The Haynes repair manual tells how to check the crankshaft position sensor with a voltmeter and a socket and breaker bar, of course in an intermittent case like this it would need to checked during that won't start time.

Masseyman, I will check that next time it fails to start. I thought it could be a sensor that goes out of range when hot.

Thanks