STEELE

I just joined today looking for some insight to an ongoing, 3 month problem I've been having with my truck. Sorry if this gets a little windy but I wanna throw out all troubleshooting I've done.

Thanks in advance for ANY help!

1996 F150 4x4
5.0L
5 speed manual

My problem started first week of Sept when the temps began to fall below 70 deg. Has magnified 10x since the highs are in the 20s now. I can go out to the truck and hit the key to start. It may or may not fire up. If it does, it may run 2-5 minutes and die or it may continue to idle for an hour until I turn off the key. If it doesn't start immeaditly, I can leave the key full on for 20-30 minutes and it will fire up. Then, it may die after 2-5 minutes or may stay running until I shut it off. When it dies after starting, it will not restart unless I leave the key on for 20-30 minutes. Check engine light has been on for a couple months.

When it won't start. I have checked for spark at the spark plug and from the coil. No spark what so ever. I have noticed a couple of times that while cranking the engine, upon releasing the key I will see a slight very faint spark. The truck has come to life a couple of times just as I am releasing the key. After a prolong period of cranking and no fire, I will smell a strong raw fuel from the exhaust. That tells me it is getting fuel. I've had it analyzed and fuel pressure checked. The only error codes that came back were speed sensor (I expected this) and left bank O2 lean. Fuel pressure is steady around 40psi. I have replaced both upstream O2s and the one downstream O2. Right after replacing the O2s, the CEL went off. Just this weekend it has come back on. For grins, I replaced the coil. No change.

It is like a ghost is turning off the key. All spark is gone until the key is left on 20-30 minutes. Then it will start/re-start and maybe run until I shut if off. Then it may shut itself down again after 2-5 minutes. Every time that it does start and shut off, I will check for spark and none will be present.

Could I have a problem with the distributor pick up assembly or another sensor? At the beginning of all this, I was leaning towards replacing my cold air temp sensor until the analyzer showed the speed and O2 sensors in error.

Any help is greatly appreciated!!!

wde3477

Welcome to the site!

Suggest to check the TFI module on the side of the distributor, the stator pick-up coil inside the distributor, as well as the ignition coil. There are resistance and voltage tests that can be done - so no need to blindly replace parts. Any decent shop manual - Chilton's, Haynes, Motor, FoMoCo - will list the test procedures as well as the expected readings.

Fuel pressure is good - O2, cold air, or speed sensors shouldn't prevent the truck from starting.

Good luck, and keep us posted!

Just call me Sean

iTrader: (1)

In addition to wde3477's suggestions, I think you should check the ignition switch. Of course you should have power in run but you also need power to that wire in start as well as power in the start wire. It sounds like the run power is cutting off as you crank it in the start position but sometimes when you let off the key the power returns quick enough to allow it to start.

STEELE

Thanks guys. Couple questions.

1st - Is it possible not to have TFI? I've looked for this some time ago and my distributor is naked. Meaning, nothing on it. Just a set of wires going in just below the cap. What took place of the TFI? This distributor reminds me of the old dura spark.

2nd - When cranking it from the solenoid I get the same indications as with the ingition switch. No spark and occasionally a weak one. Could I still have a problem with the inginition switch?

Not sure this has any bearing to the troubleshooting but I ordered this truck when I was stationed in Turkey in 1995. When it was delivered to my nearest Ford dealership, it had a Swedish sticker on the passenger window. Could it be built different than U.S. trucks?

Just call me Sean

iTrader: (1)

You do have the TFI but on the later models it's located on the drivers side inner fender, not on the distributor. If you have the same result when bridging the solenoid terminals then that eliminates the ignition switch as the problem. I'm pretty sure all these trucks were built to the same specs with exception to some countries needing different lights for the turn signals.

mitchalvin

Check the voltage of the battery. These electronic ignition need a certain voltage to fire. The longer you crank the lower the voltage becomes after letting it sit the battery will recover some of the lost voltage.

STEELE

Thanks to everyone for all advice. Here's the $50,000 question. How could my downstream O2 sensor cause all this? After working on the truck to the wee hours of the morning I disconnected that sensor and the truck started and continued to run. Just now, I started it and let it warm up. Then drove to my local gas station to fill the tank. My truck seems to back to normal 'cept the check engine light being on.

Could a shorted out wire connecting to that O2 sensor prevent ignition spark and only ignition spark? During all this, when it will not start or dies shortly after, all electrical accessories worked fine (head lights, parking lights, brake lights, stereo, turning & emergency flasher, heater fan, dome light...ect).

aliens8mycow

Sounds like a short to me. I guess when you look at the big picture, all of those sensors share a common ground and power feed (at least somewhat)... A short on the right (or maybe wrong is the better term) wire might screw up some of the other sensors on the engine too.

Might be worth looking at the wiring near that sensor to see if you have a worn wire or something that is shorting against something metal or another wire.

Just call me Sean

iTrader: (1)

If the wire was shorted then unplugging the sensor wouldn't have made a difference, so the sensor must be bad. It's tough to understand the wiring diagram of the four wire oxygen sensor, but it does share connections to many different sensors.

STEELE

Hi all! Just thought I'd update here in case anyone is searching for answers on a simular problem.

Slap the dawg & spit 'n the fire...GOT THE TRUCK FIXED!!! Disregard my previous posts where I mention the problem righted itself once I unplugged my downstream O2 sensor. That was just coincidence. Right after unplugging that sensor the problem started all over again. But...after I replaced the pick assembly in the distributor (and many hours with a voltmeter) POOF...the truck started behaving.

Thanks to all who posted and got me pointed in the right direction. I have a tendency to get off track now 'n a'gin.