I have a 1996 F150 with the 4.9L inline 6. It starts and runs fantastic. After it warms up and I shut it off it won't restart. I have installed new plugs, wires, cap, and rotor. Checked the timing. Cleaned the Mass Air Flow Sensor. Replaced the Air Intake Temp Sensor. Pulled the codes and it comes up with "bank 1 running lean" and "bank 2 running lean". Was wondering what i should check next. The problem is becoming extremely frustrating.

 

Welcome to FTE.

Check for fuel and spark when it doesn't start. Pull a spark plug wire, insert a screwdriver, hold it to the engine block while somebody tries to start it. You should see a strong, blue spark.

Alternatively, see if it will at least kick over with some ether (starting fluid).

This is the classic case of a failing TFI module with heat-related failures (google it, Ford was sued by the NHTSA over it). If you don't have spark (or can't get it to at least kick with ether) I'd take the module to a parts store for testing (although heat-related failures can be hard to find on the bench).

 

Does it drag when it turns over? Starter windings have a problem of having a high resistance and expand when hot, needing more battery juice to turn engine over, robbing the power from the spark. When cold, no problem, run to the store, restart, zilch.

 

That's a good point; I'm assuming the starter motor is turning over the engine just fine at all times....

 

It turns over just fine cold and hot. Have not yet checked spark but it will sometimes start and shake like no other. So i didn't really think about spark being the problem. However i am leaning towards fuel issue. The front fuel tank has lost its fuel pump I believe. I am wondering if the pump isn't going bad in the rear tank.

 

You can check the fuel pressure & output flow rate at the engine, you can also put an ohmmeter on the pump's leads and see if you have continuity or not. No continuity = burned-out motor.

 

My '92, 4.9l, started with running lean codes when the front pump was going out and it would spit and sputter at times when driving.

Like Ctubutis stated, a failing TFI module is a good start for the no start diagnosis and a easy test would be to take a hair dryer or suppose a heat gun would work too, and after the truck has sat overnight or cooled completely down, heat the TFI module up. If the truck doesn't want to start, this could be a simple fix without throwing parts at it. This easy trick can also be used to diagnosis bad Ignition coils too.
If you do find the TFI module is bad, try to replace with only a Motorcraft TFI. Aftermarket, OEM replacements not labeled Motorcraft may seem like a few dollars less for the same item, but if the Ford part lasted 16 years, I'm willing to bet the next will last just as long or longer! There were also 2 different colored TFI's, be sure to replace with the exact color and keep the old one handy for future reference.

Not to step on any toes, but I would steer clear of any starting fluid, unless you are using it as cleaning agent or a new sleeping aid. Just heard to many horror stories involving a blown motor when using it. If it were used correctly, it can fine, but some people tend to use to much and fill the block with it and the fumes alone can be enough to trigger a detonation.