4.0L OHV Hard to Start when Warm.

[BillRod]

4.0L OHV Hard to Start After it Warms up to Operating Temp.

Hi All

Just picked up a 96 Explorer with the 4.0L Pushrod engine, 190K miles.

When the engine is up to operating temp and I park for a few minutes to run in the store it takes a long time to start when I get back to it.
Turn the key it will spin over 30 or so seconds.
Turn off the key.
Turn the key it will spin another 20-30 seconds then slowly start to catch.
Then will run ok.

No warning lights or engine codes.
New Air filter, ran 1 full tank with a can of Seafoam.
I was running cold so I swapped in a new thermostat and now it runs in the normal range.


Any thoughts s to what to look at next.

Thanks
Bill

 

[RonD]

I would get a can of Quick Start(ether) and next time it doesn't fire up spray some into the intake, pull PCV hose or Power Booster hose, then put if back on after spraying.
Now crank engine, if it fires up then fuel was the issue, if it doesn't then spark is the problem.
The 50/50 test
You should spray ether, or anything else, lol, into the air cleaner as this can foul up the MAF sensor.

Tests:
Turn key on, count to 3, turn key off
repeat this 2 more times

Ford computer only runs fuel pump for 2 seconds when key is first turned on.
If you were losing fuel pressure while it sits then three 2second cycles would restore the pressure.

Warm part could be flooded engine, if injector was leaking.

All fuel injection computers have a "Clear Flooded Engine" routine in their software.
Key on
Press gas pedal to the floor and hold it down all the way, this turns OFF fuel injectors
With gas pedal down all the way try to start engine.

If should not start, it should not even fire a little, there is no gas going into engine.

4.0l OHV coils are pretty hardy, but they can fail, I would expect rough running earlier though.

1996 has the ICM(ignition control module) in the computer, so not serviceable.

Right next to the crank pulley there is the CKP(crank position) sensor, this is THE Big Kahuna of sensors, engine will run with pretty much any sensor removed or damaged EXCEPT the CKP sensor.
CKP sensor detects if the crank is turning and when #1 is at Top Dead Center, the pulses from the CKP sensor tells computer to start spark and fuel injectors, no pulses = no start/no run.
These usually don't fail at all and more unusual to fail intermittently, but anything can happen.

On the 4.0l OHV, the CKP sensor is on the front of timing cover passenger side almost touching rear of crank pulley