Bronco 2 2.9 liter

[Craig m]

I am having problems starting my bronco i can start it with either then I can start it with no either but if I leave it sit for about a half hour or so then I have to start with either again. I have replaced both fuel pumps, fuel pressure regulator, map sensor,throttle position sensor,egr valve, not sure what you call it but the sensor that hooks to the egr valve by a vac line, and the valve that bolts to the intake manifold passenger side. Any ideas on what might be wrong?

 

[Mark_88]

Sounds like you may have an injector leaking. The fuel pressure is bleeding off and that looks like the only thing you haven't replaced. Not sure if there is a test for the injectors once they start leaking other than checking for fuel in the cylinder/combustion chamber.

One or more leaks would or should cause your engine to run really rich initially but one that fuel is burned off it would go back to normal...so you may not get any codes tripped.

 

[RonD]

Hope you replaced all that stuff because it was old and not to fix this problem

Couple of free tests you can do.
Fuel pump will only run for 2 seconds when you turn on the key, it's a safety feature.
But if you are losing fuel pressure it also won't build up enough pressure to start engine from 0psi.
So turn on the key, count to 3 then turn key off
Repeat this 3 or 4 times, each time key is turned on you will get about 10psi more pressure, system should run at 35-45psi normally.

Now try to start it.
If it starts then you have a pressure leak in the system.

Fuel pump runs full time when engine RPMs are above 400, just FYI


2.9l will have the TFI ignition system, they were OK when new but at almost 30 years old you can expect some problems.

Gasoline needs a good hot spark to ignite in a cold engine, ether will ignite if you sneeze too hard, lol, well not that easy but weak spark will ignite it.
This has to do with heat, after engine is started the cylinders are hot so restarting just with gas and a weak spark is possible, after it sits and cools the weak spark is not cutting it.

Pull out a spark plug, have a look at the tip, good running engine will have a light brown coloring on the white part of the electrode, blackish means incomplete burn of fuel which could indicate weak spark or ^^^^ fuel leaking into engine.

You can visually look at the spark by hooking up the removed spark plug to its wire and grounding it, I use a jumper cable hooked to battery ground and spark plug base, this holds it and gives a good ground.
Pull off the other 5 spark plug wires, so engine won't start, and have someone crank engine while you watch for spark.
Spark should make a loud snap noise and be blueish-white color, yellow can mean weak spark.

 

[Andy D]

Twist the spark plug wire boots before pulling them off the plugs. After a fun afternoon changing plugs and plug wires. I use boot grease now.

 

[Mark_88]

And if you do the spark plug test...use pliers or something shielded with rubber to to keep yourself from being zapped...use an extra plug if you have one...instead of pulling each plug out...as long as it is gaped the same way... I think it's .44 but may vary.