we have a 2005 ford ranger 2.3. The problem we are having is that while driving, it will suddenly lose power. It doesn't matter how much you push the gas pedal, it just stalls. We cannot figure out the problem. We have had it in a couple of shops and no one can find the problem. We have checked the fuses, changed plugs, wires and coils, and throttle position sensor. The catalytic convertor appears to be functioning normally. Any suggestions?

 

Fuel filter or fuel pump?

 

If it sits for a while will it crank fine?

 

It cranks fine every time. Some days it runs great but others it just bogs down and won't accelerate. It is not the fuel filter and dont think it is fuel pump.

 

Couple of things can cause that.

From your post I read that at speed the engine will loose power but stay running?
You use the word "stall" which to me means the engine stops running altogether.
But then you stay it starts fine, so that part is confusing to me.

There are two test you need to do.
With a vacuum gauge you can test if exhaust is clogged
read here: Technical Articles: Engine testing with a Vacuum Gauge - at Greg's Engine & Machine
If exhaust pressure builds up then new fuel/air can not be pulled into cylinder so power drops

With a fuel pressure gauge you can test pressure
engine off = above 50psi
engine idling = 65psi
engine at 2,500rpm for 1 minute = 60psi

Engine off again = stay above 50psi

If pressure slowly drops to below 50psi then check valve in fuel pump is bad.


Another test would be to simply loosen the gas cap.
The EVAP system sucks vapor from the fuel tank while engine is running, if vent is clogged the negative pressure in tank can prevent fuel pump from pushing out enough fuel for high RPM/load, so engine starves for fuel.
Acts similar to a clogged fuel filter

 

When it stalls as I am referring to it just loses power and will not accelerate. It does not die. If the exhaust were clogged wouldn't it be a more consistent problem. It doesn't happen every time we drive it.

 

No, it wouldn't have to be consistent, collapsing cat or muffler means the inside is rusted out and when you start engine pieces move around from the exhaust flow, where they settle will decide if it clogs and how much it clogs.

Like sucking on a straw with ice cubes at the bottom of the glass, sometimes a cube will block the flow other times it doesn't.

A potato up the tail pipe is consistent

 

Thanks ron. I will definitely give that more consideration