Greetings forum.

2005 Freestar, 4.2L with 120,000 kilometers.

I have a problem that is very intermittent, and only during moderate acceleration. Van idles well (never stalls at idle), or when running (only from a stop). One clue to the puzzle is that it only happens under more rapid depression of the throttle (trying to get out into heavy traffic). If you are easy on the throttle it rarely happens. No CEL or codes appear with a standard ODB II scanner. Plugs and wiring are new, as is the fuel filter.

Any suggestions from our techies??

Thanks

 

Sometimes we try to apply a little deductive reasoning to these things, sometimes it works and sometimes it doesn't.
What happens when you mash down on the accelerator there is a demand for more fuel. As long as the fuel system can supply that demand take off is usually smooth. When there isn't enough fuel the engine can bog down, seem low on power and the vehicle has a problem getting out of it's own way. Unfortunately , newer vehicles have several things controlling how much fuel will go into that engine so to pick one without actually doing certain tests might be considered a shot in the dark.
It might be a good idea to see just what the fuel pump is putting out pressure and volume wise.
Since the problem is intermittent , it could be the pump is getting tired and producing that symptom.

 

Yep, fuel is one suspect...... however......

a) I can't find a schroeder valve to attach my pressure tester. (anybody know if there is one, and where it is hiding on the 4.2L)?

b) will happen when the throttle is barely open, and not demanding much fuel, it just seems to happen on rapid depression as opposed to slow depression of the throttle.

c) lots of power accellerating on the highway from an on ramp, so it seems to be getting lots of fuel when demanded.

 

fuel pump is weak and needs replaced