Expert: Sean Halliday - 10/27/2009

Question
QUESTION: My problem is this - When I start the car with a fuel pressure gauge attached at the fuel rail I get 45-50 psi and it will hold steady through warm up. But when I drive the car I can see the fuel pressure drop to 20 then to 10 and then to 0 and finally the car will start to buck as if out of fuel or low fuel pressure. If I turn off the key and restart the engine I get 45-50 psi on the gauge again. But it will do the same thing over and over again.

If I get in the throttle from the start I may get to 30 or 40 mph and then that's it the bucks but stays at the same speed or a little lower. It does not die but the fuel pressure is way to low.

The car seems to be running out of fuel. I have changed the fuel pump twice and changed out the fuel pressure module that feed current to the pump.

It seems that if I start the car and drive right a way I don't have any fuel pressure loose till it start to warm up. But it always return with 45-50 psi if I turn off the key and turn it back on.

I have check for bad grounds listed on the wiring diagram and found nothing wrong.

If I turn the key on and just leave it on the pressure will slowly drop to 35-40 and hold for several hours but will drop to 5-10 psi over night.

ANSWER: Did you change the fuel filter?Sounds like vapor lock or evap problem.

---------- FOLLOW-UP ----------

QUESTION: Filter changed twice same as fuel pump just to be on the safe side. As for a vapor lock I would have no idea as to where to look for it. The car running well within the heat range and fans come on and off as needed. Fuel lines have not been changed or rerouted, same as from the factory.

Just what do you mean by "evap" problem?? Any ideas as to what to look for or where??

Ps. Thanks for all the help so far.


Answer
The evap system returns unused fuel to the tank.This is a sealed system and may be blocked.There are plastic pipes under the car to the engine so look there.There may be a problem with the purge valve.The proper pressure for running is 45psi approx.Constant 45 will be ok.Check relays for injection and pump.