Stumbling At Startup

1997ThunderbirdLXV6

1997ThunderbirdLXV6

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Hello All,

This isn't a new problem, but one that occurred today for the first time in a while, potentially because it was the first warmer day in a while.

After much reading, I have an idea what might be going on, but I wanted to pass it by you all.

Situation:
  • I'm running several shorter errands around town; engine is warm; time between drives is anywhere between 10 to 20 minutes.
  • Tank is almost full; 30 miles since last fill-up.
  • At startup of the warm engine, I get significant stumbling/sputtering accompanied by a slight whooshing sound for about 15 seconds (best guess), which can be shortened by revving the engine a bit; then the idle gradually normalizes.
  • Today I actually turned the engine back off, and then I cycled the ignition a few times; each time the fuel pump primed, I could hear the same whooshing sound.
  • When driving off, everything turns back to normal, except during the first few seconds of initial acceleration, when I'm hearing a sound akin to tiny rocks traveling through a pipe; that sounds comes from the right side and seems to travel backwards (as if through the fuel return line?).

All this leads me to the conclusion that there's some sort of fuel vapor condition. There are no visible leaks anywhere in the engine compartment nor under the car, nor any fuel smells that I can tell.

Any thoughts or advice what I can do to alleviate this?
 
My 96 would stumble at startup for a few seconds randomly. Came and went over the course of a few months. Seemed to get better after a snap of the throttle, though not every time.

After a while the OG fuel pump died. Might not be a bad idea to check your fuel pressure just to give some peace of mind - bonus points if you can verify fuel pressure while it's doing its "dance".

Normal fuel pressure is 39 PSI less manifold vacuum pressure; at idle that would be in the neighborhood of 29-31 PSI.
 
O'Reilly's has them as a loan a tool. I've had mixed results from them though, many times they don't fit on the schrader valve well and either leak or won't read pressure.
 
1997ThunderbirdLXV6 said:
Fuel pressure gauge, is that something you can get as a loaner from the parts store?
Click to expand...
If you do get a loaner, be sure it has the schrader valve fitting. I bought this on Amazon ($25) and it comes with the Ford schrader valve fitting.

Actron CP7818 Fuel Pressure Tester Kit (currenlty out of stock)​


I bought another brand on Amazon and it did not have the fitting, had to return it. It was crap anyway. So be sure that if you rent or buy, it has the Ford fitting or you will need to go find one.
 
1997ThunderbirdLXV6 said:
  • When driving off, everything turns back to normal, except during the first few seconds of initial acceleration, when I'm hearing a sound akin to tiny rocks traveling through a pipe; that sounds comes from the right side and seems to travel backwards (as if through the fuel return line?).
Click to expand...

Is this a misfire sound?
 
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