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Old 11-24-2020, 09:23 AM   #1
Ten Point
kingranch's Avatar
Join Date: Dec 2010
Location: lakeway
Default Mustang foxbody 5.0 guys question

My 1990 lx 5.0 has trouble 1st in the morning to start it stumbles and will stall if I dont give it a tiny bit of gas.

Fuel pressure shows 40 psi primed and drops to 30 when car starts.

Funny thing is after it warms up for a second it runs great and restarts easily no stumble...only after it sits over 8 hrs.

I did notice if I unplug the vacuum on fpr it jumps to 40 and on a cold start in morning it doesn't stumble but idles higher like its rich...I replug the vac hose and it idles back down and runs fine then.

Could the fpr cause this early morning hard start condition? It's a ford stock fpr and holds good at 30 when running and it's not leaking that I can see or smell from the vac nipple.

Everything is stock as far as the fuel system goes.. 19lb injectors and new fuel pump and filter last year...also injectors were rebuilt.

I noticed the fuel pressure bleeds off overnight but from internet search this is fairly common.
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