Join Date: Sep 2009
Location: Socal desert
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It is the IPR (injector pressure regulator) spring that is located in the fuel filter bowl assy.
A common mod is to shim the spring with a bb (from your kids red ryder). The purpose is to raise the injector fuel pressure.
Apparently Ford sold a stronger version of the spring for Cali trucks, but it is no longer available.
GDS calls it a fuel spring which is a bit confusing.
But it is interesting to note that they measured how much the stock spring degrades (looses strength) over time, which probably explains why someone with an older truck would see a difference by adding the bb shim.
97 F250HD (Cal. model) Auto, Ext. Cab XLT, 4x4, long bed