Hello,
I wanted to post this injector info since the late model Blazers with factory MPFI seem to be rare in discussions. I have a 2004 LS with 166K, idle was a little rough, threw no codes but thought I'd service the manifold/inj. SMP advertises PN FJ503 as replacement for my year, on both RockAuto and Amazon. I received the unit, installed the injectors, but when I tried to install the plastic upper intake manifold (plenum) the metering body would not slip thru the opening. After several tries I took out my calipers and measured the width of metering body and plenum opening. The FJ503 body was ~.005" wider than the opening. The measurement was w/o O-ring so you can see there's no clearance at all. I'm thinking the FJ503 is suited for conversions from the poppet style injector and is dimensioned for a larger plenum opening on earlier years. I don't believe it's a one of a kind defect knowing what I know about production processes. Probably the biggest problem I see in aftermarket parts are dimensional errors? One other thing, my original MPFI has no crossed injector tubes, they just fan out symmetrically but the installation instructions tell you to cross #3. Anyway, I've worked on S10 Blazers for years all the way from 85 to 04. I returned the injectors to RockAuto and sent them a report with measured data that they will forward to SMP. I'm having Mr Injector service and recondition my OEM set since reliable complete units seems to be scarce.