1994 Chevy S 10 V6 Vortech 250K miles
Changed my fuel pump. Mileage went from ~250 per tank down to a current 185 instead of the original 360-380. Smart certified GM guy is guessing that it’s the injectors. Said mine was a bad design. One peice guarenteed to clog and die. GM apparently invented a new one to replace it but no recall so it’s on my dime. Otherwise engine and truck seem pretty good.
How difficult would replacement be to someone who doesn’t do this for a living but owns a Haynes manual? 
Very easy IF you can readily access the injectors. I’m unfamiliar with this underhood neighborhood. Just follow the manual.
These fuel injection questions from these years ought to include the type of fuel injection. I am 99% sure you have TBI (with two injectors) but I have a FSM that describes a 95 with multiport. Then there is the slim chance you have CPI, for those years I have to be sure of the F.I type. There are known issues with both the CPI and TBI and just normal stuff with the multiport injection.
Miles per tank is unquantifiable. An accurate assessment of mpg requires several fill ups and many accumulated miles.
487 million bolts to take off the plenum, then huge open pit with the injector sitting in the middle.
~18.5 gallon tank.
First 3 years 21 mpg
Fuel pump dying, drove for 1 year 13-15 mpg
Fuel pump fixed driven for 2 months, 10 mpg.
All of these periods have required multiple fillups.
I actually got close to 250 miles on the first tank after the fuel pump was changed, but have been losing steam ever since. In 2 weeks I’ll probably be down to 9 mpg.
I replied twice to old school but the answer isn’t showing up.
Anyways, Haynes says it’s either the TBI or CMFI. I’ll check with the dealer tommorrow to be sure. I have had the plenum off to replace the neoprene lines that run from the back wall of the cavity to the injector body. Small and black, looked like a one piece meaning that it didn’t look like a brain with 2 distinct hemispheres but more like a distributer cap with only 1 button sticking up.
If the vehicle has the CPFI or the spider assembly injection system it requires that the lower intake manifold be removed in order to replace it.
However, before replacing the spider assembly, you might first try adding a fuel system cleaner such as SeaFoam to the gas tank. The spider assembly has popit valves at each cylinder as injectors. These popit valves are a ball and spring affair where fuel pressure is used to force the popit valves open. These popit valves can form gum and varnish inside them which prevents the valves from closing completely causing the engine to use more fuel.
If the fuel system cleaner shows no improvement, then most likely the problem is with the fuel pressure regulator on the spider assembly. In which case would require the replacement of the spider assembly.
Tester
so is this s10 easy to start? how about when its warmed up and sat for 15 minutes. I ask this because the vortec engines of that vintage have a problem with leaking fuel pressure regulators which will cause crappy mileage and hards starting when warm. this engine has a huge upper intake with a round device in the middle about two inches in diameter. you can remove those two torx screws and take a look around in the hole. if the regulator is leaking it could be wet in there but more than likely if the reg is leaking youll have a nice clean spot below it.
Hmmm, 2 votes for fuel pressure regulator. Just changed my wife’s. It will take a bit some times to start but generally fires up fine. Runs bad. So when I hit a red light I’ll stomp on the gas/ big puff of black smoke runs better. Check enjine light on a lot runs rough. Light goes off, runs horrible. Fuel smell is through the exhaust only, not filling the cabin like my wife’s was.
GM certifieds actual guess was more than likely the spyder, but could also be the distributer.
Double checked with the part store. Put my VIN in the computer, the injector is definitely the CMFI, not the TBI.
So is this a semi difficult repair? Easy one? Take it to someone else type repair?
Did see the Seafoam product. $9 a can sound right? Will try that first.
You can test the fuel pressure in the circuit with a pressure gauge available at most part stores.