New 350TBI = Terrible Mileage

[jwc1080]

Try to make this short. Bought a 94 K1500 with 190k on original motor in good running order. Did a complete tune up, fuel filter, NGK plugs, wires, cap, rotor, blaster coil, regapped plugs, synthetic fluids, ect. Ran like a top and increased my mileage to an average of 16mpg which I was very happy with. Unintentionally ran it hot and cracked the block one day. Finaly got a remanufactured short block, not a gm crate and installed my old resurfaced heads and dropped the motor in. Broke the flat tappet cam in and got the valves adjusted correctly it now runs like brand new, it seems. I'm on my 7th tank of gas with about 1,300 miles on the new motor and I have gotten about 8mpg on each tank. I babied the last two tanks and brought it up to a whopping 9mpg. WTF. I know new motors will tend to get better with more miles but everyone I talked to said it shouldnt take but 1k miles. I know people don't like anything but AC Delco parts so I will buying new AC Delco coil, plugs, wires to try that. But how did i manage to get 16 with an old motor and my exact setup then drop a new motor in and get half that... Any ideas???

 

[jwc1080]

No codes, haven't checked the fuel pressure. Cat is gutted. Like I stated, runs great, good power, idles super smooth. I know some trucks will have slight variation but not that much. Something has to be wrong. I planned on keeping the truck for the long run but i cannot drive it much longer knowing i shoild be getting 300-350 miles on 24 gallons instead of barely getting 200.

 

[jwc1080]

No ideas, suggestions, thoughts, opinions....

 

[90halfton]

Check fuel pressure. Timing. Spray pattern on injectors. Ohm out temp sensor in intake manifold (resistance/temperature chart is on here somewhere). F### idk. What have you checked you can rule out?

 

[vic_v8]

What's your compression ratio?

 

[jwc1080]

Check fuel pressure. Timing. Spray pattern on injectors. Ohm out temp sensor in intake manifold (resistance/temperature chart is on here somewhere). F### idk. What have you checked you can rule out?

Sorry for the late reply. But i have checked all of these now. Fuel pressure is 11.5psi, spray pattern looks good to me but I am sending them to witchhunter performace to get cleaned and flow matched, timing was set at 0* with the plug disconnected, and I ohm'd the temp sensor cold and warm and it is pretty accurate according to the chart.

I am going to double check my TDC using a piston stop and remarking my old harmonic balancer then reset the timing.

I am unfamiliar with the compression ratio.

Im lost. I am still getting around 10mpg average to a whole tank and that is Takin it extremely easy and coasting a lot....