Sucking Gas

[Connr11]

1994 GMC k1500 4X4 40L6E Automatic Transmission 350 Engine getting 6 mpg. Replaced the following, not all related the fuel milage but needed to be done any way.
Cap, Rotor, Wires,Plugs, EGR, PVC, Oxygen Sensor, Exhaust from Manifolds back, Fuel filter, Air filter and ECU (Computer). Loking for the MAP (Manifold Air Pressure )Sensor and the IAT (Intake Air Temperature) Sensor locations. I am open to any input that will help address this. I plan on pulling the manifold to seal an oil leak soon, want to replace sensors at that time if it will fix this. Any ideas or suggestions?

[2000CAYukon]

I have a 90 GMC K1500 5.7 4L60 (700R4) and I still get 12 around town so something is very wrong.

Mine does not have IAT so yours may not have one either. The MAP is located on the passenger side of the engine. If you follow the vacuum line at the rear of the TBI, it will take you to the MAP. Make sure the vacuum hose is not cracked or leaking.

How does it run? Does it smoke? Any codes stored? How does it idle?

I finally changed the timing chain last fall (at 110K miles) and it was really loose.

I also had a bad ignition coil that was replaced when I did the chain. They do go bad. It would run but had no power under load.

If you have the stock air cleaner, there is a valve that controls how much hot air is sent to the TBI during warm up. Mine was broken so it was only getting hot air. I wired it open and that made a big difference. You should check that. If you remove the air cleaner with the engine warm, look to see if the valve is opening to let cold air in.

How is the injector spray pattern? A bad fuel pressure regulator diaphram can cause raw fuel to be dumped into the intake.

//2000CAYukon

[fuzzypuppy]

Several things could be the cause of poor mpg, driving habbits are #1,
gearing as well, tires, a bad temp sensor will cause it to run open loop and mpg would suffer, your MAP is located on the pass side next to the Tbi the box with vacume lines as well as elec plug mine is finned. but I doubt this would cause poor mpg, and if there were a problem with your MAP it would set a fault code usually.
I was getting 10/12 mpg on a good day with a tail wind untill I installed headers, and modified my cold air intake, now im up around 18 even with a 4:10 rear.
if I keep my foot in it I see as low as 6 mpg easy and I dont have 4x4.
And IAT sensor only comes on the 96 and newer TPI engines.
If your planning on pulling the manifold spend $200 and get an aftermarket intake, the stock ones flow really poorly.
I really would try and replace the temp sensor though, the one in the intake not the head, it's cheap easy to replace and wont always set a code if bad.