Bad MPG issues plus slight skipping

[pspencer15]

Ok, I just bought a 1999 Bravada with 115k only 1 owner before me. It is in very good shape and very well maintained at an Olds dealership. The first thing I did was put is up on the lift and go over it bumper to bumper. I could not find a thing wrong. Even the transfer case fluid was replaced with the correct blue stuff. But after my first few long drives, I started to notice my fuel consunption was very high: like 11 mpg! Then I also noticed that while driving and normal highway speed I can feel a slight skipping. I was told by an Olds mechanic (who happens to own a Bravada) told me not to expect great gass mileage. I pulled the plugs that are easy to access and they are fine, the wires are in good shape, the cap & rotor look almost new, the fuel filter is new, EGR, PCV valves are new.

What else should I look at? A buddy of mine has a 2000 Blazer with the same issue, but his skipping much worse. He replaced the "spider valve" in the fuel injection system because it was dumping fuel into the last two cylinder (I've been told that is a common issue with these motors). It fixed the fuel comsumption issue, but not the skipping. I don't want my Bravada to get to that point. Is there a way to check to see if I'm dumping fuel too? How can I improve my mpg?

Any help would be great!

[old_master]

11MPG is pretty low, highway mileage should be close to 20MPG. Is the SES light on? Are there any codes in memory? If you have access to a scan tool that can read the misfire history, it will tell you if there are any misfires and which cylinders are misfiring. As for plug wires, cap and rotor, they may look new, but it requires expensive equipment to tell if they are working properly. It's possible for any one of those things to screw up and NOT turn on the SES light. These engines are very fussy when it comes to ignition parts. If/when you replace parts, make sure you use AC Delco.

The 1996 and newer "W" engine uses spring loaded poppets, and the "X" engine uses electric poppets. Both engines use 6 mini injectors that are fired sequentially. If the vehicle isn't driven very often, or it sees mainly city driving, the injectors and poppets can build up varnish deposits which can cause them to stick open. Most fuel has a cleaner in it, but adding a can of good injector cleaner can't hurt. Checking fuel pressure and leakdown, or an injector balance test, will tell you if they are leaking. There is a "backwards" technology TSB that converts the CSFI system back to a 1995 and older CMFI system. That system uses one injector that is batch fired which leaves less time for varnish to build up as the injector is open for a longer period of time and a greater amount of fuel passes through it. Check fuel pressure and leakdown, those alone will tell you if fuel delivery is working properly. Key on, engine off, fuel pump running, pressure must be 60psi to 66psi. It must remain above 55psi for 3 to 5 minutes after the pump shuts off.