1988 GMC Jimmy MPG Woes

I had a 1985 S-10 Blazer that ran perfectly, everything under the hood was fixed and in great condition, the outside looked scrappy but the car ran well... until my brother ran it into a tree.

So now my parents have given me an 1988 GMC Jimmy (2.8L V6 4WD FI) and it's been one hell of a ride to make it driveable.

But if I can do whatever I can to help it then....

Oh dear... gasoline.... MPG happens to be the biggest deal to me, apparently I figured if the car is in optimal condition and that I don't drive it like a leadfoot then it should be one way of indicating that I'm taking well enough care of it.

I got my "new" car with about 163k on it. (now has 164k... haven't had it long at all) It came with a bunch of unknowns about it as well... Found out that it was running without an air filter... So there's one now.. Changed the oil and filter, front and rear brakes, added to the extremely low amount of trans fluid, changed the spark plugs... the good old basics. Obviously I'm an amateur with car maintenance, hoping to change that.

I know there are ten thousand things than can affect mileage, but I'm just making sure I can keep my mpg optimal with the gas prices on the rise.

The car gets about 16-17 mpg combined city and highway driving. Sound better comparatively to my 10-15 mpg blazer but I figured if it's possible to get better mileage with it? Maybe an O2 sensor needs to be changed? Maybe my mpg is already the best it can be?

Just food for thought, I changed the spark plug wires as well, as the hot air from the exhaust made the wires burn and crack. I have one 8 mm and 5 other 7 mm wires in there... I wonder if replacing all with new 8mm wires would do how much good...

Also wondering, if the car has O2 sensor(s).. where is it or they located?

The one lone 8 mm wire wouldn't snap on the distributor cap and so I bought a Bosch premium wire set. Now all 6 wires are new and changed also a new ignition coil.(came with the wires) I wonder about the distributor cap itself... The idle seems smooth enough so i doubt there are problems with it.

O2 Sensor: just past exhaust pipe two into one joint ie roughly underneath right hand floor pan. Make sure it has a good chassis ground.

MPG

Well you're on the right track. Make sure all the vacuum lines are gas tight at the joints. Use a gasketing compound for this such as Hylomar or equivalent.

Make sure all electrical connections are sound. Particular attention to sensor electrics so that the ECM gets true information.

Ignition timing should be checked once the lines are sorted.

I've found the Jimmy timing is retarded to compensate for the air it sucks in through these lines. So reducing the air intake through them has allowed an increase in ignition advance, hence power/mpg. I fitted restrictors to the fuel vapour canister and air injector pump lines. The EGR vacuum valve I changed to another non leaking type found in a scrapyard.

Binding brakes won't help so they should be cleaned regularly.

The front wheel toe should be checked. That's the degree the wheels point in/out from straight ahead. Incorrect toe will cost in fuel and tyres.

PS

Carry a spare ignition module. They fail and then you're dead in the water. The tow truck fee you'd pay covers half the cost of it if not all.

Buying yourself a manual is a good idea too.