where did my mpg go?

GF7PE · March 16, 2005

I was getting about 10-11 mpg all spring summer and fall but now if I am lucky I am gettin 6-7. Any ideas on what might be wrong here. Nothing has changed at all and the only issue with the truck is a tranny issue on the highway. It doesnt feel any different at all either.

ideas?

woodpecker · March 16, 2005

fuel filter, air filter, etc

GF7PE · March 16, 2005

changed the fuel filter and air filter.... nada!!

whitesnake01 · March 16, 2005

O2 or MAF?

Beer Belly · March 16, 2005

Winter time.....do you let the truck idle as you clear the Snow off it or just let it warm up ?. Does your area have Oxygenated Gas during the Winter months (not sure if that would be the problem though)?

GF7PE · March 16, 2005

no dont really warm it up anymore than usual. and no oxygas here. I'm at a loss

Haulin' 8.1 · March 16, 2005

So what is the tranny issue?

Check all ground connections for clean and tight and check the battery. Check the alternator for A/C voltage due to bad diodes. Have a trustworthy exhaust shop check the convertors for clogging (high back pressure). Change the plugs and if one or a few look really carbon black then suspect a leaking fuel injector on the corosponding cylinder. Eyeball your spark plug wires at night in the dark looking for voltage leaks, it's best to have a helper load the engine against the brakes when looking. Make sure the vacuum hose connected to the fuel pressure regulator is intact and supplying strong vacuum, check the fuel pressure while your at it. Clean the MAF sensor air passage with brake cleaner, let it air dry and reinstall it. Fill the tank, start it up parked on concrete and look for leaking fuel from tank to intake, keep in mind if it leaks near the exhaust it may evaporate before it hits the ground but you should hear and smell it.

Vernon

GF7PE · March 16, 2005

thanks for those tips.

The issue is when driving on the highway it takes about 3 minutes for it to shift into OD. then everytime you back off the throttle say going down hill it will either unlock the torque converter or down shift into 3rd. When crusing the rpm surges like 200 rpm. It does these things every time and is not random.

woodpecker · March 17, 2005

if it were me i would take it to the dealer

GF7PE · March 17, 2005

ya its going in after the owner gets back from vacation. He picks up my cars and brings them in for me. Not sure what they are going to say about the lift though. Warranty runs out in August and the truck only has 19000 miles

71GMC_3/4T · March 17, 2005

My guess would be brakes sticking. After a long run on the highway without using the brakes, coast to a stop and feel the rotors. They should be cool.