12.5 mpg

[cush]

Hey so I know everyone and their mother has a mpg thread so why not one more! I hace a 2001 3.0 manual trans. I used to get around 16mpg in town and its steadily getting worse. It's seemed to have stopped at about 12.5 mpg. I've inspected the plugs, wires, run fuel injector cleaner, cleaned the throttle body, inspected the fuel filler neck, replaced the fuel filter and nothing. Still 12.5 mpg. I was planning on smoke testing the fuel tank to really look for cracks in the filler neck and do an efi service. But i was thinking maybe i should check the o2 sensors too? Any ideas?

 

[kryptonitecb]

Yes, sounds like the O2 sensors are the only thing you haven't checked.

Sent from my SAMSUNG-SGH-I547 using Tapatalk

 

[--weezl--]

I was going to suggest o2 before you said it!

you pull codes? is it getting up to full temp? and if you have access to a scanner, see if it's going into open loop

 

[cush]

Checked the o2 sensors today with one of the master techs at my work. He said they look like they're functioning properly and it isn't going in to open loop. There's no codes to pull, no lights on. Just 12.5mpg. He suggested doing a block test and see if I've got a head gasket leak

 

[stmitch]

When o2 sensors fail, they don't typically quit working completely, they just slow down the rate at which they transfer data, so the PCM is reacting and adjusting to inaccurate data. If your O2s have more than 70000 miles on them, you'd probably benefit from replacing them.

You said parts like the spark plugs and wires were "inspected", but were they just checked and reinstalled because they looked ok, or were they replaced? Plugs and wires should probably be done every 30000-50000 just to be safe.

How many miles are on the truck?

Cleaning the MAF would be a cheap and easy step to verify it's in good condition, and eliminate that from the list of possible culprits. While you're near the airbox, pull the air filter and make sure it's clean and not impeding air flow into the engine.

 

[RonD]

MAF sensor is the main device used to set fuel/air mix, O2 sensors are just fine tuning devices.
MAF sensors do need to be clean to give computer the correct air flow and air temperature.

Pull spark plugs and see if they show a rich mix, carbon build up.
Check all the plugs could be a leaking injector so it will only show up on 1 or maybe 2 spark plugs.
If not then extra gas isn't being burned.

Next stop would be to put a fuel pressure gauge on the fuel rail and see if there is a leak after engine is shut off, '01 has the high pressure(65+ PSI) system with no return, so even a small leak would push a bit of gas out.
If there is a pressure drop pull off the intake air plenum and smell intake for gasoline, leaking injector would cause that smell.
Pressure damper has a vacuum line attached, check it for gasoline smell.

Hose with a towel around it in the gas cap opening, blow in the hose and see if it holds pressure, simple but effective, lol.
Do NOT use an air compressor for this, smoke test is fine, but only effective if tank is empty, so "hole" is exposed.


Glove test is easier than block test, and not sure that would even be needed for your current issue.
MPG is usually not the first symptom of a head gasket problem.

 

[cush]

It has 157,xxx miles on it, I've owned it since 83,000. The wires and coil were done at 98,000 the plugs done around 125,000. The MAF was cleaned a few months ago to try and help the mpg's but it didn't help. We watched the o2 sensor on a scan tool and both front sensor seemed to respond quickly. The downstream one was a little slow but my buddy who's a master tech said it was responding fine.
I can pull the plugs this weekend and check them all out and I'll clean the MAF again. I'm also going to try and smoke test or do that towel test this weekend too

 

[--weezl--]

dirty injectors? i poor spray pattern can cause incomplete burning of fuel resulting in loss of power, and a heavier foot by association... could try putting some seafoam through it, it's worth the $10 even if it ends up not solving the problem

 

[cush]

It was seafoamed a few months ago and I ran two tanks in a row with Lucas oil's deep clean. And there doesn't seem to be any loss of power. It's been running really well the whole time, the only difference is the mileage

 

[stmitch]

Maybe you're dragging a brake? Any uneven tire wear that could show poor alignment?

 

[cush]

I could be dragging a brake but it's not driving like it. I need to replace the brake fluid for sure. But the tires wear evenly, alignment is perfect. I'll check the brakes tomorrow. I've always had a cooling issue with the brakes on it, they get hot and the pads crack and the centers flake out

 

[cush]

I fell ill this weekend so I didn't get a chance to work on the truck, but today I pulled all the plugs and #3 and 4 were wet with raw fuel and 5 and 6 smelled strongly of unburnt fuel. 1 and 2 smelt more on the side of carbon and burnt fuel and looked the best out of the bunch. At this point I'm going to replace the injectors and go from there. Hopefully problem solved. I really appreciate all the help guys!

 

[RonD]

Look in the yellow pages or online for local fuel injector rebuilders.
If the injectors are a common type, which they are, you can often just take in yours and swap them for rebuilt, so an in/out and you are up and running the same day.