Sudden Fuel Economy Drop HELP!

[ClayW]

I'm on a roadtrip and I have used three tanks of gas, getting 31mpg, 24 mpg 23 mpg, in that order. What should I be looking for?

When I filled up the last tank, I checked under the hood and the vacuum hose that goes to the forward end of the fuel rail had popped off, so I put it back on. I still got 23 mpg on that tank.

What else should I look for?

Thanks in advance.

[DesktopDave]

I'd just be smelling for raw fuel.  Could be a leaking hose...I've had pinhole leaks in hard lines as well.  Don't forget to check the fuel & vac lines off the top of the tank too.

If you have a screwdriver you can do a "mechanic's stethoscope" on the injectors to see if one is stuck open.

Stomp test the old gal too - see what the DME thinks is wrong.

[ClayW]

Okay, I did the stomp test and got a 1215 code, which means AFM problems or a vacuum leak. Also, the problem is getting progressively worse. The idle is getting worse and the engine is harder to get started. The symptoms are very similar to the vacuum leak that I had a few weeks ago. The progressive nature of the problem makes me think that it is a vacuum leak as well.

I will do the carb spray test in the morning and see what happens.

[ClayW]

I removed and replaced the upper intake. I found no gas leaks, so I used a super thin layer of Ultra Black RTV to seal ul any leaks. I put it together and now it runs fine, but take about ten seconds of cranking to slowly get started. Any ideas now?

http://s119.photobucket.com/albums/o143/clayweiland/?action=view&current=2012-06-23_16-38-52_393.mp4

[monty23psk]

Hey Clay, this did you resolve this? Mine just started and before I start poking around I want to see what it might be.

Thanks

[ClayW]

Monty,

I finally installed an inline fuel pressure gauge and found that I was a few PSI low. I swapped out my spare pump and BOOM. Done.

[monty23psk]

Thanks, will take a look at few things but fuel pressure was one of them. Since I get a smell of fuel in the morning like it running rich, it seems to be fuel pressure, injector related as I do not see a leak. Mostly smell it via exhaust.

[DesktopDave]

How old is the o2 sensor?  Did you do a stomp test?
 
I'd also like to note that you should be careful with RTV upstream of the 02 sensor - unless the RTV is marked as 'sensor-safe' you run the risk of damaging the o2 sensor.

[monty23psk]

I did do the stomp test and got 1215. I have a new intake boot that I will swap. Will also check hoses and expecially the fuel pressure reg vac hose. Lastly check the connectors at the AFM. If that doesnt fix it, will clean AFM and TPS. Then move from there.