Yes, I said earlier that I let one tank run dry then switched back and forth to see if the fuller one is headed to the empty one. Answer, no its still dry after running off the fuller one for a while.

I'm wondering if a throttle body or manifold leak could be causing this.

 

If you didn't notice a vacuum line when you replaced the regulator, then this is part of the problem.

You don't even know what the problem is. Pull the codes, even if the light is off. Not all codes will set the light.

 

Pressure reg. was bad. O2 sensor was fouled too. Replaced both of them at the same time. And let me tell you that O2 sensor is a PITA. I wish they could have put it on the pipe with a little more downward angle.

 

hehe, you're right I don't know what the problem is, generally i'd say it can be narrowed down to real bad MPG with no other apparent symptoms.

 

Has the air filter been replaced? That's another MPG killer. But with a bad FPR causing the O2 sensor to fail, You may want to replace the spark plugs, they may be fouling out. Its probly best to do a complete tune up.

 

OK finally got around to pulling the codes. 128 came up. Its the MAP vacuum or sensor. I'm surprised no one mentioned that in response to my post. I will be looking at that today and post the results here. Thanks for the help to all.

 

Didn't think of that. Haven't had one go out yet. Hope that fixes your problem.

 

Very happy to report this problem is SOLVED!!!!!!

It turned out to be the MAP sensor. I learned a lot as I always do when tracking down these problems. First thing. You need a very good ear and keen understanding of your truck to spot those "little" changes in how your truck runs. I was missing the tiny bit of roughness in the idle and thought otherwise the truck was running fine. It also took me 3 80$ fillups to notice the mileage was so bad.

Getting the codes made a big diff. Funny that the Check Engine light didn't come on for this one. I guess thats part of EEC-IV OBD 1. Next time I'll get the codes right away because the light never came on. Code 128 led me to the MAP sensor -- vacuum/module was off. To troubleshoot I pulled the vacuum line while running. RPMs fall to a point where it nearly dies then it kicks back with a rough idle. Putting a thumb over the vacuum line only makes it idle worse. Next put the line back on the MAP module and pulled the connector. Once again the engine dips till it nearly dies but this time it regains its composure to a state very similar to the original pre-test running state. Putting the connector back on produces a little roughness for a second and you're back to where you started.

I decided to test the module but read it puts out frequency not volts. I don't know about you but my time is worth over 50$/hour for troubleshooting these problems and I'm going broke doing it. I took a chance and "quick-decided" it was the module. Picked one up at CarQuest for $93. Plugged it in and at first couldn't tell much of a difference. I thought it might be because I had the negative battery terminal disconnected during the operation which took about 10 minutes by the way.

I took a drive about 25 miles down the road to Sedalia turning towards Deckers. Transmission was shifting very soft but by damn my gas mileage had pretty gotten back to normal. I figured it would be down a little from all the driving I did with the bad module but hope it improves the more I drive it.

G

 

As I said in the beginning of this post, it only started doing this after I got it back from the dealership after chewing them out about their prices. I'm only guessing here but I suspect the crafty seasoned and burned out drive line mechanic ran some high voltage through the module that effectively fried the chip inside leaving it in a full gas trim state. I'll be dissecting the old module to see where it failed. Another thing I took the truck today to another more reputable Ford dealer but this time I talked with the service counter guy telling him I want to establish the ground rules before leaving the truck with them. Question: Can I observe. Answer: no. Question: Can I pay you for diagnostics and decide not to have you fix it. Answer: yes. Question: Can I talk to the person who will be working on the vehicle. Answer: no.

My response: I'll get back to you and I left.

 

Ok for the can i watch that's understandable they don't want the chance you getting hurt or whatever but not being able to talk to the guy that'll be working on it yeah that part aint right. i always talk to the person who'll be working on mine. heck i even talk to the state inspector when i get my inspection and emissions done haha. that just screams bad juju like their hiding something, like the guy working on it don't know Saturday from Sunday much less what he's doing.

My 2 cents
Kyle