Hey guys, long time no post. Got a problem I need help identifying. The truck hadn't run for about a month until last week when I finally got up the gusto to drop the fuel tank and replace the pump/sending unit. I also put on a new fuel pump relay as mine was corroded all to heck. The job went smoothly and the truck started right up with no hesitation. It took me to work all week just fine except that there was a somewhat loud tapping when the engine was cold, but it went away after warming up just slightly. Yesterday I went to get gas and on my way out of the gas station, the truck popped in the exhaust and shuddered down giving me no power and dying. This was after driving only about 200 yards or so. After much coersion, I got it started again. It runs fine in neutral or park, idles good and revs up smoothly and without hesitation. When i put it in drive, it idles good at first, then I try to go and it does it again after a few hundred yards. Popping exhaust-shudders and idles down-dies. If given any gas while in this condition, it chokes out and kills the engine. My initial thoughts are maybe distributor. I was not able to check for spark or pull codes on site, nor will I have internet access when i go out to work on it, so i wanna get the best diagnosis I can here before going out there. Any thoughts guys? I only have about a five hour window today to get it sorted out. Then I won't have another chance for a few days, so quick accurate help would be super appreciated. Thanks in advance fellas.

 

This is the 86 f150? What engine does it have? Carbed, fuel injected? All original or swapped engine? Auto or manual tranny?

 

Sorry, thought I had all that in my signature line. Wrong forum!
Anyway...1986 F150. 302 V8. EFI. AOD. 8.8 Rear. Double tanks. Stock.

 

Really? No one has ANY ideas or suggestions? This has happened to nobody but me?

 

Gut feeling tells me to check the accelerator pump on the carb. Its probably dumping too much gas.

 

I just seen you have the EFI. Sorry.

 

You have broken one rule that should always be followed on the fuel injected engine; What are your codes from the engine computer? With all those sensors and wires on the fuel injected engine, there is no use in guessing what could be wrong till you pull the codes from the computer.

 

I couldnt pull the code at the time franklin, but I went back out there today and pulled 'em.
22- MAP sensor out of self test range
31- PFE or EVP circuit below min. voltage
83- EGR Control Solenoid circuit failure
So i went and replaced the EGR solenoid to no avail. Still same problem, but this time while running it, i noticed the smell of gas and saw gas spewing out of the filler nozzle of the front tank. The problem with this is that it was the rear tank that i replaced the pump on. The front tank has been unused for quite a while. Apparently I have a gas transfer problem from back to front. I want to fix this problem, so any help on that would be awesome, but i don't think it has anything to do with the original problem. Any input?

 

The computer is going to list the most important, most critical items first in its list.

The MAP (Barometric Pressure) sensor not working correctly could be entirely responsible for your poorly-running engine.

The other two are related to the EGR valve.

Since you've replaced some parts, you should now clear the codes and re-run the tests to see what codes show up.

About the gas spewing from the filler tube, seems the plumbing isn't correct and the excess gas isn't returning to the tank from which it came.

 

So my return lines may either be leaking into each other somewhere, or they just may be running to the wrong tanks? Where do they originate?

 

Each tank has got two lines - one for supply. the other return.

They converge in an electrically-operated switching device that allows the driver to flip between front & rear tanks using a dash-mounted switch.

Flipping involves changing both the supply & return plumbing (I'd guess vapor recovery, too) as well as from which sending unit the gauge is reading.

Here is the plumbing from the parts book:

 

Fuel spewing from the filler could mean your selector valve is not working properly, and it needs to be replaced. Gas from the back tank is pumping to the front and overfilling it. I just had that same problem on my truck, but have recently fixed it.

 

Sounds easy enough. Just one more thing to add to the list.

 

The MAP sensor is a very important one on your engine. And it could simply be a broken vacuum line to the sensor that is causing the problem with it.