Alright I got a 98 f150 5.4 L code today went to start it and it went to 2k rpm drop right down and died. It did it a couple of times then I stuck my foot into it, as long as it stays above 2k it runs ok but it misses and stumbles anything below 2 and it stumbles and dies, it also has the codes for insuffcent efr flow, bank 1 sensor 1 lean, and bank 1 sensor 2 lean, and has only been getting about 8-10 miles to the gallon, the iac, dpfe and egr pressure feedback are good, no apparant vac leaks and it has good gas thinking of yanking off upper plenum and tb to clean and also replace egr valve. Oh and when i tried to limp it home it had no power and blew out a ton of black smoke. Any other ideas on things I might try or am I on the right track with cleanin the tb?

 

look at 02 sensors for the lean condition, while ur at it clean ur IAC and MAFS

 

dpfe and egr pressure feedback are good

How did you test these two items?

 

ohm'd against new ones, back probed to make sure they where getting a signal and voltage, and made sure they both where getting vac. Replaced egr and cleaned passages yesterday still has same problem just will run a lil longer now.

 

alright to update I've now replaced the maf tps fuel pressure reg. spark plugs still not running, im now looking at replaceing all vac hoses, also been told that bad fuel injector can cause this does anyone know if and how you can test injectors?

 

Have you done anything with your 02 sensors?

 

o2 sensors are fine when i replaced the egr valve the cel went off and hasent came back on yet.

 

02 sensors a definate possiblity

 

So is the truck still acting up after you replaced the egr? with no mil?

 

A bad coolant temp sensor for the computer will do what your truck is doing. It keeps it running rich constantly, thus the black smoke. What were or what are the codes that are set? Give us all of them to help you dissect this down to a manageable set of ideas. Right now, the IAC, EGR, DFPE, vacuum lines, cam or crank sensor, tps, o2 sensors, intake gasket, fuel injector, fuel pressure regulator, and many more items can cause this. The codes will help knock it down. There are a bunch of us on here who can help diagnose this problem, but we still need the codes. There'll be a hundred ideas, but that's what they are until you run the diagnosis.

I'm sure you have some of these codes. Maybe a P0171, P0174, P030*,P040*, a P0505 and probably a couple more codes set in memory. See what you are reading, then let's figure it out.