My Dad has a 1996 F150 5.8L he just replaced the egr valve, the check engine light said it was bad, so he changed it now it runs rough with the vacuum line connected to it. It will run perfectly fine when the vac line is disconnected from the egr valve. SO what is causing this? Any help is appreciated...
thanks,..,..

 

There are three major components to check - the EGR valve, the position sensor on top of the valve, and the control solenoid supplying vacuum to the valve.

Seeing that it runs fine with no vacuum, but runs rough with the line attached would suggest that the valve is working.

There were at least two different position sensors used during that era, easily identified by color. If this was changed out as part of the valve replacement - need to be sure the right type went back on, and that the new one isn't bad out-of-the-box.

The control solenoid is located on top of the intake manifold, towards the rear of the block - at least on mine. Had an experience where a little foam filter inside had plugged up.

Good luck, and keep us posted on what you find.

 

We found the issue. It was a bad solenoid, too much stuff involved for a egr system if you ask me.. Funny thing is its the 5.8l and still gets horrible fuel mileage. I don't know what else to do to it to improve that issue. It doesn't have big tires or a monster lift, its you're basic 4x4 ext cab short bed. f150.
Its only got 100k on it. Its got new plugs and wires.

 

define "horrible"

 

8-9 mpgs

 

Plenty of air in the tires, air/fuel filters not clogged, brakes not sticking, alignment good, etc??

 

Wow...I got a 92 5.8 4x4 and getting 18mpg with 31x10.5 tires. However, I either replaced or clean everything I could for a tune up.

 

Eh, my '89 with 5.0L gets about 10-11, always has. Figure part of it may be due to the relative newness of sequential fuel injection at that time, as well as the 4WD hardware and related higher stock body height over 2WD.