Serious answers only please. I have a 1995 Ford F-250 XL 5.8L 351 c.i. engine. My check engine light comes on periodically when I drive. When I bought the truck a year ago the gas mileage wasn't too bad, about 9-10 mpg. I've only put about 3,000 miles on it this past year, and now the needle drops just driving it across town. I work at a Chevy dealership, and I've worked at another Chevy dealer as well as a Ford. I've always done my own work on my cars and am currently restoring a 1967 Mustang, so I have decent knowledge under the hood. I scanned the truck and it has a stored code for EGR valve voltage too high (stuck open). How bad could this be hurting my gas mileage? It's $160 for the valve and sensor even after my discount, and being a college student that's a lotta $ to pay. I'm selling the truck and need it running perfect when I do. Please, serious answers only, and help is greatly appreciated!
EGR valve should be opening at higher RPM's and closing at lower ones. Check the shaft positioin on the EGR valve with the engine idling (you might need a flashlight and mirror on an extension rod to see it on your vehicle). When the engine is revved up, the shaft should move away from the engine. If its not moving or it moves open but doesn't close all the way, it could be that the valve seat of the valve is broken and holding the valve open. If you do end up replacing it, clean out the carbon if there is any in the opening of the engine that leads to the EGR valve.
Open the hood, find the valve and check its operation. With the engine running, watch the diaphragm and then operate the throttle. When you gun the engine, you should see the diaphragm move. If it doesn't, there may be a dried-out and damaged rubber vacuum hose (quite likely) or else the valve is clogged up with carbon. Pull the valve out and shoot it full of carburetor cleaner to dissolve out the carbon. You should be able to move the operating diaphragm by sucking on the vacuum tube. While you're in there, start the engine without the EGR valve in place and shoot carburetor cleaner into the holes that lead into the intake manifold: one should have vacuum, and the other should have exhaust pressure.
Get out your jumper leads and backprobe the egr solinoid. ok. 1st thing......attempt to kill the motor at idle using the egr solinoid. apply ground to the proper wire(not red) and see if the egr valve operates, killing the motor idle. if it does operate, but doesn't kill the motor......you have some cleaning to do. if it operates, and kills the motor.......the valve and solinoid are ok. (the solinoid should also vent the egr valve vacuum when de-energized) Now.....for the tricky part. AFTERMARKET EVP SENSORS SELDOM READ CORRECTLY. 1. Turn the key on and check the voltages at the Exhaust Gas Recirculation (EGR) Valve Position (EVP) Sensor. The Brown/White (BN/W) should be 5v, the Grey/Red (GY/R) is ground and must read 0.1v or less at all times. The Brown/Green (BN/GN) is the signal and MUST read 0.40v to 0.45v. If it does not, the vertical position of the sensor must be changed BY ANY MEANS NESSESARY. a NEW valve will sit higher than an old one......but sometimes not. There are things you can try to lengthen the shaft to increase the voltage reading, such as heat shrink tubing. This EVP issue is an annoying one (even for experienced mechanics), but has little effect on gas milage, unless it is TRULY stuck open. If it were stuck open.....the truck would be running very rough at idle or die.
EGR valve stuck open will cause a serious dent in your mileage and performance. At $160 bucks you will be saving yourself alot of money by replacing it. I would go to a local junk yard and find one on a wreck. though you dont know what you are getting going that route you could save alot of money getting another egr valve that way and solve your problem to boot. you just ned it to work long enough to sell it so maybe that would suffice.
