Does a 1992 F150 Custom 4.9 L6 have an evap cannister purge valvle/solenoid and where is it located?
Have owned this truck for 8 years. Replaced everything including 2 ECUs, EGR valve and solenoid, EPS, idle bypass valve, TPS, MAP sensor, coolant temp sensor, intake air temp sensor, Oxygen Sensor, etc. All this was done to solve a problem of loping (for lack of a better word) at low speeds and cruising speed. Checked codes again this week for the umpteenth time and 334 came up (EVP Sensor closed valve above max voltage). From various internet sources I've determined that there should be an EVAP Canister Purge Valve in the line between the charcoal canister and the throttle body. There is none. It's a strait line that Ys into 2 inlets on the throttle body. There is, however, a female connector laying beside the fuel rail that will receive 2 flat blade terminals, just as are found on the purge valve available for the vehicle. That's right, there is a purge valve listed for this application. I don't know if the valve was removed my some earlier mechanic making a repair, or am I just barking up the wrong tree. The vehicle idles rough when it first starts, then evens out at idle, but runs rough again at flat cruising speed with no load.
Whats FUEL pressure at the fuel rail? This is the old Ford "speed density" injection system in closed loop its reading Manifold absolute pressure, Throttle position % and 02 sensor to fuel correctly 14.7 It could have had a purge valve stripped off but that doesn't explain the engine loping. whats intake manifold vacuum reading at idle? ROUGH running signals misfire to me! Fuel or lack of / ignition or lack of ....intermittently any of this temp related or wet / dry detectable? I want to locate this issue! Quit counting blinking lights forget the codes for now) even if your taped into that old Ford test port with an adapter and reader. Start by trying to isolate circuits / subsystems ...Example pull the EGR vacuum hose any change 0 Ok check back Friday ..Regards
Okay. I've checked all the voltage to and from sensors. They all seem to be within range. I will check the manifold vacuum reading. But this may also be helpful: on a Ford blog sight I found the recommendation of restricting the EGR orifice to 7/32". I did this and the engine ran smoothly but seemed to have less pick-up/power. My goal is to have the engine run as it was designed. I've read where others have had the same problem, as in the blog mentioned above. It seems like a common issue. One would think that someone would know the fix for this.
I've also replaced the fuel pressure regulator, which was the only part I was able to definitively determine was bad. After removing and turning upside down, gas came our of the vacuum nipple.
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