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I have a 1998 F150 4.2l and recently I have been having issues with it starting hard, having to pump the gas peddel about 5 times to get it to start up. After it starts the idle is very rough and stays that way. I have already changed out:
Spark Plug Wires
Both rubber elbows for the PCV
Cleaned the MAF
Not sure what to do next, check fuel pressure, check vacuum lines, check the intake gaskets? Does this sound like a fuel issue, or vacuum issue? I dont think its an ignition issue, just acts like it doesnt want to start until you pump the pedel, and once its running its rough, almost like a miss. I have only gotten the codes for a miss fire on cyclinder 3 and 6, and once a code for lean bank 1 or 2 I can't remember which.
Have you checked around the base of the throttle body and intake for vacuum leaks? The 4.2's like to leak in those places. Clean the throttle body while you're in there. Might also want to change the injectors to another cylinder if the line pressure is good and see if the misfire code follows the injector.
Listen around the area for any sucking sounds, visually look for cracks around the gaskets and connection areas, then spray ether or carb cleaner around the area and listen for changes in idle. If the idle changes, the ether is getting in there through a leak. The gasket around the base of the throttle body will be the first point of attack.
Those engines have problem with head gaskets. But usually the right front cylinder with get some antifreeze in it while setting over night and after a short warm up time all cylinders with start firing. They also have a valve on the back of the intake that opens after 4000 rpms to open the longer intake runners. My brother had his head gasket replace on his and it did the same as yours. Mechanic didnt reconnect that rear intake valve and an oxygen sensor was bad.
I also found all the front intake manifold bolts only finger tight (dont think this would cause low compression, would it?), and the fuel pressure regulator had fuel in the vacuum line. I am planning on replacing the long block and any and all sensors that dont give me the warm fuzzy feeling.
Any suggestions on easy ways to pull the motor are appreciated.