I am trying to help a friend with his 99 Ranger with a 4.0 . When first started it will idle rough and hesitate for the first 300 feet or so, and then clear up and run smooth the rest of the day. If he lets it set for 6 or more hours it will repeat the problem. He has taken it to a local Ford dealer and they have replaced spark plugs, plug wires, coil pack, cleaned the throttle body, checked the air idle motor and passage. He has had it to the dealer 3 times and their latest plan is to pull the heads @ a cost of 1500.00 to start. This is where I came in to help, since it runs well, no coolant in oil or oil in coolant nor loss of either fluid, I couldn't figure why they want to pull the heads. (Older folks on limited income.)
To date it has not thrown a code, I ran it on a New Generation Star tester and cannot find a code. The truck runs great after the first intial start up and does not give any signs of cutting out or lack of power. My guess is it is losing fuel pressure overnight and is taking a while to reprime. Original fuel pump and 160K miles. Will do a fuel pressure test this weekend. Wondering if anyone else has had this problem or anything obvious I am overlooking. I appreciate any info.

 

Welcome to FTE.

Your senior citizen friend is lucky to have you looking out for him!!!!!

He may have more than one problem.

With the driveability symptoms you posted, I agree its a good idea to check the fuel pressure & leak down time. Also good to have had a look for trouble codes with the Star scantool. Interesting that it didn't find any hard or pending codes stored.

Since the Dealer has reworked the ignition system, cleaned the throttle body, (checked the IAC????) did they just check, clean, or did they replace the IAC???? Its a common problem part for idle woes, so if it hasn't been replaced, or at least cleaned in 160K miles, it still belongs on the suspect list imo.

Is the vehicle now up to date on All other past & present due scheduled maintenance call outs, like fuel & air filters, O2 sensor & PCV valve replacement, as with the 160K miles on this ride these parts have lived about two lifetimes, & a sticking open, or worn out poorly seating PCV valve, or leaking rubber fitting or hose to it, could mess with fuel trim & cause driveability problems after a cold start, as its down stream of & not being monitored by the MAF sensor, so if the PCV system is acting out & leaking unplanned for air into the intake manafold, it'll lean the air/fuel ratio out after a cold start & can cause rough idle, or stumble at throttle up????

If the heated upstream/before cat converter O2 sensors have more than 75K miles on them, they too belong on the suspect list, as their switching renge & speed gets lazy with age, so they'll be slow to give the computer fast feedback on how its doing on controlling fuel trim.

So with the Star scantool, maybe consider having a look at fuel trim for both cyl banks, along with O2 sensor switching speed & range, to see if you can glean any trouble shooting clues.

Does he have the old spark plugs & know which cyl they were removed from, so a deposit read can be done, as that could help narrow down which fuel injector, or cyl may be acting out. If he doesn't have them, then have a look at fuel trim for both cyl banks & see if anything looks amiss, as you could narrow it down to three cyls that way, then maybe have a listen to each to see if any fuel injector/s sounds different & maybe be able to narrow the suspect list some more.

If you come suspect a leaky injector, or excessive engine carbon deposits absorbing fuel & messing with/leaning out fuel trim after a cold start, maybe consider trying a 20 oz dose of Chevron Techron Concentrate Plus in the tank, at the pump, before filling up (so to get good mixing), with Chevron, Texaco, Caltex, or now Shell & run most of the treated tank out with some spirited daily driving, with rpm at 3500 for a mile or so to blow out carbon. These fuels already have PEA in their fuel ad pack, so with the 20oz additional Techron, it'll raise the treat rate 10X above pump gas alone & will usually get the fuel injectors, intake valves, piston crowns & combustion chambers tidy in one tank. A number of the autoparts stores have Techron on a bogo deal this month & its a danged site less gold to try & clean things up this way than removing the danged heads to clean them!!!!!

More thoughts for consideration, keep us posted on your trouble shoot.