I have a y2k ford ranger xlt ext cab w a 3.0 flex fuel engine, I started a thread about a month ago about bad skipping and thought it was a vacuum leak so I brought it to the shop and they determined it was in need of a tuneup, they replaced the plugs, wires,fuel and air filters, and the truck better than it had in a long time for about two weeks when it was acting up as before.

I was going to bring it back but when I drove it the next day it was fine, I thought well maybe the coil pack was bad so I replaced that yesterday, I drove it today and initially it ran fine until I got on the on ramp to the highway and had to floor it until I could get ahead of a car to get on, then it skipped pretty bad, I leveled out the speed to 60 on the flats and the skip finally cleared and I still have a occasional skip at idle, I'm at a lost where to go from here, I don't want to keep throwing money at the truck, and no cel light came on and no codes are stored.

 

Borrow, or come by the ELM scan tool & running diagnostic freeware FORScan on the viewing device of your choice as discussed here https://www.ford-trucks.com/forums/1...-scantool.html & have it scan for trouble code clues to see if it'll flag a particular cylinder/s to focus your trouble shoot on. Post All code Numbers.

If you don't want to invest in the ELM scan tool, revisit the work done to see if you can find something obvious like a loose or faulty plug, or plug wire. If so, then consider taking it back to the shop to have them warranty the repairs they made or fix it yourself if its something simple like a loose plug wire at the coil pack or on a plug. You did have the parts store bench test the replacement coil pack before leaving the store....Right?
If nothing obvious found, try a wet down test of the secondary ignition components, one at a time, after dark, using a spray bottle of water, while looking for an arcs & sparks light show from faulty or damaged insulation or cracked plug ceramic insulators. Do this while the engine idles at the temp the problem has been occurring.
Don't toss any more parts at the problem unless your tests prove positive, or at least point to a good suspect.
Just because parts are new doesn't automatically make em good, I've seen & heard of bad new parts right out of the box. I've seen new parts damaged by the Tech installing them. Some thoughts for consideration, let us know what you find.

 

PawPaw thanks for replying, I do have the ELM scan tool and both FORScan and Torque apps and when I ran them no codes popped up either new or saved and the shop used their scan tool and no codes showed, the funny thing now is that the truck is running great now (knock,knock) so if this problem comes back I'll have to start at square one again.

 

Ok good feedback, so the ELM/FORScan combo found no set, or pending codes, so lets think about this some more. Since OBD-2 is fairly sophisticated in what it can detect & its not detecting anything, it means the problem is likely something the computer isn't monitoring, like a sticking valve, or CCDF= Combustion Chamber Deposit Flaking, in which combustion chamber deposits can flake off & get deposited in a valve seat, causing it not to seal well a few times until it moves on, or a valve sticking, or a loose electrical connection in the ignition system. So, maybe try a wiggle test with the engine at warm idle, to see if you can cause the problem when you wiggle the spark plug & fuel injector wires.
If you think maybe combustion chamber deposits are present, maybe consider a 1oz/gal Techron Concentrate Plus added at the pump before filling with Chevron, Texaco, CalTex, or now Shell, all of which have some PEA in their fuel ad pack, so the additional PEA in the Techron will raise the treat rate 10X above pump gas alone. Then perform some daily rpm run up's to 3500 for a mile or two to blow out any loosened deposits. Run most of the treated tank out before refilling & let us know how it goes.

 

Pawpaw, now the truck idles fine and runs ok on short lower speed trips, when I hit the accelerator it starts to stumble and runs rough then it will quiet down, a Youtube search I found was a engine skip without a cel could be caused by leaking exhaust valves needing a valve job, I'm not willing to dump anymore money into this 18 year old truck I might bring this into another shop for a diagnoses and go from there.
Oh by the way I filled the tank with Shell gas and a bottle of Techron.

 

Ok, lets think about this some more, are you saying its idling/running better After the Techron treatment? Did you perform at least some rpm run up's to at least 3500 for a mile or two during the treated tank, to blow out loosened deposits?

Will Torque, or FORScan now perform a power balance test? This is where the scan tool disables a fuel injector & measures the rpm drop. If a cylinder is different it'll get flagged.
If so, do the power balance test to see if it'll flag a suspect cylinder/s, so you can go there & look for problems like a faulty plug, plug wire, fuel injector, or a compression problem with the suspect cylinder.
Laying down on throttle up also puts the throttle position sensor & ignition system on the suspect list. SO, after dark have you performed the wet down test with a spray bottle of water, to see if you have a secondary ignition insulation part problem, that would cause a wimpy spark that blows out at throttle up?

EDIT: Have you performed a TPS resistance test as you Slowly go from closed to open throttle while measuring resistance to see if there are any drop outs, or unsteady reading along the way, from closed to wide open throttle, that's confusing the computer about what the throttle movement is doing?

OBD-2 & the ELM/FORScan combination is a very powerful diagnostic combination, so if set up to monitor the TPS, short & long term fuel trim, maybe the fuel injectors pulse width, it should be able to flag a suspect part like the TPS, or cylinder bank, or cylinder/s no problem, if the ELM is plugged in & set up to monitor the suspects when the problem happens.
So plug in the ELM, enable the diagnostic software on your viewing device, go for a drive that causes the problem & post up what was caught in the snapshot scan mode, as it'll capture the out of spec parameter/s.

 

If the above checks out ok, have a look at fuel pressure & delivery rate. If either is low, or lays down on a throttle up, the air fuel mixture will go lean & cause a stumble. More thoughts for consideration, keep us posted on your findings.

 

Pawpaw, I found out what was wrong, I was looking in Youtube and came across this video about 19 reasons for engine skipping in Fords , one of the reasons was a loose cover on the intake air box, I opened the hood and yep that what my problem was, when I first had this problem like I said in my original post the truck was in need of a tuneup and it ran great for two weeks well maybe the clips weren't secure enough and caused the the cover to open when accelerating because of the torque, well I just took it out on the highway and it's back to normal, thanks for all your help.

 

Ok, good find, fix, feedback & to hear all now seems well & your on the road again.
Yup Ford Tech Makuloco is a really good, no nonsense source to fix Ford woes. He's absolutely right about the MAF sensor requiring Clean & Laminar air flow over its heated air flow sensor, so its not sending corrupt air flow info to the ECM. He pointed out some good reasons to use OEM air filters & make sure they're installed correctly & that we properly button up the air tube & air box too.

All of this reminds me of a no nonsense, crusty old electronic R & D engineering manager, Dan Duggan, that had a prominently displayed framed sign on his office wall, Easily seen in BIG letters as you walked in, that reminded all who came to lay their woes in his lap, to First, "Look For Something Simple, Stupid"!!! I remember the first time reading it & being kinda turned off by being referred to as Stupid, but later came to realize the wisdom of the words & began to try & heed the look for something simple part, before jumping to conclusions on my trouble shooting. Taking the time to make sure the basics are right, sure has saved me countless hours of trouble shooting time over the Decades!!!!