1998 Ford Ranger hesitation after fixing to pass emissions

I have a 1998 Ford Ranger with 4.0 liter V6 with 167,000 miles on it and just went in for an emission test with check engine light on and it had po171 and p0174 trouble codes according to that emission report. Added fuel injection cleaner, drove it for a day then replaced fuel filter and drove it for a couple days, then went in and had codes erased by OBD 2 scanner but didnt pass due to not finishing the drive cycle. Waited a couple of more days and replaced plugs and plug wires. Went in the next day and passed the emissions test. Now it ran fine after adding fuel injector cleaner, then fine after new fuel filter and deletion of the codes, then crappy after new spark plugs and wires, which is weird because it then passed the emission test. Took wires back and got new ones and runs a little better but still worse than before I did anything to the truck at all. Now I just popped a P0153 code and am not sure what is wrong. Probable cuase from forums seems to be a faulty MAF or O2 sensor. I did all of this just to pass emissions and now it runs rough at certain RPMs like around 2 G's, and popping the new code of po153 , which I just erased to see if it pops again. Could need to burn old fuel with injector cleaner in it and then refuel with full 92 octane gas which is what a guy at Schucks Auto Supply (where I;ve been getting my parts at) suggested I do befoe doing anything more expensive first like replacing sensors. BTW I did an engine oil flush before all this and an oil change just before the first emissions test... Any help would be appreciated.

Wow that is quite the unfortunate turn of events. Without sounding offensive I think you are overanalyzing alot of the symptons and working too quickly without looking at the diagnosis. The 2 original codes point to something causing the 02's to read lean more then they should. I understand that they haven't returned but I think in do time they will. I would guess you have something common to both banks of the engine that is causing a lean condition. The misfire you feel isn't likely an igntion misfire unless the wires you installed are worse then the ones you removed and although possible I'd think if that was the case it would generate a misfire dtc. The two things that come to mind right away for lean on both banks would be low fuel pressure and flow or a vaccum leak from a hose or intake gaskets. As well on Fords there is always a chance the MAF is dirty or defective and to rule it out unplug it and redrive the truck. If the drivability improves then clean it or replace it. If it stays the sam it's not likely the MAF. As well the DPFE sensors can generate these codes on Fords in some years but it's not the most common cause. It may be possible you have a defective 02 on that bank that you're pulling the code from but Im more inclined to think the cause within the engines controls is making the 02 read that way and the 02 is in turn working as it should. To replace the 02 would not be my first step. These codes on fords are probaly the number 2 or 3 search on this site so there is alot of info on here. The first thing I would do would be to check for a vaccum leak and install a fuel pressure gauge and check the pressures on an actual rad test when the symptons are occuring.

HTH and keep me postted

Jeff

Ya Im not a technician, just a backyard mechanic that only works on things when needed like in my current situation. I needed a new fuel filter, plugs, and wires anyway so no loss in $ there. Not sure what is causing the lean codes or the new O2 code but could be one of those things you mentioned to me in your post. I am heading to Oregon this weekend so I will be burning up all the leftover fuel injector cleaner and it should alleviate that as a cause or bad gas or the combo of the two. The two things you suggested I do first Im not sure how to do except look for something that isnt plugged in that needs to be, which could be the case. I dont have any equipment to check fuel pressure and am not sure how it is done, never done that before, nor am I sure how to check for vacuum leaks either. Thanks for the advice and yes I noticed that these codes were a common subject for this type of engine with both the Fords and Mazdas that use them.

As for checking for vaccum leaks there should be a link somewhere on here about how to go about it. To check fuel pressure you'll nned to buy or borrow maybe form a parts store a gauge and thread it on to the test port on the fuel rail. As well if you don' have a Haynes or Chilton repair manual for you truck I suggest you purchase one before any other parts. Lots of good info in them that you'll likely need and use in future.

Yes that is another good idea, I used to always buy them for my vehicles in the past, but havent done that for the last few vehicles that I've bought. Probably because I used to buy used cars and trucks for cash and then started taking out loans on newer models. Now Im right in the middle having a newer 2004 fully loaded Eddie Bauer Expedition (which my wife drives, and I pay for) which has an extended warranty for up to 100,000 miles (waste of money I know) that costs me $400 per month and a Ford Ranger that I bought at an auction in 2003 and have done most all the maintenance aside from a few major things myself without any manual. Maybe it is time to go get one.

check for vac. leak with a vac. guage. probably NOT fuel press.. CAUTION,driving for an extended period with a big vac. leak could burn valves. is engine running hotter than usual? do you hear any knocks? if so fix immediately, these are serious warning signs. it could be just a cracked vacuum line. the ford plastic hardlines disintegrate after so many miles.

Thanks for the advice. It seems to run fine at higher speeds and only hesitates when taking off and switching gears at lower speeds. How many vacuum lines are there on these 4.0L V-6 engines, and where and how do you test them?

AS FOR HOW MANY VACCUM LINES HARD TO SAY, DEPENDS ON OPTIONS, HOW THE ENGINE IS EQUIPPED FOR EMISSIONS ETC? AS FOR HOW TO CHECK THEM FOR VACCUM LEAKS GOOGLE VACCUM LEAK OR JUST DO A VISUAL. IF THIS IS ALL NEW STUFF TO YOU THEN IT MIGHT BE BETTER TO SEE A PROFESSIONAL INSTEAD OF DOING MORE DAMGE TO THE TRUCK OR WASTING MONEY ON UNNEEDED PARTS

you'll find a simplified vacuum diagram on the emissions decal on the core support. inspect the lines for breakage, particularly where the rubber atteches to the plastic. listen for hissing or whistling. sudden lean conditions are almost always a vac. leak.

It seems to run fine on the highways and only has trouble around town. I used 92 octane fuel for three full tanks and no check engine light came on. Two of the tanks I burned up going back and forth to Oregon and the other around town and back and forth to work. Last tank I put 87 octane gas and it seems to runner even rougher and the check engine light came on and I popped a P0133 code which is O2 circuit slow (Bank 1, Sensor 1). Maybe it is time to take it in and let a Ford tech figure out what the problem is. I dont want to start replacing sensors unnecessarily because they are $$$$.