Hey guys, newbie here.

I have a 99 F-150 with the 4.2 v6 engine. It hesitates and sputters quite a lot off the line.

I've replaced the fuel pump (which was shot), all the fuel injectors with brand new ones, fuel and air filters and spark plugs (i got the stock motorcrafts).

I don't want to keep wasting all my money fixing it with the trial and error approach.

It has over 200,000 kms and she has a lot more to go, so please help!!

P.S.: I've already search the forums for an answer, but couldn't find anything

 

Hints:
The TPS tells the PCM what to do for fuel vs throttle opening.
The mass air meter tells the PCM what the airflow is.
EGR, if open when it's not supposed to, will give grief.

 

If your sure you have good spark and its getting air and fuel then you might have other problems. I first thing i would do is a compression check on each clyinder. If you don't have the right compression at each clyinder than your just spinning your wheels so to speak. Check that out first before you spend any more money on parts you don't need.

 

Did you check the timing on it? If it is advanced or retarded then it will start to make things go haywire. Not sure what the 4.2 is like, maybe you bumped it or it just fell out of adjustment. Could also be a O2 sensor messing things up, telling the comp that its not getting enough fuel and therefore richening up the mixture at idle. Sounds like it is loading up with fuel? Does it backfire at all off the line? When you are driving highway speed and punch it does it "ping", like it's flooded? Bluegrass, maybe please explain your acronyms (i.e. TPS = Throttle Position Sensor), since he is a newbie, he might not understand them. Hope you find the cure?

If you are lucky like me, your local autoparts store (Pepboys or whatever it is where you are) has a code reader that they will plug into your diagnostic port for free and get a readout of your settings, they can then tell you what is wrong and sell you the part to fix it. Hope its that simple, call around to find out.

 

have you replaced plug wires ?/
mitchykins

 

did you try pulling the air tube off the intake pipe and clean the Throttle plate with carb cleaner and tooth brush works wounders
that and you could cut the air box

 

Hi Roy. You say you don't want to keep throwing parts on your truck, well thats what lots of people do before they seek professional assistance. Is the "Check Engine" light coming on? The vehicles we drive these days are complicated. Scan tools, not just code readers, can read what information is being sent to the computer from many of the sensors. This gives a technician an idea where to start.

Hesitation can be caused by lean fuel mixtures or ignition timing problems. Let's consider the causes of a lean fuel mixture first. The lean mixture could be caused by too much EGR, vaccum leaks or a MAP or MAF sensor malfunction. A professional with a scan tool can check this easily. He may notice that the MAF reading is not normal. Sometimes just cleaning the heated wires on the MAF can fix a lean problem, no parts to buy.

Timing problems may be a little more difficult to find for someone that does not posess a two channel scope or graphing meter. You see, your truck has a crankshaft position sensor on the harmonic balancer. This triggers your coils to fire at the right time. But when is the "right time?" I have seen Ford harmonic balancers break and then spin several degrees off. Just looking at the balancer does not reveal the problem because the center bolt is still holding everything together. A good tech, using a dual channel scope can check the crank sensor signal against the cam sensor signal to see if they line up when cylinder # 1 fires. If they don't then one of these sensors is out of phase, probably the crankshaft position sensor. I have repaired a Ford truck myself that had a severe hessitation and it was due to a broken harmonic balancer. So, save your money, have a pro at least diagnose it for you.