Hello Folks,

This is a repost of a question I asked a while back... hoping to get a few more responses.

I have a 93' F150 4.9L which has had many things fixed on it however I still have what I can best describe as a slight engine hesitation when I tap on the gas slightly. Not flooring it... just tapping it lightly enough to cause the RPMS to rise about 500 or so. What happens before the RPMS rise is the engine will shudder and appears as if the RPMS drop significantly before jumping up.If I tap the pedal in rapid succession it sometimes gets worse. When driving I don't notice it unless I have come to a stop or the RPM's have dropped to idle speed while I am waiting at a light or something. If you have the pedal pressed down a little and held there... then press further I don't have the problem. Just from IDLE.

Here are the things that have been replaced for other problems:

Fuel Filter, Fuel Pressure Regulator, O2 Sensor, Throttle Position Sensor, EGR Valve and Sensor, and the coffee can looking thing that does something with the vacuum system. The mechanic tested the injectors and said they were fine.

One of the orignal problems with the running of this engine was a massive drop in RPMS when about a 1/4 press on the gas pedal. The Throttle Position sensor was found bad and that went away.

Anyway, any ideas or possible things to look at??? What else can cause this??? Also the mechanics said they checked out the vacuum hoses and didn't find any leaks.

Thanks in advance.

 

I too had a simular problem and changed all of the tune up stuff and so on so forth,but the thing that cured it was when I removed the air intake hoses to clean the trottle plates and bores.I used a nylon barrel brush just like you would use on a .410 guage shotgun or simular and carb cleaner to swab the bores free of any gunk.Spraying alone doesn't do much good. Just hold the plates wide open and get busy! I also removed the solenoid from the air bypass valve{2 phillips screws only}and cleaned the spring loaded pintle by depressing it and spraying carb cleaner through the bore.Now it idles perfect,doesn't hesitate,and runs like a Deere,John Deere that is!
Phillip

 

Thanks for the info... I will have to give it a try... do I have to take the actuall throttle assembly off.. or just clean it while it is still attached??? Do I have to worry about any gunk getting into the engine??

Thanks again

 

No Greg,you won't need to remove the throttle body assy. for cleaning.To clean the air bypass you will have to remove the 2 phillips screws that hold the solenoid {motor}on to the port adapter,but this is very easy to do.There is an o-ring there so pull back gently to prevent tearing.Corcerning the gunk that you scrub off,it will be in a liquid form because of the carb cleaner and will easily be burned at initial start up after cleaning.You can wrap a rag around a dowel and try to remove any sludge that fall behind the throttle plates.The engine will be rough to start because of the liquid carb cleaner but will clear up quickly after a few bursts of the gas pedal.Then, drive the truck right away at highway speeds to finish burning any contaminents that may be left over.

Phillip

 

Phillip:

Went after the throttle body and such as you described with carb. cleaner and a toothbrush last weekend. Wow! what a major difference.

For others...I think this is a must do.

Thanks!

Teo
92' F150, 4x4, 4.9L, 113K, stock & standard
97' Fjord 850

 

I asked the friendly Autozone man today where the FPR is on my 93 F-150 (302). He told me that I would have to remove the intake to get to it. Is this correct? Does it need to be replaced at a given point in time...

 

The FPR is located on the fuel rail that feeds the injectors. If you look you can see it buried under the intake runners and assorted hoses, tubes, and wires. Fortunately, it is not prone to failure. The way to check is to put a pressure gauge on the fuel rail and determine if the pressure is in spec. Should be around 45 psi.